Chasm reverb strange problems

[traktop]

I´ve built a Chasm Reverb a couple of months ago. It´s been working great: The reverb is lush and versatile, the buffer is completely transparent to my ears, and I´ve got trails.

Lately I noticed something  strange happening when the chasm reverb is OFF and then I turn my naga viper booster on in front of it. The booster is set so there is a bump in volume, and when that happens, that increase in volume level trigger reverb splashes, (when the chasm is off as I said before...).
It don´t happen all the time, only when the volume increase reaches certain threshold.

The other thing started when I hooked the pedal to one of the boss es-8 loops. Every time I insert the chasm reverb loop on the signal chain, (the effect itself remain on all the time), I hear a loud "pop" sound, (without even playing the guitar), thing that don´t happen even with my cranked big muff and my other drive pedals. I tried in different loops, (and different cables of course), and every time I insert the chasm, that pop sound appears.
There is a setting inside de es-8 that allows changing the patch change time for those who are experiencing a "pop" sounds when recalling a different patch, but that´s not my case, and have zero problems with the rest of my pedals, (even high gain ones as I said before).
I tried turning on and off both input/output es-8 buffers with same result, so I came to the conclusion that the problem must be inside the pedal.
I´ve been posting on diystompboxes chasm reverb thread, but "deadastronaut", (the author of the chasm), couldn´t help much.
The thing is that the pedal switching works beautifully by itself, without any kind of popping or noise, (other people had problems with it at the forum as I could read).
I tried swapping all fets involved, (2n5457´s/2n7000), with no luck.
Any idea...?
Cheers, Gilberto.


http://www.coda-effects.com/2016/02/dead-astronaut-fx-chasm-reverb.html

[Ciaran Haslett]

I almost sounds like the voltage boost from the viper is temporarily triggering the fet switch.  Now these are just guesses....

Try adding a resistor in series from the buffer out to the wet fet drain.  This may pad the voltage enough not to trigger the switch.  It will be very awkward to try on this layout however.  You'll need to...

Move the left 5457 to the left and cut between the 2 connected drains
Reconnect the left most get drain to the opamp out with a resistor (test values)

OR

Try replacing the link from pin 1 to the fet drains with a resistor (test values) but do not remove the link from pin 1 to 2.

OR

The dry path has a 22K in series with its fet but the wet path only has a 1k (centre of the board).  Maybe try upping it to pad any signal hitting the 2N7000.

These are just guesses so take it with a pinch of salt.  I'd try the easy ones first haha.

[strewel_peterson]

Might it be worth changing the switching so it also grounds the wet input when the effect is switched out? That would stop any wayward input pops going into the reverb.

Could probably be done by either adding a jfet to ground from the wet input, after the first jfet and controlled by the same arrangement as the dry signal. Or even by replacing the two switch jfets with a mechanical switch.

I could be talking through my *hat*, though.

Also, there doesn't seem to be a pull-down resistor on the input: probably no need when in normal use, but the looper might be introducing true bypass type switching with the usual current inrush to charge the input cap on the pedal when it's switched on.

[traktop]

Ciaran Haslett wrote

I almost sounds like the voltage boost from the viper is temporarily triggering the fet switch.  Now these are just guesses....

Try adding a resistor in series from the buffer out to the wet fet drain.  This may pad the voltage enough not to trigger the switch.

I forgot to say that I used 2n5458s instead of 2n5457s since I had no 57s availables.
I remember reading that they are pretty much interchangeables, but a deeper research shows a difference on average Vp's of 2.5V vs 1.5V respectively, (I really don´t know what that means of course...), so maybe that could be the cause; What do you think?

[traktop]

"Might it be worth changing the switching so it also grounds the wet input when the effect is switched out? That would stop any wayward input pops going into the reverb.
Could probably be done by either adding a jfet to ground from the wet input, after the first jfet and controlled by the same arrangement as the dry signal."

You mean dumping signal to ground before the 2n7000 by replacing the switch with a 3pdt using its extra pole, right?

"Also, there doesn't seem to be a pull-down resistor on the input: probably no need when in normal use, but the looper might be introducing true bypass type switching with the usual current inrush to charge the input cap on the pedal when it's switched on."

The schematics don´t show a pulldown resistor, but I seem to see a 1M resistor at the vero layout from tl074 pin 3 inverting input, (correct me if I´m wrong).

[strewel_peterson]

Hi Gilberto,

Yes - dumping any signal to ground before the reverb input (though with the effect "off" there shouldn't actually be any signal at the input - this would just make sure of that). The reason I suggested a switch is that you could be sure that the input to the reverb would either be grounded (and not connected to the input at all) or connected to the input.

The 1M resistor in the schematic connects to VB - the 1/2 supply voltage bias for the op-amp input, rather than ground. My reading of the circuit here is that with the input connected to nothing, C1 gets charged through the 1M resistor (R2) up to VB. If the input is then connected to something which allows C1 to discharge you might get a pop, but I'm not an expert by any means.

Cheers, and good luck.

[simon ff]

I know this is an old thread.  But I was wondering if you were able to solve this problem.  I have ran into a similar issue with my build.  It works fine on its own but when I run it through a looper I get a pop when I turn it on.  thanks

[traktop]

I don´t have it on my pedal board right now, but I seemed to remember that it got better.
I ´ve got a similar problem with my naga viper build but couldn´t solve it properly. Tried  pull down resistors and stuff, but couldn´t avoid that annoying loud "pop" noise.