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Try adding a 100u cap between supply and ground. I did that layout verbatim to the schematic, but really I should have included one on the board.

Tried some stuff.
Tried to use LM741 and LM351 opamps, no difference.

Tried to use a capacitor parallel with the 100k feedback resistor, didn't help either.
Tried to use a capacitor in parallel with the 470p capacitor, oscillation disappears but the gain reduces drastically.

Any ideas?

^^

Tried, but no luck.

I think I will build this layout on pcb and check if this will help:
https://dl.dropbox.com/u/3131065/Pedale ... oject2.pdf

Hey guys, I just built a Mojocake, and I think it sounds pretty rad, but the only thing is that when the DPDT is switched, the signal goes dead for half a second, before fading in to full volume. I've been trying to figure out why it's doing this, and I was thinking I might have mucked up the switch wiring somehow. Anyone have any ideas as to why this unit might be doing this? Maybe just a bad switch?

Hello,

Firstly, thanks for all the comments in this forum, it has been really useful.

I've just built my second one of these and I'm having some issues. Sadly, the first one has been taken off my hands so I can't set the measurements to check where I've gone wrong. Basically, I'm getting noise as an output. My IC readings are:
0.14 0
4.46 8.14
4.04 4.46
0 0.09

I've tried knifing gaps and have been over the components again to check I've not missed anything or had a bad cut. I've attached front and back pics. Any help would be appreciated.

https://dl.dropboxusercontent.com/u/762 ... ke%201.jpg
https://dl.dropboxusercontent.com/u/762 ... ke%202.jpg

Please ignore the above. It was a case of a 'User too stupid' error, I'd missed a ground link on my 3pdt daughter board.

hello .... I am with a doubt in the original DPDT connection. (1977)
how about it?
1 - 4
2 - 5
3 - 6

Hi, guys!

A friend of mine built a Hot Cake and a Jetter Gain Stage Red into one case. The Hot Cake (based upon the Soulsonic Mojo Cake) has tons of gain but only at full settings. Below 3 oclock the gain disappears along with the bass and turns into an unusable, thin, weak, akward distortion. Should I remain crying or theres something we can do?

Plus, the Jetter seems to roll some bass when engaged, so Im thinking about change the cap at the cliping stage (from .047 to .68 or something) in order to recover bass and smooth a little the mid hump. The GSR it's supossed to be a "Dumble like" pedal, but it sounds like a simple TS808 to me, just a tad more dark.

Please, folks, a little help

Hi all.

I just built one of these but am not getting any audio in bypass or active mode.

I checked all connections, knifed between rows, checked for cold solder, etc, but no dice.

Perhaps it is the op amp I am using? I am using NTE857M, which NTE says is the equivalent of the TL071. Anybody tried this chip?

Voltages on the IC:

0.14 0
3.55 7.84
3.71 4.27
0 0.14

I can't find what the voltages should be to test further. Any direction would be appreciated.

if there's no audio in either bypass or engaged modes then the issue is unlikely anywhere on the PCB.
check your wiring on the 3pdt and/or i/o jacks. my money says you've got a short of audio to earth.

Thanks for the quick reply!

When you say Audio to Earth, Any suggestions on how to test for that?

To clarify, I built the Mojo Cake rev. 1 here http://www.sabrotone.com/?attachment_id=1350

As far as I can tell, the switch wiring called for is only SPDT, as the layout calls for SW1 (Gain1,2), SW2 (Gain3), and SW3 (Ground). The other side of the DPDT would be used for the LED (which I haven't hooked up yet, want to get the circuit working first). Could be that I am completely misunderstanding the switch wiring directions.

jdix123 wrote:Thanks for the quick reply!

When you say Audio to Earth, Any suggestions on how to test for that?

To clarify, I built the Mojo Cake rev. 1 here http://www.sabrotone.com/?attachment_id=1350

As far as I can tell, the switch wiring called for is only SPDT, as the layout calls for SW1 (Gain1,2), SW2 (Gain3), and SW3 (Ground). The other side of the DPDT would be used for the LED (which I haven't hooked up yet, want to get the circuit working first). Could be that I am completely misunderstanding the switch wiring directions.

stick your multimeter between the audio (in, then try out) and earth.. it'll likely be zero ohms.
I've had this happen a number of times (zero audio) and invariably I've shorted the signal to earth somewhere. divide and conquer - remove the i/o jacks and switching from the setup and test the board on it's own (use alligator clips)

Ok, at the input jack I get no change - ie the meter doesn't change from the 1 it shows with no reading (near infinite?) and on the output jack I get 6.6 ohms with the circuit unpowered. That suggests a short somewhere?

Also, if I don't have i/o jacks wired in, how do I test the circuit? Sorry if this is all painfully obvious, I've really just been teaching myself.

Check your input socket.
Is it pcb mount or wire connection?
Probably you had soldered your input signal to the sleeve lug.

If that confirmed no error, time to get a audio probe to do point to point trouble shooting.

jdix123 wrote: Also, if I don't have i/o jacks wired in, how do I test the circuit? Sorry if this is all painfully obvious, I've really just been teaching myself.

no worries - we all started somewhere..

firstly, these kinds of questions have all been asked and answered before. start here
https://www.freestompboxes.org/viewforum.php?f=51

audio probes:
https://www.freestompboxes.org/viewtopic.php?f=51&t=6820

help in debugging still required?
some of the basics when asking:
post links to schematics (you posted link to the layout)
post links to the layout (check)
post links to high resolution photos of your build (including all wiring) - somewhere like photobucket.
be patient. folks don't always answer within the first 5 minutes

OK, so I figured out the issue, my input jack was doing something I've never seen before: with the plug pushed all the way in, clicked in place, there is no signal. But as soon as you connect the tip to the tip piece (so the pluck all the way in, but not clicked in) the signal goes through and the effect works. But as soon as the cable is seated, or clicked into place, the signal cuts. I don't get it. I tried different cables, etc.

I replaced the jack and now there is no signal pass through, but I can hear when the effect is engaged (I turn the volume knob and get more white noise, like turning the volume up with no signal).

Great advice - Thanks for the audio probe link, I' going to give that a shot.

Layout posted already.
I couldn't find a schematic for this particular circuit.
The red and black wires off to the right are going to +9v and ground on the battery I'm using for testing (which is still good)

from the picture posted it looks like when you push the jack plug fully in the socket contacts the metal case and shorts the input socket to ground. Solution: turn the socket around by 90 degrees and try it again

That sure seems to be it! Thanks for looking

Derp.

I sorted the instrument jack grounding issue, managed to wire up an LED and get that working (after sorting through a power jack issue - did you know a LOT of power jacks ground to the case where you mount them?).

But now there is something wrong in the circuit. I'm not even sure how to describe it - lots of noise, crackles, etc. The signal seems to fade in and out, etc.

I'm noticing a delay between kicking the effect on and it actually kicking in, much like described elsewhere about this circuit (http://www.sabrotone.com/?attachment_id=1350), except that the layout I am using supposedly fixed that?

At least one of the pots seems to work reverse of how it should. If that is the case, can I just swap the outer two lugs?