SS SPRING REVERB

[TIMBO]

Hi guys, Just trying to find a simple SS reverb as an addon to an existing SS circuit. Some thing a bit old school.

[shooter]

not 'ol skol, but the mesa-boogie nomad 45 is a start

[2deaf]

If you are looking for discrete device SS reverb, then Peavey Deuce, Deuce II, and PA400 have examples.  Musicman RD-50 is another example.  I adapted this one and tested it with an 8E tank.

[TIMBO]

NICE

[TIMBO]

Thanks 2deaf, I been dragin the heals on this.
I thought I'd try a couple of SS reverbs I took out of some old organs, but not much luck with those.

I will try your design, but I need to know how you inserted it into the amp circuit.Thanks

[2deaf]

This one was inserted a little bit different than the usual way.  The driver was feed from the second stage via a voltage divider and the recovery went to the effects send via a mixing resistor.  You would probably insert a resistor in the signal path and draw the driver signal from one side of that resistor then insert the recovery on the other side of that resistor.

That jFET recovery was designed for the 100K load it saw going to the effects send and probably isn't optimal for your application.  You referenced a hybrid amplifier in your "New Project" post recently that has a standard two transistor gain stage after the tone controls.  This kind of stage can easily be adapted as a reverb recovery and would fit right in with the rest of the pre-amp.

The driver will drive an 8E tank with a little bit more than the published nominal current at 1KHz with a clean signal.  It won't drive the tank grossly beyond the recommendations as we are accustomed to doing.  The drive signal starts to round with an input signal of about 0.85Vp.

This driver is not a constant current driver.  It puts out more current as the frequencies decrease, so you would want to limit the lower frequencies going into the driver.           

[TIMBO]

Thanks mate, You kinda lost me with your post, Technically challenged here.

Yes this is what I'm trying to glue the reverb into.

[2deaf]

Thanks mate, You kinda lost me with your post, Technically challenged here.

Yeah, so am I when it comes to SS.

What kind of signal level comes out of the tone control and into the Vol. pot?  You might be able to put a resistor in there and patch the reverb across it.  The gain stage between the Vol. and Master Vol. could be altered for more gain to make up for the loss from the resistor in series with the Vol. pot.

Or, you could insert it between the gain stage and the Master Vol. with an additional mixer stage like a Fender.  You would probably need an additional 13 or 14 ma out of your power supply to do this (the driver alone takes 8 ma).  Your pre-amp as it is now probably draws between 4 and 5 ma.

[TIMBO]

Ok, I've put together 2deaf's circuit and not much luck with the boing.
I used this schem as a bit of a guide.http://el34world.com/charts/Schematics/files/musicman/musicman_rd50a.pdf
I'm just not getting any noise going through the springs and because of this I can't find a good place to insert it.
I tried a few tanks with different input resistance and no go, not even a hint of noise.

[shooter]

not much luck with the boing

sand isn't much different than glass when troubleshooting, are you getting DC volts at the driver, what do you have at the collector-2k junction?  The emitter - 100r junction?  Do you have a listening amp? do you hear anything at the output side of the 1uF with tank unplugged?

[2deaf]

I re-visited the experiment and added a BJT recovery.  I included some DC voltages so you can compare them with your setup.  I tried to get some AC voltages with a guitar because reverb responds to transients.  It's hard to read transients on the 'scope, but I included my best guess on the schematic.

[TIMBO]

Thank to 2deaf, Your circuit works well.
The problem with it not working was when I connected the power supply to the circuit it was draining power from the preamp supply. After a battle there I was able to get the volts to where I needed it on both circuits.
Next was where to insert it..........
My final option for the reverb input was at the volume input (pin 3) as I could see that the reverb driver could handle the 0.6vp that I was getting at that point.
The reverb output I thought would work with a pair of mixing resistors to blend the two signals.
And with this setup all was good till I turned off the amp, I was getting a loud squeal on power down. 
After a lot of  I was just trying anything I could think of ( took nearly a week  ) but I was able to reduce it to a very faint fart at power down.
Without the R/C network I was also getting scratchy volume and treble pots, adding the network fixed it.
I do not understand the reason for the squeal as I tried paralleling a resistor with the .01 at the circuit input but that didn't help but adding the R/C at the pot terminal worked to a point.
I'm thinking that the squeal is some kind of oscillation.

[shooter]

I do not understand the reason for the squeal

My last all tube does something similar, sounds like "vvvrreeEEP"

I think it has to do with the caps discharging to slow 

[TIMBO]

Thanks shooter, Tried various drain resistors and no luck.

[2deaf]

That BRIC digital reverb by Accutronics puts out a nasty sound on power down.  Apparently nothing you can do about it.

Once upon a time, I tried using a LM386 power amp to drive a 4A tank (doesn't have enough power to drive the tank sufficiently).  Those things make a weird sound as the power supply gets toward its final discharge.  Seems to be inherent with this device and it doesn't seem to matter what the application is.

I'm pretty good at making circuits squeal when they are powered up, but I don't recall ever making one that only squeals on power down.
 
I came up with another design that drives an 8E tank better than the Musicman driver.  The emitter-follower transistor has a power dissipation that is closer to its limit than I would prefer, but you can still touch it.   

[shooter]

Tried various drain resistors and no luck

if you're still in the experimental phase you might consider a DPDT power switch, one side is overall amp power on/off the other side is 32volt power on/off.
disclaimer: might be a waste of time 

[2deaf]

With the BRIC, one side of a DPST switch turns the power off and the other side disconnects the power tubes.  Real, real quiet at power down.

It might be better to track down the problem rather than to attack the symptom?

[shooter]

DPST

My bad, it should be st.  been awhile since I played with transistors for design, but seems like as long as there's enough *residual* voltage to overcome the np junction they will conduct?

[TIMBO]

Thanks guys, I even tried a few tanks as I don't have an 8EXXXXX and they all worked well but the power down squeal is still there.
Also I noticed that the when turning up the treble to max also emitted a nasty squeal and I was getting scratching on the pot. When adding the R/C this cured the scratching but not the squeal.
It's a pity, as I am more than chuffed with the amp's overall sound and quietness. 

[TIMBO]

Thanks 2deaf, works well, with no nasty noises.