Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Hi
Just thought it was time to introduce myself.
My name is Chris but everyone calls me Nodz.
Been lurking around various guitar/amp and hifi/diy audio forums for a while.
Have four guitars (3 electrics and one acoustic) and two SS practice amps.
Have made some SS and valve audio equipment, thought is was about time I started skimming around the net and try and design my own guitar amp.
So after a bit of reading, designing, redesigning, borrowing circuits from others I've come up with the attached.
Due to constraints both time and financial, will probably build amp in modular fashion, that is step 1) preamp, 2) stand alone reverb 3) then the PA. 
Possibly will include an overdrive section but the idea is to have an organic modular amplifier, that can be altered as I go along so if I don't like certain developments, I can revert back to the previous state if desired.
I also haven't decided on the final PA.  At the moment, it uses a couple of PP 12AQ5 (just because that's what I found in my junk box) but I may use LM3875 and have 2 x 50W output channels, 2 x 6L6 (50W) or 4 x 6L6 (100W).  I just haven't established what kind of O/P I require yet.
Cheers
Nodz

Hi Chris and a big welcome to ya matey,,
Yep there are a few Aussies here. :tu:

Plenty of project ideas float around here, so plenty to keep you experimenting.
Yes modular is darn good idea and is the approach I've been using for a long time.

I assume you are wishing for a real spring Rev unit then hard to beat ESP circuits.

IME Outboard Reverbs tend to work better than inbuilt setups.
I have built a few stand alone Tank circuits with the aid of Rod's wonderful reverb ideas.
Phil.

Hi Chris, and welcome to SSguitar (from Creswick, Vic).

I suppose you've seen the Lamington (15W) and Lamington-II (50W) designs.  I designed the HT quadrupler in those because I wasn't all that impressed with back-to-back trannies for HT, particularly at higher power levels like 50 watts, and I think they would be a lot more practical at the 100 watt level.  Those 12V QI trannies are starting to get a bit thin on the ground now that they are being displaced by Switch Mode "solid state transformers", but then that whole QI lighting scene is about to get a monster shakeup with the arrival of plug-in replacement LED's.

I notice you've used a 100k pot right at the input.  This is fine for active guitar or always using a stomp, but for passive guitar straight in I find that even 1Meg input is a bit low and have been building FET buffers with 5Meg input resistance to go ahead of things like amps and stomps with lowish input resistance, and the difference is quite noticeable, the liberated pickup resonances really sing out.

I've just had a glowing report from someone who built a Lamington using the M1115 and replaced it with a M1120, gave it a stage test this week, and is very satisfied with the improvement.

A couple of little points around the standby switch; I'd personally put it in series with the first 100r resistor to limit the current surge through the switch contacts, and you don't have a bleeder on your HT line.  These days I put something like a 47r/10W right across the OPT secondary after I had to repair a Bandmaster with a boofed OPT because the lead hadn't been plugged in at the speaker end and a shorting jack on the amp didn't help.  Not that M1120's are expensive, but a dead amp at the off is a real pain.

@norv at AGGH has just done a build using Rod's s.s. reverb mated into a valve Lamington, the Watson Wipeout (http://www.guitargear.net.au/discussion/index.php/topic,35752.0.html), and that seems to have worked out well.  We've also got a s.s. LDR trem add-in well advanced (no heater demand), boards done and test built.

That's quite a developed design you've got there.  :dbtu:  Be interested to see how it turns out.

welcome to the forum.

A detail often overlooked in your area is that for proper operation, amplifier designs from the USA must be operated upside down.

Hi Everyone, thanks for the words of welcome.

@Enzo
Yes everything from the US uses an 'inverted' input down under...lol

@phatt
As you said I think that modular is the way to go.  I think that it helps with the trouble shooting.  I have an amateur radio background and nothing worse than getting to the end of a project and you have to debug it from the beginning.  I learned early on that it is much better to get one section working before moving onto the next.  I was thinking modular too, from the point that, I have other pieces of equipment around the house for instance an SS Sansui audio amp, some SS guitar amps, SS preamps and it would be good to develop each of the valve pieces independently and see how they affect the sound/performance of the other items.  Also would be good to build something like the real spring reverb unit and then be able to use it with other amps etc

@Roly,
Yes I am familiar with the Lamington but hadn't seen the Lamington II.  Have been around the ozvalveamps and AX84 sites, so have seen various schematics but must have  missed the 50W version. 

Thanks for your helpful hints with respect to my circuit.  It is quite developed. I have been piecing the design together for about five years.  As I've done further reading and gained better understanding or seen a design feature I've liked, the circuit has been modified.

I agree totally with your statement about the back-to-back HT transformers. Originally, I was going to use this configuration for the whole amplifier (which was far simpler), as it only had to deliver power to 1 x 12AX7 and 2 x 12AQ5.  So about 600mA in heaters/filaments and then about 95mA max signal current.  So not really an issue for these transformers.  However, I have now added the second 12AX7 for the reverb unit and I was thinking of adding a 5879 pentode for overdrive, so these transformers will not be sufficient.

You are right about them getting thin on the ground though.  I bought mine for $7 for the pair when Dick Smith's got rid of all there components and became a computer/audio equipment store. 

I was going to maintain this back-to-back PS config, purely for the preamp stage.  As part of the modular design concept I will include separate power supplies, one for each of the PA, the tube reverb and tube overdrive sections, this may be overkill but each modular piece can be completely stand alone (including power supply and enclosure/housing) so that I can chop and change and use them with other gear.  I will probably put together the Lamington type supply for the PA.

In regards to the input, I don't always use stomps but I do sometimes use the Behringer GDI21 which is a DI/amp modeller.  Because I don't always use that would you suggest that for a simple improvement, I change that 100K pot to 1M?

The 12AQ5 are probably not the best output tube but i thought that they would give me about 10W for a nice practice amp and seeing I had them laying about, I thought, why not?   The M1120 was used to give 16K at primary for 8ohm speaker.  This would reduce the output somewhat as the 12AQ5 requires a load resistance of about 12K in PP config.  This was taken into account when doing the biasing calcs etc.  The M1115 and M1120 are a good value option, seeing that things like the Hammond OPTs are so expensive.

I can change the position of the standby switch.  I will put it in after the 100R resistor.

The bleeder resistor, put it in parallel with the 220uF or at the end of the filter chain?  Something like 150K/2W? Take about 5 seconds for V to drop from about 240V to 30V on the 220uF.

The 47R/10W across the secondary of the OPT is not a problem.  That's easily done.

Cheers Chris

Quote from: nodzIn regards to the input, I don't always use stomps but I do sometimes use the Behringer GDI21 which is a DI/amp modeller.  Because I don't always use that would you suggest that for a simple improvement, I change that 100K pot to 1M?

In a previous era I held VK3YFF.

Yes, at least.  I discuss the issues in some detail here (http://www.ozvalveamps.org/pickups.htm).

Rule of thumb for bleeders is 1k/volt; 300v supply, 270k or 330k.  You're experienced, but I like to encourage builder to also put in a neon tell-tail on the HT supply, helps to avoid those "OUCH! ghoddamit!" moments we can all have.  Because the neon goes out at about 45-90 volts this should be separate from the bleeder.  Both generally on the first filter cap where the voltage is highest, but if you are going to move the standby switch you really need a bleeder each side

Nuthin' wrong with a 10 watt amp, these days with PA's generally available at venues it seems like the favorite power for gigging guitarists is around 10-15 watts; you can go deep into output stage clipping without blowing down a wall.

You should find the Lamington-II on Grant Will's site valveheaven.com.

Just out of curiosity, what Melb suburb are you in?

I hold what was the limited license VK3TUB, which was the frequencies above 50MHz, I was interested in mainly 6 and 2 metre bands and 70cm, but when they did away with the Morse code requirements, I got into homebrewing for the 80 and 40 metre bands.

I'm in Narre Warren on SE side of Melb.

Rightho, so bridge, then 220uF cap, then bleeder of 270k to 330k and neon in parallel to them, then 100 ohm resistor with standby switch in series, then another bleeder of 270k to 330k to gnd.  I'll redraw and post, to ensure that I've got it right. 
Cheers Chris.

Made the additions of the 2 x bleeder resistors and the neon lamp.  New schematic attached.
Cheers Chris

Quote from: nodzwhen they did away with the Morse code requirements

They did?  I'm so out of touch with that world now I didn't know.  All that time spent slaving away at Morse, and now I wouldn't need it.  Ho hum.

Yeah, Rabbit Warren, used to service industrial tramp metal detectors in a pit at Harkaway (among others).  Don't know if you've ever see a "shot" fired, but even a small one is pretty impressive.  Servicing electronics in quarries has to be one of my least favorite passtimes - hanging upside down on a bouncing conveyor (they don't stop anything for the likes of me), being pelted by rocks from the nearby crusher, trying to read a meter and make sense of what's going on, knee-deep mud just getting to the equipment - makes guitar amps seem like a doddle.   ;)

Yeah, that looks good, remembering that the neon either has to be a "240V" one with an integral limiting resistor, or you can use a naked NE2 with 1k/volt resistor in series.

It's an idea I picked up from working on Variable Speed drives that had one neon for the mains in and another to mimic the output to the motor; a useful reminder when working direct-on-mains.   :loco

I've just seen a nifty idea on one of the audio forums.  I can get a 16V, 1.25A AC wall wart and use this as the mains input, step down transformer.  I went rummaging through the junk box and found a transformer that had 2 x 15V, 0.67A secondaries.  I'll parallel the secondaries and use them for the step up transformer.  Voila 256V out.  I'll use 2 x 2A bridges for the HT and heaters and an LM317 for 12.6V out.  Preamp PS done using a simple wall wart and a 2.1mm socket for the mains input.

16 * 1.25 = 20 watts, less heater power, divide by two for output power, multiply by 0-point-something for second transformer inefficiency - doesn't leave a lot of margin...

I despise those co-axial DC connectors with a passion - 'orrible things.  Have a look at CB microphone connectors with locking rings.

Only talking about the PS for the one 12AX7 tube in the preamp, 20W should be plenty, shouldn't it?
From my reckoning (and I am probably wrong :-) )
Heaters 12.6V @ 0.15A gives approx, 2W.
Less than 1mA on each plate, call it 0.5W combined.  Even at 25% efficiency in second transformer should be enough, shouldn't it?

Quote from: nodzOnly talking about the PS for the one 12AX7 tube in the preamp, 20W should be plenty, shouldn't it?

Oh sorry, misunderstood, thought you meant the whole amp - yeah, should be ample.

Will definitely have a look at the microphone screw ring connectors and sockets, good idea that.  Won't take much to rewire the tip of the AC wall wart.  Have got a lot of the components already, will have to see what else I need including the hardware.  Getting the PS operarational might be a project for the Easter weekend.

Re-did the power supply.  Powered by the 16V AC wall wart and then transformed back to 256V, however, will be using 6.3V, elevated heaters to recuce hum etc.   Updated circuit now attached.

Headscratch?,, I'm not sure this is right.

Better minds will reply I'm sure but in my understanding you have not established a correct reference voltage?
It would just float ? xP
Phil.

Ed: My guess you would need a voltage divider from HT to ground to create a reference voltage that is fixed?

Ed 2 forget that,, I missed the ground reference,,, long day :-[

With 256V in and the voltage divider of 100k and 220k resistors, should give an elevated voltage of approx 80v.   :dbtu:   Hopefully, with this set up, providing I get the hardware wiring right, this should be a fairly quiet supply. Ideas initially taken from audiophile circuits.

Did a stock check of the parts required, off to Jaycar tomorrow to buy a couple of resistors and a few hardware bits and pieces.  Hopefully come Monday afternoon will have a working PS.  Not boxed up but a working PS, none the less.

Quote from: nodz on March 28, 2013, 04:36:19 PM
Did a stock check of the parts required, off to Jaycar tomorrow to buy a couple of resistors and a few hardware bits and pieces.  Hopefully come Monday afternoon will have a working PS.  Not boxed up but a working PS, none the less.

:dbtu:

Got everything required, except the case.  Was thinking, that as I am building a modular unit, I might have to use something like 19" rack cases

Yeah but Unless you use those flat donut transformers you will have to use a full height case?

I assume this is for some kind of preamp setup in which case you'll likely want plenty of control over parameters.
Which often leads to many knobs on the front and many modification before you are happy.
I'd  go cheap as you can get before outlaying on powder coated silk screen fronts.
Phil.

Building in a modular fashion over a period of time, so would like everything to match.  19" racks is probably the way to ensure that the cases are always available.  Agree with you about the height, even with using toroidal transformers, still think you will need at least 2U cases.  I want to build a PS, preamp, reverb unit, overdrive unit and power amp in separate cases.  I don't think the reverb tank will fit in the 19" case either, so I might struggle with them.

Edit:  Just had a look at the Accu Bel site for the different types of tank, the outer dimensions of the long tanks are 16.75" so a 19" rack should be alright.

This is a stand alone reverb unit,,, fits into a half rack case,, and I doubt you will ever need nor want for much better Reverb than what this little mongrel can produce. winky

full story here;
http://www.ssguitar.com/index.php?topic=2773.15

Adding pic of my PhAbbTverb.
Phil.

Very nicely done.  However, I was going to build a stand alone tube reverb, using a single tube, similar to these

http://www.el34world.com/Forum/index.php?topic=7957.0

Don't know how they'll go.

Going to use an effects loop bypass unit, so that it's not in circuit all the time like the units shown.

http://www.beavisaudio.com/techpages/PedalHacker/

The one with the 3PDT and indicator light.

Hi Nodz,

Yep I understand the attraction of glass but as I have discovered once you dig deep enough you don't need it.

Having spent years working on this I am fully aware that there is little interest in SS reverb stuff.

Mainly because a lot of Modern Valve Amps use pathetic SS reverb circuits and I can certainly understand the casual observer thinking He might need a Real Valve reverb and assumes SS is no good for reverb.
But as I've found this is just not so.
Too late the damage is done and SS rev gets the thumbs down.

The Big names just shoe horn in any cheap *Untested* SS circuit as long as it works the average kid will not know the difference.
If Amp makers actually paid for brains instead of advertizing space A SS reverb can work as well as any Glass power device.

Heck I did it!!! and I'm just a back yard hobby novice,  go figure?? :lmao:

Don't get me wrong I love Valve gear and would love to own a lot of famous gear but I'll never have the funds. :'(

Somehow I always knew a SS reverb could work as well as any Valve driven device and after years of failed attempts I was with help able to produce such a beast. <3)

Try looking at some of these as options;
http://sound.westhost.com/project34.htm

Rod Elliot was a huge help while I struggled to come to terms with reverb circuits.
As should be evident from my Reverb circuits I used his mixer setup as it worked straight up, unlike most of the *Claimed to work* stuff found on the net.
All I did was improve the Driver setup as that is the critical part of tank verbs.
If the drive end is weak then forget the rest as you will be forever searching.

Re those ideas you linked;
I'd err a bit as I don't think an AX7 would have what it takes to drive the tank. (if that is the one you refer?)
An AT7 has ~ x10 the grunt of AX7 as can be evidenced by looking at fender circuits where the AT7 has the plates strapped to drive the tank Tr.

Better minds here can explain the indepth details if you need help with that.

Re the loop;
The Tverb has both a true bypass (Front panel) as well as the mute foot switch (back panel).
Depending how you setup the whole chain of events The mute is all you may need.
I only use the true bypass as a back up in case of trouble with a rig setup.

Phil.

The amateur has several ace-in-the-hole advantages over the big boys, not least because we are personally attached to the results, and you just can't buy that at any price.  We don't have the time or cost pressures, or accountants second guessing technical or sonics matters.  We have the luxury of time to ponder, think and think again, research what others have done, experiment and tinker, let it brew on the back burner, perhaps for years.  There is nothing I could do as a professional designer I can't do in my home workshop.

Take a look at freeware, put together by enthusiasts, and it's very often better than anything you can buy.

James Lovelock, CH, CBE, FRS, Ph.D is a fair dinkum scientist (who once remarked that to do creative work you have to get as far away from the nearest airport, freeway and city as possible) and he did two really remarkable things; firstly he devised the ionisation detector that lifted the sensitivity of gas chromatography by a factor of ten in a single stroke; secondly he used that invention to discover how widespread chlorofluorocarbons were, which directly led to the discovery of the effect they were having on the ozone layer - and he did it as an independent in his own workshop in his cottage in rural Devon.


Yes, a reverb line doesn't require a lot of drive power, but it does require some, and the 12AX7 is a bit light-on in that respect.  There are still a number of small power pentodes available which would be a more logical choice, however I agree with Phil that solid-state is a serious contender.  The tank itself utterly swamps any subtle "tube tonality" that might be in the reverb sidechain.

QuoteHaving spent years working on this I am fully aware that there is little interest in SS reverb stuff.

Yeah, I totally agree with this, especially in the audiophile area, although a lot of the newer generations are turning away from valve, due to the cost of the valves, PT and OPT.  Much easier to get a 18-0-18V, 300VA toroidal that can deliver the requirements of a 50W chip amp etc.

I have no problems with SS per se, I was predominantly raised in the SS era and all my amateur radio homebrew stuff, including the audio amps etc has been SS.  I have two practice amps and both are SS, so I am not averse to it  :)

QuoteMainly because a lot of Modern Valve Amps use pathetic SS reverb circuits and I can certainly understand the casual observer thinking He might need a Real Valve reverb and assumes SS is no good for reverb.  But as I've found this is just not so.  Too late the damage is done and SS rev gets the thumbs down.  The Big names just shoe horn in any cheap *Untested* SS circuit as long as it works the average kid will not know the difference.  If Amp makers actually paid for brains instead of advertizing space A SS reverb can work as well as any Glass power device.

Again you raise a valid point.  Many of the modern amps, use poor quality SS reverb circuits.  The stomp boxes and amp modellers can be as bad, if not worse.  I must admit that I like the idea of both SS and valve reverb, as long as they have the spring tanks and are not computer modelled, although some of the top end amps are starting to improve.

QuoteDon't get me wrong I love Valve gear and would love to own a lot of famous gear but I'll never have the funds.

How right you are.  $2500+ for a Fender twin reverb reissue.  I will never own any of this type of gear either.  So bang for the buck when I make my own is important.  As I said the amp itself will be modular and I was thinking of putting it in racks.  The reasoning behind this is I can put all the racks in a case and I can develop bits and pieces of gear as I go along.  I will probably build the 10W 12AQ5 PA to start with but later I might try one of the 50W chip amps for an SS PA.  So an SS reverb is not ruled out either.

QuoteTry looking at some of these as options;
http://sound.westhost.com/project34.htm
Rod Elliot was a huge help while I struggled to come to terms with reverb circuits.  As should be evident from my Reverb circuits I used his mixer setup as it worked straight up, unlike most of the *Claimed to work* stuff found on the net.

I am familiar with the ESP stuff.  I was looking at building the solid state preamp and the 60W? amp at one point.

QuoteI'd err a bit as I don't think an AX7 would have what it takes to drive the tank. (if that is the one you refer?)
An AT7 has ~ x10 the grunt of AX7 as can be evidenced by looking at fender circuits where the AT7 has the plates strapped to drive the tank Tr.

Yeah, I noticed this and was then toying with the idea of going with somethig like the 6BM8 pentode/triode set up.

Quote
Re the loop;
The Tverb has both a true bypass (Front panel) as well as the mute foot switch (back panel).
Depending how you setup the whole chain of events The mute is all you may need.
I only use the true bypass as a back up in case of trouble with a rig setup.

Will check this out.  As I said, open to suggestions and there are no hard and fast criteria with the actual final configuration. 

Cheers

QuoteThe amateur has several ace-in-the-hole advantages over the big boys, not least because we are personally attached to the results, and you just can't buy that at any price.  We don't have the time or cost pressures, or accountants second guessing technical or sonics matters.  We have the luxury of time to ponder, think and think again, research what others have done, experiment and tinker, let it brew on the back burner, perhaps for years.  There is nothing I could do as a professional designer I can't do in my home workshop.

This is how my design has progressed.  It originally started, with a single tube preamp and a SE PA for about 4W out.  Over a period of time, it has become quite a developed design, moving to PI with prescence control, I/P drive and O/P volume for the preamp, a PP 10W PA and also with the reverb and O/D ideas being added.  So the thing is still fairly amorphous  :cheesy:

QuoteYes, a reverb line doesn't require a lot of drive power, but it does require some, and the 12AX7 is a bit light-on in that respect.  There are still a number of small power pentodes available which would be a more logical choice, however I agree with Phil that solid-state is a serious contender.  The tank itself utterly swamps any subtle "tube tonality" that might be in the reverb sidechain.

As mentioned in the above post, was thinking of going to something like a 6BM8 pentode/triode device.  However, I will seriously look at the SS option.  If I'm building modular, it might very well be easier with respect to the power supply and componenty and provide me with the necessary tonal device I'm after.

BTW do you have a circuit diagram for the PS?
Is it a 15-0-15V, 20VA troidal transformer centre tapped that you have rectified and then used the +, - connects of the rectifier to get the +15V, -15V as per Image 1 (although this diagram is for 25-0-25 to give +/- 35V)
or have you used each secondary and rectified and then filtered as per Image 2
or have you used a 18-0-18V transformer and rectified and regulated with something like a 7815, 7915 pair as per Image 3?

Also while tooling around the net, I found an SS reverb circuit but using discrete components rather than ICs.
Design originally came from a Heathkit TA-27, 20W amplifier with tremelo and reverb.

The Transformer ACV is low (15-0-15 I think)
So yep all I needed was rectification and a pair of reg chips, As per image 3 :tu:

The halfrack case was a dud Alto Feedback buster gizmo I picked up cheap and so why make life hard :)
Once I gutted the inside I was left with everything I needed for a quick reverb build that also looked half decent.

I had about 4 different small signal OT's in my junk pile and as long as you go from low to high they all work to some extent.
As Jaycar had a part number with Z labeled on it I used that because it helps others who may want to try it out.
So just go find a small signal Tr with ~ 8/1k Z.
Obviously a 1/1 ratio is going to do nothing. :'(
The Jaycar part number is MM2532 which is a 350mW output transformer, sell for around $5

The circuit *Without Tr* works like most other dead pan boring reverbs of this type mounted in many Amps But the moment you introduce the TR,,, A Whole new world of reverb awaits you. :):):)

The final result will obviously depend on the match between the OT and the drive transducer.
That kind of maths I'll have to leave to better minds to Decipher/ Ezplain xP

My dear old Laney KD linebacker has a very similar Reverb circuit and after building reverbs again it dawned on me that All I needed to do to dramatically improve the reverb was insert another line TR at the drive end ,, sure enough same result.


The SS Laney Amp also has a short tank so I've not had the chance to try this out on a long tank but One day if I'm lucky enough to stumble onto a long tank I'll bet it will come close to slapback reverb.
Longer springs does help the delay a little bit better,, getting that ding-gading-ga slapback effect is not so evident with short springs. :'(
My Original MaxiVerb had the long tank and it *Definitely* had the slap effect when playing fast staccato notes.

These little Tr's are low quality and you loose some bottom end which is *Exactly what you want to have happen* as excess bass destroys the definition effect of reverberation which is the whole magic of reverb for guitar.
From my experiments the magic freq seems to be between ~ 1kHz and 3kHz.
The more I've studied Amp circuits the more I've come to see that often little attention is paid to the freq response of reverb circuits and yet it is critical to how well it works.

I recently fixed a SS Magnum Combo and as the board was upside down and the rev circuit was obvious,,all I did was kill the bass going to the driver and it made a world of difference.

Total System EQ is by far the most important aspect of guitar sound, even in the response of the reverb.

Re the heathkit circuit,,, Unlikely you will be happy. :duh
BTDT,, Well not that one exactly but I've breadboard tested a lot of Reverb circuits,,,,, now Did I mention I'm nuts?  :lmao:
The Maxiverb took me ten ish years to perfect,,, so call me mad methodical or even slow to catch on at times but I did get there in the end.
I think I learned more about amplifiers and guitar audio in that time than if I had gone off and just built a hundred fuzz boxes.
Phil. 

Lightglobe!

I think your observation about putting in a driving tranny can be explained by one of those easy to overlook details.  A valve output stage, particularly without NFB as reverb drivers are, acts much like a constant current source, meaning that the power delivered to the line driver coil tends to track its impedance.  This is more significant than driving a speaker because these tend to have a characteristic that rises steadily with frequency.

(http://www.ozvalveamps.org/generic/reverblinez.gif)

Solid state driving circuits are constant voltage sources, and you see in better designs a fairly large supply voltage and a largish resistor in series with the driving coil, and this again results in something close to current drive rather direct connection which would result in voltage drive which would over drive the bass and under drive the upper register.

@phatt/Phil,
I was reading the reverb information on the Elliot Sound Products (ESP) and from the information that he presents, I assume that the phabb-tverb circuit that you present is for low impedance coils only.
If a standard coil, like the Accutronics 4FB3A1C is used then discrete componentry is required as the op amps can't provide the necessary drive?
If this is the case, is the drive transformer not required either, as per the ESP page and the schematic of the Orange stand alone reverb unit below?
If you really wanted to, would if be possible to include a reverb transformer into the below circuit and rather than take the output off the emitter of the BFY51 transistor, include a transformer between the A+ voltage line and the collector of the BFY51.  I assume that this would need to be something like a 1:1 transformer as impedance of both transistor and tank is high?

Hi Nodz,
Ohh?
I have not seen that one before?

But a fair bet it will fair no better than others from that era.

Roly or Mr Fahey might be better qualified to answer this one.  :-\ :-\

Up to you if you want to try things out but I've done my bit and it works and I'm not really qualified to comment on stuff I don't fully understand let alone explain. xP

All I know is my Reverbs *WORK as claimed* with the Tanks I have been able to accrue over time.
Heck I'm a pensioner mate and this is a hobby for me,, so I can't go out and test everything that sounds like a good idea. I just do not have the funds.

There are many reverb circuits around but I found that few actually worked when breadboarded.
What really scared me was finding the Accutronics site which has a page of suggested circuits for their products and I thought I had found the answer,, Surely they would have the ideal circuit for reverbs?????

Well what a complete and utter load of crappus. @##$$%^&*&* Don't even bother with them.

As to Your post??
Your observation/explanation is a little confusing but this might help.

A Low impedance 8 Ohm transducer will measure 1 to 4 ish Ohms DC.
A High impedance 100 Ohm transducer will be more like 20~30 Ohms DC.

The DC reading will always be less than the Z Ohms.

There is a reference page somewhere showing how to decipher the number on Accutronics tanks but if you have a tank then from the above rule tiss not hard to work out if the drive is low or high.

There is no exactly right with these things as this is Spring Reverb and the bandwidth is shocking and you are not shooting for .001 distortion figures to impress hifi idiots.

At the end of the day you do have to suck it and see,,,I've given hours experimenting and just sharing my findings so I'd hazza guess that anything that reads above 40 Ohms DC should work with my setups.
If you have a very low Z drive transducer then my idea may not work.
Note; Rod Elliot mentions the *SOT* (select on test series resistor),, well that is Exactly what it means.
*You do have to tweak the driver with the Tank you have for best results*.

I did have a very low Z tank for a short time and had no luck driving it with my circuits.
Those circuits where likely for Valve units and may not be worth the hassle.
Unless I'm sadly mistaken, Rods Circuits are mainly Aimed at the medium to high Z units.

As most tanks I come across are medium to high Z that is what I've worked with so other ideas
I'll leave to those who wish to experiment.

The other hidden thing to bear in mind is the Tank design and quality itself, this can vary but Accutronics seem to be the best bet although I've heard good reports about *Mod* brand tanks being as good as the others.

Keep in mind the Tank design, Magnet quality, spring mountings, rubber dampers all come into the final result.

Heck I've got a nasty cheap one here that wobbles for a good 5~6 seconds as they forgot to insert the dampers inside the mount tubes which makes for some Wild reverberberberbebrations. lol.   
Completely useless for guitar. :(

Sounds to me like you just need to go breadboard some ideas and with the info you have already it won't take very long to work out what works and what is rot.
Phil.

Quote from: Roly on April 03, 2013, 11:22:11 AM
Lightglobe!

I think your observation about putting in a driving tranny can be explained by one of those easy to overlook details.  A valve output stage, particularly without NFB as reverb drivers are, acts much like a constant current source, meaning that the power delivered to the line driver coil tends to track its impedance.  This is more significant than driving a speaker because these tend to have a characteristic that rises steadily with frequency.

(http://www.ozvalveamps.org/generic/reverblinez.gif)

Solid state driving circuits are constant voltage sources, and you see in better designs a fairly large supply voltage and a largish resistor in series with the driving coil, and this again results in something close to current drive rather direct connection which would result in voltage drive which would over drive the bass and under drive the upper register.

Yes Yes,,, I get it now. :dbtu: :dbtu:
Once again You have put into words what would take me a month of Sundays to grasp and then another year to explain to others. :lmao:
Thanks heaps,, I think I now have a much better grasp of this tricky subject.

I've actually grabbed that and filed under my Reverb folder,, cause I'll have to read it ten times for it to sink in xP
Phil.

Here is the mods I did for my (pick up and go play a gig) Laney Amp.

6 alterations and an OT.
What used to be,, Is the reverb on or off?
Is now,, Opps I better back off the reverb too 3 for normal playing <3)

I've noted the DC reading of both the OT and the transducer in the tank.
This is a nothing special short tank with no names as found in a lot of these low budget SS combo Amps.
Phil.

Try this for help in defining Tanks specs;

http://www.amplifiedparts.com/tech_corner/spring_reverb_tanks_explained_and_compared

So in the case of tank 4FB3A1C,
Then;

4 = long tank (2 spring rows)
F = 1,500 input Z
B = 2,200 output Z
3 = long decay time
A = both input and output grounded to case  (potential problem)
1 = no locking device
C = mounting side on

The DC reading will be around 200 Ohms on both ends.
Both ends grounded to tank can cause a ground loop so be warned.
Phil.

Sorry Nodz I did not reply fully, so now rush hour is over I've had more time to ponder an intelligent answer.

Quote from: nodz on April 04, 2013, 07:05:27 PM
@phatt/Phil,
I was reading the reverb information on the Elliot Sound Products (ESP) and from the information that he presents, I assume that the phabb-tverb circuit that you present is for low impedance coils only.

No the opposite.

Quote from: nodz on April 04, 2013, 07:05:27 PM
If a standard coil, like the Accutronics 4FB3A1C is used then discrete componentry is required as the op amps can't provide the necessary drive?

Yes they can with the aid of the small OT

Quote from: nodz on April 04, 2013, 07:05:27 PM
If this is the case, is the drive transformer not required either, as per the ESP page

Either or seems to be the case.
The beauty of the Tverb OT is that it really simplifies everything and allows the whole thing to run on low voltage.

Quote from: nodz on April 04, 2013, 07:05:27 PM
If you really wanted to, would if be possible to include a reverb transformer into the below circuit and rather than take the output off the emitter of the BFY51 transistor, include a transformer between the A+ voltage line and the collector of the BFY51.  I assume that this would need to be something like a 1:1 transformer as impedance of both transistor and tank is high?

Yes I did try all that but found the booster circuit to be the better option.
The booster circuit is common but few run the booster pairs from a much higher voltage.
My MaxiVerb unit runs the booster pair from +/- 35 VDC and that was the key.

The original article that ESP had did not have much in the way of better Drive setup and
If truth be known it was likely my constant complaints about lack of drive that caused those booster circuits which he added later.
All Credit to Rod as I've never purchased any of his kits but He helped me out a lot while I wasted a couple of breadboards designing many many Reverb ideas.

The Maxiverb is a little complex and requires extra voltages and I only know of 3 people who have built that unit but the Tverb idea is very close to the same result and a lot less work to get up and running so understandably I'm very impressed as even with limited electronic skills this can be made DIY.

I'd say if you have a 4FB3A1C tank then go with the Tverb :tu:
just watch the potential ground loop.
Cheers, Phil.

Thanks for your input Phil, very much appreciated.

I'm just trying to get my head around the use of the op amps and the small OT to provide the drive required  :cheesy:

I must admit that I am reticent to use the op amp type circuit.  This is purely my issue.  I have always struggled to get the op-amp type circuits working and have had much better success with discrete components.  This is not to criticise yours or Rod/ESP's work, I just don't have enough experience with them.  For instance many of the reverb recovery circuits I've seen on the net include an LM386 chip.  When I was in amateur radio, oscillation of these chips in audio circuits was the bane of my existence  :-[

Many of the problems that I fear, could probably be overcome by purchasing the ESP pre-etched circuit boards and I may not have the issues that I am concerned about.

Another thing is the type of music that I listen to/play.  I play punk/hardcore (noise the older generation would call it :lmao: ) so I do not require huge amounts of reverb, just some to add depth to the guitar sound.  So I probably only require short tank/two spring/medium delay that is not driven particularly hard.  Having said that, designing/building for maximum amount of reverb possible means that I can turn it off if I want to ;)

I don't have any tanks yet, that was just the one that the Orange circuit used, that's why I picked that one as as example.

While writing this response, I was searching around the net and found an old Gibson reverb schematic (see below), that uses that OT connected between the HT (17.5V compared with the +/-35 that the Tverb uses) and the collector of the reverb tank driver transistor, just as I suggested between the HT and the BFY51 in the Orange circuit.  The tank used is RV4C which is a 4BB2A1C equivalent in the Accutronics range.

4 = long tank
B = 150 input Z
B = 2,250 output Z
2 = medium decay time
A = both input and output grounded
1 = no locking device
C = mounting side on

Unfortunately, I can't find any info on the TF-1000R reverb transformer, but obviously got to match the o/p impedance of the BFY51 to 150 ohms.

These discussions on this thread have opened up a can of worms.  So much to try/experiment/do.  Might be another ten years of reinventing the wheel.   :duh 

Cheers Nodz

Quote from: nodzoscillation of these chips in audio circuits

The most common cause of this is supply bypassing, or lack of it.  You can get away with having an electro on each supply, +v & -ve, in the bench supply with long leads trailing across the bench, but only if you have a high frequency bypass from +ve to -ve (not ground), right at the op-amp.  Naturally it's better to have low frequency bypassing close to the amp, but high frequency bypassing is not optional.  Some op-amps like the LM833 have such high bandwidth that you need to think of dealing with them "VHF-style", but it's not a bad idea generally.

Trying to get gains higher than about x100 from a single op-amp, or across a dual or quad, tends to get problematic.  By the time you get up to needing gains of the order of x1000, say in a distortion meter, then spaced singles, tinplate shields, and other "RF-like" techniques help a lot.

Rod's reverb circuit is pretty conservative in this respect, so take care of your supply bypassing and you should be okay.

The reason that reverb drivers tend to have high supply voltages is mainly because they tend to act as constant current sources and need a fair bit of voltage headroom, particularly for "high-Z" springline drivers.

I have actually heard the GA-3RV but only on the net. :(

Double bum because the local pawn shop had one but it was the 110V import and he had no way of running it to hear it in the flesh,,Since then it has been sold.  :'(

Yes the idea is valid but hardly worth the fuss when other stuff here will be easier to source parts for and perform better.

I note you mention the style of music you wish to play,, So i doubt you need a dripping wet surf sound reverb? Maybe you are over thinking the whole idea.
Phil.

@Phil/Phatt, yeah probably am over thinking it, the type of music means, that the original single pentode driver on the spring tank will do nicely...lol

Well now we probably are going over the top  :loco

Yep - that looks suitably OTT.

Just some observations;

- the power supply filtering points A-C not shown.  More importantly you can't feed three successive stage from the same HT point "D" because the first and third will be in phase; the reverb drive/recovery (and overdrive) stages may have a similar problem - stages that are/may be in phase must be decoupled from each other or you risk instability.

- unless you are expecting signal sources of several volts (e.g. CD players) I'd personally go for highest possible input impedance over front end attenuation ability ("Input Drive" control).

- the Overdrive "Output Level" control strikes me as being rather curious, more a "amount of tone" control - shouldn't it go between tone wiper to ground?

- the tremolo "Speed" and "Depth" controls are swapped over, and I'm a bit dubious that you are going to get sufficient depth with that method of coupling into the anode; the cathode is more common, and because of DC pumping the most common method these days is a neon in the LFO anode coupled to a LDR either across the signal path or in series with a cathode bypass cap.

- rather than have the output socket present a dead short to the OPT I'd be more inclined to hard wire a 47 ohm 5 watt resistor across the OPT secondary.

HTH

Hi Roly,
Thanks for the input.

Re: PSU

The PSU shown is for the preamp only, due to the fact that it has powered by a 16VAC @ 1.25A wall wart.
I was going to build modular, so the other units will each have their own PSU.  May be a little OTT for each stage to have its own PSU but as you said:

• Avoids the in phase/decoupling issues
• I can take my time to build
• I can spread the cost of the build over a longer period of time
• Makes debugging easier
• Makes refinements/alterations to circuits easier
• Makes repair easier, should anything go wrong

I was also going to simplify the PSU.  Originally when it was first designed, it used back-to-back transformers and it did have filtering points A, B, C and D.  Now that I am using a wall wart for the preamp only, I can dispense with the other filtering points.  I just haven't got around to modifying/simplifying the PSU circuit yet.

Also the fact that we are discussing AVA106, the 450V hextupler off-line for the quad of 6L6GC, negates the use of the PSU shown for the PI/PA.


Re: Input Impedance

I'll probably just go with a 1M resistor rather than the input drive control. As you mentioned previously only really duplicating the effects of the volume control on the guitar and as you also said, still probably not as good as the 5M/FET combination that you have been developing.
However, having said that, with the input control and the unit being built as stand alone, there is the option to be able to use it with other devices such as a cd player.  Originally I was considering duplicating the preamp for stereo channels for hi-fi listening. That's why the heaters of the 12AX7 are running 6.3V and elevated, as I am sure you are aware, common practice in the audiophile world.  However, I haven't decided whether I am going to do this yet.  In all likelihood I won't and therefore will change the input drive as suggested.


Re: Overdrive

I can't for the life of me find the circuit diagram that I used for this part of the circuit.  I know that it came from the EL34World/Hoffman amp site and was labelled as something like a Blues Amp.  I am trying to find the circuit to determine if I've transposed it incorrectly.  Ah, I've just found it Tweed Overdrive Special or Carolina Overdrive and yes you are quite right. I have got it wrong.


Re: Tremelo

Oops my mistake on the labelling.  When I moved the diagram around, I reattached the labels incorrectly.

The circuit was taken from the article:
http://www.preservationsound.com/wp-content/uploads/2012/07/Vibrato.pdf

I know that is says that it can be capacitively coupled to the first audio stage, but I inserted another stage prior to the effects loop and PI because it and the oscillator will be a stand alone unit.
I take your point about the possibility of obtaining sufficient depth and that the LFO/LDR is commonplace these days but I did find the uniqueness of this circuit appealing.  However, uniqueness doesn't necessarily means that it works...hahaha.


Re: OPT
You've mentioned this mod previously and I thought I had included it.  I must have missed it in the subsequent diagram revisions.

Updated the diagram and attached

Cheers,
Chris

Hi Roly,

Also, if you have time, would it be possible for you to do an LTSpice on the PSU, I have modified the PSU to have only two points, for the two stages of the preamp
I have done one but I am not sure of the resistors I have in place.  What I'm actually struggling with is how to load each stage in LTSpice, so that I get an indicative voltage.  I've put a 1K resistor to GND at each filter stage.  Is this correct?

Cheers
Chris

The voltages in LTSpice are a bit of a trap - they are the peak voltages, not the RMS values.

Well if you want to model it under around 300mA load current 1k would be fine, but that's an awful lot for a small amp and I would be inclined to apply Ohms Law to the maximum currents you expect each section to draw and select load resistors of those values.

Your series resistors R2 and R5 look a bit on the low side.  In a low power amp these would typically be in the range 1-10k.  This should also reduce the hum levels on the preamp HT lines.

Ah right that explains it.  From the circuit diagram of my amp.  Wishing to feed the 150k plate resistors with 250v rms or approx 350v peak.  The amp was designed to drop about 100v across the plate resistor so the tube was fed at about 150v.  Therefore plate current is about 100/150k or 0.7mA.  This checks out on the valve curves using grid voltage of -1.25v and a cathode resistor of 1k8, gives voltage of 145v and a current of 0.7mA.

Now on to the spice load resistors.  Require 250v at 0.7mA which means they should be 357k.  Selecting nearest standard value of 330k to load each stage, I can change the values of the filter resistors R2 and R5 to get 350v peak on the traces.

You only need to use standard values for the real series resistors.  The resistors that simulate the draw of the preamp stages can and should be set for the current at voltage, i.e. 357k.

The most direct way to find the required resistors however is to add the DC portions of the triode stages to your power supply sim.

RIghtho, Just wired up the PSU for the preamp as shown in the diagram.  All voltages as measured as shown also.
All seems to check out except for the heaters.  I was expecting a calculated 6.34V from the LM317T as per spec sheet, that is,  1.25 x (R2/R1 + 1).
R2 is 1100 ohms (a 1K and 100R in series), R1 = 270 ohms.
No matter what I do, all I get is 1.247V, which to me, doesn't seem correct, effectively R2/R1 appears to be 0???

Pin 1 is the adjust
Pin 2 is the output
Pin 3 is the input

My understanding this was from left to right when the device was viewed from the front, i.e the plastic part closest to you and the metal tab at the back furthest away from you.

Can anyone offer any help please??

Cheers
Chris

That's looking pretty good.  :dbtu:

1.25 x (R2/R1 + 1)

1.25 * (1100/270 + 1) = 6.3425925  - Check!

I've never actually used one of these, but the same idea applied to a fixed regulator such as a 5 volt is that a current I flows in your R1 (270r) given by the 5 volts from output to common, and this same current flows in the grounded resistor, R2, giving an elevation of I * R2 volts (to which the regulator output is added giving the actual output voltage).

In the case of this chip the nominal output appears to be 1.25 volts, so;

I = 1.25/270 = 0.00462963 or about 4.6mA

elevation = 0.0046 * 1100 = 5.06 +1.25 = 6.31 - confirmed.

Your understanding of the pinout seems correct.

With only 1.25V out it is behaving as if there is no current flowing in R1 and R2, that the Adj pin is simply grounded (via R2).

Since the circuit and your calculations seem to be correct there is really no other option than to check the actual build very carefully for silly stuff like a dry joint on R1, R1 cracked, misread a 270k as 270 ohms, &c.

BTW, since you are running the heaters on DC you could run them in series at 12.6 volts and reduce the stress on the regulator, half the current and less voltage across it (if it's getting a bit too hot).

Appears to be a problem with R2 supposed to be 1K and 100R in series.
When I measure R2a its 100R, when I measure R2b it's also 100R even though it's marked 1K.  When I measure the resistance across both R2a and R2b expecting 1K1 I get 0 ohms.  Something very fishy.

Yeah, you've got a ground fault on the Adjust pin.

Rightho,
Will have to check over, especially around that area
PSU is on veroboard.
Attached diagram shows how it is wired
Anything obvious from that?
Cheers,
Chris

Unless I'm sadly mistaken 4,700uF is way overkill and if my memory serves me I did read that large cap values on the output can actually blow the reg. :o
The DC has just been filtered by the reg so a large cap is not needed.
I believe a 10uF will do the job.

Another thought is why 6 volt?
You have 22 volts to play with,, I'd run the filaments at 12 volts.
just my 2 cents.

Phil.

Most of the ideas are taken from audiophile circuits.  Pretty much a standard circuit for hi-fi preamp.  Perhaps may be overkill for a guitar amp but was potentially going to use the PSU for a hi-fi preamp as well.  Might try losing the voltage elevation link for the moment and just working on the heater by itself. I can change out the 270 resistor and replace with a 220 and I can just have 2 x 1k resistors in series for R2, voila 12.61volts.   I''ll see what else I have in my junk box by way of a smaller cap with approx 25wv to replace the 4700uF.

Quote from: nodzAudiophile

Ah, well there's ya problem right there.

Quote from: nodzAudiophile reasoning goes something like large capacitors for increased filtering, 6.3 volts and elevated to reduce hum.

Electronic engineering reasoning goes something like this.

The object of a bypass or filter cap is to reduce the source impedance of the supply.  The output impedance of a three pin regulator is already a fraction of an ohm, so putting an ohm or two in parallel with that in the form of a big electrolytic isn't going to make much difference.

What it will do however is store charge when the supply is turned off, and lacking a protection diode across the regulator will potentially drive current backwards through it and damage it.

The idea that a 6.3V heater circuit will have less hum is based in the wrong idea that the hum cause by the heater circuit is due to voltage.  In fact it is due to the magnetic field arising from the current, so a higher voltage heater will have less hum field.

But it's all pretty moot when the heater circuit is DC and doesn't have any hum field to start with.  A similar consideration applies to elevating the heater circuit above earth - if the heater is DC then there can be no AC leakage currents to the cathode.

The sad fact is that Audiophilia is an affliction, a kind of cult where the blind lead the blind.  Most of the concepts I've encountered from audiophiles have a tiny grain of truth at the origin, such as skin effect in cables, capacitor dielectric relaxation, and a hundred others, but are then expanded and misapplied by people who don't/can't get their facts right and in proportion.

Much of this codswallop sounds plausible, like the little copper oxide diodes behind OFC, but like that most of it is high class tommyrot.  There are people who are trying to be helpful, but there are also lots of sharks in the water making a good living off bulldust like gold-plated mains cables ot $1000+/metre speaker cables which are basically a con.

Rightho changing heaters to 12.6v. I did have a diode across the lm317t but I thought that this may have been the cause of the problem so I removed it.  Will change the capacitance to something like 10uF, will see what I have.  Will remove the elevation link then when put the circuit board into the case ensure that both circuits are earthed properly.

Woot, woot.  Preamp PSU completed.  R2 - 2 x 1K2 in series, R1 - 270R for a calculated 12.36V.  Actual measured voltage 12.5V with no load.
Changed out regulator, just in case.
Replaced the second 4,700/50V cap with a 100uF/25V, no problems  :tu:
Placed a diode across I/P & O/P, may not be required now that large cap has been replaced but for the sake of a 2 cent diode.
Simplified circuit diagram attached.

Board is larger than probably necessary, but I deliberately spaced everything out for ease of trouble shooting and repair, should it ever be required.

Tested supply on heaters of an ECC83 valve.  Nice glow.  :cheesy:

Thanks for the input, definitely some head scratching there for a while.

Now to start rounding up all the parts for the preamp.

Chances are if you fully account for the operating current from the regulator itself your voltage will work out exactly, but 12.5V measured for a required 12.6V is such a small difference it doesn't matter.   :dbtu:

The protection diodes may never come into play, but as you say, since they can be recovered from old gear free, why not?

A lot of builders make the mistake of miniaturising their board build, then putting it into a large case  :loco - just making life difficult for themselves.

Quote from: RolyA lot of builders make the mistake of miniaturising their board build, then putting it into a large case   - just making life difficult for themselves.

Since I am building modular and probably going to build into 19" racks for ease of use and storage around the home, size is not really an issue, except height that is.

The 2 x 100uF/400V caps that are in the HT supply line, were snap-ins.  I just straightened the pins slightly with a pair of needle nose pliers and soldered them to the board.  I'm a fan because of their half height, although they have a larger footprint.  For some reason this type of capacitor is cheaper new than many of the others.  I bought a packet of 6 for $9.  It means that they fit in a 1U rack easily.  If i need to buy, rather than scavenge, I buy at www.rockby.com.au (http://www.rockby.com.au) and they quite often have specials like that.

Years ago when i was regularly building amateur radio projects and when Dick Smith's was not just a home entertainment store, i used to buy in bulk.  I have 200 x 1N4004 diodes, that I think were $5 for the bag, so as I said for the sake of a 2 cent diode to protect a $2 regulator, cheap insurance.

Over the next few days, will be sorting through the junk box to determine what is needed for the preamp.  I think that I have most of the components, just a few pots and resistors needed, I think.

I rat caps out of CRT TV's at the local dump and I've noticed that the low profile ones get used a fair bit even where they aren't needed, so it might be a bit of a positive feedback thing where high demand produces lower prices produces higher demand ...  Thanks for the tip about Rockby, Oatley are always worth a net browse too.

Quote from: nodzwhen Dick Smith's was not just a home entertainment store

They could be a barrel of laughs in the shop as well;   ::)

"Where do you keep your transformers?"
Blank look from young sales dweeb.
"We don't stock toys" he sneered.  (Thornbury TechStore, now closed)
(By the time I left they didn't stock electrical transformers any more either, armloads at a couple of dollars a pop.)


"I'd like to look at the oscilloscope in your flyer"
Leads way to a reflecting telescope.  When told I meant an oscilloscope, an electronics test instrument with a display screen, he literally threw a tantrum about how he sold a thousand bucks worth of stuff a day and "didn't have time to piss about with this *s!!t*" and stormed off - astonished, I'd been in the store roughly sixty seconds and it was a $100 item.  (Melb city basement store)


Bought a Set Top Box from DSE Northland.  Over the next few weeks it went into a kind of software meltdown the like of which I've never seen before, a kind of creeping cancer of dysfunction (mind you I was mightily unimpressed to discover that the sense of "up" and "down" inverted between different menus, so it wasn't entirely unexpected - "you never find just one roach in a kitchen").  Finally clagged out so took it back for an exchange, and ran into a reasonable and knowledgeable older guy.

"Forget it" he said, "we aren't stocking those any more" (huge wink), "Here, have one of these" and handed over one marked at twice the price.  It also has a bit of a mind of its own, but at least it didn't rapidly sink into premature senile dementia.


As one of the tech's who helped pay for Dick's first helicopter, these days the only time I will darken DSE's door is if, like Hardly Normal, they have a $2 loss leader on USB flash drives, otherwise, may they and their parent company {"Woolworths is selling electronics chain Dick Smith to private equity group Anchorage Capital Partners for a bargain price of $20 million" - SMH}  just die by fire.

Quote from: RolyI rat caps out of CRT TV's at the local dump...

I get them from CRT too.  Whenever a mate gets rid of one, I get them to drop it over to my place.  I then take various bits and pieces out of them and then dump the rest.

I will be doing that with the old computer PSUs now, so that I can gather together enough hi-voltage caps for voltage multipliers.

Quote from: Roly"Where do you keep your transformers?"
Blank look from young sales dweeb.
"We don't stock toys" he sneered.

Oh you had this problem too. :lmao:  Towards the end of the component stocking days, I'd walk in there and they wouldn't have a clue.  I wanted an electrolytic cap of a specific value, bloke looked on the computer and said they had stock and then tried to sell me a ceramic cap for $20.  What I wanted was a hi capacity one for use in a 13.8V, 10A PSU for amateur radio supply.

Hopefully, I won't need too many bits to get moving on the preamp.  I'll be reviewing over the next couple of days

Just wondered now, that I have built the PSU by taking the AC output from a wall wart and then multiplied it back to 240V from a back-to-back transformer, whether I need some kind of over-current failsafe to prevent damage to the Wall wart, PSU and preamp.

I believe they use Fuses for that. 8|
Phil.

Hahaha yes Phil.  What I meant was, is all I need a fuse of a small value on the ht side of the transformer because I am using an a.c. wall wart multiplied up

AFAIK just about all low voltage transformers, and wall warts in particular, these days have internal thermal fuses.  I've actually gone for a dig and repaired a couple just out of curiosity.  If you look at the "Euro-glyphs" on the average wall wart (non-switch mode) one of the symbols means it has a thermal fuse, a sort of square-wave I think, like;
   __
_|   |_

That's good if they have their own fuses. Makes the wiring up much easier.  Just an on off switch and the standby switch to worry about.