Mojo Cake Overdrive Pedal

Moonibopper · February 19, 2012, 11:46:29 PM

So I just put together Soulsonic's version of the Crowther Hot Cake as layed out here: http://www.sabrotone.com/wp-content/uploads/2011/09/MojoCake.gif

The effect is great! The only issue is, wired up exactly as shown (with buffer and DPDT) it takes a second or two for the effect to come through the effect is engaged. Is this a result of the buffer? Any help would be greatly appreciated.

PRR · February 20, 2012, 12:59:41 AM

Is there a schematic?

> takes a second or two

Try 100K from Gain12 to Ground.

Moonibopper · February 20, 2012, 08:59:39 AM

Thanks for the reply. The schematic is at http://www.box.com/s/da2mzsrsm7ysy0u555ts in a zip file

artifus · February 20, 2012, 09:32:13 AM

correct me if i'm wrong prr

Moonibopper · February 20, 2012, 10:11:12 AM

Artifus you having the same issue?

artifus · February 20, 2012, 12:03:21 PM

nope, just trying to help.

Moonibopper · February 20, 2012, 12:34:21 PM

Awesome, thanks!

Can either of you guys explain the reasoning behind the issue I'm having? Just for learning sake... thanks.

PRR · February 20, 2012, 05:23:43 PM

I am not convinced the plan is correct. At least the off-board wiring confuses me.

Open up. No plug in output. Put your DC voltmeter from tip to sleeve of output jack. Engage/disengage effect, various Volume and Tone settings. Is there DC on the output jack? Seems to me there is, and different engaged/disengaged.

Moonibopper · February 20, 2012, 06:23:49 PM

So, tried the 100k resistor from Gain1,2 to ground. Still the same issue.

Checked the DC voltage on the output jack - when disengaged, 4.3V. When engaged, 0.3V.

Can you tell me what in the stripboard layout is incorrect? Really appreciate the help.

PRR · February 20, 2012, 07:25:45 PM

> disengaged, 4.3V. When engaged, 0.3V

No good. The effect may actually be working through the transition, but that 4 volt JUMP in a 0.1V-signal world may be knocking-out the next amp in the chain (possibly your guitar amp) and it takes a second or two to recover.

> what in the stripboard layout is incorrect?

I'm looking at the original (PCB) drawings and I'm not digesting them. Being spread-out over 3 files in 2 formats is not helping. But clearly the output jack has DC path through pots and resistors to an opamp output sitting at +4.5V. In FX mode the bottom of the Volum pot is grounded; in Bypass it seems to float up to 4.5V.

I wonder if the design was originally bipolar power. Then the opamp output would sit (nearly) zero V either way.

Trying to "fix" this schematic, then identifying the mods to the PCB, then transposing to your stripboard, is non-trivial.

I see the name of "that other place" on the drawings. Have you looked/asked there?

Moonibopper · February 20, 2012, 07:40:22 PM

Okay will ask there. I thought it would just be a matter of comparing the stripboard layout to the schematic.

PRR · February 20, 2012, 07:53:46 PM

This may be the simplest "fix":

Moonibopper · February 20, 2012, 08:12:00 PM

Hmmm... tried that but now there's no sound either in bypass or when engaged. Appreciate the help.

LaceSensor · February 20, 2012, 08:14:34 PM

I had the exact same issue.

Moonibopper · February 20, 2012, 08:19:36 PM

LaceSensor, did you ever figure it out?

LaceSensor · February 20, 2012, 08:58:03 PM

No just gave up and made another that worked.

Moonibopper · February 20, 2012, 10:04:34 PM

Made another copy of the same pedal? What made it work the second time?

LaceSensor · February 21, 2012, 07:41:02 PM

Quote from: Moonibopper on February 20, 2012, 10:04:34 PM
Made another copy of the same pedal? What made it work the second time?

No another hotcake vero completely

News:

Mojo Cake Overdrive Pedal