More reverb from a single tube reverb circuit

[panhead]

I built an amp for a customer using the single tube reverb here (from tubenit?) and the customer would like a bit more reverb. I currently have a 500pF cap in series with the reverb circuit input. It seems that if I increase this value the reverb driver will see more signal. Any experience with that? Also, I thought about using an unused triode in series with the recovery triode, but I'm not sure if this would be too much, and would rather swap a capacitor if I can. Comments?

Thanks

Panhead

[tubenit]

In the ARCHIVES, there is a thread on the one tube reverb with a schematic called "tweaks" that shows how to increase and/or change the reverb.

http://www.el34world.com/Forum/index.php?topic=7957.0

I personally prefer a .001 cap instead of 500p because it verbs more mids.

With respect, Tubenit

[HotBluePlates]

Is he wanting "more reverb" as though he can't turn the reverb knob up high enough? Or does he want "more reverb" as in the stock circuit is getting close enough to surf drip?

The first one implies that the dwell (how hard the pan is driven) is good, but there needs to be more recovery amplification or a mixing circuit that favors the reverb path over the dry path. The second one implies that the tank needs to be driven harder to get more "boing" out of it.

Knowing exactly what the customer wants is key to making the right change. "More reverb" needs more information.

[dwp]

http://www.

I used this one, a slight difference from the other three on the thread posted above, and it has great strength. Still don't turn much past three.....thanks again Tubenit.

[tubeswell]

I have mucked around with reverb designs quite a bit in the last year or so, and have found by trial and error some things I like and some things I don't like.

The way that reverb pans 'loose highs' means that increasing that 500pF is not a really good idea. (There's an explanation of why here:
 http://www.freewebs.com/valvewizard2/reverbdriver.html )

Also, increasing the signal going into the driver stage past a certain point can just end up with unpleasant distortion from clipping or OT saturation. (tried it)

Similarly increasing the recovery stage strength can just cause the wet signal to clip (but not necessarily - tried several variations of that too)

However if we aren't talking about adding more gain stages, AFAICT, the 'best' way to get more verb is to take into account the relative signal strength from the dry side. This means attenuating the dry signal more in order to allow more of the wet signal to come through. In the blackface type reverb circuits, this means playing around with the voltage divider formed by the 3M3/470k(+100k level pot). In the case of the dumble style 1 tube verb, the equivalent would be increasing the 100k that is in series with the dry signal path (but you may want to add a small pF bypass cap as this resistance gets higher) 2CW

[panhead]

HPB,

He can't turn the know high enough. The dwell is maxed without getting too much splash. I'll putting in a bigger cap and see how that sounds before messing with the recovery stage.

Thanks

[Fresh_Start]

Without any component changes, one of the Ruby medium delay, 3-spring tanks from Mojo Musical Supply produces A LOT MORE reverb than a stock Accutronics tank.  In a Princeton Reverb circuit, I usually don't go over about 4 on the Dwell control and still Reverb over 3 is just plain silly.  At $26 it ain't cheap, but it's an option:
http://www.mojotone.com/amp-parts/Reverb-Tanks/3AB2C1B-Ruby-Tubes-Reverb-Tank-Fender-Style-3-Spring

Unfortunately, it's even more expensive when you add in shipping unles you're buying a lot of stuff and we all need to support our kind host Mr. Hoffman.

Another thought would be to use the lower mu, higher current output of Section 2 (pins 1, 2 & 3) of a 12DW7 as the driver triode.  The other triode is a 12AX7 equivalent.  Working out the details for this is on my "To Do" list but who knows when I'll get there...

Chip

[tubenit]

Have you tried a 2.2M reverb pot?   You can experiment by adding a 470k or 330k resistor from the ground terminal to ground on a 1M reverb pot.  IF that improves what you're looking for ......... replace the 1M with a 2.2M pot.

Tubenit

[panhead]

Have you tried a 2.2M reverb pot?   You can experiment by adding a 470k or 330k resistor from the ground terminal to ground on a 1M reverb pot.  IF that improves what you're looking for ......... replace the 1M with a 2.2M pot.

Tubenit

I currently have a 2.2M pot and a 330K resistor, but it's not on the ground side of the pot, it's on the side that goes to the PI.

[tubenit]

If you currently have a 2.2M pot then that's plenty. If there is a lack of reverb, it's not there.

If you could post an accurate schematic for all of us to look at, it would be helpful. For example, I was not paying attention on a previous build and found I was dropping reverb signal to ground accidentally by not paying attention to other components surrounding the reverb and insertion points.

Post a schematic that is accurate & it will help us to help you.

With respect, Tubenit

[panhead]

Here's the schematic:

[tubenit]

I am surprised there isn't enough reverb available?  

I have drawn some options to consider and experiment with. IF changing the component values doesn't get it for you, then I would try changing the location of the insertion point prior to V1-7.

As was already mentioned by Tubeswell you can increase the 100k mixing resistor to a higher value and use a bypass cap.  Maybe try a 330k with a 68p?  The problem with a 3.3M is that you will lose alot of signal with that.  OR instead ......... try a 220k resistor between the current insertion point and the 500p cap going into the dwell pot.



IF none of that works, then I think you'll need to use a typical fender type tone stack with 12AT7 & 12AX7 triode.  OR you can use a 6BM8 pentode into the triode side. I've got a schematic for that somewhere?

With respect, Tubenit

[LooseChange]

Way too much reverb on my single tube reverb Princeton.

[tubenit]

Way too much reverb on my single tube reverb Princeton.

Does "way too much" mean it's problematic or that there is plenty of reverb and then some?   I'm curious.

With respect, Tubenit

[LooseChange]

Does "way too much" mean it's problematic or that there is plenty of reverb and then some?   I'm curious.

Plenty of reverb and then some.  Got the dwell hooked up and everything is good.

[Baguette]

Hello Panhead,

That's quite funny because I've just finished an amp that is pretty much the same, minus a few different cap / res values and a different trem on mine (it's got a single triode trem, and wiggles the bias at the power tubes - works great).

At first listen, I too was thinking the reverb was a bit weak. I think it's inherent to the design. I messed with input cap, cathode resistors / caps to increase the gain, mix pot value etc... with not much results.
As Tubeswell said, it's better to tune the 100k bleeder resistor. However, I sure don't want to mess with the dry signal so I haven't touched it.

Fresh Start gives some good ideas too. Some tanks are way more sensitive than others. The Ruby (Belton) are IME (limited) more sensitive than the Accutronics. I have a Belton 9 springs / long delay in mine.

That being said, the reverb as it is in my circuit (and yours is really close) sounds VERY good. Not boingy / surfy / extra wet but, it's rather a subtle, enveloping, natural reverb. It sounds wonderful in a band setting, and as good with cleans than when the amp is overdriven.

In a nutshell:
- tell your customer to appreciate it as it is, especially with the band
- try different tanks
- higher up the 100K mix resistor, but it will lower the dry signal level.

Cheers

[panhead]

Thank you to everyone offering suggestions here. I think I'm going to increase the 500pF cap in the input path to the reverb driver and try a 220K mix resistor as a start. I really like the sound of the reverb, too, but it could be a little more pronounced for someone who is really looking for some splash. I'll play with it this weekend and get back here with how it works out.

Panhead

[Baguette]

Hey Panhead,

So, what were your findings in the end?

Cheers