Polytone Mini Brute II

[Fred Petersen]

Is there anybody out there who has access to, or can tell me, where I can find the schematics for The Polytone Instruments Co.
Mini Brute II guitar amplifier.

I found one at a garage sale for nothing, however it's missing the 12" speaker, and there's a problem with the power amp.
My friend said he'll repair it for me for the cost of the speaker and if I found the schematic for it.

I think the one I own is the early incarnation of this amp, The Murch Music web site (Polytone page) shows 2 user manuals (early + contemporary) no sign of a schematic on their site however.

It would be nice to have access to both schematics to see if it's easy to bring mine up to the newer specs.

I'm currently running my bass through a vintage Garnet LiL'Rock
bass amp(taller version with sealed back) which is getting to heavy for this 50+ boomer to be schlepping around.

The Bottom Line bass newsletter has some references to using the Mini Brute II for bass even though it is a guitar amp.
Apparrently Polytone made a Mini Brute bass amp.
I'd be interested in a schematic for this amp too if any one can help.

I'd appreciate any help on this........................

Thanks...................Fred Petersen

www.audiofileoptions.com

[jazzpeter65]

HI!

I have built a copy of the Polytone amp. Sounds much better than the original since I have upgraded the circuit with better components.

Try to attach the pictures of it here.

Best,

Peter Lund

[jazzpeter65]

Picture of my "Polyclone":

[jazzpeter65]

Picture 2 of my "Polyclone":

[Fred Petersen]

Hi Peter:

Thank you for your e-mail & the pictures you attached

Is the schematic you sent of the mods you made or is it the stock schematic.

.................. Thanks again Peter

...................... Fred petersen

[jazzpeter65]

HI Fred!

The schematic is stock. There is very little difference on the different Minibrute series. The pre amp is similar on 95% of all models. The power amp is a traditional bipolar. Nothing fancy.

My mods are only using better parts. The stock amp parts is not actually high-end....;-)

I'm using a mix of OPA2604, OPA2134 and NE5534 in the pre amp. For the power amp I'm using a Mosfet.

It's a good mix. It sounds fantastic, and I have used it on many gigs without any problems.

Also I have reduced the number of caps in the signal path - using only film caps where necessary.

This have really made a difference.

I have a few OPA627AP that I would try for the output buffer. The amp is still a little too noisy.

As you can see the input impedance is around 680K. This is quite normal in music amps for some reason. Finding a way to lower this would make it quieter.

If you need a better scan of the original amps I can mail them for you. I think I have all of them.

Are your Polytone the one with a 12" speaker? If it is, you can help me: I'm building my next clone and this time with a 12" speaker (the first was a minibrute 8").

I need all the mesurements of the cabinet. Maybe you could make a basic drawing?. Like thickness of the wood etc. I think keeping the original dimentions is important.


Best,

Peter

PS: A great deal of the genuine Polytone sound is of course using ONLY Eminence speakers. You can get the very easy and they are cheap too.

[Fred Petersen]

Hi again Peter:

>Thanks again for your help.
It's been awhile since I first posted this thread.
Since then I've installed an Eminence 12" speaker
in the cabinet and the minor repairs on the amp
have been done.

>However I have been having some problems with hum
and I also noticed the hnoise level of the amp is
high. I'll talk about your solution to the output
buffer noise problem with my bus. partner who is
also an excellent tech.

>Because of the problems I'm having, the Mini-Brute
is going to be dis-assembled while it's apart I'll
take the cabinet measurements for you and put together
a simple drawing. It may take a few weeks but I will
put the info together for you. Keep an eye on your e-mail.

>In return I'll take you up on your offer of sending me
better scans of the schematic thru the mail. You can get
my mailing Address from my web site which is referenced
on the thread it should be a direct link in case it isn't
here is my web site www.audiofileoptions.com

.............................Thanks again Peter

.................................... Fred petersen

[Fred Petersen]

it's me again:

ps.to previous post

Let me know what you think of my page

...................Thanks again Peter

..................................... Fred petersen

[Fred Petersen]

Attn. members who have been trying to reach me regarding
The Polytone Mini-Brute schematic and ay one else trying to
Reach me thru DIY Audio.

I’ve been out of circulation for health reasons (Kidney Stones)
And am feeling well enough to attend to some of my repons-
-siblities.

For those of you interested in the schematic please send me a
Mailing address and I’ll send you a copy. The one in my
thread doesn’t have enough resolution.

For those of you e-mailing me about not being able to access
My web page the new domain name is www.audiofyle.com

……………………. Thanks for your e-mails

……………………… Fred Petersen

[Tall Shadow]

Wow! That amp must be really loud!

The volume goes up to 11 !!

J/K! Looks really great!

Tall Shadow