Question About Rehousing Danelectro Fab Metal with True Bypass

[SenorAmazing]

Extremely new to this so excuse any idiotic thoughts. Looking to rehouse a danelectro fab metal pedal in a standard metal enclosure with a true bypass switch and new neutrik jacks. The pedal has an I/O buffer board that I'm going to completely eliminate. You'll see in the picture that it connects to the effects board via a set of 5 wires. What I need to know is, where the 5 wires connect to the effects board, which are the input and output so that I can wire the 3dpt switch to? Or how would I be able to find out?

[Rob Strand]

I seen to remember it's not a simple matter to chop off the JFET analog switching PCB.   

There's buffers (on the switching PCB) which are part of the circuit in effects mode.  Yes, you could removed those as well but you might need to keep the input buffer as the input impedance of the remaining effects pedal loads down the pickup in an unintended way.   On the output side you might find there output caps on the switching board that are still required for the basic pedal to work.

Off hand I think there's some power related items on the switch board as well.

This thread is sort of doing the same thing.   However, you might find the pickup loading problem isn't resolved.

https://www.diystompboxes.com/smfforum/index.php?topic=104383.0

I traced the switching board over 10 years ago but I never transferred the schematic to CAD.   It could literally be drawn on the back of envelope somewhere in my large stash of stuff.   It's too long ago to remember all the details, other than the "easy way out" solutions are probably wrong.

Bottom line is it will take some work to do it properly.

Something else, the switch board on the Flanger wasn't the same as the Overdrive, possibly because they couldn't fit the whole Flanger circuit on a single effects board.

[marcelomd]

Hi,

Suggestion: keep the buffer board, hardwire it in the engaged position. Use the switch to bypass the buffer+effect together.

Way simpler. You keep the effect intact and just need to wire the jacks.

How to trace... power pins can be found with a multimeter. You can make an audio probe and test which wire is which for the signal.

[Rob Strand]

Suggestion: keep the buffer board, hardwire it in the engaged position. Use the switch to bypass the buffer+effect together.

Here's the details how to force effects mode.



Audio switching PCB

FAB OD and FAB Metal use same audio switching PCB.

The FAB flanger has a different switching PCB and extra
components possibly used for the Flanger.


PCB pics:
https://mirosol.kapsi.fi/2013/09/danelectro-d3-fab-metal/


Comments:

The Audio Switching PCB contains buffers and power supply components
so the effects PCB cannot be simply cut from the Audio Switching PCB
without causing problems.

The Audio switching PCB uses a CMOS 4053 analog switch chip for
analog switching and a CMOS 4013 D flip-flop for the footswitch state.


1) Polarity of switching signals

The 4013 chip does the footswitch.

- Transistor on left of 4013 drives LED (located on effects PCB).
  Collector pulls low.

- Transistor base driven via 47k base resistor which connects to
   pin 5 (D1) and pin 2 (/Q) of the 4013.

- When 4013 pin 2 is high the transistor is turned on and
  the LED turns on.

  Note 4013 pin 2 also wires to 4053 pin 10.

Conclusion

- 4013 pin 2 (/Q) is high in effects mode. 
   So, 4013 pin 1 (Q) high is bypass mode.


Addtional Info:

- 4013 pin 4 (Reset):  tied to ground

- 4013 pin 6 (Set):
  Pulsed high on power-up by the Cap + 100k located just below the 4013.

  This means on power up the effect is forced to bypass.


2) Forcing Effects mode

Two options:
1) Force 4013 pin 4 (reset) high.   
  That requires cutting the ground track from 4013 pin 4 and wiring 4013 pin 4 to +V.

2) Cut the track between 4013 pin 5 and 47k resistor then wire
  the same end of the 47k to +V.

Option 1 needs to be checked on all 4013's, so option 2 might be slightly preferred.
After looking at the datasheet, both options should be OK.