Yamaha G100 Reverb tank

[Lynxtrap]

Does anyone know what reverb tank goes with the Yamaha G100-112 amp? Early 80's solid state, parametric EQ, not the one with coloured knobs.
If anyone happen to have one, I'd be happy if you could check..

I can't find much info on the net. Service manual simply says "Accutronics", no specs.
One source says 4AB2C1A, but somehow I'm a bit sceptical about that. It's the impedance that worries me. It doesn't have to be exactly the original unit, as long as it's compatible.
Here is the service manual with schematics: http://89.228.128.119/RemoteDownloader/ ... ual-EN.pdf

By the way, does anyone know how to date these amps...?

Thanks!

[FUCHSAUDIO]

You could ask Mike Soldano (nice guy)...he designed it and is very reachable and I'm sure would help...

[Lynxtrap]

You could ask Mike Soldano (nice guy)...he designed it and is very reachable and I'm sure would help...

Really? I feel like if I corresponded with Mike Soldano there would be a thousand other questions I'd rather ask But why not.
I guess it could be figured out from the schematics but that's above my head.

Anyway, it's a well designed amp. I bought it as trash to use the chassis, but after I got sound out it I changed my mind. It's a great sounding solid state amp.
They are sort of classic, so I thought maybe someone here had one lying around.

[FUCHSAUDIO]

Oh, solid state ? My bad...may not be Mike. In that case, that pan number could be correct... sorry about that.

[Lynxtrap]

Oh, solid state ? My bad...may not be Mike. In that case, that pan number could be correct... sorry about that.

Think so? It says TA7220P by the driver IC, but I'm lost when it comes to solid state. The data sheets I found for that says nothing about output impedance.

I read somewhere else too that Soldano is supposed to have designed it while working at Yamaha. I think they were made around '79-'84 before they changed the look and maybe the circuit.

Pat Metheny, Robben Ford and Mike Stern are among known users of these amps, as a curiousity.

[FUCHSAUDIO]

Well, a quick look at the data sheet for that chip shows it's a power amp, so that pan may not be so odd at all. It's a low Z input, so it may work ok after all.

[LeftyStrat]

I don't think that code is right. I'm no expert on solid-state reverb, but the ones I have seen use something closer to 'F', 1.475k.

Also the last letter in the code is for 'horizontal mounting, open side up', though it looks like it mounts like a traditional Fender in the bottom of the cab, with open side down.

Well, I googled "TA7220P Reverb" and the top link was a page in Japanese about repairing this amp. It specifies 4EB3C1B:

http://translate.google.com/translate?h ... CDIQ7gEwAA


The TA7220P is a high voltage, low power amplifier/voltage amplifier. 600 ohms is probably right. I remember the Craig Anderton Hot Springs Reverb used two 300R tanks in parallel.

[M Fowler]

http://www.amprepairparts.com/reverb.htm

[LeftyStrat]

I've used AES tanks in a couple of applications, and they are nice also:

http://www.tubesandmore.com/products/P-RK-4EB3C1B

[FUCHSAUDIO]

I don't think that code is right. I'm no expert on solid-state reverb, but the ones I have seen use something closer to 'F', 1.475k.

Ah yes, but the TDA chip is a power amp looking for a lo-Z load...like 4 or 8 ohms. The 'A' input is 8 ohms....

I get what you're saying. We use a 9EB3C1B in our amps, driven by a servo op amp, but this is an actual power amp driving the transducer...

[LeftyStrat]

I don't think that code is right. I'm no expert on solid-state reverb, but the ones I have seen use something closer to 'F', 1.475k.

Ah yes, but the TDA chip is a power amp looking for a lo-Z load...like 4 or 8 ohms. The 'A' input is 8 ohms....

I get what you're saying. We use a 9EB3C1B in our amps, driven by a servo op amp, but this is an actual power amp driving the transducer...

Gotcha. Like I said, my experience with solid-state designs are limited to a couple of Craig Anderton designs.

[Tillydog]

It says TA7220P by the driver IC, but I'm lost when it comes to solid state. The data sheets I found for that says nothing about output impedance.

This data sheet consistently specifies 150 ohm output impedance R(L):

Page 1
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The accutronics site suggests that the 150 ohm tank is optimum under a very similar scenario (+/-15V supply vs +/-20V in your amp):

[img:432:382]http://www.accutronicsreverb.com/design ... erload.jpg[/img]

http://www.accutronicsreverb.com/

(I can't post a direct link, but it's under application-->Drive Circuit / Overload Margin Chart )

I'd be inclined to go with a 150 ohm tank... 4BB2###, but that's just my 0.02p

(I'd guess that the 56R resistor in series with the reverb tank was added to tame it a little.)

Can you measure the resistance of the input & output transducers on the existing one? It will give some clues.

[Lynxtrap]

Thanks so far everyone. Lots of different suggestions though
The Japanese guy along with the data sheets Tillydog found is along the lines I thought initially. Thing is, I don't know much about reverb circuits in general. How big a mismatch can be tolerated? Do I risk blowing the IC?

This also made me wonder, can you measure the output impedance from the driver?

I can't measure the transducers, the tank is MIA. Wasn't there when I got the amp.

[Tillydog]

How big a mismatch can be tolerated? Do I risk blowing the IC?

This also made me wonder, can you measure the output impedance from the driver?

I don't think you'll blow the IC unless you put too low a load on it. Given that 150R seems to be the lowest impedance tank you can get anyway, and is the load that the IC was designed to drive, I think it's fairly safe.

I don't think you can physically measure anything regarding the IC that will be of any use (you know from the schematic it's running off +/- 20V supplies).

If you go too high in tank impedance, the driver won't be able to swing enough voltage to drive it fully, and will start clipping instead. That said, I doubt there would be that much to choose between 150 & 250 ohm tanks.

[Lynxtrap]

Ok, thanks! I guess 150 would be pretty safe.
But I don't understand how that would be the lowest you can get. The one I mentioned in the first post would be 8 ohms, for one. As are all Accutronics with the first letter A.