Hi everyone,
I will start this off by saying I found this forum via a bit of googling but everything y'all are talking about is well above my pay grade. It's like reading a foreign language. That said, this seems like the place to ask, so I figure I'll do so - I am basically trying to see if the modifications/build I am thinking of is even possible - not "affordable," "optimal," or even "sensible," but possible.
I have a 1970s Peavey bass amp. I love the tone I get from Channel A to death. I don't necessarily care about Channel B or the combined two channels. There is a pedal manufacturer who makes a pedal replicating Channel A, and I may buy one at some point in the future. However, these amps are currently a dime a dozen, I think I paid a hundred dollars for mine and less functional ones that have been stripped for parts are even cheaper.
Being a 1970s Peavey, it has a number of drawbacks - it's 2 feet long by 1 foot high by 8 inches deep, it weighs about forty pounds, and even at that size it's 130W RMS. It has 1/4" jacks rather than Speakon outputs, and it has no balanced/XLR output to run to a board or front of house.
Now, the sensible thing to do here is to get a small class D amp that has these features and run it through the effects loop, and indeed I have done this with some success in the past. But I don't like carrying around multiple amps and having to hook things up. I want it to be in one package, and having something totally different than everyone else appeals to me.
So - is it possible to build a single, elegant solution, combining the preamp from Channel A with a lighter, louder, class D power amp (ICEPower or the like)? Can this be done for a price that does not rival that of a used car? Is this just insanely stupid and not at all worth pursuing? Assuming the answer to the last question is "no," who, if anyone does this kind of work? I mean, in theory I could, but given that I don't even know how to read a schematic I'm not sure it's a project I'd like to tackle.
Cheers!
I will start this off by saying I found this forum via a bit of googling but everything y'all are talking about is well above my pay grade. It's like reading a foreign language. That said, this seems like the place to ask, so I figure I'll do so - I am basically trying to see if the modifications/build I am thinking of is even possible - not "affordable," "optimal," or even "sensible," but possible.
I have a 1970s Peavey bass amp. I love the tone I get from Channel A to death. I don't necessarily care about Channel B or the combined two channels. There is a pedal manufacturer who makes a pedal replicating Channel A, and I may buy one at some point in the future. However, these amps are currently a dime a dozen, I think I paid a hundred dollars for mine and less functional ones that have been stripped for parts are even cheaper.
Being a 1970s Peavey, it has a number of drawbacks - it's 2 feet long by 1 foot high by 8 inches deep, it weighs about forty pounds, and even at that size it's 130W RMS. It has 1/4" jacks rather than Speakon outputs, and it has no balanced/XLR output to run to a board or front of house.
Now, the sensible thing to do here is to get a small class D amp that has these features and run it through the effects loop, and indeed I have done this with some success in the past. But I don't like carrying around multiple amps and having to hook things up. I want it to be in one package, and having something totally different than everyone else appeals to me.
So - is it possible to build a single, elegant solution, combining the preamp from Channel A with a lighter, louder, class D power amp (ICEPower or the like)? Can this be done for a price that does not rival that of a used car? Is this just insanely stupid and not at all worth pursuing? Assuming the answer to the last question is "no," who, if anyone does this kind of work? I mean, in theory I could, but given that I don't even know how to read a schematic I'm not sure it's a project I'd like to tackle.
Cheers!
Hi.
Eminently possible to do.
A reasonably competent DIYer could tackle this. "Reasonably" and "competent" are the watchwords here: you must consider electrical safety, mechanical robustness, etc. Electrical safety in particular: you are connected to the amp directly when you plug an instrument into it and play that instrument. We hope it is electrically safe to do that, but get that wrong and this can kill you. There's enough ex-musicians who have found this out the hard way over the years.
If you were wanting to commission someone to do this for you at any kind of commercial rate, it would get expensive very quickly. There's a lot of hours in design / sourcing / constructing / testing, etc. (DIYers get this labour for free, of course.)
So: sorry to say, but if you aren't going to DIY, you're probably better off finding an existing commercial offering that has the features you need. There's any number of lightweight class D bass amp heads out there these days that would fit the bill.
Cheers, and regards,
Ant.
Eminently possible to do.
A reasonably competent DIYer could tackle this. "Reasonably" and "competent" are the watchwords here: you must consider electrical safety, mechanical robustness, etc. Electrical safety in particular: you are connected to the amp directly when you plug an instrument into it and play that instrument. We hope it is electrically safe to do that, but get that wrong and this can kill you. There's enough ex-musicians who have found this out the hard way over the years.
If you were wanting to commission someone to do this for you at any kind of commercial rate, it would get expensive very quickly. There's a lot of hours in design / sourcing / constructing / testing, etc. (DIYers get this labour for free, of course.)
So: sorry to say, but if you aren't going to DIY, you're probably better off finding an existing commercial offering that has the features you need. There's any number of lightweight class D bass amp heads out there these days that would fit the bill.
Cheers, and regards,
Ant.
Thanks for chiming in - I was hoping that since the preamp boards are cheap and plentiful in used applications and the schematics are available online (two details I neglected to mention in my initial post) combined with the availability of class D power supplies, it would not be prohibitively expensive.
While there are many wonderful Class D heads out there, none of them have this preamp circuit and Peavey has shown no indication that they plan to re-release it, so if this is the sound I want I either need to model it, run it out of a different power amp, learn to build amplifiers, or find a reasonably competent DIYer to help.
I appreciate the input!
While there are many wonderful Class D heads out there, none of them have this preamp circuit and Peavey has shown no indication that they plan to re-release it, so if this is the sound I want I either need to model it, run it out of a different power amp, learn to build amplifiers, or find a reasonably competent DIYer to help.
I appreciate the input!
Get ahold of that Peavey service manual earlier than later. Make sure the preamp is indeed responsible for the “tone” you’re after, and not some not-so-straightforward-to-implement interaction with the power stage. Some early solid state amps used a current-mode output stage in an attempt to replicate tubes. No ready-made class D board will do that. Bass amps dont usually resort to tricks like that, but just make sure you dont have to before sinking money into this. It might have one of those “totem pole” output stages and they have a distinctive “sound” too. More easily replicated, though.
I am inclined to think it's the preamp, as a pedal made of the preamp section following these schematics replicates the tone faithfully, but hey, y'all tell me, I can't read these things. 🙂
https://www.audioservicemanuals.com/p/peavey/peavey-centurion/1335120-peavey-centurion-schematics
https://www.audioservicemanuals.com/p/peavey/peavey-centurion/1335120-peavey-centurion-schematics
Last edited:
@mandu - it's a MkIII Centurion. Ideally I'd use a MkIV "Bass" as I like that tone slightly better, but those are hard to find in good shape, more expensive, and have a more complicated circuit with built-in compression, a bright switch, and an additional graphic EQ. The general preamp between the two is the same, though.
@rayma - yeah, I'm in Portland OR so it's basically all boutique tube amp builders who probably wouldn't touch it, though I may know of a few other guys I could bug for a crazy custom build.
@rayma - yeah, I'm in Portland OR so it's basically all boutique tube amp builders who probably wouldn't touch it, though I may know of a few other guys I could bug for a crazy custom build.
It can be done there are pedals more complicated than CH1, but one question, What IC is U5?, I do not recognize that symbol with the arrows inside a triangle.
It looks like an analog switch. Just a solid state way of doing audio signal switching (without mechanical contacts).
I can't read schematics but I'll try to answer your question - I am assuming each triangle on that diagram corresponds to one of the knobs on the front of the amp. If you are referring to "U5 - 604," the third triangle from the left, with all the numbers going around it and a bunch of lines inside, that's a mid frequency selector. All the way counter-clockwise is 150Hz, all the way clockwise is 1.5KHz. It does not have any notches, it turns smoothly between the two points.
You can see the front panel clearly on this old reverb ad: https://reverb.com/item/584031-peav...series-1978-bass-amp-head-non-lee-urban-waste
and it's detailed here: https://www.manualslib.com/manual/306148/Peavey-Mark-Iii-Series-Centurion.html?page=2#manual
You can see the front panel clearly on this old reverb ad: https://reverb.com/item/584031-peav...series-1978-bass-amp-head-non-lee-urban-waste
and it's detailed here: https://www.manualslib.com/manual/306148/Peavey-Mark-Iii-Series-Centurion.html?page=2#manual
In Peavey's schematic notation the triangles are integrated circuits. Peavey sometimes uses their own part designations for those that you need to cross reference from their documentation but fortunately not in this case.
The "604" is a TL604 MOS analog switch.... and has not been made for ages. But it is no special part and in DIY such as this you could just substitute it with any other suitable IC, with suitable corrections to the switching logic / drive circuitry. Naturally. If you are building just a single channel you likely will not need one at all or can just use any plain mechanic switch too.
IMHO, I don't think the old Peavey design is anything to bother about these days; ultimately just a plain and very generic soft clipper followed by bunch of rudimentary tone controls. I'm very surprised if you can't find a lot of pedals capable of doing the same and preamps of the modern compact class D output bass amps are at least on equal level, if not vastly better, than these half a century old things.
They were very good amps back then but by today's standards most of this vintage stuff would not get a pass or would be just incredibly "generic" stuff for "reissuing".
The "604" is a TL604 MOS analog switch.... and has not been made for ages. But it is no special part and in DIY such as this you could just substitute it with any other suitable IC, with suitable corrections to the switching logic / drive circuitry. Naturally. If you are building just a single channel you likely will not need one at all or can just use any plain mechanic switch too.
IMHO, I don't think the old Peavey design is anything to bother about these days; ultimately just a plain and very generic soft clipper followed by bunch of rudimentary tone controls. I'm very surprised if you can't find a lot of pedals capable of doing the same and preamps of the modern compact class D output bass amps are at least on equal level, if not vastly better, than these half a century old things.
They were very good amps back then but by today's standards most of this vintage stuff would not get a pass or would be just incredibly "generic" stuff for "reissuing".
Last edited: