How does the 350k pot in the Fuzzrite function?

[sixstringphil]

I built a fuzzrite from this schematic... http://fuzzcentral.ssguitar.com/schematics/fuzzriteschem.gif at fuzzcentral.  Everything is exactly like the schem except the pots.  I used 50k and 500k. I think it's sounding pretty good now, but I'm trying to determine the effect of changing the pot value from 500k to near 350k.  I am noticing some change in the pot, but I can't exactly put my finger on what it's doing.  The purpose of the pot is to blend the levels of the two transistors, correct? And that would create a series resistance with the volume pot. So would reducing my pot from 500k to 350k change anything other than the "volume" of the final blend? Should there be any difference in the "tone" of the sound?  I realize that I may be way off, so feel free to correct my ignorance!  To make things even more difficult for me, I've never been a fuzz fan, so the whole sound is unfamiliar territory for me. Thanks guys!

Phillip

[Pedal love]

What is difficult about it? The first stage works as a preamp. The second amplifies the first, making the signal saturating. The 350K is for balance of the first and first plus second stages. The types of changes, you have made, will not affect the sound greatly.

[sixstringphil]

Yeah, I get that part. And I know the changes are subtle. Just wanted to learn what effect increasing or decreasing the pot value would have on the circuit. Thanks for the response!

[Pedal love]

NO MAJOR CHANGE!

[Pedal love]

Look at the math. The original version pots would have 70% of the total resistance of the newer pots on the fuzz control. the original volume pot would have 66% of the total resistance of the newer pot. There is just going to be more signal. What that means can put down as speculative most likely.

[sixstringphil]

Thanks, but I know the math. I guess I was coming at this from my understanding of variable resistors as volume controls in guitars. Changing between 500k and 250k volume pots can have a significant effect on the brightness or muddiness, depending on the pickups. I was just trying to cross this over the the pedal world. Not worth shouting over; I was just trying to learn. Probably should have re-phrased my subject line to better clarify my question.

[Pedal love]

If I sounded too coarse I apologize.

[sixstringphil]

No worries. My frustration is directed not at you but at my lack of understanding something this simple. I know I'm hearing something different with the change, but can't tell if it's just level or if there are tonal changes. I'll keep playing around until I can better pinpoint what I'm hearing. Thanks!

[jacobyjd]

Onboard a guitar, the difference in brightness between 500k and 250k has to do with the amount of signal allowed to flow to ground--with a 500k, there's simply more resistance to ground at full volume than with a 250k.

It's hard to apply that to stompboxes unless you're dealing with the same application as in a guitar (i.e. a voltage divider to output and ground), and then it's a little different due to impedance mumbo-jumbo.

In this case, it's likely that what value pot you put in there doesn't matter a whole lot. Try adding a 10 or 100k in the same spot, then a 500k, and see what the difference is. You'll be able to hear more contrast by just experimenting with some other values. In reality, a 350k pot is a pain in the butt, so I'd try a 250 first, then branch out from there.

[Solidhex]

If you use a lower value pot in the fuzzrite your range of tones won't be as wide as a higher value pot. If you use a higher value pot though, the outer edges of the pot travel will be louder than the middle. The 350k is a good happy medium in that application. Just use a 500k and put a 1meg across it. 1.2meg if you want to be exact. It does make a difference.

--Brad

[albertozioli]

If you use a lower value pot in the fuzzrite your range of tones won't be as wide as a higher value pot. If you use a higher value pot though, the outer edges of the pot travel will be louder than the middle. The 350k is a good happy medium in that application. Just use a 500k and put a 1meg across it. 1.2meg if you want to be exact. It does make a difference.

[albertozioli]

Guys I'm trying for ages build my fuzzrite clone and I have some problems, could you guys give me a hand, I'm talking to other guy on the mosrite forum, he is tring to help me as well, this is the link has some pictures of the project there...

http://www.mosriteforum.com/forum/viewtopic.php?f=20&t=3807

Cheers!
Albert

[Electron Tornado]

I'm building a Fuzzrite clone right now. I used a 1M pot with a 470k resistor across it for the blend pot. Works great. However, I found that there were some tones in the middle that I liked, but there was such a volume drop when the blend pot wasn't at either extreme that I added a boost circuit.

Something else I came across when researching the Fuzzrite is that between the blend pot and the cap from Q2, there is aparrently a 22k resistor to ground that is missing from most of the schematics around. The resistor creates a high pass filter with the cap and helps get a much more raspy fuzz. The addition of the resistor will cut the volume a bit, however, which is to be expected. Next step is to try a pot in place of that resistor to see if I can tweak the tone a bit.

Another simple mod, kind of like a "fat" mod, is to take the cap from between Q2 and the blend pot and add a 0.01uf in parallel with it. Add a switch to make it selectable.

BTW, I'm using BC108s for the fuzz circuit and a 2n3904 for the boost circuit.

[petemoore]

  The value of that pot wafer is what separates the two out of phase output tap points.
  Calculating the LP filter effect as the shaft is moved away from Cw and CCw postitions...easier to turn the pot and test for HF's, use a 500k with treble bleed on one side or the other, low impedance to HF's on both sides again would be OOPhase and cancel.
  I built that one and wanted the pot to turn farther to the right [more effect], so I put a booster in front etc., didn't like the bias of 470k collector resistors...at the time it seemed gnarly but not particularly fuzzy.

[Electron Tornado]

I posted some pics and a schematic of the finished pedal over here:  http://www.buildyourownclone.com/board/viewtopic.php?f=9&t=28505

(Hope it's OK to post that link)

[brett]

Hi

Something else I came across when researching the Fuzzrite is that between the blend pot and the cap from Q2, there is aparrently a 22k resistor to ground that is missing from most of the schematics around.

That's and excellent find.  The Fuzzrite sure does sound harsh in its usual form.  An interesting thing about this is, as was noted, it is a hih-pass filter, which cuts bass, not treble (the cutoff frequency fc is about 3.6 kHz, or 3 octaves above middle A  ).  I wonder whether the main effect is to reduce the volume being blended from Q2, and make the opedal a lot more subtle?

Previously, I've tamed some of the harshness by using transistors more like the old ones (e.g. hFE = 150, BD139s etc).
cheers

[John Lyons]

The 22k is a trade off.
It sounds good with it but it loses a lot of the cool stuff in the middle attack positions.
Makes the variability kind of limp.

[brett]

Hi again
thinking this through some more.....
a 2.2k resistor would make for a 360 Hz filter...much more reasonable for removing bass but leaving mids in.
Could someone try this out for us and report back?
(My gear for builds is packed away and I can't play anyway (car ran over me))
cheers

[Electron Tornado]

The 22k is a trade off.
It sounds good with it but it loses a lot of the cool stuff in the middle attack positions.
Makes the variability kind of limp.

That's why I added the switch to be able to remove it. Gives some boost, helps fatten the tone.

[John Lyons]

Yes, A switch is the best of both worlds.

Brett
I've played with a pot in that position.
But not with the Fuzzrite so I'm not sure how it
will affect the blend between those two stages.