Karpathian and whomever, SS page amp conversion? lotsa pics

[King IzzO)))]

TOA A-912A 120w SS Muzak amp, I've got two of these and a bunch of the L41 600 ohm balanced preamps with the mute function. Might be fun to mess with, and a first foray into amp modding where it's no big loss if I screws something up.

I'd like to convert one for XLR mic use to go with my also pirated from a plant shutdown TOA 400w 4x5/tweeter cab. I'd need an 8 ohm 1/4" speaker jack for that one. That would be the practice space vocals rig.

The other one maybe try as a guitar amp if I can redo one of these pres to work, if not maybe as a slave off of my Butcher into the TOA power amp input. A 16 ohm jack would be better, but I don't think that's possible, so I guess I'd want to put an 8 ohm 1/4" jack on that one too.

Pics on my 66 Nova workbench, this one says it's bad, it's not, was a bad preamp module and some dip**** decided they needed to buy another one (thus I have two):














Manual is here: http://www.retrevo.com/support/Toa-A...3220ci571/t/2/

[MetalManiac]

Re: Karpathian and whomever, SS page amp conversion? lotsa pics

Looks like its got a power amp in /pre out . You got your 4 ohm out ( just hook up a female 1/4 jack with two wires.. You might be able to use that for bass as is, but I think you'd need to scrap the whole circuit and start from square one depending on the transforemrs..I dont even know if just any transformer is okay for a Guitar Power amp..I've never heard of anyone using PA power amps for guitar.

[karpathion]

Re: Karpathian and whomever, SS page amp conversion? lotsa pics

I thought you said this was a stereo reciever? And Jerry is "kinda" right. But, you can always try it.

It looks the way that thing is setup you would have to use that power amp in, but then it's just gonna be a power amp. You would need a preamp of some sorts, like a multi effects unit or something. Keep in mind I have no idea what that input impedance is. I don't know if it's the 600ohms it show on that tab or not.



Now, if you just want to try it to see if it will work. Get 2- 1/4" jacks, 1 RCA cable, and a little speaker wire. Plug one end of the RCA cable into the power amp in. cut the other end off of the RCA, and hook it to the 1/4" jack the way you would a normal jack. Tip to tip and common to the sleeve.
Then hook your speaker wire, + to the 8ohm terminal, and the - to the com terminal.
connect the 8ohm side to the tip of the jack and the common the sleeve.

Plug 'em in and see what happens. Just make sure it's hooked to an 8ohm load, and turn the volume all the way down on power up. Gradually increase the volume until you get sound.
Try to use a speaker your not scared to hurt either.

You should get some sound, but I can't promise it will sound very good.

[karpathion]

Re: Karpathian and whomever, SS page amp conversion? lotsa pics

Changing to XLR in, would be a little more involved if you need phantom power, as some mics do.

[King IzzO)))]

Re: Karpathian and whomever, SS page amp conversion? lotsa pics

Changing to XLR in, would be a little more involved if you need phantom power, as some mics do.

This is what I don't know about. Why would you need it for a plain old SM58? The amp was designed to have mics connected to it, but using different preamp modules than the ones I have.

On these I don't think the mute is a big deal, I can turn the sensitivity off so it's active all the time, but 600 ohm balanced -2db, eh, I dunno wtf? Can I replace that 3 terminal connector with an XLR and go or do I need to reduce impedance there somehow? Is that even possible? To make an instrument input I'd have to raise impedance there and figure out how to convert the balanced input into a two wire unbalanced (disconnect the common maybe?)

Or maybe I just need to lookout for the correct modules. They even made 1/4" inputs, according to the manual.

I'm also wondering if I can remove that terminal strip and just cut the leads to the board for the outputs I don't need. I'd like to install a 1/4" jack in place of the 8 ohm screw terminal output. There's something weird going on there though. The shorting plate takes it to the OT, apparently, so to get 8 ohms I'd have to keep that shorted, right? The manual says the 4 ohm terminal is direct unbalanced. Direct from what? Weird.

Looks like the 10K ohm 1V power amp in might work with the "booster output" on my butcher, so that's in play too.

I'll try it with the TOA cab (400W) before I connect it to anything else.

I have no misgivings that this thing will sound good. This is all in the spirit of experimentation. This amp was used for muzak (elevator music) and paging, so it might be cool to do some lofi nonsense on, and I need something to run vocals, which is basically just a bunch of screaming nonsense, so quality isn't high on the list of priorities there either.

[karpathion]

Re: Karpathian and whomever, SS page amp conversion? lotsa pics

I'm gonna go ahead an man up and say, someone else needs to get in on this. I mean, I could make it work, but I need it right here in front of me.
I've never seen those inputs or the preamps it has. If I could trace them around and see whats what , I could figure it out, but from here I'd just be guessing.

You could probably hook an XLR up to that preamp, and use it as a vocal amp. I'm guessing the wires on that preamp are, White= +, black= common ,and blue = -. I think.

Maybe someone else can tell you more than I can. Like I said, I need it in front of me.

[King IzzO)))]

Re: Karpathian and whomever, SS page amp conversion? lotsa pics

Haha, no problem, that's why I havent tried it yet, they've been in the garage for 5 years. I think I can make it happen, the hi-z input is what I'm most concerned about, other than that I think I can work through everything. I know a good amp tech, and my old man used to work in electronics years ago. I'm sure between us we can make it happen, I just wanted to do this myself for the experience.