Can Maestro Sample Hold FSH-1 be used like a wah?

[vanessa]

I was looking at the filter and it looks like a 100k value (nice for a wah pot). Would an expression pedal (used like a wah) work with this?

[slacker]

If you mean the "filter range" pot R15 on the ggg schematic that just sets the range over which the envelope follower sweeps. You couldn't use that for a manual wah effect.
On the ggg schematic a control voltage from either the envelope follower or the sample and hold generator is fed into the bottom of R22, that makes the filter sweep. I guess you could wire a pot up as a voltage divider and use that to feed a control voltage into that point. That would give you a manual wah effect.

[Mark Hammer]

Note that the control-voltage summing node is really the emitter of Q3.  It receives:

• the envelope voltage via R22
• the sampled and held random voltage via R22
• a fixed bias voltage off V+ via R21
• a variable bias added to (or subtracted from) that via R23

Stick all those voltages together in assorted combinations and the circuit does the voltage-to-current conversion and feeds the OTAs whatever the emitter of Q3 sees.

So, let me ask users of the FSH-1: How much adjustment range does R26 provide?  Maybe that's the component you could stick in a footswept pot, or perhaps replace while switching out all the other control voltage sources.

[slacker]

I wondered if R26 might do the trick, but the way it's hooked up to the switch confused me as to what it did.
It does look like an ideal candidate to make into an external pot anyway as presumably it lets you set the resting frequency of the filter.

[Mark Hammer]

That was my thinking too.  Having only a partially populated board for one, and never having used it, what I don't know is the extent to which it is directly replaceable with a foot-controlled pot or whether it is one of those things where only part of the full range of the trimpot is actually usable.  It make be that the trimpot needs to be replaced with a smaller-value pot and two selected fixed resistors, one on each end.

[vanessa]

Wow! That would be cool. It's 100k (R26) and it looks like you could set the range on top of that (via the filter control).



Might prove to be a very useful wah. I have not built it yet but from the sound samples I have heard it seems like a very strong wah type filter that could be useful for the player that wants something a little different in their wah?

[Rectangular]

its definitely a strong filter, if you've ever used a dual OTA sallen-key type before (Korg ms-20s, for example) its the same family.  my experience with sweeping this thing however, is that isn't doesn't have a linear response the way a wah filter does. the filter range pot has a very select few "sweet spots" and then the rest aren't anywhere near as audible/useful . you really have to manually dial in for the right wah-type responses

as for this r26 replacement, I might give that a try, I can let you know if it does anything useful 

[Hambo]

I call mine the tomcat emulator. I think it doesnt work quite right, though its still pretty cool, but I was more interested in the S+H anyway, now a footcontrol on the speed of that would be EXCELLENT, matching changes in tempo in a song. Maybe you could rig it so that you have that available too if you perform this mod- Just a suggestion.

[chemosis]

so does the 100k trimpot set the frequency for the envelope filter. how do you controll the freq of the envelope filter??

[Kevin Mitchell]

EDIT- I answered a nine year old question  Oops

I have the FSH on breadboard at the moment. I put an lfo with a long sweep on there. I wanted to hear how it sounds with slow sweeps and also to check out it's range.

If you already have an FSH-1 built (I'm looking at a tonepad schematic), there is a 22k on Q3 (the PNP transistor) instead of it going to the filter | s/h switch (lug B0) put it to the center of a SPDT switch with one side to that B0 connection and the other side to the middle lug of a 100K pot. Put lug 1 or 3 to ground. (depending how which side you mount the pot in enclosure).

You may want to throw on some resistors to the pot to adjust the range limits.

EDITED ANSWER
The 100k trim in the schematic set the frequency for usability and desirability. Try to not rehash old threads with irrelevant questions. I'm sure you could find the answer in a few places already.