[Harp-L] Squeal Killer anti-feedback pedal

[Ronnie Schreiber]

I'm not going to knock someone for being able to sell 5 resistors 
(including a 5 watt wire wound in a low current 9V circuit!), a small 
electrolytic capacitor, some connector strips, a 12AT7 preamp tube, an 
enclosure, a wall wart power supply, and some jacks for $300, but this 
is what an engineer who I hire to design circuit boards says about the 
Squeal Killer:

> The squeal killers tube could probably be replaced by a ~47pf cap. 
> Pretty astonishing he was able to patent that circuit! You’re right, 
> it’s just in there for marketing, and it’s probably working! I showed 
> it to some of the PhD’s at work and they all had a good laugh. 
> Essentially he’s using the parasitic capacitance of the tube and no 
> signal is passing _thru_ the tube.

I'm not saying it doesn't work. It probably works as well as any other 
simple notch filter or EQ will, but I think that's pretty much what it 
is, low pass and high pass filters where one of them is using a tube as 
a capacitor. If I'm wrong, please correct me. Heck, adding a pot to give 
you some control would have just added about 80 cents to the cost of the 
circuit, but then they'd have to drill another hole in the enclosure.

Disclaimer: I make the Harmonicaster, the electric harmonica that is 
feedback free in normal playing conditions, but if I find an 
anti-feedback circuit that works and is not too expensive to produce, 
I'll gladly make and sell them to harp players who are married to their 
microphones.

Ronnie Schreiber
The Electric Harmonica Co.
http://www.harmonicaster.com