Fuzz Face Si BC108A+B : Tone Problem ?

[billou_35]

Hello,

I made a Fuzz Face clone with BC108A for Q1 (Hfe=200) & BC108B for Q2(Hfe=300). I made my own PCB with 2 layers, plated thru holes, ground planes, carbon resistors, ...

I'm very happy with the sound I get. The Fuzz & Volume controls are at Full and I use the guitar volume pot to control the Fuzz (Fender Standard US Strat).

The problem is that with Volume Guitar pot at Full, I got Full Fuzz (no problem) but I don't have so much treble. If I lower the guitar pot to 8 or so, the fuzz is less (normal again) but I got much more treble...

My question is : Why do I lose some treble when my guitar volume pot is at 10 and why do I get more at 8 ? It's not logical, is it ?

The volume pot of the guitar is behaving with the output cap of the FF like an High Pass Filter... The cut frequency is for a guitar signal at 5KHz : 1 / (2 * pi * f * R * C) with R = more or less 10 Ohms (when guitar volume pot at Full : 10) and C = 10nF so cut frequency = 318Hz.

With guitare volume pot at 8, I guess we got something like 100K(?). The only thing important here is that the cut frequency is then much more lower... And anyway, this is a High Pass Filter, not a Low Pass Filter

I got the same result with my old guitar cables or with my brand new Georges L's. My amp is a Music Man 212 Sixty Five and an Hiwatt Custom 100.

Thanks for all of you and especially RG Keen for sharing his knowledge ! 

[GibsonGM]

Fuzz Face is a very low input impedance circuit, which makes it difficult to control the tone - strange things happen at the input.  This article will help explain what I frequently have trouble conceptualizing...
In essence it has to do with lowering your pickup's output impedance, which if frequency-dependent, and therefore you experience a loss of highs.

http://www.muzique.com/lab/imp.htm

[billou_35]

Thanks a lot GibsonGM ! 

What I wonder is if you think there is a lot of drift between single coil pickups of Standard US Start ? Because then, I guess a lot of people experience this problem ? 

I knew for this lady and low impedance, that's why I had to remove my EMG DG-20 system because the result with Fuzz Face was awful and that's not a surprise because of the very low impedance at the output of the guitar...

Thanks again ! 

[billou_35]

In fact, I just don't know what to do to solve this problem... ?

I just cannot add a buffer before the FF as it will modify the impedance and so the sound and the FF is "sized" for the US Strat... so for its own impedance... ?

Is there no workaround ? It seems that my guitar volume  pot is acting as a cut frequency of a High Pass Filter ?

Thanks for your help ! 

[slacker]

The simple answer is that it's just what fuzzfaces do, there's not a lot you can do about it.
If you want more treble you could try lowering the value of the input or output caps that will roll off some low frequencies giving the impression of more treble. For example the vox tonebender has a 0.0033uF output cap and sounds a lot brighter than a fuzzface.
Personally I don't think the interaction with the guitar's volume pot is a problem I like the effect.

[billou_35]

Thank you Slacker for your very precious answer !
In fact, I never had a "real" Fuzz Face in my hands so I just don't know how a "real" one behaves 
I will try to change the output cap because I'd like just a bit more treble at Full gain...

Again, thanks to this wonderful forum ! 

[tcobretti]

Another factor here is that you used medium gain transistors.  It might help a little to lower the 100k feedback resistor to the 33k-47k range.  You'll lessen the gain of the pedal, but you'll get a little of your high end back.

[petemoore]

In fact, I never had a "real" Fuzz Face in my hands so I just don't know how a "real" one behaves  
  Me neither, but I heeded the reads I've done on them, and figure the reports aren't all conspiring against early production FF's...I'll stick with my DIY FF's.
  Early production FF's reportedly:
don't sound,
sound gated,
  oscillate,
  sound extremely harsh,
  don't perform in certain temperatures and moon phases [lol, finicky sometimes].
  and may occasionally sound magically fantastic [I read a report that 1 in 50 factory FF's tested at a music store had the 'magic'].
  Is 'real' in a ff...one that hasn't had attention to the transistor choice or biasing?
  Can't believe everything you read, but I can believe I've built enough FF's to know what they don't do when just thrown together, from what I understand this is how most FFF's were shipped/sold.

[billou_35]

Thanks for your answers !   

In fact, you're right Pete, I should replace "real" FF by "magical" one instead means good Hfe, good Biasing, good sounding !   
Thank you sharing this information, it's funny how this lady makes everyone completely mad ! 

In my case, Bias = 4.5V and Hfe = 200 (Q1) & Hfe = 300 (Q2) so makes me think about 2 questions :

1/ Do a major part of the "Magical" Vintage Fuzz Face Si have Hfe like 'Magical" Ge FF means 70-90 for Q1 and 90-120 for Q2 ? I know that everyone has his own taste but I guess, as for the "magic" numbers for Hfe & Bias, there are some reported numbers for this too ?

2/ I like RG Keen way of thinking that leads me to only believe my ears (with their imperfections) and my ears tell me today, the sound I get is Fabulous but that at full volume, I don't have enough treble so as Tcobretti mentioned (Thanks), my solution would be to increase treble to :

* Lower feedback resistor 100K
* Lower Hfe to a more "vintage" range
* Lower input & output caps
* Do nothing, the FF quest is endless... 

What would you do ? To help you, I'd say the sound I tend to have is, as many I guess, Gilmour's sound from Live at Pompei & Eric Johnson. I don't need strictly the same, I just know that my ears like this sound and I'm near today.

[Michael]

I would only change the output cap... it is now what? i think standard is 0,1 uf or something like that ( i dont know what you used).

Personally iin my own FF with BC108 i used a 0,022 uf cap (like the ones you use in guitars.... i also like a 0,047).

I would not use a lower value input cap.... you probably have a 2,2 uf now, and changing to a 1,0 or what its called, would make the unit very bright and buzzing. Not at all Eric johnson like....

By the way some say taht eric uses ""How does he get that particular sound? Did he pull out his tone control in his Dallas Arbiter Fuzz Face and replace the 100k pot with the 500k?"  " i dont know...

But i would look into the output cap, and make sure you use a 330 resistor instead of a 470 ( to increase output level).

Michael

[billou_35]

Hello Michael,

In fact, I use the Silicon NPN version :
http://fuzzcentral.ssguitar.com/fuzzface.php

I got the 330R and I use a trimpot instead of the 8K2 to have the proper bias at 4.5V.

The output cap is as specified a 10nF cap (0.01uF). In fact, everything is standard except the trimpot.

[tcobretti]

Using a smaller input cap will make the pedal less fuzzy and won't affect the EQing as much as the output cap.  It might be a good idea to try something a little different, but I wouldn't get too small.

[billou_35]

Thanks for your advice tcobretti ! 

I think I'll play with this output cap tonight.... I'm sure it's just a question of nanofarads... My actual output cap is 10nF, I may try 8nF or so...

The thing is that I use also the FF as a cleaner... It is so beautiful when you got a clean signal for arpeggio using the volume pot of the guitar and then with attack having a well distorted sound... In this configuration with guitar volume near 3 or 4, the treble amount is perfect so... maybe only the 10% tolerance of the cap is enough so maybe it's just a matter of tweeking the output cap ?! 

[petemoore]

  When I don't socket an in or ouput cap, I start 'big', then, 'smaller' it with an offboard wire or on a lug, with a series cap, sometimes bypassing the series 'smallering' cap with a SPST for a two-tone selector.

[billou_35]

Yes, this is a GREAT idea !!! Just adding a second 10nF in serial with a switch will make it tunable with 5nF and 10nF position ! 

Thank you Pete ! 

[GibsonGM]

You may have to tweak quite a bit, Billou!  There is something about a FF that makes us go back over and over to make it "better", lol.  It's about finding  a range of sound you can live with and be happy.  Remember, all those impedance issues are frequency dependent.   I believe FF sounds best with single coils like a Strat...my Les Paul is way too creamy and muddy with one!   So what sounds good on chords might not sound good during a solo, etc.    See how those cap changes affect your sound, remembering that really small caps may also make that rolloff problem bigger.   Everyone mods their fuzz faces, sometimes over and over again!  I know I don't have 1 that I consider totally finsished 

[billou_35]

Thanks GibsonGM !!! 

I think I will try one change and then, good or not, I'll stop tweaking and play the guitar ! 

[GibsonGM]

Ha ha, I bet you'll keep messing with it for a long time  I always do.  After you totally understand what FF is capable of, and its limitations, you'll probably move on to another circuit that's closer to what you want. As a learning tool, the FF is great!  Those limitations are why we all seem to have about 5 different distortion devices on our pedalboards! 
In the end, I mostly use a booster & my amp's distortion, funny enough.  But for that once in a while 60's thing, you gotta have a FF....   

[Dragonfly]

Actually...a fairly simple solution is to use a 2K pot for the fuzz. It helps prevent oversaturation, which causes bass "mushiness".


AC

[billou_35]

=> GibsonGM : In fact, in my pedalboard, I got a BK Butler Tube Driver from '86 which is so so so so good and should be so very far from the Chandler copy or wallwart version. I even got a reissue and I found the '86 better than the reissue, there is Mojo in it... I got a Tonebone Hot British for the "Marshall" sound, a FF for all 70s & a Green Big Muff to be used with the Tube Driver... Too much ? 

=> Dragonfly : Thank you for the advise, very interesting info... I'll try it but to be honest, I like when the FF is harsh too...  I think that Slacker makes me understand what is my "problem". As he said, I thought there is less treble but in fact, it was more that I got more Bass at full volume because of the cut frequency which becomes less & less and so the bass becomes more & more present...