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Bass Micro Synth Mod for Expression Pedal?

#2
It will work - easiest way is to literally have the exp. pedal potentiometer replace the stop frequency slider potentiometer - the two pots must be the same value, or at least very close. If you're clever, you might even be able to work it such that the slider pot still works when the exp. pedal is not plugged in.
 
#4
niftydog said:
It will work - easiest way is to literally have the exp. pedal potentiometer replace the stop frequency slider potentiometer - the two pots must be the same value, or at least very close. If you're clever, you might even be able to work it such that the slider pot still works when the exp. pedal is not plugged in.
Click to expand...

+1

Anything that you can conceive can be done given the knowledge and the tools.
 
#5
Somebody at DIYstompboxes.com did that. If you go over there and do a search you should be able to find it. I don't think they explained how they did it but they did have a clip.

I began doing this mod but haven't finished it yet. If you look at the schematic you'll see there's a resistor in series with the stop frequency slider. If you replace that resistor with a pot you get a second control. So, wire up a switching jack that switches that resistor out of the circuit when the expression pedal is plugged in and you're pretty much done. I don't have an exp pedal to try it yet, but I did wire a plain pot and it worked. I found a 1Meg pot worked best, though I don't know what value is standard in expression pedals.
 
#6
sonicvi said:
Somebody at DIYstompboxes.com did that. If you go over there and do a search you should be able to find it. I don't think they explained how they did it but they did have a clip.

I began doing this mod but haven't finished it yet. If you look at the schematic you'll see there's a resistor in series with the stop frequency slider. If you replace that resistor with a pot you get a second control. So, wire up a switching jack that switches that resistor out of the circuit when the expression pedal is plugged in and you're pretty much done. I don't have an exp pedal to try it yet, but I did wire a plain pot and it worked. I found a 1Meg pot worked best, though I don't know what value is standard in expression pedals.
Click to expand...

Is the slider part soldered to the PCB? Did you have to cut the trace to isolate it?

Thanks to all for the information, I'll to a bit more searching over at DIY Stomp and see what they have to say. I think this is an ultra-worthy mod, wild spacey goodness lies at the end...

:ninja:

out

Col Monk
 
#7
Colonel Monk said:
Is the slider part soldered to the PCB? Did you have to cut the trace to isolate it?

Thanks to all for the information, I'll to a bit more searching over at DIY Stomp and see what they have to say. I think this is an ultra-worthy mod, wild spacey goodness lies at the end...

:ninja:

out

Col Monk
Click to expand...


The sliders are all soldered to one of the PCB's. You only need to desolder the resisitor, not the slider.

Here's the post I was referring to: Invalid Link Removed

I'll see if I can do a quick drawing of how I planned on doing it.
 
#9
Colonel Monk said:
Wonder what this "charge pump" circuit looks like -- would be nice to eliminate the 24V wall wart. Any ideas?
Click to expand...

You can't do it that way. Believe me, I tried (see link below). I used the Godlyke Power Pump, too (which is what he was referring to). You'll run into serious grounding issues because of the BMS' circuit design, and fixing them would require a complete redesign of the entire circuit.

http://www.talkbass.com/forum/showthread.php?t=340125

That doesn't mean you can't get rid of the wall wart, though.

What you could do instead would be to use a Y-cable and isolated-output power brick approach. The Voodoo Lab Pedal Power 2+ can do this, by switching two of its outputs to 12VDC mode, and linking them with the proper Y-cable to get 24VDC. That's what I did until I sold the BMS for entirely unrelated reasons.
 
#12
Colonel Monk said:
Got it. Elimination of the wart is just icing anyway, I'm more interested in how this bad mother sounds, which is awesome.

True Bypass and an Exp Pedal would just make it better!

Monk
Click to expand...

True bypass is simple, as simple as any other pedal anyway.

Here's a crude illustration of how I plan to add the expression jack (if I do, my pedal is vintage and I dunno if I want to drill it).

bmsmod.gif


So you see, the resistor is wired to the jack. When no plug is inserted the switch is closed and the resistor remains in the circuit. When a plug is inserted the switch opens and the resistor is replaced by the pot in the expression pedal.
This way you'll need an exp pedal with a TRS cable, but with only the tip and ring connected to the pot. To clarfy, the black things are the slider and R66 is located between two of them.

Also, here's the schematic: [Invalid or Expired Link Removed]
 
#13
sonicvi said:
Does the Godlyke charge pump with with + and - ground supplies?
Click to expand...

It works fine with both, but the barrel on it is a standard 2.1mm center-negative one. I attached a conversion plug to the power pump to get the 2.5mm, center-positive barrel I needed.

Alone, with no other pedals involved, the BMS works great using the Power Pump. But bring in even one pedal that's negative-ground, and they all lose power. It's the reason why we targeted the BMS as the suspect.
 
#15
sonicvi said:
Even if you use it on an isolated circuit?
Click to expand...

I don't think I ever tried it on an isolated circuit, unfortunately; it was tested using a 1 Spot and a Dunlop DC Brick (the results were the same on both). I don't recall if I tried using two 9VDC adapters (with one just for the Power Pump / BMS).

...maybe I did... I'm not sure... but AFAIK it would be fine on an isolated supply; it'd be no different than having it on its own original wall wart. It's just a transformer, after all.
 
#16
MysticBoo said:
I don't think I ever tried it on an isolated circuit, unfortunately; it was tested using a 1 Spot and a Dunlop DC Brick (the results were the same on both). I don't recall if I tried using two 9VDC adapters (with one just for the Power Pump / BMS).

...maybe I did... I'm not sure... but AFAIK it would be fine on an isolated supply; it'd be no different than having it on its own original wall wart. It's just a transformer, after all.
Click to expand...

Right, that kinda defeats the purpose.
 
#19
MysticBoo said:
Well, if you were using it on the Voodoo Lab Pedal Power 2, it'd work on a single output. But if I'm not mistaken, the problem then becomes a matter of available current on that output, since you've increased the voltage.
Click to expand...

Quite right.

And even if with isolated power, given the requirements of the power pump (stated 1700ma), you'd be drawing most if not all of the available power. I don't think I've seen a brick with isolated power than can deliver 1700ma, nor is it typically necessary.

Though I'm sure the BMS doesn't need all the power available via the powerpump - about 400mA @ 24V...

Has either of you guys measured the current used by the BMS@24V?
 
#20
squarewave said:
Thanks for that. Could you take it down one more level for those of us who are real electronics newbies and show us how to wire the three lugs of the expression pedal pot? Thanks.
Click to expand...

Just a word of warning, the BMS is a real chore to work on even for the experienced. It has two pcb's sandwiched together in there with LOTS of short wires connecting them. Even Howard Davis (one of EH's original designers) says on his page he doesn't like working on them.

The pot is wires with the middle lug wired to either one of the tip or or ring and one of the outside lugs wired to the other of the tip or ring. It doesn't really matter which goes to which. the only difference it will make is the direction of sweep. It will probably depend on the pedal you're using which way is correct. If you wire it and it sweeps in the wrong direction just reverse the wires on the pot. I think a 250K or 500K pot in the pedal will work the best, not a 1Meg like I said before.
 

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