A Polytone is also what I always wanted to build. I already got the schematic and started working through it, but I'm still lokking for some kind of PCB Layout. Can anyone help me?
Simplified Circuit diagram
Yes, same here. I too am looking for assistance with PCB layout.
I obtained a simplifed circuit diagram without the drive circuit (I think I got from from Jazzpeter65) which is attached if that helps in any way. I would love to build this amp somehow (or have a the circuits buit for me if I could persuade some great person). This scematic looks more simplified but I'm an absolute tech beginner. Any way here it is.
Yes, same here. I too am looking for assistance with PCB layout.
I obtained a simplifed circuit diagram without the drive circuit (I think I got from from Jazzpeter65) which is attached if that helps in any way. I would love to build this amp somehow (or have a the circuits buit for me if I could persuade some great person). This scematic looks more simplified but I'm an absolute tech beginner. Any way here it is.
Attachments
I know this is hopelessly out of date, but I have 2 schematics that came w/ my Mini - Brute IV. I can scan and e-mail to whoever needs them. One is for "power amp model 378"; the other: pre-amp and valid for "I, II, III, IV, Baby Brute, Teeny-Brute". Mine has, among others, a horrible noise in the clean vol. pot which contact spray can't fix. That's because, I'm told, it has to be sprayed from the INSIDE. The amp also distorts and I believe the cabinet is now shaking as well. Aside from that, Mrs. Lincoln... ! And if my grandma had a wheel, she'd be a wheelbarrow. Who would like to come over and fix my accursed implement?! I know way too little to do it myself.
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Yes, and you have to take your socks off to wash your feet.
Inside is where the control is dirty, inside is where you spray the celaner. YOu have to take the rear panel off the amp to get at it.
Inside is where the control is dirty, inside is where you spray the celaner. YOu have to take the rear panel off the amp to get at it.
POLYTONE AMP. UPGRADE SCHEMATICS
🙂HI PETER,...WILL YOU BE ABLE TO SEND ME A COPY OF YOUR UPGRADE SCHEMATICS TO MY MAIL ,..I DO NOT GET THE PICTURE TO CLEAR,...MY MAIL,..xanclon@hotmail.com
🙂HI PETER,...WILL YOU BE ABLE TO SEND ME A COPY OF YOUR UPGRADE SCHEMATICS TO MY MAIL ,..I DO NOT GET THE PICTURE TO CLEAR,...MY MAIL,..xanclon@hotmail.com
Hi Guys, yes this is an very old thread but I've only just acquired a baby brute there like hens teeth here in Australia & reading some of the earlier comments I to would like to MacGyver my unit so to speak. From what my amp Technician has found is that my reverb recovery is faulty & finding anything to replace is near to impossible, but I'm also interested in upgrading components & upsizing the 8'' speaker to the 12'' as mentioned, I do love this little amp any help will be muchly appreciated, cheers Joe
The reverb recovery is a plain vanilla circuit, all components available over the counter, no mystery parts.
You measure/troubleshoot it and replace what´s wrong.
You may "upgrade" components (spend more $$$$) but that won´t change sound, which comes from design, not "parts".
Only valuable replacement is the original input Op Amp(s) by newer lower noise ones but they must be pin compatible to fit.
Post the original schematic matching your version here.
If it´s the tiny model built around an 8" speaker I much doubt you can fit a 12" there.
Thanks PRR
For those who like the Polytone sound and would love to DIY, but are somewhat flabbergasted by the complex schematic for the full version and even worse for having to design such a PCB, it can be simplified to its core, retaining all sound but with NO frills ... which is fine for many.
In fact a few Polytone originals are real simple, and all sound the same.
1) Preamp: you can make its core: Hi/Lo inputs > U1b > Tone pots > U1a > Volume > U3a > main/Power Amp OUT
That´s it, no Drive, Reverb, Switching, etc. but a true Polytone preamp, very doable.
2) Power Amp: any Class AB power amp, including an LM3886,but using Polytone NFB network instead of the plain original one.
You need mixed feedback to increase amp output impedance (kill damping) so add a 0.15 ohm 10W resistor from speaker "-" terminal to ground and use: R22 - R23 - R9 - R6 - C6 - R8
Original NFB would have used something like R8 - C6 - R6 so replace them with "Polytone values" and add the few components needed, easy peasy.
3) Speaker: use an Eminence "Guitar" type, not any Hi Fi/Woofer/whatever type.
4) Cabinet: clone a Polytone cabinet as close as possible, including its heavy internal fiberglass damping, boxy stuffy closed claustrophobic IS part of its sound.
"Warm" Jazzy sound in part comes from low mid resonance created by a speaker inside a way too small box.
FORGET Thiele Small/Hornresp/REW adjustment, tuning, "improving" speakers, etc. , this is not the place for refinements.
Also forget silver caps and wiring, Audiophile stuff, etc.
You might make a cabinet out of beautiful polished fine woods or anything you fancy, it will not affect Sound ... which is good.
For those who like the Polytone sound and would love to DIY, but are somewhat flabbergasted by the complex schematic for the full version and even worse for having to design such a PCB, it can be simplified to its core, retaining all sound but with NO frills ... which is fine for many.
In fact a few Polytone originals are real simple, and all sound the same.
1) Preamp: you can make its core: Hi/Lo inputs > U1b > Tone pots > U1a > Volume > U3a > main/Power Amp OUT
That´s it, no Drive, Reverb, Switching, etc. but a true Polytone preamp, very doable.
2) Power Amp: any Class AB power amp, including an LM3886,but using Polytone NFB network instead of the plain original one.
You need mixed feedback to increase amp output impedance (kill damping) so add a 0.15 ohm 10W resistor from speaker "-" terminal to ground and use: R22 - R23 - R9 - R6 - C6 - R8
Original NFB would have used something like R8 - C6 - R6 so replace them with "Polytone values" and add the few components needed, easy peasy.
3) Speaker: use an Eminence "Guitar" type, not any Hi Fi/Woofer/whatever type.
4) Cabinet: clone a Polytone cabinet as close as possible, including its heavy internal fiberglass damping, boxy stuffy closed claustrophobic IS part of its sound.
"Warm" Jazzy sound in part comes from low mid resonance created by a speaker inside a way too small box.
FORGET Thiele Small/Hornresp/REW adjustment, tuning, "improving" speakers, etc. , this is not the place for refinements.
Also forget silver caps and wiring, Audiophile stuff, etc.
You might make a cabinet out of beautiful polished fine woods or anything you fancy, it will not affect Sound ... which is good.