Tweakers' Asylum

Re: 0.001 caps

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djk

(M)

In Reply to: Re: 0.001 caps posted by chris_w on April 17, 2005 at 12:56:18:

do you even know what that circuit does?

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Re: Re do i know - chris_w 16:50:11 04/18/05 (1)
I do have a good appreciation of what the circuit does.
however i assumed that the .001 caps would still be in the signal path when the drive limit transistors were off as the diodes were biased on asuming the voltages stated were at quesent levels, this would give a 3db/octave roll off -Was I wrong in this repect ?
Arn't polystyrine caps inductive at high frequencies ?
- Re: Re do i know - djk 23:39:46 04/18/05 (0)
  "Was I wrong in this repect ?"
  The caps feed the speaker output through a 1K resistor, if they went to ground they would represent a load (but they don't).
  The slew rate is determined largely by the current in the differential pair being able to charge and discharge the 15pF cap around TR05.
RE "do you even know ..." - dickmc 18:22:19 04/17/05 (2)
"do you even know what that circuit does?"
Not in detail beyond TR01 other than driving the bases of output power transistors TR701 and TR705 in what I presume is some kind of following and error detection circuit. That's why I asked the question hoping for enlightenment (which Chris was quite helpful in capacitor type selection).
If someone knows "how" the middle works from TR03 through TR13, I would be most interested.
- Re: RE "do you even know ..." - djk 23:07:42 04/17/05 (1)
  Chris doesn't even know what that circuit does, how can he recommend changing it?
  TR15, 17 are the foldback current limiter. Protects output stage from short circuits.
  TR1, 03 are the differential pair and provide voltage gain, TR05 is the second voltage amplifier (also called the VAS) and provides most of the voltage gain for the amplifier.
  TR07 is a current source, allows the voltage to swing negative.
  TR09 bias transistor.
  TR11, 13 are the driver transistors.
  TR701, 705 are the outputs.
  The drivers and outputs provide the current gain to drive the speakers.
  The schematic has an error. R17 does not hook to ground, it hooks to the junction of R37 and ZD01.
  - Loud applause.....Great post.... - Russ57 08:45:37 04/18/05 (0)
    and the type we need more of around here. Far too many people are offering advice without understanding. Are into the tubes too by any chance?
    
    Russ

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