Voltage sag control in a fuzz

[theundeadelvis]

Hey guys! I recently built a couple fuzzes, and I put a voltage sag control in both using a 10k linear pot setup just like this (without the battery leads):

In one fuzz it works great. In the other fuzz it won't drop below 4.6v, so basically, it has no effect. Why is this one not dropping the voltage more? I measured the pot and it does travel from about 10.2k to 0 ohms, and at 0 ohms it's reading 4.6 volts. Am I missing something obvious here? Thanks as always!

[joegagan]

dunno, but i always prefer a 50k in this position as i will sometimes slam the starved fuzz with a signal hot enough to resurrect marylin monroe. values less than 50k would sometimes not get me to the gating.

[theundeadelvis]

Thanks Joe! I may just replace the pot with a 50K and see what happens.

[boogietone]

It would seem like you should have 9V at 0 ohms across the pot.

[theundeadelvis]

Good point boogietone. I think I fixed by using the 50k pot Joe suggested. Although, I must express a little disappointed towards Joe's suggestion. I was unable to resurrect Ms. Monroe. Thanks guys!

[theundeadelvis]

OK, very strange behavior that I don't understand. The sag control only works with the fuzz turned all the way down? Is this a characteristic of this particular design or a mistake on my part? The fuzz it's in is a variation of Dragonfly's "Dirty Sanchez" fuzz. Basically, I used this layout:

Schematic (without one of the controls here):

[slacker]

Something doesn't sound right there, I built that and a 10k sag control between 9 volts and the board turned it into a self oscillating monster like a fuzz factory.

[joegagan]

[theundeadelvis]

Thanks Joe, one of those things I'll never be able to un-see. 

Yeah, something is awry. I went through and checked my traces (perfboard), and everything looks ok to my eyes (I realize I could have missed something still). I'm noticing when the pot is at 50k and the adapter isn't plugged in it reads 50K on the DMM. If I plug the adapter the pot reads ) ohms? So if I turn the pot one direction I get about 2 volts and the pot reads ) ohms, rotate it the other direction I get 9 volts and 0 ohms. Not sure if this is because my DMM can't read resistance while there's power or what? On top of that, the fuzz sounds better to my ear when it's a 2 volts than it does at 9. 

Some voltages (at 9 volts)
Q1
E - 0
B - .61
C - .91

Q2
E - 0
B - .55
C - .55

Q3
E - 0
B - .55
C - .43

At 1.94 volts
Q1
E - 0
B - .55
C - .76

Q2
E - 0
B - .50
C - .50

Q3
E - 0
B - .5
C - .360mV

Ok these numbers look completely out of whack to me.

[Zipslack]

No multimeter can read Ohms with power applied...it's one of the first rules of meter usage.  The meter uses the internal battery to supply current to the resistance to develop a voltage and that is used to give the resistance (simplified explanation).  Having external voltage/current messes things up and could damage the meter.  Just set to 20VDC setting and read the voltage drop across the potentiometer with power applied.  You should see the full 0V at one extreme (0 Ohms resistance) and closer to 9V at the other extreme (50K resistance).

[theundeadelvis]

Thanks Zipslack. That makes sense, I was kinda thinking that might be the case. It seems to working alright. Thanks guys!