CHASM REVERB

[Mgt280y]

No problem, tbh I'm surprised I've built this as my first ever pedal and these are the only issues! I'm am now feeling that I'm either being really stupid or ....
With the toggle I cant see an on off only, these are what I'm looking at
https://flic.kr/p/JCGNqE

[deadastronaut]

oops...on off on...     middle one 'll do ya,..

youve done well for a first pedal man... cool.

a baptism of fire,.

[Mgt280y]

Ahhh.. And the penny drops lol, to any noobs chasm is a cool first project and with amazing results I am proof anyone can build, roll on graphics

So atm I'm using the top one (on-on) what difference is this going to make cant work out the trace on the pcb

[traktop]

Let´s see if you can help me on this one.
My chasm reverb is working beautifully.
My problem started when I hooked it 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 followed by its own reverb trail, (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.
Any Idea?
Cheers, Gilberto.

[deadastronaut]

hmmmm....

it stays on all the time? in a loop...

but its working fine on its own, or not in a loop?

[traktop]

hmmmm....

it stays on all the time? in a loop...

but its working fine on its own, or not in a loop?

The pedal remains on all the time when I use it inside a boss es-8 loop. The pop sound appears when I turn the chasm loop on, (thing that don´t happen with any of my other pedals).
On the other side, the chasm switch is working fine on its own. The dpdt on/off switch works smooth without any kind of noise or "pop" sound that others experienced due a faulty 2n7000. The only strange thing I experienced lately, (inside a es-8 looper or by itself), is that being the Chasm reverb off, when I increase the signal level of my guitar with a booster for soloing, (in front of the Chasm),  that rising in level seems to trigger reverb splashes on the hardest picking parts. All this happens with the chasm reverb disengaged... So Time for a 2n7000 swapping maybe...?
(The reason I didn´t do it yet is because my transistor shockets wear way fast, so I wanted to consult what to try first).
Cheers, Gilberto.

[traktop]

Replaced like ten 2n7000s, with same result.
One thing I noticed is that I used 2n5458s instead 2n5457s, but made a research and seemed that they are pretty much interchangeables.

[deadastronaut]

im not sure whats going on there with the boss es8..

i just had a quick browse at it..

apparently it has switchable buffers on/off...not that it should make a difference

but have you tried it with the internal buffer on and off?...just curious


so your chasm is working fine without this es8 loopy thing?.

[traktop]

I use to have the output buffer on, but I tried without buffers with same result.
I tried the chasm in all es-8 loops and every time I introduce the chasm reverb on the signal path, (when the es-8 is feeding the chasm with the guitar signal), the pedal makes a loud "pop" sound.
By itself, the chasm works smoothly outside the es-8, with no noises related with the switching system. The only problem that persists, (even outside the es-8), is that when the chasm reverb is off, if I throw a booster or any other pedal with a volume boost, (about 4dbs), before the chasm, this increase in signal volume triggers splashes of reverb when reaches certain threshold. This issue is inherent to the pedal, (by itself, or inside a es-8 loop), and happens even after I replacing a bunch of 2n7000 and 2n5458s. 

[deadastronaut]

hmmmm...

all i can suggest is maybe a wrong value on the chasm board maybe...

this might be the issue,

[traktop]

I will take a deep look at it.
Cheers, Gilberto.

[traktop]

 I checked the board and everything seemed ok.
The only thing that differs is that I used 2n5458s since I didn´t have 2n5457s available as I mentioned before. I thought they were pretty much interchangeables, but a deeper research showed a difference on average Vp's of 2.5V vs 1.5V respectively, (I really don´t know what that means though...), so maybe that could be the cause of wet path fet don´t switching properly with a higher than average signal voltage coming from my booster¿?
A different option could be trying a 3pdt switch, using the third pole to dump the wet signal to ground just before going into the 2n7000, (for example).

I´ve been thinking about the pop sound when into a es-8 loop. Do you think that circuit behaviour could be improved with a pulldown resistor on this specific scenario?, (and where to insert it).
Cheers, Gilberto.

[anotherjim]

I found a schematic that shows no pull-downs on in or out. I would add some.
Fit from 2M2 to 10M (highest in that range that you have) from PCB signal in to ground. 100k from PCB signal out to ground. Depends on your build where it's easiest to fit them -  on the pcb or the jacks.

Higher FET threshold could be causing bleed thru grief at the switches when signal level is high. Check your 9V supply and +UB voltages first.

[traktop]

Thanks.
I will add pulldown resistors, but don´t 100k resistor to ground at the output would be too low of a value?
My 9v supply reads exactly 8.98v.
I don´t know what are +UB voltages. You mean fets and tl074 IC?

[anotherjim]

100k would be fine. The output op-amp can drive a low impedance and the output cap is large. 1M will work too.

Do you have access to the schematic? +UB is the reference voltage used by the op-amps and also the bias for the FET's. The difference between +UB and the FET gate control from the footswitch determines how well the FET switches are turned on or off.
+UB is I believe, produced at the junction of 2 10k resistors close to the +9V input before the 5volt regulator. You should get close to 4.5V there. You can also check for a similar voltage on the drain and source of the FET's and on the outputs of the TL074 amps (corner pins).
I found some info on this page...
http://www.coda-effects.com/2016/02/dead-astronaut-fx-chasm-reverb.html
R23 & R24 junction is UB.
Also check FET gate control voltage across C14 & C15. It should be very close to +9v or 0v depending on footswitch.

[samhay]

Pulldown resitors were not included in this build as it is not designed to be true bypass. As Jim said, 100k or 1M on the output would be a good idea to stop popping when you switch it on/off and if that doesn't help, try 1-10M on the input too.

I would guess that the Q1 JFET is the problem regarding signal bleed-through. A better choice (and cheaper) than 2N5457 here would be a J112 or similar (N channel switch rather than amplifier). But as Jim said, make sure the FET switch is working properly and pulling the gate to 9V and ground.

[anotherjim]

I had an idea to help us use high pinch off JFETs as signal switches.
What if, assuming N-channel, the signal input to the switch also drove a negative voltage diode charge pump. This supplies the gate "off" switching instead of 0V. When the signal swings down towards 0V, the pump charges the gate control more negative, maintaining the off state. Would that work? Has it been done anywhere?

[traktop]

Sorry, I´ve been out for a while.

I´ve just measured Q1 and Q2 gates at their respective electrolitic caps, and this is what I´ve found:

Q1: Sw.On: 8.98v---Sw.Off: 0.08v

Q2: Sw.On: 0.08v---Sw.Off: 8.98v

Measured the output of the transformer and reads 5.00v.

Readings seemed ok, right?

[anotherjim]

Yes, those gates are ok.

[Lothric]

hi everyone, I have decided to wire OSC selector to a foot switch and I would like to have some sort of indicator (LED light) to show me that I am in the oscilator mode. How can I make it? Cheers and big thanx to Dead Astronaut for a great reverb pedal!