Rad Shack "Dallas Arbiter Si NPN - Esoteric Questions

[Vinnyjojo]

Thanks guys/gals.  As always, lots of questions, but am having a hard time searching out these particular answers.

This is my 3rd pedal build, a Dallas Arbiter Si Fuzz [NPN, (-) ground] - all Rad Shack parts.  It uses a pair of 2N3904's.  Everything else is to spec but for the pots and a non-polarized input cap

Tonally, it's ok. 

Pros:
- The gain can really be dialed in dynamically with pick attack - very useful
- Quiet as a church mouse - no hum at all.
- My tone has this artificial, almost compressed sound to it.  Best way I can describe it is "slinky"...almost Zappa-esque.

Cons:
- Both my volume and gain "sweet spots" are well past 8/10ths of the pot rotation
- Major loss of volume when I switch to my SG bridge pickup
- It just doesn't have the harmonic resonance of other Si fuzz pedals I've thrown together (that E power chord "wah...wah...wah"). 

So while my questions are all rather "noobish", I really appreciate the feedback.  I'm figuring all this out as I go alone, and can only trust my ears - but I really need some technical context so I can learn from my results.

1. Why do all my fuzz pedals drop out in volume when I switch to my bridge pickup?  Assuming this is input cap related?
2. In lieu of A500k and B1k for volume and gain, respectively, I used an A100k and B5k.  Does this have tonal implications?
3. What's this compressed tone I'm hearing?  I noticed this especially on a different 2 transistor fuzz build when I swapped out the input cap with a tiny 472.  No fuzz at all; rather, that "slinky-pop" zappa "watermelon in easter hay" tone.  I like it enough that I'll likely build it again with the 472 input cap.
4. What causes that harmonic resonance with certain fuzz pedals?  The last build I made, a single 2N3904 transistor, 2 diode (Electra Distortion based) setup really shined in this regard.  How can I dial it in to my liking?  Better yet, can I actually "dial it in" with a pot?
5. Think I'm ready for a more advanced build with better parts.  Any recommendations?

Thanks again.

Schematic


Final Build (next to a boss for dimension)

[ayayay!]

As someone who has only built one fuzz, and it was a Silicon one, I can tell you these things:

1. Why do all my fuzz pedals drop out in volume when I switch to my bridge pickup?  Assuming this is input cap related?

Probably because neck pickups tend to be boomier, just because of their placement.  Therein, more bass is perceived, which seems like overall output is higher on the neck.  Note: mismatched pickup sets also become more of a reality when using a fuzz, IMHO.  That may be just me.   Still, more importantly, read on...

2. In lieu of A500k and B1k for volume and gain, respectively, I used an A100k and B5k.  Does this have tonal implications?

Very much so, yes.  The 100k is going to change the output impedence quite a bit.  I'd use the 500k.  But the real biggie is the 1k on for the gain pot.  Yes, you're stuck with that.  I fiddled around with other values and some parallel resistor combos too.  Stick with the 1k, and a reverse taper does wonders.  (1KC)  

I recommend you take a look at the Dunlop JH-2 (google it,) and compare these two schems.  I highly recommend you at least add the 180k (or so...) to ground from the input.  That should/could also help with your bridge pickup sound.  


One last thing:  As you noted, there isn't a whole ton of output on tap.  Both knobs will be mostly cranked.

[Vinnyjojo]

Headed down to ACK Electronics by GA Tech and stocked up on parts.  As suggested, I replaced by B5k pot with a B1k pot.  It sounds terrible though.  Tried a few - all the same result - sparatic and farty. Old pot works fine. 
Is it the pot wattage?  The new one I got is 2 watts.  Too high?

Here are the specs
http://parts.digikey.com/1/parts/737708-pot-1-0k-ohm-carbon-2w-rv4naysd102a.html

Thanks and merrry Christmas

[DavenPaget]

Headed down to ACK Electronics by GA Tech and stocked up on parts.  As suggested, I replaced by B5k pot with a B1k pot.  It sounds terrible though.  Tried a few - all the same result - sparatic and farty. Old pot works fine. 
Is it the pot wattage?  The new one I got is 2 watts.  Too high?

Here are the specs
http://parts.digikey.com/1/parts/737708-pot-1-0k-ohm-carbon-2w-rv4naysd102a.html

Thanks and merrry Christmas

Basic electronics back at school or any books that i've never read nor even began basic electronics ( Okay , i lied , nobody teaches electronics properly here )
tell you that the wattage clearly doesn't matter , it's a measurement of capacity of power handling of heat dissipation before burning up the pot .
Go back and get a 1KC pot ( Reverse 1K pot ) , it would be better and a 2W pot is huge 

[WGTP]

The 5k pot may mess up the bias and require a change to the other resistors.

Here is one with a 5k pot that may help.  Aron's Hornet.

http://www.diystompboxes.com/pedals/hornet.jpg

[Gus]

Here is a circuit that controls the first transistor gain and allows biasing adjustments.  I make the 5K an external in builds.
 
http://www.diystompboxes.com/pedals/gusFuzzFace.gif
The 5K is part of the adjustment you can use a fixed 820 ohm(like in the Vox circuit you can see in the tech of the ff writeup) or 1K or "under" the 1K gain control.  The 5k is wire 0 to 5K and adjusts the DC operating points the wiper bypass cap is the AC path  Making the 5k bias control external allows gated to compressed adjustments to the sound.  The .01uf across the 1K is a low pass filter that can be adjusted (I like 1K for more output) takes some of the "edge" away.
The 10K collector and 100 ohm emitter control the open loop gain of the first transistor.  I also like a 47K feedback/bias resistor with Si transistor FF like circuits.
I like a 100k volume control for less SERIES resistance to the following stage when the volume is turned down.  Shown with a 10uf input cap make smaller to taste(adjust C3, C4 and C1 to taste).  Uses almost any NPN Si small signal transistors I like Motorola, On Semi 2n2222s you can use 2n5088s MPSA18

Now if you study the schematics on the web you will find that some of the older FF types had 2K gain controls and one of the VOX circuits has a 820ohm under the 1K gain control.  Other circuits have different value feedback/bias resistors

[seedlings]

See that 330R and 8k2 voltage divider?  Change the 330R to a 10K trimpot wired as a variable resistor and change the 8k2 to a 1k resistor.  This does 2 things- first, gives you heaps and heaps of output, plus allows you to bias Q2 with the trim pot (this means you can bias it 'correctly' to 4.5V OR... you can bias it wrong for crazy sounds).

I just built one with 2N2222 transistors using the setup I just described plus a 10k gain pot instead of 1k.

One other idea is to replace the 330R and 8k2 with a 10k 'volume' pot, with the wiper going to output cap, then you just need a 270K resistor to ground instead of the 100k volume.  This is similar to how the Fuzz Factory is set up.

CHAD