TL072 spring reverb in a Fender amp

[Bob M.]

Hi all,

I'm wondering if there's any consensus about which spring reverb circuit in a (newer) Fender amp using a TL072 op amp and a reverb tank sounds the best? I've looked at a few schematics and the ones using a TL072 (and sometimes using a 4560 op amp) are all pretty similar is design but I think many of these sound pretty different from one another in application. Is there one (or couple) that stand out a great sounding reverbs?

Bob M.

[olddawg]

Hi all,

I'm wondering if there's any consensus about which spring reverb circuit in a (newer) Fender amp using a TL072 op amp and a reverb tank sounds the best? I've looked at a few schematics and the ones using a TL072 (and sometimes using a 4560 op amp) are all pretty similar is design but I think many of these sound pretty different from one another in application. Is there one (or couple) that stand out a great sounding reverbs?

Bob M.

I remember from tech school that an opamp is an opamp... that's the whole point. Especially in audio applications. Now... some are noisier than others. People can go on and on on about their low fi preference for LM741s or 4558s. I would say that a proper designed opamp driver and recovery is just that. The variation would be in the tanks which are by far more inconsistent than any opamps. You might have to try several tanks. If you are building a circuit around a particular tank you have laying around, you may have to experiment with the bandpass to your liking.

[Enzo]

Plus the amp circuits around the reverb circuit matter. What freq range is even sent to the reverb? ANy tone shaping on the return? etc.

[loudthud]

In some reverb circuits, the opamp driving the tank is configured as a current source. There is usually a resistor between the low side of the drive coil and ground. (Note tank can't have a ground on the input side.) Opamps have built in current limits so there is only so much drive available. The NE5532 has the highest limit for a commonly available opamp. (Not sure about the 4560.) A tank needs to have the right input impedance or the opamp will run out of Voltage before it's current limit is reached. As noted above, frequency response plays a big role in how the reverb sounds, but an opamp can't compete with the tube drive found in an old Fender.

[g1]

Opamps have built in current limits so there is only so much drive available. The NE5532 has the highest limit for a commonly available opamp. (Not sure about the 4560.)

I seem to recall some circuits that use paralleled sections of dual or quad op amps to get more drive current?

[Gingertube]

Depends entirely on the Reverb Spring Unit you are trying to drive. Most of the common spring units have an 8 Ohm Impedance drive coil which a TL072 will not drive directly (needs buffer transistors) but other options are available.
A good resource:
::::::::: Accu Bell Sound Inc :::::::::
Go to the Applications Page - lots of good info including a schematics page for drivers and recovery circuits.
Also some info on the "new" Digital Reverb options and also on the DSP Modules which offer Digital Reverb as just one of the effects they can do (along with Wah, Tremlo, Flanger, Chorus).
Cheers,
Ian

[J M Fahey]

Depends entirely on the Reverb Spring Unit you are trying to drive. Most of the common spring units have an 8 Ohm Impedance drive coil which a TL072 will not drive directly (needs buffer transistors) but other options are available.

Maybe you mean "common spring units in Silverface and Blackface Fender amps" which are tube driven and use a small OT to drive the Reverb; 99% of others, including most tube amps use mid or high impedance tanks , precisely to be able to drive them with Op Amps, augmented or not.
Typical impedance is around 150 ohms for simple drive and going down to 40 ohms or so for augmented ones.
Old Japanese amps (Roland/Yamaha) used 8 ohm tanks but driven by a car radio type power amp, fed around 12/18V supply.

[Bob M.]

No, I was wondering what most players/techs thought of the more recent Fender designs using an op amp for drive and recovery with a spring reverb (either long tank or short tank) and if there was one (or more) version that stood above the rest as the best sounding. Yes, I feel, as most do, that the tube driven, transformer coupled spring reverb of years gone by produced the very best Fender reverb sounds we've heard from an on-board amp reverb circuit. But this is a different question; I'm not necessarily building anything.

Bob M.

[Mick Bailey]

I think the reverb in the Deville is pretty good. Securing the driver coil with a dab of glue improves the poor mechanical fit on the armature that can lose some of the energy - I've just fixed up a 4x10 (alnico) Blues Deville reverb and the tonality is excellent - easily enough 'wetness' at 2 on the reverb, and splashy surf sounds on 6 and above.

An interesting twist to that repair; it came to me with very little reverb - even on 10 it was barely discernible. Opening up the amp showed someone had really messed up the reverb circuit - loads of clipped components with replacements soldered onto the old leads, incorrect op-amp in a socket, RCA connectors cut off and the cable soldered to the sockets, pot bridged with resistors and caps. The problem? it had a tray with a low-impedance driver coil intended for a tube amp with transformer drive. So it looks like the original fault was a duff tray and it got swapped for the wrong type, so the circuit got shotgunned in an attempt to fix it. A quick coil swap and some board fixes and new connectors had it working perfectly again.

For me, there are too few controls on inbuilt reverb setups; no dwell and no proper mix and no tone. There's a good deal of difference between a moderately driven tray and one that's being spanked due to a high dwell, but is at a lower level in the mix. My own standalone reverb design has dwell/mix/tone/output level settings and can go from 100% dry to 100% wet and enough output level to overdrive a tube amp.