Chasm Reverb, Bypass Drain

[HarryDell]

Hi,

I've built the Chasm Reverb with DeadAstronauts PCB (https://dl.dropboxusercontent.com/u/7464107/chasmverb.jpg)

The Effect Works Fine, but the when Bypassed some of the Signal leaks and you can still hear the reverb(https://soundcloud.com/samuel-riedel-4/chasm-reverb-bypassed)

I swapped Q1(2N5457) Q2(2N7000) D1(1N4148) and C14(10uF) but it doesn't changed anything.

I Measured following Voltages:

Bypassed:
FS1: 0
FS2: 9,36

Q1: D 3,68  S 3,68   G -2,5
Q2: D 3,68  S 3,68   G -1,1
Q3: D 1,5  G 1,5   S  7,3

Effect on:
FS1: 9,36
FS2: 0

Q1: D 3.68  S  3,68  G -1,1
Q2: D 3,68  S  3,68  G -2,25
Q3: D 1,51  G  3,68  S  7,32

If I eather remove Q1 or Q3 the bypass works properly, so no solder bridges.

I assume there is a problem in the FS1 circuit(D1, D2, R18, R19, C14), i checked all values and for any short-circuit fault.

I'm thankful for any sugegstions.

[Kipper4]

Doesn't this suggest that Q1 isn't turning off the audio to the reverb path?

[HarryDell]

Which then leads to Signal draining into the Belton Brick. I just don't have an idea why.

[stallik]

The Chasm circuit has a switch which enables the reverb tails to continue after the effect is turned off. Are you sure that this is not what you're hearing?

[HarryDell]

It's no oscilation. It's the normal reverb effect, a bit distorted and quieter than the activated reverb.
I updated the soundcloud link, a short recording of the "bypassed"  effect.

[samhay]

Do you have any other JFETs you can try? - preferably something other than your stash of 2N5457s.

[HarryDell]

No, i will look for a replacement. Does somebody has voltages of a working one? I'm not quite sure how a mosfet behave, but Maybe the biasing on Vb is to high and Q3 doesn't close Propeller.

[samhay]

You can use much cheaper JFETs for this application - save your 2N5457 for amplifiers. The FET switching is borrowed from Merlin (valvewizard) and he recomends J112s, but others will/may also work.

[HarryDell]

Thanks. Just ordered some.

[HarryDell]

So,  i was experimenting and Put a 500ohm resistor in parallel to R24 and it fixed the Problem,but now the Signal gets distorted. So my question is, does make more sense in a voltage divider to decrease the "grounded"  resistor or to increase the "positive" resistor?

[samhay]

Which schematic are you working off?
The one you posted has R24 as the bottom half of the Vref voltage divider. I'd be surprised it works at all with a 500 R strapped across it.
https://dl.dropboxusercontent.com/u/7464107/chasmverb.jpg

Going by the above schematic, you can remove D2, D4, R13, R21 and the switching will still work.

Are you sure you have the ground wire connected to your switch?

[HarryDell]

I work with the schematic you posted.
The switch is properly grounded.
Do you Think that a wrong biasing of Vb and Q3 can't be the Problem?

[HarryDell]

I switched the 5457s with j112 and it make it worse, you almost can't hear a difference between effect on and of. Do i have to change something in the footswitch section?

Edit : i did a quick read of this article http://www.geofex.com/article_folders/millenium/millen.htm
I will try to switch a Diode with a transistor.

[deadastronaut]

havent had this issue myself,

the only issue i ever had was a little pop when swtching, swapped a fet
and it sorted it...

if i get time i'll post voltages later ok..

[HarryDell]

Thank you.

Edit: i received a new batch of 5457s and it didn't solved the problem.

[HarryDell]

So worked out a temporaly work-around. The DPDT got swapped with a 3PDT so i can disconnect the Source pin of Q1. Not elegant, but it works. ☺

Gesendet von meinem D6503 mit Tapatalk

[italianguy63]

NOTE:  New issue, but similar, so I am posting here.  Rob suggested I post here for some guidance.

Built a Chasm Reverb.  Newest version, on board pots.

Board won't "engage" into effect mode.  However, if I momentarily short the "gate" and "source" of Q1, it will engage and start working.

Also, in "bypass" mode, the Level control does control some volume-- so this indicates when the pedal is bypassed, it is still sending some signal into the OPAMP region.

I have replaced Q1 twice.  (so 3 different JFETS).

I have not replaced Q2.  Samhay-- you out there brother?

Ideas?
MC

[italianguy63]

I've had this thing apart about 4 times today... So, while I was waiting.. I decided to go in and socket Q1 and Q2.  I swapped them out again.  And, issue #2 resolved.

In bypass mode.. the Level is no longer functioning (which is correct).  Appears to have been Q2.

It still will not engage.  I have tried several different 2N5457's and even a J201 in Q1.  Still no dice.

Thinking maybe Q3 may be at risk too....

MC

[italianguy63]

Schematic

[samhay]

If you pull the 2 JFETs and jumper the source and drain connections of Q1, you should get effect out. Sounds like this is working, so Q3 should be fine.

Sounds like the JFET switches are stuck somewhere between on and off. Are you using known-good JFETs?

To check the switch is working, measure the voltage on the cathode of D3 (which are hanging off the gates of the 2 JFETs). If these toggle between ~ ground and ~ 9V then the switch is working. If not, you switch is not wired correctly and/or the 10u caps are suspect and/or the 1N4148s may be in backwards.