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I have had this amp for a long time, over 10 years but I forget exactly and it has had the issue since I got it. I mention that because it has seen heavy use since I got it as well as being left outside for part of a day, having had a stray cat spray it and me wash it as best I could which probably got the speaker wet. It is a late 70’s/early 80’s Mini Brute IV (diamond tolex, textured foam speaker cover).
The problem is that all notes have this fuzzy distortion present that is more audible as notes decay. They seem to be the same pitch as the notes themselves and are much softer than the notes but as the output gets lower (notes decaying) they are more audible. On gigs this has not been any kind of issue and I get compliments when I use it because it actually adds a break up kind of sound that doesn’t sound like distortion, at least that is how people have described it, like an old school not distorted but slightly broken up sound when played loudly. So while that is a plus, I can’t record with it because although it sounds kind of cool live, a recording would make this fuzziness much less appealing.
Coincidentally my old Roland Cube 30x does the same thing, although to a much lesser degree. I know that this is abnormal because I have not heard it with the two other polytones I’ve had or any polytones I’ve played through.
There is smoother occasional problem that I’ll mention in case it’s related. This problem I have had with one other polytone which is at the conservatory I teach at and is the same age if not older, a 2 channel 2 speaker Polytone (not sure what the model is). When turning the amp on there will be no sound or very quiet sound and the only way to get it to work is to crank the volume and play short, loud low notes and then it will “pop” and work normally at any volume.
So if you know what I’m trying to describe, does anyone know what causes this? I use other amps more than the Polytone so it isn’t crucial to fix, but it has still bugged me and if anything I am curious as to what is causing it. I guess the second issue is more of a problem since if I were at a quiet gig and had to crank the volume just to get it to work then it would be a huge issue so if you don’t know about the first problem but do about the second I would love to hear about that too.
Also I can get a recording of it if that helps - I didn’t know of this is a common enough issue that people might know what I’m talking about without needing to hear it.
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02-12-2018 10:48 PM
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Turn the distortion knob all the way up and down several times and make sure that it clicks off--full left (counter-clockwise) the last time. Sometimes the distortion knob will be a wee bit on, i.e., not clicked off. You get a low-level distortion that way.
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the first part sounds like you might have a bad speaker...it doesn't necessarily have to be dead all together to be blown...they fizz and sizzle first...
try plugging in a different cab or "hot-wiring" something (speaker wise) up...
cheers
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Thanks for the suggestion - it might be related to the distortion since it does have that sound but even with it firmly clicked off it makes that sound. I am wondering if it is some solid state issue since the Cube 30x has a similar issue.
Originally Posted by Greentone
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Is this with any guitar plugged into those two amps?
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Yup, any guitar I use. Originally Posted by Cunamara
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My first inclination would be to check for anything loose anywhere on or in the amp. There are all sorts of things that can be a little loose and cause something like this. I've had it be a loose shaft in a pot, really difficult to find. It could certainly be the speaker, and that should be easy enough to determine if you have another known good speaker available. But first I'd check every nut, bolt, and other connection, as well as wires against the cabinet walls, anything that could possibly vibrate.
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Thanks for the suggestions. I will have to look to see if I have the original speaker for the Cube 30x. I don’t have a replacement for the Polytone. Originally Posted by sgosnell
It is definitely not rattling - the quality of the fuzziness is coming though the speaker and happens at low enough volumes that it certainly couldn’t be causing a rattle. I know that some rattles can sound like they are coming through the speaker but this is something that I can only deceive as an electrical fuzziness. It’s hard to explain...I don’t know what harmonic distortion sounds like but I’m wondering if it is something like that or something being caused by power issues?
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Well, if you're sure it's not a mechanical buzz, the next thing I would check is the speaker. I try to troubleshoot by trying the easiest fix first, and on in that order. The speaker is easy to change. If it's something in the electronic circuit, that can be expensive to fix, and hard to find a competent repair person.
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These amps are built so that you can connect an external 8 ohm or more ( this is important) to the speaker jack. Try connecting any good external speaker, and see if the fuzz is present in that speaker. My guess is that it won't be - I have found that Poly speakers from the diamond tolex era get fuzzy-sounding after a few decades of use, and I replace them with eminence beta speakers. After all, speakers wear out too..
edit..uuuh this was suggested above
- twice... but maybe worth repeating,,
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Thanks guys - Franz, I didn’t know the specs of the external speaker jack
so always hesitated to use it. That is good to know that 8 ohms should be safe - I always assumed with the 3 ohm speaker that the external speaker might be weird like that too.
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Which Polytone model do you have that is acting fuzzy? Mini Brute I or II? (12" speaker) III or IV? (15" speaker) Teeny Brute? (10" speaker) Baby Brute or Mega Brute? (8" speaker) The I, II, Teeny, Baby, and Mega all used 4-ohm speakers. The III and IV came with 3-ohm speakers from the factory.
The extension speakers that Polytone made were the same as the internal speakers. I have a Polytone MiniBrute III extension cabinet with an original 3-ohm CTS speaker. Hmm? It could be an Eminence--it's from right at the transition from one to the other.
GT
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Now that you mention it... I have a little open-back Polytone BabyBrute that had a buzzy speaker. I replaced it, and that speaker starting buzzing. I wonder if it's maybe a symptom of a problem with the amp circuitry? Originally Posted by rio
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It is a Mini Brute IV (that is the one with the reverb, yes?) I haven’t looked into it but the shallow depth of the cabinet combined with the 3 ohm speaker made me think that finding a speaker replacement wouldn’t be easy. Originally Posted by Greentone
That’s what I was wondering too, particularly since I can hear the same sound coming from another solid state amp, and the Cube 30x did have the sound with both the original speaker and the replacement speaker. Originally Posted by lawson-stone
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I just checked the old polytone manual; yes, 8 ohms or more will be OK. Originally Posted by rio
This manual is a bit of a hoot to those of us who are familiar with the amps; e.g. "distortion circuit allows you to create your own sound".....Hmmm, good if you like wasps in bottles....They describe the amps as 'short circuit proof' but that's far from the case; in some cases, plugging in headphones can actually blow the speaker fuse ( fortunately, easily replaced once you know where it is hidden). The most interesting is the claim that Poly's provide 'the mellowness of tube amps" and " the sound improves with age" ...so, now we know. Some parts may improve with age, but definitely not speakers; they wear out.
Like old cars, you have to work with their particular eccentricities to get the best out of them.
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I have four of those amps/cabinets. They are great. I have two from the fuzzy felt era (late-70s), one from the diamond Tolex (Boltaflex) era (early-80s), and one from the blue Tolex era (early-90s). I like them all. My favorite is the oldest one with the CTS 15" speaker.
There are plenty of 15" speakers that will work in there. Changing a speaker isn't too difficult. IIRC, the speaker is mounted on the front lip of the baffle board, so you actually don't have to remove the back to swap out the speaker. (That's good because there is a LOT of fiberglas in there.
My preference would be to stay with a 3-4 ohm speaker, but you can put an 8-ohm speaker in there and it will sound great, too. Many people have done this. The amp will lose about 3 db of acoustic volume, but you will likely not notice this.
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Hi Rio,
did you solve the problem with a new speaker ?
I think i have the same problem with a Mini Brute 2
A sizzle around the notes, a sound between a bee and snare trainer ?
All the notes sound great but with this parasite sound in addition
that's right ?
Personally the problem is the same with a another speaker
Is it a recurring problem of Polytone amps ?
Thanks
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Good advise here. I have had issue with buzzing that was caused by from unevenly tighted bolts of the speaker. It is cheaper to check that before buying a new speaker.
Eminence Betas are often used as a substitute. The sensitivity of Eminence Beta 15A is 98dB, so I believe it will be even louder than the original speaker.
https://www.eminence.com/pdf/Beta_15A.pdf
If You live in US You could try ordering a 4 ohm version of it from Eminence Custom shop. They are very helpful.
I have a MBIV too from the red knob era. I have tried 8”, 10” and 12” versions of the Brutes but none of them could beat the 15”.
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Have you tried holding down the Boost/Cut switch? There is a thin sheet of plastic inside that switch that will sometimes buzz like crazy. Drove me nuts until I shoved a scrap of paper in it to shut it up. Just a thought. Originally Posted by Phil13
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i tried anything and it's not that.
The static (i'm not sure of the world), this sizzle sound, comes well fron the speaker.
But, the speaker has no problems, i tried it on another amp and it worked fine, no static.
I tried a headphone and then the same crackle noise on my ears...
Do you think that the headphone circuit could be guilty ?
Very mysterious...
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Rio,
On the 2nd issue, where it is dead until you crank it and then it "pops" to life
is a bad connection somewhere in the chain. I would use a bit of contact cleaner any
place where a connection is made and see if that helps. Had a PA preamp do exactly
the same thing, had to have the drummer scream until it "popped" ... repeated this
technique for months, then fixed it in ~5 minutes on a day where drummer was late.
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