Boozhound Choke Tail Pair for HiFi - diyAudio
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Old 4th April 2008, 02:04 AM   #1
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Default Boozhound Choke Tail Pair for HiFi

I was musing over the problem of largish resistors (and subsequent large voltage drop) of LTP circuits and the resulting large B+ requirements and wondered whether a choke might help with that problem. In searching the internet I came across this circuit by Boozhound.

Choke Tailed Pair

My thought was to replace the tail with a choke but he makes a good case for using only the cathode bias part with no tail at all.

What do you think of this circuit in general and what about using it in a hifi amplifier input stage (or preamplifier)?

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Old 13th June 2010, 01:15 PM   #2
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I just built a Conn organ conversion using the choke and I noticed an improvement over the existing setup, which was not a LTP, however there is no way to add negative feedback from the output xfrmr to the PI.
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Old 13th June 2010, 02:06 PM   #3
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A choke works better than a resistor in the tail, because the AC impedance is high and the DCR is low. However, you can do better (IMO) with a 10M45S constant current sink (CCS). The IC occupies less space, weighs less, costs less, and provides a higher AC impedance.
Eli D.
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Old 13th June 2010, 06:12 PM   #4
Bigun is offline Bigun  Canada
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A choke acts very much like a CCS but it has the additional advantage that it allows the supply voltage to swing above B+. Of course this is only useful if your circuit will benefit from this.

The other thing I'm starting to appreciate with chokes - they are very robust.
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
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Old 14th June 2010, 02:25 AM   #5
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however there is no way to add negative feedback from the output xfrmr to the PI.
Yes, there is - add NFB to the second (grounded) grid, using a low-value resistor between grid and ground.
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