Modify solid state reverb driver/recovery?

[MissionBrown]

Hi Guys,

I have a Peavey Delta Blues, it's a nice amp, but the reverb is a little underwhelming.
On maximum it's only just enough to play with, also a little on the noisy side.

The driver and recovery circuit is based around an op amp, and there's quite a bit of hiss in there too.
I'm wondering if putting in a higher grade opamp like the opa3124 in place of the 4558 would make a difference to the noise floor (I have some left over from pedal builds).

Also from looking at the schematic, would there be any benefit from increasing the value of the reverb pot from 10k to 50k or 100k? Would that give me a bigger boost or would I need to mess with the feedback resistor/s on the opamp circuit?

I know enough about electronics to get me into trouble, but not enough to always get me out of it.

http://www.freeinfosociety.com/electron ... ablues.pdf

[Mr. Bill]

I'm not really familiar with that amp's reverb, but typically Peavey amps are designed with enough reverb to satisfy the average player. None will get the stand-alone surf levels, but normally not many players would need that.

The driver circuit for the tank places the transducer coil in the feedback loop of the opamp, so it is more current driven than the typical circuit. I don't know if the OPA3124 has enough drive to handle this application.

Have you checked the tank itself for any problems, like dirty or loose connectors, or a loose transducer coil? Some people suggest using a small flat wooden toothpick as a shim to hold the transducer coil tight to the laminated iron core. And sometimes I find that a tank can just be weaker than another one. If it's possible can you swap the tank with one from another Peavey amp?

As for changing the output control, a higher value will give you a little more output signal, but too high a value will reduce the output from the opamp.

[JimPage]

I have an old Peavey Artist 240 and I just bought a new tank from Accutronics (http://www.accutronicsreverb.com/).

I hadn't realized that was an option until our own Danny (Dubtrub) recommended that. The new tank is just amazing.

The fellow there emailed me several times with great guidance and the service was excellent. Seems to me the cost was just over $120 or so, but I bought Tolex covers and all kinds of other stuff you might not need.

There are tons of options, though, so make certain you get the correct one if you go that route.

--Jim

[MissionBrown]

There's nothing actually wrong with the reverb (I think), as far as I have read this amp has a fairly quiet reverb section. I do have a couple of other tanks, with the right output, but unfortunately the input coil is only 8ohm where the 4558 is currently feeding a 600ohm inductor.

It's just enough for the surf reverb, but can't really get dripping.

I do have a digital verb(Line 6 m13), which actually sounds excellent with the Delta Blues.
You can stack 4 reverbs back to back on it for some really insane echo. It feeds back within itself too.

My problem is that I like tweaking things.
No need to do it for the Mosrite, but my other electronics gizmos.....
Modding a valve amp kind of terrifies me.

I thought the 2134 just had a lower noise floor than the 4558?
They work very nicely in Tube screamer circuit

[Mr. Bill]

Working on a tube amp can be dangerous if you don't know what you are doing, but as long as you follow all of the normal safety procedures, there should be no problems.

My concern on the opamp was that I don't know if it can handle the current demands of that circuit design. The other question is where is the noise in your reverb coming from? Is it the opamp or is it from other places in the circuit?

Take a look at the transducers on your tank, to see if they are a loose fit on the core plates. You could try to shim them into solid contact with the cores to see if that helps.

[MissionBrown]

Thanks Mr Bill.

The Delta Blues recovery stage is very hissy and introduces a lot of hum too.

I've gone and looked at the datasheet for the 2134 and agree it might not be up to the task.
That said, I might just breadboard the circuit and run the verb externally just to see what happens with different opamps.

Alternatelty, could I place a low gain booster circuit on the output of the reverb and into the recovery stage? I'm thinking a single transistor booster, like an EHX LPB 1.

Off topic slightly:
I was messing about with some 6418 valves as a recovery stage for my 8 ohm tanks this morning (Same output coil impedance as in the Peavey). They work quite well and are low voltage, so loads of fun to play with. More than one valve is require

My driver circuit is a simple 386 based 1/4 watt amplifier.
It does ok, but distorts when driven directly by the guitar, likely due to the low input impedance on the chip. More experiments are needed

[Mr. Bill]

The hum may be from the tank itself. Make sure that the output end of the tank is as far away from the power transformer as possible.

Adding an additional gain stage would boost the signal, but if there is any hum or noise being generated by the tanks output coil, it will be boosted as well.

If you really want to modify it, I guess you could just use a different opamp, and adjust some of the resistors and caps in the circuit to increase the recovery stage gain and adjust the high frequency response as well.

[MissionBrown]

Thanks again.

I'll start with moving the tank to see what happens with the hum.
Is there any point attempting to magnetically shield the transformers?

[JimPage]

Moving the reverb tank does reduce the squeal a LOT. Also, I bought an extra reverb bag from that source I mentioned before, so that the tank is in an inner Tolex bag inside an outer Tolex bag, which is affixed to the inside of the head enclosure.

Evidently this was done on some Mesa Boogies and early Fenders, and it also reduces the squeal.

I was forced to fiddle around with the reverb tank in this Peavey setup I did, because the head cabinet I used was tight on space. It was worth it, though.

As a final touch I redesigned the Peavey logo on the front and made a new amp faceplate. Looks cool now.

To me, the real Peavey logo looks like something a Ninja warrior would throw at an opponent.

--Jim

[MissionBrown]

To me, the real Peavey logo looks like something a Ninja warrior would throw at an opponent.

--Jim

Sure does, on my old 50 head I replaced it with "now on tap" off a beer poster I found.
Fortunately they decided on a more sedate logo for the delta blues.

My tank is in a tolex bag, and someone stapled some carpet on the inside.

I ordered the tube guard as I was feeding some cables behind the amp and heard a ping through the preamp tubes. Oops. darn fine amp though, especially for my Mosrite and plywood guitars.

Nothing seems to be able to redeem the surfcaster though. Looks cool, sounds not so great.