Problem with Stereo mod for Tonepad Small Clone

Govmnt_Lacky · July 13, 2010, 09:00:59 AM

I am thinking that the resistor values (100K) should be lower. Any other ideas about this crazy circuit??

Fender3D · July 13, 2010, 09:39:16 AM

Quote from: Govmnt_Lacky on July 12, 2010, 11:01:43 PM
If I jumper from "D" to the 22K/20K/10K junction, I do get a chorus output however, it is extremely louder than the normal output.

THIS ONE IS RACKING MY BRAIN!!!!!!! BUT I CANT PUT IT DOWN.... MUST.....FIND.......FIX!!!!!

this suggests your IC1a is malfunctioning.
It may either be the IC itself or the 220k resistor on the main board providing the bias voltage.
This resistor might have a different value according to ic specs

Govmnt_Lacky · July 13, 2010, 09:49:47 AM

Fender,

Can you explain your reasoning behind your faulty IC1a claim. It will help me if I understand your thinking. Possibly the ENTIRE IC is bad as I lose not only the wet signal after the 100K (possibly due to internal grounding if IC1a at Pin 2)..... AND I lose the dry signal after the 10K (possibly due to internal shorting of IC1b at Pin 6.

Your thoughts?

Fender3D · July 13, 2010, 10:00:02 AM

well,
you have chorus signal at D and you haven't it after the phase inverter (IC1a)...
then you have a signal at pin 7, so IC2b should be functional...

remember that a wrong bias voltage brings you to the same results (no signal)
try and change it (either a 100k trimmer instead of the 2 56K bias resistors or changing the 220k resistor),
swapping the ic with another one is simplier indeed...

Govmnt_Lacky · July 13, 2010, 10:11:25 AM

Fender,

Thanks for the input. It is a great help. I agree that I should probably swap out the IC first (Not looking forward to it as I did not use a socket due to space restraints) however, let me ask you this... you said that since I have dry signal at Pin 7 that my IC2b should be functioning properly. If this is true, then why do I not get an audio probe signal when I probe Pin 6? Shouldn't I get something there?

Fender3D · July 13, 2010, 11:08:48 AM

I never used Aron's probe, since I have a signal generator, and usually check signals with my scope...
so I don't know if you miss the reading 'cause a wrong tension provided by ic1a (if malfunctioning) or 'cause the impedance on pin 6 or whatever. But, signal on pin7 means the op-amp is working (with a scope you could check for the proper gain (~1 feeding A).

Govmnt_Lacky · July 13, 2010, 11:32:59 AM

I guess I will start with replacing the IC (socket it this time as I think I can make room) and go from there.

Thomeeque · July 13, 2010, 12:04:58 PM

Quote from: Govmnt_Lacky on July 12, 2010, 08:41:58 PM
Now, when I put the audio probe on the other side of the 100K resistor (the side leading to IC Pin 2 / other 100K resistor) I LOSE ALL SIGNAL!!!
...
I DO NOT get dry signal anywhere between the right of the 10K, the left of the .01 cap, the bottom of the 33K and Pin 6 of IC. Nowhere in that junction do I get dry signal?

That's correct behavior of this configuration (both IC1a and IC1b of STEREO MOD board form Inverting Amplifier), where inverting input makes "virtual ground". Check pin 1 (wet-signal-invertor output) instead, you should hear the same signal as at D point..

T.

EDIT: Sorry guys, if I'm saying something already said, I did miss page [2] of this thread

Govmnt_Lacky · July 13, 2010, 12:15:32 PM

Thome,

I think I posted earlier.... I get the "wet" signal at the input ("D") and on the input side of the 100K resistor (the one immediately following input D) but, that is the only places I get the wet signal.

There is NO signal on ANY pin of the IC except for Pin 7 which is the dry signal.

Thanks for the help, do you have any top suspects? I am thinking bad IC

Thomeeque · July 13, 2010, 12:16:38 PM

Quote from: Govmnt_Lacky on July 13, 2010, 10:11:25 AM
If this is true, then why do I not get an audio probe signal when I probe Pin 6? Shouldn't I get something there?

..and I see that my previous post has still it's value

Thomeeque · July 13, 2010, 12:29:27 PM

Quote from: Govmnt_Lacky on July 13, 2010, 12:15:32 PM
Thome,

I think I posted earlier.... I get the "wet" signal at the input ("D") and on the input side of the 100K resistor (the one immediately following input D) but, that is the only places I get the wet signal.

There is NO signal on ANY pin of the IC except for Pin 7 which is the dry signal.

Thanks for the help, do you have any top suspects? I am thinking bad IC

OK, turn it off and check (visually and by DMM) that:

(1) - left* leg of the first 100k (between D and IC1/pin2) is properly connected with D
(2) - right* leg of the first 100k is properly connected with IC1/pin2
(3) - left leg of the second 100k (between IC1/pin2 and IC1/pin1) is properly connected with IC1/pin2
(4) - right leg of the second 100k is properly connected with IC1/pin1
(5) - IC1/pin3 and IC1/pin5 are properly connected
(6) - value of both 100k is really 100k
(7) - there is no bridge between IC1/pin1 and IC1/pin2
(8 ) - there is no bridge between IC1/pin2 and IC1/pin3

*(left and right sides are related to the schematic)

If all answers are YES, IC1a is most probably dead (if you are really 100% sure, that there was no signal at IC1/pin1)..

T.

Govmnt_Lacky · July 13, 2010, 12:33:38 PM

Thom,

I will check this tonight and post this evening or tomorrow. Thanks for all your help. Tune in tomorrow for the results.

bside2234 · July 13, 2010, 12:40:26 PM

Here's my voltages. I colored mine red. None of mine oscillate. They were all steady as far as I could tell. I'll try to audio probe mine later and you can compare.

Stereo board IC voltages:

Input voltage - 9.2V - 9.02

JRC4558D Pin 1 - Oscillating from 4.25 to 4.45V - 4.02
Pin 2 - Same as Pin 1 - 4.02
Pin 3 - Same as Pin 1 - 3.90
Pin 4 - 0V - 0
Pin 5 - Same as Pin 1 - 3.90
Pin 6 - Same as Pin 1 - 4.0
Pin 7 - Same as Pin 1 - 3.98
Pin 8 - Oscillating from 8.2 to 8.75V - 7.96

Govmnt_Lacky · July 13, 2010, 01:50:15 PM

Thanks bside. So now the questions are:

What would cause the Pins on the stereo IC to oscillate like that?

What does this problem have in common with my other posted findings?

This is getting challenging.... Could a bad IC cause the oscillations? Stray voltage?

CALLING ALL EXPERTS.... NEED HELP!!!

Govmnt_Lacky · July 14, 2010, 08:16:50 AM

SUCCESS!!!!!

I guess it was the IC! I pulled out the 4558 from the stereo board and replaced it with a socket and the first replacement IC worked!

Thanks to all who helped out. This forum is an invaluable tool for diy'ers

chromesphere · July 17, 2010, 05:36:05 AM

Believe it or not, had the same problem. Exact same problem. Effect was working mono, stereo module was dry. Tried replacing the IC to no avail. Using an audio probe checked "D" track. Dodgy joint between D pad and 100K on the stereo board. Re-soldered, fixed!

Thanks for everyone who posted in this thread and govmnt_lacky for your persistance ;-)

CS

stringsthings · July 17, 2010, 12:59:47 PM

Quote from: Govmnt_Lacky on July 14, 2010, 08:16:50 AM

I guess it was the IC! I pulled out the 4558 from the stereo board and replaced it with a socket and the first replacement IC worked!

as a way of thanking the forum, can you describe your process of trouble-shooting so that others can benefit from where you made your mistakes? and while you're at it, how's about posting a soundclip? that would be a nice gesture of thanks to all of us that took time out from our day to assist you ...

the next time that you have a pedal problem, how are you going to handle it?

disabled_shredder · July 30, 2013, 10:01:31 PM

i built the tone pad small clone stereo chorus pedal i get great stereo wet signal but when in bypass i only get output on the mono side. so i thought to myself why no run a line from the bypassed leg of the 3pdt switch to the stereo jack. when i did that it had great signal loss and sucked all high end out of it almost as if doing the broadcaster mod on a tele and using the 3rd pos. any ideas on getting dry signal through both jacks?

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Problem with Stereo mod for Tonepad Small Clone