Spring Reverb does not give enough wet signal. (Gaussmarkov)

[Lurch]

Hey,

Have just finished building my spring reverb, Gaussmarkov's circuit + an Accutronics 4AB31B. It does work, but can't get much reverb actually, which I guess means that the circuit cannot drive the reverb tank enough. I know the tank isn't the one specified in the parts list, but what could I do to match it better? Change the transformator? Any ideas?

EDIT: Forgot to give you some info about the circuit and reverb tank.

Schematic image
Parts List

My tank:
4AB3C1B
Input: 8 ohms
Output: 2250 ohms
Decay time: Long
Input Insulated / Output Grounded

Specified tank for circuit:
8AB2A1B
Input: 10 ohms
Output: 2575 ohms
Decay time: Medium
Input Grounded / Output Grounded

kind regards

[petemoore]

  Guessing the clean side of the side-channel mixing is coming through ok.
   Plugging a source into the reverb return circuit should produce a boosted signal output.
  This ensures the reverb output has enough gain recovery to set mix knob to thick reverb.
   Another way is to touch/disturb the springs into thunder-verbing [set controls to low to start off with.
  Since the impedances and words 'recommended circuit' are in the thread title post...pardon the grammar, I would make sure the impedance match of the reverb tank::driver circuit is workable. Worth to check unless has already been done when it is suspected the drive-transducer is having insufficient mechanical effectivity vibrating the springs.
  The driver circuit for reverb spring transducer is basically a little guitar amp that has a speaker type transducer. instead of a cone, the coil is physically attached to the input side of the springs. An impedance mismatch would cause 'limp' spring drivability.

[Taylor]

From Gaussmarkov's site:

Rangelife said:
vhbram:
I've just built one of these – Set the voltage at the collectors of the two 2N3906 transistors to 6V.
vhbram & george:
The transformer in the partlist doesn't seem to be able to drive the springs har enough. Do what george suggests, use a matching transformer. I used a 42TU013 (as suggested to me by Solderman) and it sounds much much better!

[PRR]

> I guess means that the circuit cannot drive the reverb tank enough

_OR_ that the recovery amp Q2 is not doing its job.

Basic tests on spring-reverb:

Reverb tank output is weak. When Reverb pot is full-up, you should hear hiss. If you can't get good hiss, it isn't going to boost-up the tank's output enough.

With Reverb pot full-up, bump the tank. It should sound like The End Of The World. If nothing, the tank is not connected well. If you don't get a BIG BOOOOIIIING, the recovery amp isn't working.

This plan needs a bias adjustment on Q2. I don't know what the designer says. By inspection, Q2 collector (top of reverb pot) should be like 4V to 7V. If 1V or 8V, it isn't going to work right.

Hiss and BOing OK?

The tank is OK. The 8/10 2250/2575 differences are the way Hammond measures different series; these are actually the same transducers. Be sure in and out are right (try swapping the RCA plugs).

Now check the driver. This is a part-Watt power amp. Since it is adapted for an 8/10 ohm, you can connect a speaker. Haywire a speaker to where the tank would be (transformer secondary) and play. It should work like an extra-small practice amp. Plays well up to a point but won't annoy the neighbors.

It is a large and convoluted circuit. A wiring error is VERY possible.

[Lurch]

Indeed I get much hiss and huge boings when hitting the tank, so the output signal seems to work allright. I will check the voltage at the Q2 collector ASAP.

Posted by: Taylor
Insert Quote
From Gaussmarkov's site:


Quote
Rangelife said:
vhbram:
I've just built one of these – Set the voltage at the collectors of the two 2N3906 transistors to 6V.
vhbram & george:
The transformer in the partlist doesn't seem to be able to drive the springs har enough. Do what george suggests, use a matching transformer. I used a 42TU013 (as suggested to me by Solderman) and it sounds much much better!

Sounds like the same problem as I've got! Might get another transformator as well then, all to improve.

[Joe Hart]

With Reverb pot full-up, bump the tank. It should sound like The End Of The World.

Whatever you do, DO NOT do this at 6:00 p.m. today.
-Joe Hart