Hello,
I have a Fender Super 112 Combo Tube Amp (Reb Knob, 1990ish, 60W, 2 x 12AX7, 1 x 12AT7, 2 x 6L6). I've had the amp removed from the original enclosure to create a separate head. The thing I'm having trouble with is what to do with the spring reverb tank. Mounting it inside the head will likely produce unwanted noise and I've been advised against it. Personally, I would like to ignore the reverb as I rarely use it, and when i do use any reverb, I have an external effects unit to handle it. As such, I would like to bypass the circuit, but I wanted confirmation/a second opinion to make sure this all tracks. This is a link to the amp's circuit, and a link to specs on a drop in replacement spring reverb tank.:
Fender Super 112 Schematic
Replacement Spring Reverb Tank
The reverb circuit is located between B5 and C7. The spring unit is driven by a single TL072 and not tube driven. The replacement tank lists the input (800Ohm) and output (2575Ohm) impedance. I understand resistance =/= impedance.
My question: What would be the best route to go?
1) Simulate the Spring tank transducers by using resistors matching the input/output impedance.
2) Measure the spring tank circuit with a meter and use those values to simulate the transducers.
3) Alternate suggestion?
If anyone has any experience or advise it would be greatly appreciated. I have an Electrical Technology background, but am just a bit unsure on this application.
I have a Fender Super 112 Combo Tube Amp (Reb Knob, 1990ish, 60W, 2 x 12AX7, 1 x 12AT7, 2 x 6L6). I've had the amp removed from the original enclosure to create a separate head. The thing I'm having trouble with is what to do with the spring reverb tank. Mounting it inside the head will likely produce unwanted noise and I've been advised against it. Personally, I would like to ignore the reverb as I rarely use it, and when i do use any reverb, I have an external effects unit to handle it. As such, I would like to bypass the circuit, but I wanted confirmation/a second opinion to make sure this all tracks. This is a link to the amp's circuit, and a link to specs on a drop in replacement spring reverb tank.:
Fender Super 112 Schematic
Replacement Spring Reverb Tank
The reverb circuit is located between B5 and C7. The spring unit is driven by a single TL072 and not tube driven. The replacement tank lists the input (800Ohm) and output (2575Ohm) impedance. I understand resistance =/= impedance.
My question: What would be the best route to go?
1) Simulate the Spring tank transducers by using resistors matching the input/output impedance.
2) Measure the spring tank circuit with a meter and use those values to simulate the transducers.
3) Alternate suggestion?
If anyone has any experience or advise it would be greatly appreciated. I have an Electrical Technology background, but am just a bit unsure on this application.
I do not see any big problem putting the tank in the head. Experiment to find the least-buzz placement; pickup should not be over power transformer.
I have seen spring-reverb fashions change several times. As a custodian of history, I would tend to keep, even repair, a reverb even if the current player does not use it.
If you won't keep it:
The reverb driver certainly does not need termination. Any more than your Preamp or Line Out jack. It isn't the kind of power amp that will bust a gut if not loaded.
The reverb recovery will happily amplify all the buzz and hiss that reaches terminal BT3. If Reverb knob is set to zero, this should not be any big problem. To ensure against knob-bump buzzing-up a quiet set I might put a jumper (obvious) across BT3 BT4 so it won't pick up stray fields. For extra paranoia, lift one leg of C115 (secure it so the remaining leg don't break) or put a jumper (obvious) across R123 (makes recovery amp gain way-low).
I would not muck with the mix network downstream because its losses have been scaled for proper dry-path gain.
I have seen spring-reverb fashions change several times. As a custodian of history, I would tend to keep, even repair, a reverb even if the current player does not use it.
If you won't keep it:
The reverb driver certainly does not need termination. Any more than your Preamp or Line Out jack. It isn't the kind of power amp that will bust a gut if not loaded.
The reverb recovery will happily amplify all the buzz and hiss that reaches terminal BT3. If Reverb knob is set to zero, this should not be any big problem. To ensure against knob-bump buzzing-up a quiet set I might put a jumper (obvious) across BT3 BT4 so it won't pick up stray fields. For extra paranoia, lift one leg of C115 (secure it so the remaining leg don't break) or put a jumper (obvious) across R123 (makes recovery amp gain way-low).
I would not muck with the mix network downstream because its losses have been scaled for proper dry-path gain.
Fender made many heads with reverb pans in them, no reason to ditch the reverb just because it is a head. If you don't want the reverb, just remove the pan and be done. The IC won;t care. And leave the reverb control turned down.
There is no need to bypass anything.
There is no need to bypass anything.
It occurs to wonder if you understand how reverb fits in.
It is a side-path. When the reverb knob is on Zero, the reverb system has no effect.
In this amp, 4(!) stages boost the signal. This signal flows through R115, to the FX loop jacks and on to the power amp.
After that 4th stage, a tap is taken aside to feed the reverb driver. Boiiiing, weak, so a reverb recovery amp. Dial wet-sound to taste with a Reverb pot. This reverb is mixed-in with the dry signal via R116.
Yes, this mixer (and perhaps the drive tap) influence the gain of the dry path. The drive side comes through 1.2Meg so has little effect on V102B plate circuit. The dry and wet sounds are mixed with 390K and 150K, dry signal is reduced. But it was already plenty strong, "too strong", to make distortion happen. The power amp (and FX loop!) do not need THAT much signal. The roughly 4:1 reduction of dry is about right here. This type passive mixer risks interaction with the channel pot, but here a way low 5K pot feeds the high 150K mix resistor, so turning the Reverb knob has little effect on dry sound path.
It is a side-path. When the reverb knob is on Zero, the reverb system has no effect.
In this amp, 4(!) stages boost the signal. This signal flows through R115, to the FX loop jacks and on to the power amp.
After that 4th stage, a tap is taken aside to feed the reverb driver. Boiiiing, weak, so a reverb recovery amp. Dial wet-sound to taste with a Reverb pot. This reverb is mixed-in with the dry signal via R116.
Yes, this mixer (and perhaps the drive tap) influence the gain of the dry path. The drive side comes through 1.2Meg so has little effect on V102B plate circuit. The dry and wet sounds are mixed with 390K and 150K, dry signal is reduced. But it was already plenty strong, "too strong", to make distortion happen. The power amp (and FX loop!) do not need THAT much signal. The roughly 4:1 reduction of dry is about right here. This type passive mixer risks interaction with the channel pot, but here a way low 5K pot feeds the high 150K mix resistor, so turning the Reverb knob has little effect on dry sound path.
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What Enzo said is fine, being SS driven means you will damage nothing if you remove the reverb tank and set the "Reverb" potentioneter to zero.
That said, I´d add an extra protection layer and short the reverb drive Op Amp input to ground, so it does not even *receive* drive signal (let it take a quiet nap if unused 😉 )
To that end, short across R118 (39k) with a short piece of wire. Glue a small post it sized note inside tha chassis or cabinet explaining this, so if in the future somebody wants to connect a reverb tank there he does not get crazy about "everything fine but reverb not working".
That said, I´d add an extra protection layer and short the reverb drive Op Amp input to ground, so it does not even *receive* drive signal (let it take a quiet nap if unused 😉 )
To that end, short across R118 (39k) with a short piece of wire. Glue a small post it sized note inside tha chassis or cabinet explaining this, so if in the future somebody wants to connect a reverb tank there he does not get crazy about "everything fine but reverb not working".
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