[Harp-L] Squeal Killer anti-feedback pedal

[r_buschner@xxxxx]

This and low gain in combination.
Additional advantage: With high gain amps we all know that the volume pot is to 
“handle with care” – and is reduced to a small useable range. 
In a low gain setup the useable range increases and the pot isn’t so difficult to 
adjust between too low volume and way too much feedback.

We used these principles in the Harper Amps Alligator, 1 x 12AX7 (which can replaced
by a 12AT7 or even 12AU7) in the pre scection, 1x 12AT7 as phase inverter, 4x EL84 similar 
to VOX AC30 driving 6x 8” Jensen ceramics. 

The 12AX7 in the preamp is a concession to guitar players, I (as a harp only player) use it 
with the 12AT7 in both stages. Way more ooomph than needed. On stage, close to the amp 
it sounds pretty harmless, the full sound builds up some meters out, similar to Bassman and such.

http://harper.amplifier.ch/?project=the-alligator-30w-harp-amplifier-6-x-8%e2%80%b3



From: John Thaden 
Sent: Monday, September 11, 2023 6:26 PM
To: r_buschner at xxxxx ; harp-l at xxxxx 
Subject: Re: [Harp-L] Squeal Killer anti-feedback pedal

So is it as simple as "use big speakers"?


  On Mon, Sep 11, 2023 at 11:23 AM, r_buschner at xxxxx
  <r_buschner at xxxxx> wrote:
  The ticket to feedback or not feedback is open loop gain.
  With an amp/speaker setup, you want to move air. Much air.
  This can be done by higher gain forcing low speaker membrane
  surface area with more amplitude, or with lower gain forcing a
  big surface area with lower amplitude. The first one is more
  sensitive to feedback, because a small change at the input leads
  to a big (to big) change at the output, reacting like a warm coke.
  Keep over all gain low and there you go with high volume of moved
  air (high volume) and low sensitivity to feedback.

  Seeya,
  Ralf


  -----Ursprüngliche Nachricht----- 
  From: Ronnie Schreiber
  Sent: Monday, September 11, 2023 10:00 AM
  To: harp-l at xxxxx
  Subject: [Harp-L] Squeal Killer anti-feedback pedal

  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