Polytone Mini Brute V Preamp to power amp connection?

[jerseyjoe]

Hello. New to the forum. After searching the internet and every forum I could find for an answer to my problem, figured that maybe somebody here could be of help.

I'm in the process of converting a 1998 Polytone Mini Brute V Combo amp into a head that I can run with different speakers. I pulled the control board and power amp and disconnected everything. Now that my new cabinet is basically finished, I wanted to do a test run and realized that I've got one wire that that must have broke free from it's solder during the manhandling. It's the black wire (in the circle) that connects to the control board somewhere? and then to the power amp with a single rca jack... I didn't see it disconnect and after scanning the board for something that looks undone, still nothing. Regrettably, the only pictures I have of the board are no clearer than this. The polytone schematics I've seen online don't really make sense to me. I believe this black wire connects the preamp to the power amp, but how or where? Can anybody here help with this? Thanks.

[Enzo]

Same response I gave elsewhere: At least one end of the wire must still be connected to SOMETHING, and in that photo we can see neither end. tell us or show us where the wire is now connected, and we might figure out the other end. I suspect it is a ground between subassemblies.

[jerseyjoe]

going around in circles here. the end not attached to circuit board is a male rca that connects to a female rca jack on the power amp. the mysterious other end was attached somewhere on the bottom of this board. others say that it's a power amp to preamp thing.

[52 Bill]

Not sure of the exact connection on your amp, but typical of Polytones, the Master Volume control is the last thing before the output to the power amp. Look at the board where the Master Volume control is and follow the trace from the wiper (middle) terminal. See if it connects to a terminal that looks like there was a wire connected to it. They used one set of boards for any number of amps, so often there will be resistors jumpering across the board to connect sections that normally wouldn't be connected. This may make following the signal path a little tricky.

I think that on the earlier amps, the preamp out jack was also connected to the same point as the output to the power amp. So that may be another way to trace back to where the wire was connected.

[jerseyjoe]

thanks a lot. that's the kind of answer i was looking for. i know how to build speaker and head cabinets, but other than soldering jacks. i'm at loss with everything else electrical. i'll post something when i get a chance to wire everything up and have a report on whether that was the fix.

[52 Bill]

The black wire is a shielded cable so there will be two connections to the board. The center conductor will connect to the signal line and the shield will connect to the ground.

It looks like there is a cut shielded wire on the board, but it looks like it is a grey cable. Maybe a reverb tank wire?

[DrGonz78]

I just posted my reply to your problem here... How many websites do people need to post in simultaneously these days?

Polytone Mini Brute V preamp to power amp connection

Not only to mention that if you look at your picture there are no connections to E13 and E14, they are missing. Look at the schematic I posted and I am pretty sure it will start making more sense.

[jerseyjoe]

thanks. it looks like you are right about missing connections on e13 and e14. and sorry for the multiple forum posts. i'm new to both and don't know how active either are in regardless to repairing polytone amps.

[DrGonz78]

Sorry to come off as a crude dude. Welcome to both forums!! I understand the feeling of wanting answers to questions as fast as possible and then posting in two forums. This tends to lead to confusion though.

Also follow the advice of Enzo and the other's about where does the other end connect to. There are probably two other RCA connections for the reverb tank right? Look right at E13 on the schematic and you will see R21. Looking at your pics I see R21 right next to the E13 connection. So make double sure that it is right too.

[nsubulysses]

Don't worry, in short time he'll realize that it's mostly the same people on both forums

Actually I'm kind of talking out of my ass since I never read ssguitar, but a quick perusal of your link shows a lot of the usual suspects chiming in.

[Enzo]

Yes, we are usually aware when the same project shows up on multiple sites.


My issue was when someone says something like "goes to an RCA" we are not sure what the person is describing. When the wire is shown in its entirety, we can see it has a male connector on the end, but other posters can use the same language to indicate the wire soldered to the same point as an RCA connector, meaning it might simple be a ground. Seeing the center section of a black wire with one end up behind a circuit board, and the other off screen at the bottom doesn't clear anything up. As an example, in post #3 above, the first photo shows the end with the yellow RCA on it, but the other end of the wire is up under the board somewhere, so it APPEARS as though it is connected to something up under there. But apparently it is a cable that happened to be partially hidden under the board, as th next photo reveals a bare end.

But I am spending too much time on that detail.

What you seem to have is the output cable from the preamp having come free. Its likely terminus is E13 at the end of R21. You preamp board appears to have silk screened part numbers so find U3, C16, R21 to identify the E13 solder point.