Fuzzy Polytone sound?

[C#risM]

I had a similar problem with an Evans amp. Per Evans' instruction, I cleaned all the contacts between the various PC boards and that took care of the noise. They said it might return if the contacts got dirty (oxidized) again. This is on about a 30-year-old Evans 80.

Thank you for the tip, dconeill. I will go through all the pots and visible contact points, snap connectors, etc. and clean them with Deoxit and see if that does the trick. I'll post back here with any results.

[C#risM]

If you love the sound of the amp (I certainly do), it's definitely worth getting repaired. I mean, think about it. They're all 40 years old at this point. Don't they deserve a trip to the doctor?

Bring it in, spend 150 bucks on getting it back into shape, and it will be good for another few decades.

How many of today's smt constructed, class d amps are still going to be alive in 40 years? I suspect it won't be many.

Thanks for the comment, vintagelove. I definitely love the classic sound of these amps and would happily pay $150 or more to get it sounding the way it should. However, I live in a major metro and can't find anyone willing to even look at it. Maybe people are really busy, but at least one said too much of a headache others say no solid state amps. If anyone has a tip on a shop in the Pacific Northwest US that could fix it please chime in or PM me.

[Mick-7]

Manuals and Schematics for Polytone amps -- Polytone Schematics

I have a Polytone 102 amp that I bought from Good Will a few months ago. Everything worked on it, however, I figured since it's about 50 years old I should have my local amp tech look it over. He checked it out and said it didn't need servicing.

He mentioned that a particular part tends to wear out after many years and need replacing but unfortunately I can't recall what it was. I'll ask him the next time I talk to him. He said that the innards of Polytones tend to be hard to get to, with all the paneling and what not, so he has to dismantle them before he can give them a proper inspection.

[Herbie]

Manuals and Schematics for Polytone amps -- Polytone Schematics

I have a Polytone 102 amp that I bought from Good Will a few months ago. Everything worked on it, however, I figured since it's about 50 years old I should have my local amp tech look it over. He checked it out and said it didn't need servicing.

He mentioned that a particular part tends to wear out after many years and need replacing but unfortunately I can't recall what it was. I'll ask him the next time I talk to him. He said that the innards of Polytones tend to be hard to get to, with all the paneling and what not, so he has to dismantle them before he can give them a proper inspection.

Woah! 20$ for a schematics of a 30-50 year old ”outdated” amps?!

At least someone sees the value of Polytones!

[garybaldy]

At least someone sees the value of Polytones!

There are a few of us.

[Mick-7]

Woah! 20$ for a schematics of a 30-50 year old ”outdated” amps?!

At least someone sees the value of Polytones!

Yeah, that is annoying but if anyone has found a free or cheaper source for amp schematics, by all means share it.

[vintagelove]

Yeah, that is annoying but if anyone has found a free or cheaper source for amp schematics, by all means share it.

just about every polytone Schematic is posted free numerous places online. Just Google polytone schematic.

there may be some oddball models, or perhaps some of the newer amps, that would be difficult to find. However, the core of the amps they made are easy to find

[vintagelove]

Thanks for the comment, vintagelove. I definitely love the classic sound of these amps and would happily pay $150 or more to get it sounding the way it should. However, I live in a major metro and can't find anyone willing to even look at it. Maybe people are really busy, but at least one said too much of a headache others say no solid state amps. If anyone has a tip on a shop in the Pacific Northwest US that could fix it please chime in or PM me.

this might sound harsh to say, but it certainly closer to the truth than not. Guys who refuse to work on SS amps, at least old ones like a poly, aren’t real service technicians.

there are guys like me who can fix your tube amp, and make easy money doing biasing and fixing the simple stuff.

then there are guys like that, who are actually really good at it and have been doing it for 20 years and have seen the bulk of what goes wrong in most amps that walk through the door.

Then there are real service technicians. Guys who went to school for electronics, or learned it in the military, and they actually understand ALL the circuits. All the little details, all the component values, etc…

A real tech would look at a poly and laugh thinking “there’s almost nothing in there”.



Seriously, they are a dead easy amp to service. Look around your area for a general electronics repair shop (not a guitar store). The type of shop that repairs tv’s and radios, appliances etc. These guys are generally pros and can fix damn near anything. They’ll take it, put a scope on it and go “oh, it’s xyz”.

And it probably won’t take 3 months to get your amp back like the guitar store techs…. That being said, if you do find one of those places, try to do a little research to make sure that they have reasonable/reliable return times.

Good luck.

[C#risM]

Update: I was able to get in contact with a well-known and respected audio repair shop in my area with an amp tech that has experience with older Polytones. They suggested I clean the mechanical switches and quick-connect wire contacts (D5), and clean and lubricate the pots (F5), which I did (similar to what @dconeill suggested above). Afterward the amp was louder, the volume pot was no longer slightly scratchy, and all felt nicer to turn. I also tried the "speaker out" to a known good speaker to rule out a bad speaker. Unfortunately the trailing fuzzy sustain was still present exactly the same as before.

So I brought the amp in to the shop that gave me the advice. Based on my verbal description of the sound, they suspect that it is "crossover distortion" resulting from a biasing issue between the power amp and the preamp.

The shop has a several months backlog of work (piles of spectacular looking vintage amps!), so it will be a while but I will share what I learn here when I get results.

C#ris

[Mick-7]

The Mini-Brute has the red push-pull Distortion knob on top of the Volume knob like my model 102, doesn't it? If I turn it on, I'll get a fuzz tone sound similar to what you described, I wonder if your problem is related to it?

[Bob_Ross]

Update: I was able to get in contact with a well-known and respected audio repair shop in my area

For others of us with aging Polytone amps, where is the "upper far west US" and what's the name of this repair shop? Thanks.

[C#risM]

The Mini-Brute has the red push-pull Distortion knob on top of the Volume knob like my model 102, doesn't it? If I turn it on, I'll get a fuzz tone sound similar to what you described, I wonder if your problem is related to it?

This Polytone does not have distortion or reverb. It only has three pots (bass, treble, and volume) and a brite/dark switch. I think it came out before the red distortion knob or the mid tone control were introduced. Based on a sharpie marker number on the preamp housing (120183) I'm guessing it is a 1983 model.

[C#risM]

For others of us with aging Polytone amps, where is the "upper far west US" and what's the name of this repair shop? Thanks.

Hi Bob Ross. I'll share the name of the shop here when they finish with it, since I'd rather hold off until I can recommend one way or the other. It is a well-known audio repair shop in the Seattle, WA area. If you need to know sooner PM me.

[rjfoscato]

I have two Amp I have been reconstructing, a PolyTone Mini S15L (Jazz?) it maybe a Taurus?. I've attached two jpgs of the amp. It's two channels so easier to trouble shoot. I'm looking for a schematic of the pre-amp.

Problem 1) When I turn it on, I get a Very Loud Pop, All volume controls are zeroed out. Could be biasing on power amp.

Problem 2) If I input on Channel one Very low volume and Very High Distortion. Channel 2 is very clean and loud.

Ideas: I will try the distortion Pot solution. Not Speaker, Pretty sure it is 4 ohm, 15 inch.

Very Important, I need the schematic.

Thanks. I just want to restore and then sell.

[C#risM]

Hi All:

I wanted to follow up on my messages since I got the Polytone Mini Brute (80's era diamond Tolex, no reverb, no distortion) back from the shop this weekend after three months in the queue.

First off, the amp now sounds great! So, it was definitely fixable and the shop I took it to (Aviator Audio in Edmonds, WA near Seattle) did an outstanding job. The trailing distortion on sustaining notes was caused mostly by crossover distortion that biasing the power amp transistors fixed. This took out the "notch" where the signals did not meet up correctly - it now has a fantastic clean warm tone again.

A couple other items the shop did was re-glue the magnet to the speaker which was slightly loose (and apparently had a prior sub-par glue repair job). They also swapped the RC4739 ICs in 14 pin DIP sockets (beyond my technical depth) to minimize static noise. A few other minor maintenance items included re-gluing the mesh over the speaker (under the original grille foam) and fixing the worn out strain relief on the AC power cord which was loose through the back panel.

All told: $300 USD plus tax. Given the work and labor costs in my area, I think this was a more than fair price and will set this amp up for another very long run.

Now the other side of the coin: I needed a small portable inexpensive amp during the time the Polytone was in the shop. As I mentioned in a previous post I was uncertain I could even find anyone willing to service the Polytone, and wasn't sure it was even fixable, and at minimum would be in the shop for 3+ months. So I bought a cheapo used Roland Cube 30X to tide me over for about $100 USD. It is much lighter and a bit smaller than the Polytone - and with a touch of reverb puts out a fantastic jazz tone with both single coils and humbuckers - easily sufficient for my needs. It also dials in some other tones (I probably won't use them) and is just about as loud as the Polytone with fairly high clean headroom.

I'm not a huge tone snob and my ears are certainly not as refined as others on this forum, but on the tone/cost/portability equation, the Cube is, for now, my go-to for classes and jams.

Cheers, C#ris

[rjfoscato]

Update:
Found the schematic's, pic's from a Facebook. Usable but difficult to read. Don't know where to post.

Problem #1) solution, replaced power caps on amp/power supply, (on bottom of cabinet back left. Fairly easy to get at. Per Print, upgraded Caps from 7300uf 50v to 8400uf 50 v.

Problem #2) Solution Washed all pots with electrical contact cleaner FROM back of pot to shaft. Could have been dirt, could have been smoke, whatever.... Also checked and tighten down pot assembly brackets (not hold down screw) but clips. Works now.

Discovered Speaker is an Eminence 15 inch, 2.9 ohm. May have been (at one time a 2 ohm or 4 ohm). My feeling is it probably was a 4.0 ohm (common), print called for two ohm. I may or may not work on the speaker depending on the sound. Voice coil may need work.
End

I have two Amp I have been reconstructing, a PolyTone Mini S15L (Jazz?) it maybe a Taurus?. I've attached two jpgs of the amp. It's two channels so easier to trouble shoot. I'm looking for a schematic of the pre-amp.

Problem 1) When I turn it on, I get a Very Loud Pop, All volume controls are zeroed out. Could be biasing on power amp.

Problem 2) If I input on Channel one Very low volume and Very High Distortion. Channel 2 is very clean and loud.

Ideas: I will try the distortion Pot solution. Not Speaker, Pretty sure it is 4 ohm, 15 inch.

Very Important, I need the schematic.

Thanks. I just want to restore and then sell.

[Bob_Ross]

Problem 1) When I turn it on, I get a Very Loud Pop, All volume controls are zeroed out. Could be biasing on power amp.

Problem #1) solution, replaced power caps on amp/power supply, (on bottom of cabinet back left. Fairly easy to get at. Per Print, upgraded Caps from 7300uf 50v to 8400uf 50 v.

That's good to know. fwiw my 1980 MiniBrute III (which I bought new in '80) has always had a -- I don't want to call it "Very Loud" but let's say fairly conspicuous POP when I turn it on.
It also has an even more conspicuous THUMP when I turn it off.
Wonder if replacing the psu caps would address either of those.