2k Fuzz pot for Fuzz Face clone

[yeeshkul]

Guys can i use just a 5k pot and put about 3.3k resistor in parallel to it ?

[Ardric]

Yes.  But instead of a linear taper, you'll get a curved taper like an audio pot.  The interesting end of the range will all be bunched up near the max.

Why not just use a 1k linear pot and put a 1k resistor in series with the CCW lug that went to gnd?  It's then a 2k linear pot that you can never turn below 50%.  I never want to turn it down that far anyways.

[raulgrell]

may be a dumb question.... but when there's a higher resistance to ground from the emitter, the gain/boost is higher, right? Or does this only happen in emitter fllower circuits?

[Ardric]

Increasing the emitter resistance would lower the gain, but it all depends on the bypass cap too.  The fuzz pot varies how much effect the bypass cap has, and it's also the emitter resistor.

An emitter follower is a buffer.  It isn't for signal (voltage) gain.  It provides current gain to go from a high impedance input to a low impedance output.

[yeeshkul]

thanks Ardric, i just wanna get rid of one 5k pot

[Mark Hammer]

The 1k pot in the Fuzz Face does 2 things.  First, it presents a fixed 1k path from emitter to ground.  Second, using the wiper as a tap along that 1k path to "borrow" resistance, it also permits a variable resistance path between the emitter and the cap to ground.  There is absolutely no reason why you could not separate those two functions and have a Fuzz Face that works perfectly well.  Run a 1k resistor from emitter to ground, instead of the standard 1k pot.  Solder one lug of the 5k pot to the emitter connection, and another to the cap to ground.  Tack on whatever parallel resistors on the pot give you the sort of feel you want, using the guidelines in The Secret Life of Pots (at www.geofex.com).

Incidentally, where the gain is applied is a function of the cap value.  Smaller cap values apply the gain at a higher range of frequencies, and leave the low end as if there were no bypass cap.  It occurs to me that it might be interesting to have a small value trimpot, or even pot, to adjust the balance between bypass caps.  In other words, imagine you had a 1k pot set up as I have described the setup of  your 5k pot above.  However, instead of that pot going between emitter and bypass cap directly, it would go to the wiper of a second pot of perhaps 500R.  The outside lugs of that pot would go to the standard 22-33uf bypass cap on one side, and a smaller cap, perhaps 4.7uf or less, on the other.  That way, you could use the first pot to adjust how much gain will be applied overall, and the second pot to adjust how disproportionately that gain would be applied to just the mids and highs vs the entire spectrum.

Given how many variants of the basic Fuzz Face circuit have emerged over the years from the many clever minds here, it is hard for me to imagine this has not been explored.  But, just in the event that this is one of those permutations that has managed to somehow elude us, I mention it here for erstwhile experimenters.  It may actually not yield anything different than what one gets by using a pot for a variable bypass on the input cap.

[Elektrojänis]

There is absolutely no reason why you could not separate those two functions and have a Fuzz Face that works perfectly well.

There is a nice picture of this kind of "separation" here: http://www.muzique.com/news/?p=15

[Mark Hammer]

I kind of figured Jack or someone would have come up with this already.  Thanks for pointing that blog entry out.

[yeeshkul]

hehehe, that's pretty clever, thanks guys

[yeeshkul]

By the way what could have been the reason Roger Mayer used 2k pot instead of 1k? Is it a stronger negative current feedback from emitter to base of Q2?
In his article, R.G says that the mods had been done to increase gain, but i can find any relation between the bigger Fuzz pot and the bigger gain 

[Dragonfly]

Given how many variants of the basic Fuzz Face circuit have emerged over the years from the many clever minds here, it is hard for me to imagine this has not been explored.

It has been... 

[joegagan]

if i remember, this one worked pretty well , posted at ampage in 2002 or 03:(note the Gus smalley 220ohm at Q1 emitter)
 

[nooneknows]

By the way what could have been the reason Roger Mayer used 2k pot instead of 1k?

He modified the collector resistors too. I bet some of the changes has been done to correctly bias that particular tranny...

[yeeshkul]

He indeed had to modify the collector resistor as well to get the right bias, but i am wandering why he changed the pot itself. To make it go even cleaner? To make it more stable? ... 

[Elektrojänis]

I kind of figured Jack or someone would have come up with this already.  Thanks for pointing that blog entry out.

Your explanation is great and has some extras... After reading that I startet thinking that somewhere I saw a good drawing of that kind of thing. At first I just could not remember where.

When I remembered it I came back to post the link as I think the schematic makes it easier to understand.

[Plexi]

Bump an old thread 

I'll try with a B500E pot in series with a 500R resistor and see how it goes.
As all we know, the most usefull part is on the last 1/3 of the pot.

[mac]

With an emitter resistor, or pot, of about 1k8 - 2k you can put a 8k2 resistor at Q2 collector when Q1 is silicon.

mac

[Plexi]

Bump an old thread 

I'll try with a B500E pot in series with a 500R resistor and see how it goes.
As all we know, the most usefull part is on the last 1/3 of the pot.

Update.. finally I found an 500R pot.
Which is the correct way to get 500k fixed, and the last 500k with the pot?
500K res to ground before the pot, or the resistor from emiter, then pot to ground/cap? Is the same?

Thanks

[Cozybuilder]

For a fuzz face pot try a reverse audio- you'll get a more even (linear) response from twiddling the knob.

[Plexi]

Thanks Cozy, but I made the change a few hours ago.
500R pot, and 470k resistance to ground: really clean NICE ... believe me.
At 0, it's a good od: I think the 1k pot at around 30%.

BTW, I replaced Q2 with a beautiful BC140 that I found lying in an old radio shak..Q1 2n2222.
Replaced 10k pot I used for bias (Q2) for a b5k plus 4k7 resistor: now bias have 100% usefull range.

I'm in love again with this beauty ... Now I know what Gilmour felt when recording Time solo (¿)