Alpha Dog Clipping

[Aentons]

Thanks, I wasn't sure about the 33pf cap. My main target for the mica swap is the 10pf low pass cap in the feedback loop which is supposed to affect the clipped waveform corners.

One of my first and still favorite pedals is a 1998 Maxon made Ibanez TS9DX that was modded (not by me) with a silver mica cap for the 51pf cap in the feedback loop. I have bought several other TubeScreamers that didn't have that particular mod and none can hold a candle to the smooth sweetness that comes out of the one with it. I have a BYOC Overdrive 2 that at first had a ceramic and then was modded to a mica and it now has a very similar smoothness as well. Btw, I believe the AM "Silver" mod is essentially the TS9DX in + mode(4 diodes), the 808 mod, and the 51pf cap changed to a silver mica.

I am hoping to achieve a similar result with the Alpha Dog

[zgrav]

I finished my Alpha Dog build and I am very happy with the range of adjustments in the clipping options.  I get noticeable volume drop dialing away from the center position on the hard clipping know, but no BBOF anywhere in the settings that I have played with.  I am using the OP07 chip in my build, so perhaps that makes a difference.

[Aentons]

Good idea. I have a couple of OP07 chips that I pulled from the aforementioned Duecetone that I didn't even think to try. I also have a metal can LM308 from Small Bear on the way. The chip I'm using now is a National Semiconductor version so maybe it is different enough to make a difference.

My burning question is still... What does that cap across the BS170 do?

[somnif]

My burning question is still... What does that cap across the BS170 do?

I imagine its rather like the cap across the LEDs in a Tube Screamer, in that it "softens" the clipping edge. To quote master R.G. Keen:

"When a diode (any kind) clips, it goes from effectively non-conducting to conducting sufficiently that the voltage across it doesn't change much any more.

Before the diode turns on, it has essentially no effect on the signal impressed across it. Once it turns on, it acts like a very low resistance.

A capacitor across a diode acts like... a capacitor. Capacitors eat current to keep their voltages from changing quickly. So with the diode not conducting, the capacitor is the only operational device. It slows the rise and fall of the signal in concert with the signal source impedance.

Once the diode starts conducting, it limits the voltage change of the signal as well, so the capacitor has less work to do, and participates less. When the signal declines below the diode conduction voltage, the capacitor sources current to keep the voltage from changing as fast.

The net effect is that the capacitor keeps the "corners" of the diode's clipping from being as sharp. This reduces the higher order harmonic production of the clipper. "