Quote from: Minion on March 21, 2010, 12:59:27 PM
I personally built my First circuits by designing and etching my own PCB"s which is a great thing to learn if you plan on building a lot of your own Custom projects but it is an art within it"s self ........ There are several free PCB design programs out there and tutorials on how to etch your own PCB"s then all you need is to know how to read a schematic and a Datasheet properly and you can start .....


Cheers

Yep I did that for a while ,,,till I realised it was painfully slow.
A bread board makes lite work of it all as you can quickly weed out all the hickups and worms.
THEN commit to PCB.
Phil.

Quote from: odecius on March 21, 2010, 11:36:49 AM
Hello,
Thank you for your advice. I do just want to attempt to build an amp from scratch and I will post a schematic when I find one of my choosing.  I am thinking about trying to build the ax84 amp from the same name website.  But my question about that is in regards to the ground.  Am I just grounding it to the chassis? I apologize for the lack of schematic and I will post it later. thanks again.

Oh well ,, whole new ball game then if you want to build a tube Amp LOL.
Even harder to do but it's your call.
There are just huge amounts of data on valve gear layout,, though right at the moment I'm no use cause my computa puttad out recently and lost all the links
Again I say don't start out building BIG complicated stuff.
FWIW my first valve build was a simple cathode biased PP EL84 with only a volume and tone control.
I've built 3 other tube amps but after 4 years I'm using the *First one I built* LOL IT works better far less hassle than the exotic stuff.

My advice is read up big time untill you grasp it ,,, then build simple gear which gives you confidence to go on to bigger things.
A lot of folks fail to realise that if you take on conplex circuits you can build your own mouse trap!
Like who is going to help you if it does not work or blows up and you have no idea of what to look for?
Ouch! that can be defeating/expensive/ demoralizing.
Try *Valve Wizard* (sells books) 
*London Power* , Kevin O'conner's site. (AKA King TUT,, also sells books)

Look quite frankly just pick a word you don't understand (like say Fixed bias verses Cathode bias) or in your case
(Grounding techniques in valve amps) and Google it as you are bound to read somthing you did not know before.
This way you will catch all the forums as well as valve site Geeks.
Tread carefully with it all and use your common sense,, Some info on tube gear is a little iffy I've noticed.
You soon learn to weed out the useless stuff.
Cheers Phil.

Arrh good find,, you can go to the top of the class :tu:

No doubt a lot can be found elsewhere but nice to have one big list like that.
Cheer's and a welcome to you, Phil.

Hello heineken,  
LM3886 is 50Watt cont output into 8Ohms. 135W instantaneous power
Using 35/35VDC rails.

TDA7294 is 60Watt cont output into 8Ohms. 100W instantaneous power
Using 38/38VDC rails.
Edit; In answer to the reliability, it's not really an issue with most of these chips.
I'm not the expert but LM3886 is proly the better one.

Re, the POWER AMPLIFIER 200W-K8060
There is one thing that those starting out should bear in mind when hunting for power ratings.

I'll use that K8060 as a good example.
You read 200Watts and you get all excited BUT?? hang on look carefully at the real power.
It's only really a 70 Watt Amp. (I quote from page,,,70W rms power @ 8 ohm load)
Not so flash in the real world,, only just above average. 8|

If we hung a 2 Ohm load off the output we could make it look like a *killer watty*
You would likely get over 300Watts @ 2Ohms and the thing would also blow up in a faily short time.

It's always wise to convert any *Whatty* numbers into 8 Ohm Loads as 8 Ohms is generally the ideal load for such things.

Always look for x amount of Watts RMS @ 8 Ohms ,, that will give you a fairly good idea of real power.
Get those *Peak music power* rating out of your mind they always make things look better.
Even worse when you see PMPO ratings. :duh

If you want more power than 50/60 ish Watts then IMO forget chip Amps and go dicrete components for power Amps.
This means big Transformers, big filter caps and a serious heat sink.

The *Samick 60 Watt* you mentioned is likely a chip amp so at a guess the PSU inside is only capable of 50 ish Watts,, any more and you just waste money.

Yes you could drop a great big poweramp inside it but it will only deliver 50 ish watts as the transformer is not designed to give what it has not got. You would likely fry the trans windings anyway.
Cheers, Phil.

Hi odecius,
               Well I doubt I can be of much help unless you *post the schematic* or link to the file in question.
Generally for hobby builders the preamp boards maybe on a seperate PCB's as it simplifies things a bit.
Also enables you to build another preamp board if you are less than happy with the results.

IMO, just build a brilliant preamp circuit with it's own PSU.

With so many cheap S/Hand guitar amps floating around as long as you have a good preamp then via the EFX loop (or pre output/poweramp input) you can tap into a lot of guitar rigs bypassing the internal preamp and save yourself a lot of extra work building the poweramp stage and the speaker driver.

(that is effectivly how I do it on the cheap and saves a whole stack of messin about,,  shush don't tell em I'm lazy!)

Depends on the situation in your part of the world or you may just want to experience the whole thing of building from scratch.

There is a good collection of preamp circuits on these pages if you care to look around. Talking with some of the builders here might give you some insight as to what you wish to build.
Phil.

Quote from: Steve Conner on February 27, 2010, 08:30:07 AM
Hi all... I've been a long time contributor to the MEF, but this is my first post here, and I've been thinking about this subject a lot lately.

You can copy the transfer function of a tube as closely as you like, with circuits of ever increasing complexity, but what I'm wondering is: How close does it really need to be?

It seems to me that all a "tube simulator" needs is a gradual, soft clipping characteristic that starts with low-order harmonics, moving to higher-order as you push it harder. It shouldn't hang up from saturation effects, and it should draw "grid current" so that you can have duty cycle modulation.

I don't think any finer level of detail than that really matters. It might change the "flavour" of the tone a little, but it won't make the difference between caviar and cr@p.

Thoughts?

Hi Steve,, Hold onto that thought,, as it's a faily good grasp of reality. :tu:
Yep it's all just so over rated.
I've spent years building my own gear and quite fankly it's more smoke and mirrors than fact.

There are just so many viariables that it becomes damn near impossible to even establish what
even constitues a good amp Sound/Tone in the first place.

Whether you build with Glass or Sand if you are chasing exact Sound /Tone /Dynamics then there is a lot you need to know about how circuits work to extract the effect you want.

IMHO, whether it's Valves or Transistors
Tone shaping all the way through the circuits becomes super critical if you want stunning results.
This includes Pup's and speakers as well.

Having built some reasonably complex circuits systems even a soaked tubepoweramp running back to line and reamped via a SS poweramp.
It's a toss up between my very simple SS setup and the vastly complex tube hybrid setup.
When asked which one sounds better. I use both depending on how much gear I wish to carry to a gig.

If you are interested my old school analogg SS system is here;
http://www.ssguitar.com/index.php?topic=1446.0

The demand now is for every possible sound all in one neat box but it's all just gimik stuff
if you happen to be a *Real Working Guitar player* you end up realising you only need 2 maybe 3 basic tones/sounds and the rest is how good you can play.

What may sound stunning in the gararge at home may fall well short when used live at a venue.

Half the time my fellow musicians don't know if I'm playing through valves of SS gear.
In a Live stage gig very few in the audience would even know.

You asked for thought's on the subject well that's mine.
BTW, What's *MEF* stand for?
Cheers, Phil.

Hi it's called a breadboard and about twenty years or your time perfecting it all.

And NO I'm not kidding you 

NO It is absolutely not that simple..................

Read/test/ read/reread/Test test testing and more testing.

After 5 years you will have at least learnt to understand the first line I just wrote,,,,,
It's not that simple. :duh

If you have an incerdible amout patience it will be very rewarding.

Without that kind of patience just build a kit and hope like hell that it is the Sound/Tone/Dynamics that you wish.
(Unlikely,,,, but possible.)

My Advice is start with simple circuits.
Cheers, Phil.

Hi GEM,
          Not sure I understand what it is you are chasing but you have the best part covered as it uses a tube poweramp section.
Depending what sound you require a lot can be done with the power amp to make it compress earlier.
(remember nearly all tube power stages compress but it's dependant on a varity of factors)
Contry to what you have been told it is very easy to make a SS rectifier section *Sag* like a glass one.
(also far cheaper to do that than rebuild the PSU to run glass)

A Compressing power tube stage is regarded by some as the holy grail of tube tone but unless you play at full volume or close to it then most tube power setions don't get worked hard enough to hear much power stage compression.
The modern tube amps tend to be multi cascaded triode stage distortion units with *master volumes* and rarely do they get pushed loud enough to attain power amp compression.
(IMO Master volume tube amps kill tube amps unless you play meatal thrash ,,in which case none of it matters much as it becomes impossible to tell the diff)

Remember that all that is needed for power tube dist/compression is to just make the in-coming signal *Bigger*.
A dedicated valve preamp might be nice but can be expensive and you may not need it.
Adding a pedal that creates much of its own distortion but hardly increases the signal swing voltage will do little to evoke power stage compresion.

Fet boosters running from 18 volts or so will work wonders for such a situation as they often make the signal much bigger.
With some work you maybe able to evoke a bigger signal from the SS preamp that already exists in the circuit.
Hope it helps you out.
Have fun, Phil.

The experts will know more bout this but,, I'm sure the pos input terminal of Opamps needs to see a DC path to ground ?  (In this case a single supply rail needs a half voltage refference)

Hey good idea though and it obviously works :tu:
Phil.

Sounds more like a psu problem not a signal transistor issue.

Look for how/where that voltage is derived,, ei some just use a Zener to clamp the voltage. if that goes futt the voltage will climb to the next highest voltage in the psu.
Look for a drop resistor (often a large wattage type,, ie 2W or even 5Watt next to a diode)
Others here might know more about your particular amp,,, be patient. :tu:
Phil.

Hi Zappa,
               I would be doing some homework before I use SMPSU.
Rather than me trying to explain it have a read of this.
http://sound.westhost.com/articles/external-psu.htm#kil

Rather than reading all of it,,,halfway down is a couple of pics which should be self explanitory.

Seems there are some hidden supprises in some of those Cheap psu's.
Ye good ol tranformer is about as safe as it will ever get. :tu:
Phil.

Hi, if you wish to refresh your memory this covers most of them.
I found this extremely helpful some years back.
http://evatco.com.au/ham_files/hampwrselect.jpg

If the jpeg does not load,, go here first, http://evatco.com.au/hamptchoke.htm

click on,, Transformer Selection Guide

There are some hidden gotch-ya's with rectification, wise to note the "I" (current) as well as voltage obtainable from AC secondaries.  8|

(I would post the pic direct but not sure of copyright)
Phil.

Hello Findeton,
Explanation excepted, 8|

Be aware that (to the novice),, comments like that need clarification otherwise it
implies that you just need to emulate a triode to get a full blown tube powerstage
sound and *That is Obviously not the case*.

As one of the lesser motals who do not have the gift of being able to grasp
complex things it took me many years of wading through the endless claims from the
experts who often don't even play guitar.

I've now at least learnt enough to know when something does not sit right.

I respect the fact that every electronics teck has their own idea on what is the *Best* approach to a given subject and I think the wise amongst them respect that there are often many ways to effect the same thing.
At the end it may not make any audible improvement,, just different.

ie; Find 2 technicians who will agree on how to correctly bias a power tube? :lmao:

That's not a criticism of teck's, just an amateurs observation of what I
personally encountered while trying to track down some valid useable information
when I was starting out playing with circuits.

Now I've interupted your work for long enough so Carry on,,  :tu:
Best of luck with it all.
Phil.

Quote from: docz on February 18, 2010, 05:11:56 AM
So bridging the two chips will draw more power than running them in stereo (which is what I did now)?

Selling them is a no no, I allready hacked them up to test it out.

Oh well. I guess I will use them in the testing phase, and the fork out the cash for a real transformer.
But it was a fun thought to power the circuit from a $2 source

BTW. I have an old PC ATX power supply laying around, it has lots of coils in it. Is there any way I can identify voltage/windings and so from the numbers printed on top of them? Or will I have to hook them up to a power source and test?

DocZ

Puter psu is a *Switchmode* PSU and does not use a normal transformer.
I would steer well clear of them until you develop a deeper understanding of how they work. (some of the internal parts are *MAINS LIVE*)
Phil.

Damping comes into it I'm sure but keep in mind that you can build tube amps that go down way past 100hZ (with damping) and a guitar through such a circuit will likely sound horrible.

If you simulate a (Classic guitar type) tube power section note the best sounding tube amps for guitar have a big steep roll off below 100hZ. So in my limited understanding low freq limiting may have more to do with the final result.

The *super TS10* does use a vaugely similar circuit but here again the mistake is made by trying to do everything around 1 little opamp. (I had a TS10, it was way to peaky)

My concern for the *Presence circuit* is *Peaking*. On it's own it may sound good but adding a lot of gain in other circuits (before or after) may lead to oscilations.

With my setup this is working ok but does introduce a fair bit of noise which is why I say,, don't get to keen on uping the boost/gain and it will likely be a good idea.
Have fun, Phil.