Realistic MPA amplifier

[saturated]

Hi everybody

 

I got to thinking I need something to work on.

A friend has lots of stuff but not really any cool guitar amps

I remember seeing a Realistic MPA amp that looked cool I guess it is a mono PA amp

I just wondered if this would be a cool thing to try to get it working if so I can go get it

 

(Maybe there are some unobtanium components idk)

[Tassieviking]

I would find out what the model is first and then see if you can find a schematic for that model, I know ElectroTanya has the REALISTIC MPA-40 schematic so there might be more out there.
There will always be a use for an amplifier on your workbench eventually, I have a tube preamp pedal of the Mesa Boogie Dual Rectifier that might sound great through a PA amp as long as you have a nice speaker cab to play through.

At worst there will be many great parts to salvage from it and most likely a fantastic chassis to build a proper guitar amp in, just make a new faceplate and it can look professional.

[saturated]

Yes sir thanks in fact I was gonna post

"I've been around here long enough to know that the absolute first order of business is to come up with a schematic " 

Seems I recall he had at least two different MPA models I'll have to take a look one had a silver face and one was black face.

[J M Fahey]

Just in your favour;

* being Commercial amps, their schematics are often found in many repositories, service pages, Sams Photofacts and maybe even a Realistic dedicated fan page.
Or Elektrotanya as mentioned above.

* those amps were *robust*: a Hotel, Hospital, Supermarket, Auction site, Bus station losing its PA is a far worse event for many more people than a Guitar player missing a rehearsal so they were made long lasting.
Meaning: it´s very possible that amp *electronics* work fine, but you meed to clean pots, switches, connectors, the "mechanicals"
Which does not really require Schematics.

[saturated]

Yes sir thanks 

And...two rusty dusty boat anchors later 

You cannot view this attachment.

You cannot view this attachment.

You cannot view this attachment.

The cover screws on the MPA-100 were missing not sure what's up with that

You cannot view this attachment.

And on the MPA-200 the left volume? knob spins 360 without stopping 

I hoped the plastic knob was slipping on the pot shaft but the metal shaft spins 360 

You cannot view this attachment.

Before I got there I was gonna mention kinda like you warned...Realistic and Peavey seem to have a "bad" reputation of being unearthed from a pile of crap and still working 

I'm kinda pumped that one of them is stereo that's kinda cool I guess 

[saturated]

Well decided to  try em on the ol ugly DBT

First up was the MPA-100 and it was dead as a doorknob 
But then I remembered....oh yeah 

You cannot view this attachment.

Next up was the MPA-200

And I got a bit of a surprise 

You cannot view this attachment.

 

[saturated]

I wish I had a tuner or something to hook to the RCA inputs but I only have one and I didn't want to unhook it from its current set I have rigged up.

You cannot view this attachment.

So I noticed the upper input jacks might take a guitar cord so that's what I did and hooked up two small speakers

It worked but at max wasn't very loud.  Then I tried the left side the one with the broken wiper stop(?) and got sound but nothing linear or controlled.

So I opened it up to have a look at the volume pots and here is the back of one

You cannot view this attachment.

May be time to Google "A 50k " idk or lmk if you recognize what it is or can recommend a suitable replacement

I figured it would be crazy loud maybe a guitar signal isnt much idk.   
Thanks 

[saturated]

Pic of the inside

You cannot view this attachment.

Kinda confused about these speaker terminals maybe they take a crimped on U-shaped connector

You cannot view this attachment.

 

[J M Fahey]

Two beasts, door anchors in a good way, lots of iron and heatsinks
Connect one or two 8 ohm speakers at the proper speaker outputs   and be certain they can handle that much power.

Are those RCA/Guitr Jack inputs on the power amp?

If so, you need to build the proper cables.

It is always good to have spare 1/4" plugs, RCA plugs and a few yards of spare shielded Audio cable just in case, it NEVER is wasted, so next time order 10 of each tp spread post cost or add them to your next "something else" order.

You will most probably need 1 V (or more) to drive those Power Amp inputs, so a direct guitar will barely make any sound at all, same with a Phone pr MP3 player headphone out which gives around 100mV RMS BUT a table radio/Boombox/Tape Recorder etc. *Speaker* out can probably drive that amp loud

Don´t you have some old Transistor Radio (even if Mom´s AM one) lying around?.
Or get one at Goodwill/Salvation Army for $1.

A guitar cable tack soldered across speaker terminals (without removing speaker) will do.

For DECADES I had a permanently ON Lafayette AM/FM receiver on a bench shelf, with an added volume pot and a 1/4" jack as a ready made "known" Audio source.
Since at least 1975 or so!!!!!!!!!!!

Doubles as a background Music source when doing boring repetitive work such as soldering transformer pigtails, filling bobbins with EI laminations, drilling PCBs, etc.
Just tune a good Rock/Jazz/Classic station.

Undocumented Bonus: FM sounds way better/smoother than ANY MP3 and most CDs.
Probably FM coding/transmitting/decoding smooths out rough edges.

[saturated]

Yes sir thanks 

I think I lucked out getting the black one 

Black one MPA-200
-"normal" output 
-Stereo output so I can possibly use it to listen to ball games etc (loudly  )
-to my noob eyes looks evenly divided two channels each the same 
Kinda like working on drum brakes...don't take both sides apart at the same time

Silver one MPA-100
-weird multi voltage speaker output   
-Output transformer ?!   

So I'm hella glad to have the MPA-200

I need to order a volume pot just replacing that should take me about six months