Extracting the overdrive channel from a multi-channel amp.

[mrbadwr3nch]

This is just my opinion but instead of trying to remove all the extra, I'd start with the output section and build a pre-amp that suited my tastes.

Well Jim, I'd do the same thing if it were my project but, my friend bought this amp company because he loves the high-gain tone of this particular amp.

It was being manufactured overseas as a PC board, bells and whistles, type of amp that no "real amp guy" wants to buy. He wants to retain the high gain overdrive sound but produce it as a hand-wired, stripped-down, bare-bones unit.

We'll see how it goes...

[gui_tarzan]

I understand, my point was that there is so much extra "stuff", transistors, etc. that it will be a huge undertaking to try to re-vamp it. Taking all of that out of the circuit will likely change the tone so much he may just be very unhappy with the result.

[vibratoking]

There is a lot to remove.

That might be the most poorly drawn rats nest of a schematic that I have ever seen. I want to charge you just for looking at it. Connect by label all over the place. Like writing War and Peace on a matchbook cover. If an engineer brought that to a design review, it would not get reviewed. But he would get sent back to his office with a list of action items on how to fix it and make sure it never happens again. It documents the circuit, but not in any organizational fashion that I have ever seen.

I hope your friend didn't pay too much for that. What CAD package was it drawn in? He has the raw data files for the schematic, layout and gerbers, correct? He also has the theory of operation documentation and the BOM, correct? If not, he made a serious error and should approach the seller to rectify the situation because this is some ugly stuff. If it were me, I'd want the data files. Then I would want to reorganize, run checks and modify it from there. Tell us if he has the data files and what the CAD package is. We might be able to help you do this the right way.

[Smokebreak]

Is this the channel you're trying to extract: http://www.youtube.com/watch?v=8YuduSoYK9M, or this one? : http://www.youtube.com/watch?v=AOyPKYMVDKQ

[vibratoking]

Was there a difference?

[Smokebreak]

Yea big difference. The first one had me intrigued by the comedy that either was or wasn't intended. Those riffs were tight, too. The second one was too scooped.
I'm more intrigued with what exactly is going on with this amp, and what the hell is going on over there at this amp company that can't quite design an amp.

[mrbadwr3nch]

Lol. Come on, that tone kills;-) I too need Advil to look at the schematic.

Let me begin by stating I don't have a lot of inside info. I met my colleague when I was trying to find some tolex locally for a rush job a few weeks back. Madison Amps was, for all intents and purposes, dead. He's was an owner and fan of a Divinity head and apparently struck up a deal to buy the remnants of the company. I don't know if he knows the previous owners or, anything really. I have no idea what he paid or what he got aside from the schematic and some tolex. Hopefully, it wasn't a very big check. He's not really an amp builder (I guess he has built some kits) and was having no luck finding someone to redesign the amp so I told him I'd take a shot at trying to help him, you know the whole "pay it forward" thing. The tone of the amp isn't exactly my bag or a lot of other people's for that matter but, I figured that really didn't matter. I figured, if someone could extricate the overdrive channel from the clusterf*&k schematic, figure out which components in the circuit were the important ones to that channel, get a hand-wiring layout drawn up, he could wire up some amps and see if the death metal crowd takes a shine to them.

I'm not sure which of those videos has the tone he's after. I don't think that really matters. I think he's mostly intent on building this amp as close to the specs of the schematic as possible, not starting from scratch to get to a tone in his head. Starting from scratch would make more sense but that would also mean that there was no sense in buying the company. I think you can see where I'm going with this.

I'll see about the CAD package, data files, etc.

I'm going to have to discuss remuneration for being associated with this little project and the heckling I sense is bound to get ever more creative

[katopan]

It's a mess, but you can follow it through. I'm surprised at how much preamp is still there if you made this OD channel only. Going around clockwise - Preamp across the top, with the (only one!) extra OD gain stage in the middle between RL1 and RL5, separate normal and OD tonestacks in the right top corner. Opamps below that are the reverb send, receive and mixing. Below that are send and return for effects loop. Bottom right corner is the PI. Across the bottom right to left is the quad EL34 power stage and power supplies. Going up the left side are the switching relays. Follow the relays and understand what all the FETs are switching and cutting it down wouldn't take too long.

[roberto]

I don't want to seem a pita, but if the owners of the company can't even read a schematic, how they think to manage the aftersales?

Just sell some copies made by someonelse and then disappear?
I wouldn't be part of that...

[mrbadwr3nch]

I don't want to seem a pita, but if the owners of the company can't even read a schematic, how they think to manage the aftersales?

Just sell some copies made by someonelse and then disappear?
I wouldn't be part of that...

Hey roberto. I know it's a lot of reading to go back through the whole thread so I'll say it again, he wants to cut it down to something much more simple that he himself is capable of wiring (I guess he's wired up some kits) instead of having it mass produced overseas. It doesn't seem like the ideal method for starting (or continuing) an amp company but stranger things have happened.

It would seem that if you buy a company and you don't have all the necessary expertise to produce the product, you hire people who do. Which is exactly what's happening here.

Now that you mention it though, it seems like your concern is maybe what happened with the company in the first place.

I hope this post doesn't come off as snide, that's not the intent.

[matt h]

(deleted)

[mrbadwr3nch]

It's a mess, but you can follow it through. I'm surprised at how much preamp is still there if you made this OD channel only. Going around clockwise - Preamp across the top, with the (only one!) extra OD gain stage in the middle between RL1 and RL5, separate normal and OD tonestacks in the right top corner. Opamps below that are the reverb send, receive and mixing. Below that are send and return for effects loop. Bottom right corner is the PI. Across the bottom right to left is the quad EL34 power stage and power supplies. Going up the left side are the switching relays. Follow the relays and understand what all the FETs are switching and cutting it down wouldn't take too long.

I see at RL1 it looks like the overdrive channel goes down to RL3 which looks like two switchable gain voices with RL3 at the "only one" extra OD stage- V1-B. I guess I need to find out which of the two voices he wants. Or leave that switching in.

Then the signal reintegrates at the first mention of RL5, goes through V2-A and B then the second mention of RL5 in to V3-A then V3-B which looks like a CF and into the switchable tone stack. From there the PI, and for some reason, a JRC4558DD that I just noticed. Is that chip necessary?

I can read the schematic for him but I'm not sure which components need to stay/go and how to go about a hand-wiring layout.

[roberto]

That chip is taken from the Marshall 2000 series.
It's a fixed depth.

[mrbadwr3nch]

That chip is taken from the Marshall 2000 series.
It's a fixed depth.

Ah! I see what looks to be the NFB now.

This schematic is a little confusing.

[mrbadwr3nch]

The more I look at this amp, the stupider I get.