Yamaha G100 Reverb tank

[Lynxtrap]

...and now I got confused by the "grounding"/"insulated" thing, Accutronics digit #5. I honestly didn't think there was so much to know about reverb.
So, how do I know which one it's supposed to be?

[Tillydog]

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.

Oops!, my mistake, of course there are 8 ohm ones, sorry (I was looking at that graph ).

(I still think 150 ohm is the one, though)

Will have a look at the grounding options....

Is there anything metallic that the pan contacts, other than the RCA jacks in & out? (Is it in a bag?)

[Lynxtrap]

Is there anything metallic that the pan contacts, other than the RCA jacks in & out? (Is it in a bag?)

The bag is still there, and I haven't seen any obviuos other objects. I can check again tomorrow. You mean like it was grounded on the outside somewhere..?

[Tillydog]

...and now I got confused by the "grounding"/"insulated" thing, Accutronics digit #5. I honestly didn't think there was so much to know about reverb.
So, how do I know which one it's supposed to be?

You'll be an expert soon


I don't think the schematic is particularly helpful, as it just shows the connections to the pan - it doesn't show what goes on inside the pan.

This is my 0.02p, based on 1st principles:

1) The drive signal is referenced to ground, so there's no definite need for the input to be insulated (as there could be with a push-pull driver) or grounded (as there could be if it were driven by a transformer, for example);

2) The return amplifier is independently referenced to ground, so there doesn't look to be any need to maintain continuity from drive ground to return ground;

3) We want the metal casing of the pan to be grounded somewhere;

4) Accutronics say: "The best system, and the most applicable, is to insulate both the input and output from the chassis, grounding the chassis separately."

5) We want to avoid ground loops, so if the pan is grounded separately (through its mounting or an earth strap, etc.) we don't want the return connection ground common with this;

6) If the pan isn't separately grounded, I would say that, for best shielding, the metal casing of the pan should be grounded at the return amplifier input.

7) If all else fails, it's possible to add a jumper to the pan from the RCA connector to create a ground connection. What is harder to do (but not impossible) is to break a ground connection.

So I *think* you need a type 'C' - Input insulated, output grounded *unless* the pan is grounded separately, in which case you need a type 'D' - Input and output both insulated.

Have you come to any conclusion about the output impedance (digit 3)?

The recovery circuit has a 100k input impedance. The 10k ohm ('C') recovery transducer *probably* needs something a bit higher than this (its impedance becomes 60K ohm at 6kHz acording to the data). I would *guess* that it was designed for the 2.25k ohm transducer ('B') - I'm pretty sure it would work.

Any thoughts from anyone else would be appreciated.

[Tillydog]

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

Scratch what I just said - I only just got this(^) to work - that looks pretty credible to me.

The 600 ohm transducer needs ~9V RMS to drive it fully at 5kHz (from the data on the Accutronics site) which is about what the TA7220P is capable of from a 35V supply (and the amp has got 40V). Should have worked that out before - it would probably over-drive the 150 ohm transducer.

Output impedance & grounding arrangements look sensible, too.

So another vote for 4EB#C1# (eventually)

[Lynxtrap]

Thanks again! With one eyewitness and now also the math supporting 4EB3C1B, it seems like a winner. I don't think I will find more credible information in the near future, unless I'd see the original unit with my own eyes.

This shows three things:
1:Don't trust what people write on the internet.
2:Trust people who can back up things with logic, reasoning and mathematics. Even if they write it on the internet.
3: Such people hang around in the Amp Garage.