Taming an overly bright reverb

[Fred G.]

I've been working on taming an overly-aggressive, too-bright reverb circuit on a Deluxe reverb clone. I've BF'ed the circuit and installed a 250K audio pot. It's nearly there - still just needs the brightness/harshness tamed down some.

I'm wondering if the input cap could be raised in value from the standard 500pf to a higher value might warm it up some. I already tried a 12EU7 driver tube, but didn't get the results I'd hoped for. Any suggestions?

[txstrat]

You could try to shunt high frequencies with a cap to ground before either recovery stage. See the Deluxe Reverb II schem (http://www.schematicheaven.com/fende...ereverb_II.pdf). There it is at the first grid of the recovery stage (a .0022). If you want to tame even higher frequencies, just decrease the value of the cap.

[MWJB]

Also try a different tank, just to eliminate yours from being the cause of the brightness...tanks themselves are the most variable component in the circuit.

You could try a small cap (a few hundred pf?) accross the outer terminals of the reverb pot, make sure it doesn't short to the wiper or it could have the opposite effect.

[Bruce / Mission Amps]

You could try to shunt high frequencies with a cap to ground before either recovery stage. See the Deluxe Reverb II schem (http://www.schematicheaven.com/fende...ereverb_II.pdf). There it is at the first grid of the recovery stage (a .0022). If you want to tame even higher frequencies, just decrease the value of the cap.

Well, no.
That is not the way a capacitor works.
It has less impedance as the frequencies go up so there will be no additional high frequency roll off by using a smaller cap.

Also... the 2.2nF cap is in parallel with the inductance of the transducer coil in the reverb tank. So, what you have is a parallel cap, resistor and inductor.
That is kind of like a tuned "tank" circuit with a 220K swamping resistor across it to lessen or broaden the "Q" of the 2.2nF||transducer tank circuit.
Subtle stuff but it all matters.

[txstrat]

Thanks Bruce. I didn't know how to put it right, although I should have to.
Take out my words "even higher frequencies" and put in "only at higher frequencies".
Would that work?

[Fred G.]

I figured a cap to ground was the trick - I wasn't sure if their was a better or worse location for it, or whether there was some clever trick somebody knew to get more frequencies through the reverb circuit (ala the Torres reverb mod). I've also read that the resistance values following the pot should be changed, if the pot is bumped to 250K - any comments regarding that?

I'm thinking a 47pf - 120pf cap across the pot outer lugs like MJWB suggested is probably the simplest trick. I just want to slice off some high end, but I'm open to any other tricks as well. Opinions?

[Bruce / Mission Amps]

I figured a cap to ground was the trick - I wasn't sure if their was a better or worse location for it, or whether there was some clever trick somebody knew to get more frequencies through the reverb circuit (ala the Torres reverb mod). I've also read that the resistance values following the pot should be changed, if the pot is bumped to 250K - any comments regarding that?

I'm thinking a 47pf - 120pf cap across the pot outer lugs like MJWB suggested is probably the simplest trick. I just want to slice off some high end, but I'm open to any other tricks as well. Opinions?

Look up T filters and low pass T filters.
I think there is usually more reverb then really ever needed and you could experiment with a couple resistors in series with the output of the reverb recovery triode... at the junction of the two resistors, drop another 1000pF to 2200pF cap to ground.
I haven't tried it but it seems like something like this it could work.
It acts like a fixed tone control.
Don't shocked to find out the "highs" you don't like are actually in the upper end of the mid-range though... a common mistake when trying to identify annoying freqs.
Another mod is to run the output of the reverb recovery triode into a larger value cap (now .003uF) but the larger value cap feeds the wiper of a larger value reverb level/volume pot... maybe 500K to 1M.
Ground the bottom (audio low) lug and tie the top lug of the pot (audio high) right out or into the mixer stage... forget the 470k and grounded 220k and don't use those.
Hope that wasn't too confusing.

[Fred G.]

LOL! Yup, Bruce, I'm definitely confused as hell now! I'm not sure what I just read...BF'ing the circuit and moving to the 250K pot really took out the excess Dick Dale wash - I can crank it up to about 6 or 7 now to get the same amount of 'verb as I used to get at 1 or 2. It may have been too much attenuation, I might go back to a 100K audio. I just need to get rid of the "shock" value of the 'verb in this amp - too many highs, too much wash, at too low a pot setting (before I changed it to 250K aud).

When I turn the 'verb pot all the way down, the amp sounds fine. When I begin to add in reverb, it gets harsh and shrill, and...ugly. Not a sweet reverb, the amp sounds better without it. Which sucks, because I cut my teeth on Fender reverb amps ('70's Twins).

I'm thinking of going to 100K audio, and then just lopping off some of the highs - am I making any sense? I thinik it's just a case of a tweak now, but...

I appreciate any further commentary on your part! You've been a treasured resource here for over 12 years!

But you sure went over my head in the last paragraph...lol.

[Fred G.]

Well!

I went down in the basement and put the cap across the reverb pot - it did the trick! I had the amp sounding pretty dang good.

But then the demons took over. I had originally somewhat Dumblized this amp (with the little local nfb loop at v1B and the somewhat different tone stack ala Steve Ahola - I've had it this way for 12 years). I went nuts and totally turned it into a BF Deluxe reverb (it's an old Allen accomplice). Oh, silly me!

Now I have to re-tune the whole damn amp. Back to the 12AT7 PI tube from a 12AX7, re-tweak the cathode bypass caps, re-bias, LOL. Bwaaaa ha ha ha .....A soldering iron and several beers are a recipe for madness.

It actually sounds pretty damn good.

[Bruce / Mission Amps]

LOL! Yup, Bruce, I'm definitely confused as hell now! I'm not sure what I just read...I appreciate any further commentary on your part! You've been a treasured resource here for over 12 years!

But you sure went over my head in the last paragraph...lol.

I thought I posted this but here it is again...a picture might be better:

[Fred G.]

Yes, the picture is better! I see now what you were saying.

Thanks, Bruce!

[Fred G.]

Hey Bruce,

Another question about that diagram...the pot across the wiper and ground lug of the pot - should that also be in the 4n7 to 10 nf range?

And lastly, any suggested values in that range for a DR clone?

Thanks and Merry Christmas!

[Bruce / Mission Amps]

Hey Bruce,

Another question about that diagram...the pot across the wiper and ground lug of the pot - should that also be in the 4n7 to 10 nf range?

And lastly, any suggested values in that range for a DR clone?

Thanks and Merry Christmas!

I'd be careful with that one because as you bring the reverb level up louder, the reverb tone will get darker and muddier.
I like reverb that is not too loud, well back in the mix but still bright and splashy sounding.... kind of like when you drop a big wet ride cymbal on a hard surface.
Hard to say as everyone has different tastes in "effects" things like this but best thing would be to start with a 500pF to 1nF and work up to probably no more then 4n7.
In any case, 90%-95% of all reverb is to simulate a natural room ambiance, not really a special effects sound.

[Fred G.]

Thanks again Bruce!

I was looking at a schematic of the old Fender stand-alone - I can see where this mod derived from - I'm very intrigued by this approach, I think I'll give it a shot while I've got the amp out of the chassis (after I can pick up some parts - I'm completely out of .0047, .001, .01, .0022 caps).

Much appreciated info!