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Topics - phatt

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Amplifier Discussion / interesting amplifier circuit
« on: September 11, 2014, 02:37:44 AM »
I found this while searching forums for ideas on power amplifiers. (Schematics are a bit hard to read.)

Looks like a fair bit of effort went into this unit. He should get a SSGuitar award for such an effort. :tu:

Note the spring reverb unit as well,, looks interesting.

Amplifier Discussion / Thermal limits chipamps
« on: September 04, 2014, 09:12:57 AM »
Hi  all,
Just thought I'd share this for the benefit of chip amp builders.

Seems the die area in poweramp chips is not really up to the task.
It's not just about a bigger heat sink.

3/4 down page he mentions those LM1875 and like chips, between the red graph and the deep fried poweramp chip picture.


Schematics and Layouts / Phatt's Tridozer
« on: June 23, 2014, 07:27:39 AM »
Has been a while but the mind has been quitely growing new plans.
Here is a little OD circuit under test right now, might even build this one.

No it's not a heavy metal gizmo but does a reasonable job of making a clinically clean SSAmp sound a bit more convincing by adding a little rattle while boosting the signal. Works very well in front of my distortion units as a clean boost.
It does not change the tone when boosting on my gear at least.

More testing when time permits meantime here is a screen shot of what it does-zes. This won't put triodes out of production but good enough till a can buy a factory,,, in my next life.  :lmao:.

Have fun, Phil.

Amplifier Discussion / Discrete poweramp build
« on: January 03, 2014, 03:06:55 AM »
Something I whipped up over the Crissy break.
Well I decided to have a crack at a discrete power amplifier circuit and ESP p3 looked like a simple straight forward build so lets see how long it takes to let the magic smoke out. xP

Use this page for any reference;
(Figure 1a is what I've used as reference)

OK I built it on a bread board for testing and after much double checking I fired it up with 40 watt limiter lamp and all seemed ok for a while but when I pushed a big volume of audio signal the lamp lit up and big DC volts on the output. arr-huh? not as simple as it seems.
Now I'm not the sharpest tool in this place but I've had quite a few attempts at discrete power amps long ago and I know that even with the best advice I'm always a little nervous about claims of stability.
Without the tecky knowledge background I can't say why but my breadboard does have rather long wires and that may not help stability.

I do remember ~20 odd years back (while learning that I still had a lot to learn)  about DC coupled pwramps that low values of R4 can cause all sorts of wacky things to go wrong. So I changed this from 560R to 1k which fixed the situation. I assume the latchup might also be due to the lamp limiter but was not brave enough to take the chance that it would work without.

I decided after an A/B test with another power amplifier that I needed a little more output so I changed R5 down to 360 Ohm and this made a big improvement. Of course my concern was would this upset something else but to my surprise it seemed stable and nothing got excessively hot.
To my surprise, all the 5Watt resistors seem to run rather cool, the hottest (make that warmest) part at idle seems to be Q3 and output devices only get warm with high signals for extended periods.
R7/R8 do get warm but again nothing concerning.

The circuit is now working with no limiter lamp so running full rails of 33-0-33VDC and has done so now for a many hours. So just wanted to run this past better minds to see if I've missed something.

Can this be improved by say use of MJ802/MJ4502 (or better) or am I just wasting money for little improvement.
Maybe this is capable of more power but I don't wish to run it on the bleeding edge just to bragg that I can fry eggs on the heat sinks.

Oh yep,, The PTC short protection seems to be working as I did my short circuit test by bridging the output socket and nothing has blown,,, Yet.

Thanks chaps, Phil.

Amplifier Discussion / Chip or Discrete PwrAmp-rebuild
« on: December 17, 2013, 07:47:35 AM »

I recently purchased some kit amps (LM3886) But seems these have trouble driving 4 Ohms,, hum got me thinking again maybe I should just build a simple discrete circuit and be done with it.
My guess is with 35~37 volt rails and 4 x TO3 3055/2955 devices I'd have little trouble driving an extra speaker when needed.

I'm not after the Big wattage,, just the load drive ability.

Here is one that looks like a good candidate.

With 4 power transistors it should drive low loads without much issue.
BUT I want to keep the bandwidth similar to the Laney (KD50) which I note has a hi-pass on the input. (C2 on schematic)

As I use this for both keys and guitar,,I don't want 10~30 Khz bandwidth as digital synths can get gawd damned awful harsh if played through full bandwidth equipment. :grr

So Q is; Can I tweak the Project 03 or similar circuit to react like my Laney KD50 pwramp?
Maybe the diff is negligible and hardly worth the effort but I know from experimentation with other gear there is sometimes a notable difference.
Some power amps have heaps of bottom end yet others do not.
Depending what you are chasing sometimes this is good but maybe not so good if you have a digital keyboard with massive bass output and patches can be quite different, can be a ripe royal pain
trying to balance your sound patches if there is a bottom heavy or top end peaky poweramp.

I know from earlier attempts and simulations that the value of R6 (820R on Laney schematic) does affect freq somewhat but this can upset other parameters,, even going up in smoke.

The other thing of interest is the heat from the laney is not extreme even though the heat sink is about as cheap as you can get the back panel never gets hot, just warm and I do belt this thing hard at gigs so it obviously has no issues with heat.
I don't want to build something that runs on the bleeding edge and needs a fridge mechanic to keep it cool.

I've got plenty of PSU bits to work with just need to drill the TO3 holes in alloy to mount the 4 Pwr Tr's and some bread-boarding will begin.
Looking for clues guys,, open for suggestions.

I could just rebuild the Laney design but after reading Rods insightful observations it might be better to setup a bread-board test and see what I can discover.
I like how this page explains the difference between output designs.

Adding the laney PDF schemo for reference but it's the KB80 but they are very similar.
I've included another schem of The actual values on my KD50 Amp.
My guess is the KB80 runs higher rail voltages? Mine reads +/-37VDC.

Obvious differences are;
R1 =6k8 not 1k
C2 =4n7 not 2n2
D1 and D2 are inverted
Tr5 and TR6 are different

Also C1 is now 47uF which is my attempt to get a little more low end response.
Oh yeah I don't need the protection stuff as I've had wonderful success with those
PTC units (poly thermal fuses) also makes less tracks on the PCB.


Amplifier Discussion / LM3886 at 4 Ohms?
« on: October 28, 2013, 02:07:09 AM »
I've been messing with LM3886 power chip and run into a maybe not so small issue.

It seems these chips suffer with low impedance loads, i.e. 4 Ohm loads. The issue seems to be even moreso with higher supply voltages, so thought I'd ask greater minds for advice.

Without looking hard enough I purchased 2 kits which I assumed where LM3886 powered BUT are instead LM3876 chips and did not notice till after sale that there maybe issues with 4 Ohm loads.
A note on the paper work clearly states that IF you wish to use 4 Ohm speakers you need to use LM3886 instead. Also adding that even with the LM3886 to keep supply rails below 30 VDC. ???

The 2 short form kits are from Jaycar, KC5150 (Silicon Chip Mag, March 94)

It seems I've got everything against me,
As I've got a 36-0-36 VDC supply and I need to drive a 4 Ohm speaker. Bummer!  :(

I'm adding what I think shows the current rising dramatically as it approaches 4 Ohms.
(It's lifted from page 13 on the LM3886 spec sheets)

Obviously this is not good?

I do however have an old stereo transformer which does deliver 30-0-30VDC and I assume that will drop under load. The power amplifier section of the stereo unit is dead, not worth fixing so might be worth the effort to pull it down for parts.

The old amp has four 2Amp fuses on the main supply rails so looks like it would go close to delivering enough power for 2x LM3886 chips.

The new build will be for a small 2 channel pa mixer circuit I'm building which will be used for voice and will not need super low doof doof bass response so that should help relieve some need for massive supply grunt.

So I'm thinking this might just work but as I'm not sure of actual current ratings of either the transformer nor the lm3886 chips I'm askin for help.

The transformer in the old stereo is actually a C section design and I believe these are very efficient designs, only surpassed by those donut types.
Thanks all,, Phil.

Schematics and Layouts / PhAbbZone pedal
« on: March 25, 2013, 09:05:26 AM »
Hi all,
        Here's my latest venture which at first was looking like a fail but after last weeks gig I'm very happy with the result. <3)

This is my New front end floor control board,,, A bit bigger than I wanted but it makes life easier to tweak. I've learned not to squeeze things into tiny boxes especially as I'm the fool that has to fix it *IF* it stops making music. 8|

This took forever to prototype but hey It finally worked the way I wanted.

A hybrid with 1 AX7 and a tricked up distortion with 2 EQ stages as well as a switchable notch filter.

Also a parallel loop for the LessLee and other tricks I've built.

Due to the 2 years this took to perfect The front panel and internal pictures are from the first build but should give a clue as to the layout and basic setup.

The switching is all straight forward simple analog switching. No relays to ef up,  :trouble just plain old switches which unlike tecky circuits usually give a hint they are about to fail.

Powered via a plug pak from a dead printer delivering 18VDC which powers all the chips.
The high voltage is derived from the nixie psu using a 555 and inductor.
HT is around 260 VDC while the extra lm317 is set at 12VDC for filaments and also drives the nixie supply.

As to Why all this complexity? :-X :duh

Well I've discovered that distortion is actually not that hard to get,, what is insanely hard to nail is all those in between sounds. as a lot of that magic may have more to do with the quirks of triodes.
See member KMG's Work on Fets,, really helped me grasp the finer details of how they work
(or don't work might be a better term)
I would have gone with some of his ideas but I had already got halfway through this build and I knew Real triodes where a sure bet.

The rattle of those old famous Amps has been the hard part for me to reproduce and that is the sound I wanted more than just the distortion.

I know some will want sound clips but you will just have to wait. 8|
Meantime here are some pictures and some of the schematics.
there are 8 boards in the final build so you will have to join up the schematics.

Anyway have fun with it may give ideas as to what can be achieved.

Schematics and Layouts / Kustom 100 head
« on: March 11, 2013, 09:50:58 AM »
Thumbs up for this one,,I've been playing at the local pub (Sunday arvo jam) and I noted a chap used this Amp through a PA which at first sounded horrible but I was impressed that he quickly dialed in a sound that was Very much the classic thick marshall sound.
He was playing a stock Mex strat,, no pedals.

So I looked it up and first hit was this;

Wow how lucky you can be sometimes.
Note the link to a PDF of the Schemo as well. :dbtu:

I'm not much interested in the digi efx trip, it's more the analog preamp section that impressed me. This is likely considered a cheap Amp but boy oh boy it nails that classic sound very well.

My guess (after some quick and dirty simulations) I Note the input is much like a lot of fender SS inputs which kills everything below ~100hZ. Then C13 and C15 roll off a big slope above 3khZ forming a close to perfect Marshall response curve.

IC8B is obviously some kind of cab sim (which I've not yet simulated). This drives IC8A , a balanced line out. Which is the output that drove the PA and the sound I heard.
I've not had time to play through the rig myself but my ears are experienced enough to recognize that classic sound. 8)
May not be a heavy metal machine but a few pedals might evoke some other tones.

Having spent many hours trying all sorts of cab sim type circuits which are often complicated,, this might be a much simpler build as I would not need all the fancy switching for crunch, clean, drive, boost and efx.

Hum, I might have to get out the bread board and do some testing.
Damn so many ideas I get but I run out of time to test them all.  >:(

Interested in hearing others who have heard/used this Amplifier?
Ed; Oh forgot to ask;
Any of you talented folks wish to make observations pro or cons,, I'm all ears.

Amplifier Discussion / Performer 1000 help
« on: December 04, 2012, 07:52:14 AM »
My mate's Performer 1000 is back. ::)
This Amp has way too much bass as well as harsh treble.
His guitar is a stock 80's strat and he is chasing a classic blues/rock tone.

OK I've tweaked the preamp but I'm still not happy (and neither is the owner).

I feel that I may have more success working from the other end but as the power stage is not straight forward I'm a little reluctant to start poking a stick at what I do not fully understand.

Anyways the detail and some Q's;
What I'm trying to get my head around is the bass roll off point for the power stage as I feel
that is going way too deep and may need some tweaks but it's kinda confusing.
This power stage obviously has fancy FB via R117 and C51 while the normal FB around U7 is via
R94 680k.
Obviously R92 and C50 will also effect the roll off, then there is R93 and C52.
As well R95 27k looks really wacky and it also connects to the output which I assume is also a form of FB.

I'm open to any suggestions,, hopefully I'll learn something lol.   

I know it's basically an opamp with a booster hung off the end but these suckers can go poof
faster than Roly can type idiot so I was wondering if the excess bass could be rolled off
without danger of a meltdown.

I'm starting to think that I should have left the preamp as it was and focused on the other
A recent comment from J M Fahey prompted me to swap a few speakers but I feel after some testing it's not going to fix what maybe a deeper design issue.
PDF attch.
Cheers, Phil.

Schematics and Layouts / Spring Reverbs again
« on: November 26, 2012, 08:21:49 AM »
Hi all,
        I have been re-visting Reverb circuits so I thought I'd share my findings.

I scoured an old bit of junk a Ross 5 channel powered mixer. A rather poor performer for audio but did have a 3 spring 9 inch rev tank.  The tank has high Z transducers at both ends. bum. :grr
My Maxiverb circuit will only drive the lower Z units so I came up with a plan and it certainly works way better than I expected. <3)

My original Maxiverb needed two supply voltages and had a rather oddball output but
This circuit only needs split 15 volt rails and lower parts count so it would be much easier to build.

So if you have one of those high Z reverb tanks this might just be the ticket for a very good Reverb unit that won't break the budget.

The small Output/Line Transformers should be easy enough to find and likely dirt cheap.
The DC reading is around 190 Ohms / 330 Ohms. The Resistance can give a clue as to the Z.
My guess is this one I've got is 600 Ohm / 1k Ohm Z.

I've spent a few days A/B testing between the original *MaxiVerb* and This one and although it does not have quite the big slap there is little between the two circuits.
The short tank does sound a tad different but on stage you would not be able to tell.

If you specifically need the country slap-back effect then you will likely need a long tank for that.
With short springs the slap delay is way too short to get that particular effect.

Just like the Maxiverb this one is bright and airy due to plenty of bass roll off which allows a higher output of reverb before it all turns into undefined mud.

With the Dwell full up this is dripping wet reverb reminiscent of the old surf sound which is what the Maxiverb does so well. Not quite the big tank slap of the Maxiverb but I hardly ever use that anyway.

As The Maxiverb (long tank) takes up more space the short tank might be well suited to a smaller chassis and I might even be able to implement it as a floor unit.
Time will tell, still a long way from a working unit but no point in rushing it.

I have no doubt that other chips will work just as well maybe even the tiny LM386 but it's single supply and may not have enough drive and you would likely need an 8 ohm/ 1k Ohm transformer.

I'm Not sure about the NE5532 as they have compensation pins I'm assuming they are not needed here but if anyone knows more about those fine details feel free to comment.  :tu:

Anyone have a background on the 3 spring tank?
OC Electronics, Milton Wi and 2 long patent numbers, on the side reads 756
I assume Wi means Wisconsin?

Schematics and Layouts / Roto effect
« on: August 17, 2012, 10:08:06 AM »
Thought it time I posted something for folks to tinker with. This one has been sitting on my breadboard since last year.
I'm calling it the LessLee ,,cause it weighs a lot less than a real one.

I doubt it will come across as good as the real thing but it seems to do the trick.
Now just a matter of producing a board but other things taking up time.

I intend to use an old volume pedal for speed control (VR1) so if I layout my board small enough I might get the whole thing into the volume pedal housing.

The main part is the XR2206 chip which is likely capable of many options and many ideas where tried and although some produced interesting results I only needed the basic subtle rotation effect.
At slower speeds this certainly produces a very rich spacial effect different from straight chorus or phasers I've heard.

At high speed some glitching may bleed through depending how well you set it up. I made better progress by uping R4 and keeping R6 and R8 smaller.

You can of course insert other phase circuits in place of U4 and U5 but this seems to be doing a fine job and chaining more phase stages does not seem to improve the sonic result if anything they sound wonky at high speed.
I'm running this from 18VDC plugpak and testing showed it did not run well below 12VDC.

Now I just have to find time to build the darn thing. :(
Have fun with it,,Phil.

Schematics and Layouts / Small Amp fix
« on: May 29, 2012, 04:27:22 AM »
Casino 12 Amp fixup.
Normally I would just keep this stuff for spares but I realised there is a lot of interest in small amp builds on this forum so with a little effort on my part might help those who wonder which circuit to build.
I'm not claiming it will sound like a bedside Soltarno but I think I've dramatically improved it with little effort.
Hum, So What to do with an unwanted toy amp that shows no sign of life.

This was thrown my way not working so a quick inspection showed the LM2030 power chip was blown. Lucky I keep junk and sure enough I had a LM1875 which was pin compatible so I had it working in no time. ;)

But oh what a horrible piece of trash it was, *insanely bright and harsh* even though it was powering a big 15 inch driver which did not have much treble output. :duh

I pulled it all out, traced the pcb to a schematic, input the data to the simulation and sure enough way to much bandwidth. So after a long head scratch I came up with this, see schematic.
Delete C5 and break the signal,
add 4 components (green circle)
and change the value of 4 resistors.
Bingo success, now it at least sounds like a guitar Amp  :dbtu:

The 15 inch driver now shows it's darker tone and you need to wind the treble but most of these amps will be driving much smaller speakers so it would sound close to ideal running a small 6 inch speaker which generally have more high frequency output.

A classic *Too much bandwidth* issue which just kills these things dead as soon as you turn up the bass they just splatter because these little power chips are just not capable of very low freq.
It's wise to wipe it out if you can.
And most distortions sound trashy and cheap with high frequency much above 3kHz so again you need to wipe it.

Stuff in the green circle;
If you want more Treble content, make the 33nF smaller.
If you desire more bottom end, then increase the 10nF.
both values will likely be very dependent on R5 being 10k.

If you need values for the power supply and power chip they can be found on the data sheets.
This rig runs 16-0-16 for power chip, preamp power via 270R drop resistors.
Have fun,, Phil.

Schematics and Layouts / KiCad Tips
« on: February 21, 2012, 08:27:15 AM »
For those interested in Kicad.

I found some Kicad user help.

Seems to be well worded with not too much reading involved,,, I like that idea  :dbtu:

Unlike Eagle the library parts system is a little tricky and I'm still trying to get my head around that.

Preamps and Effects / A bit LessLee
« on: January 04, 2012, 08:10:46 AM »
Is it a Tremolo, a Vibrato, or Rotary speaker? ???

Most Phaser systems use an LFO to work the phaser setup which is nice but most can't replicate the rotary effect like a Leslie Speaker. In this case the signal is the LFO tremolo effect which is then passed through a phaser circuit.

My guess is a real rotating speaker has phase modulation as well as level modulation which delivers a much closer resemblance to the real thing.

Please don't ask me how it works as this was just one of those days when I stumbled upon something.
Every now and then even a novice like me does something really cool.
So glad I tried it. :)

It will likely distort too much on a 9 Volt supply,, I'm using 18 Volts.

The separate bias for the XR2206 is definitely needed just fine tune the trim pot it until the hash disappears and it's then very quite.

XR2206 is a function generator IC and I'm told it is fairly common chip though I had to spend  $15 to get one.

I also tested the phase circuit used in the *ROGphozer2* which works well but adds to the part count and circuit complexity.

In Use;
       This Schematic is on the breadboard and I have another slightly altered unit being used live.
The speed should be obvious. The Tremolo and Vibrato are mixed separately allowing for many combinations. Some may wish to simplify it with one dual pot.

This can go from straight Tremolo (Volume up, down) to full on modulated head spin phase modulation.
(Depending how you mix the levels) Turn the *Dry mix* full off and it will go back to straight Tremolo no matter where the other knobs are set.
The rotary trick relies on a dry mix always being present in the mix.

As I'm sure you can appreciate I don't have a warehouse full of every efx unit made to compare this to but I DO Own a real rotating speaker so I've got a fairly good example of what constitutes a Leslie effect.

This is still not as good as a real spinning speaker but I'm very happy with what I've stumbled upon and it's a lot smaller than a speaker. Winky. 

Any interest and I'll get some samples recorded.
hope you all have a happy 2012. Cheers, Phil.

Tubes and Hybrids / PhAbb NowWatt
« on: July 07, 2011, 10:41:17 AM »
Hi all,
Yet another circuit for you to play with. ;D

This is the first part of what is basically an elcheapo Guytron GT100 inspired concept.

For those that don't understand this idea, it's basically a dual Amp setup where the first Valve  Amplifier is driving a load (Not a speaker) and the signal is tapped off and Re-Amplified via a Second Main Amp.

This gives *ABsolute Loudness Control* no matter how hard the first amp is driven.
You now have the ability to dial the Valve rig to the sweet spot and not have to ever worry about playing too loud.

This lifts the dreaded restriction of setting SPL levels in smaller venues or just playing at home. You can now play full up without annoying the folks next door.  A great asset for practicing those fast high gain licks.

The Guytron is a *2 Valve Amps in one Box trick* which would be fantastic but the cost is a little scary for the average player.  I've gone down the *Modular path* which allows me to swap things around if need be and because I'm using cheap S/hand bits I've kept my costs to a bare minimum.

The floor pedal is a mix of Mesa Vtwin ideas and my HiWatt inspired PhAbbTone. Sadly the Vtwin like most valve powered preamps tries to do the OD/Distortion all in the preamp stages but anyone who understands valve teck well would know that **Triodes can't do square wave like Pentodes** and although these circuits can produce copious amounts of crunch/ distortion they tend to lack the richness of a pair of output pentodes driving through a transformer.

*Pentodes where actually invented to overcome the sevre shortcomings of triodes,, hum.*
One wonders at the wisdom of rows of fizz bottle triodes??? :loco

As will be obvious to those who know the Vtwin circuit, I've only used the *Clean section* as the crunch channel is basically useless for the sound I wanted and was just wasting space.
**The main Valve Amp does the magic endless sustain and touch dynamic ODrive**

So don't build this floor unit thinking it will be a monster crunch pedal as this produces a very clean signal but with greater voltage swing than an all SS unit.
Although it does do a very nice rock (half wave) triode rattle when driven hard on the Clean channel. <3)

If you desire the *Mid scooped Metal sounds* you will need a Graphic in the final Loop before main SS power Amp and most will want a bigger main Amp and speaker setup as small amps struggle with low freq.

For the small gigs I do this little Laney is just so damn convenient.

A quick post of the first schematic section.
(I will Update this if there is some interest and give more details of the finer points of building such a rig.).

Enjoy, Phil J A.

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