Interesting CG info (no, no schematics)

[benoit]

This is a thread on the gear page where people were posting their rare/cool amps, and about halfway down there's a carmen ghia, not just BASED on a certain hammond reverb, but built from one. I'm not out to prove/disprove anything, or to make any points, just to offer this interesting info.

http://www.thegearpage.net/board/showth ... 593&page=3

[skyboltone]

I'd sure like a look inside. Is it built on a board or point to point, that sort of thing. The Goodsell 17 is PtP wired. Same chassis.

The topside of that looks just like the one I built for my son but with a MV knob.

Dan H

[benoit]

I'd sure like a look inside. Is it built on a board or point to point, that sort of thing.

I'd have asked him the same thing except you have to have a "real" email address over there and I've never really been that into TGP except to occasionally browse the amp threads. If you've got an account there and find out anything, please share here.

[dartanion]

The CG is well known to have been built directly from the A0-35 reverb amp which was part of the M-100 organs. No big secret there, save for that the Dr. would like us all to forget that fact

[Noel Grassy]

When I saw that I couldn't help but think of Allyn's comment about Zenith TV and our friend Nick. There's one fellow who had to mutter about the amp he was proudly having built by "*****" amp builder. Yet they're heaping rose petals at the feet of the fellow who's product was the result of a trip through the dump grabbing organ chassis and TV bits. Mike Z was very helpful to me 10 or 12 years ago when I had novice amp building questions & I expressed a desire to build something on my own.I'll hush up now.

[benoit]

It IS common knowledge, but some people tend to take a little convincing in matters like this. As I said, just throwin info out there. It was interesting to me because the only shots I've seen have been of ones with new chassis and cin-tran iron as opposed to old AO35s. Speaking of, has anyone ever tried getting transformers wound by those guys (Cin Tran)?

[Noel Grassy]

Nope. Is Cin Tran a foreign enterprise? Sounds like the guy who makes my Lau Thap Cam [combination fire pot=shrimp,squid,lobster w/nooders] All aspersions aside, I'm thrilled with the Heyboer iron after many builds with Hammond's stock. I've got no desire to buy in bulk just yet. The market seems a little too fickle at the moment.

[benoit]

I believe it stands for Cincinnati Transformer, and is based out of Ohio. I was just curious if they did one-offs. I found a phone # a while back but not a website.

[Sonny ReVerb]

Here's a little more info on Cin-Tran:

http://www.electronicsweb.com/storefronts/cintran.html

They were acquired by Standex in 2002:

http://www.standexelectronics.com/aboutus.htm

http://phx.corporate-ir.net/phoenix.zht ... highlight=

[bueller]

I guess I don't see what the fuss about the Ghia is. Owned one, sold it. Friend has one, I don't ever ask to play it and he rarely does. It has one basic sound and although I admit it's a good one especially through a 1x12 Celestion Blue, I found it too limiting for the variety of music I need to play. I will couch that with I do feel that the Dr Z stuff is really some of the best stuff on the market. And since the CG is his bread and butter, I won't share the exact schematic. I have made similar such style amps and side by side with a Ghia they did not sound like the real thing. That may be because I never exactly cloned it (my bad design) or maybe it is the transformer set he's using. But generally speaking, I like the Marshall 18 tones better than the CG.

There are some interesting ideas he's using though in the CG design:
The basic pre-amp topology is two gain stages. The first stage is the same as the first in any large Marshall and the second is the same as any Fender or Vox recovery stage. But he's dropping the B+ voltage to the first gain stage quite significantly, before hitting the 100k plate resistor. That's different for a 2 gain stage amp, but would be more common in say a 4-stage amp where the B+ keeps getting less and less as you move toward the input. Maybe it browns-out that stage a little more. I think this is an idea worth pursuing. Some people claim higher pre-amp voltage is better (headroom?), but I find lower is better for overdriving ~ 227VDC

The tone control is almost the same as the old Matchless Chieftain mid control. I've employed this on Fender circuits too. And if you lift the ground it gives a nice mid boost. I have made this footswitchable for leads (eliminates the signal loss of the tone circuit and give all the mids back) You can play with the 500pF cap and the 0.01mF to ground to alter the treble and bass responses and the pot values as well.

He's also using the conjuntive filter idea across the plates of the EL84s same as the Trainwrecked Expresso. Which I've tried on several amps, but never liked how it killed the high end. Kind of neutered the tone so to speak. We also see no screen resistors at all, wouldn't Kevin O'Conner have something to say about that, LOL. Negative feedback is employed but to the signal path buried between two caps and a resistor at the input rather than the bottom of the phase inverter. I have played with this idea. It really kills the gain though. You have to use 1 to 2 meg feedback resistor.

And lastly the phase inverter design is completely different than the standard long tail or the split tail. I don't even know how to describe that idea as I'm too much of an amatuer.

My advice is if you really want the Ghia sound, then buy one. It would hardly cost any more than the parts to make one and think of all the free time you'd have to play!