Re: Interesting Electrolytics



Gilbert Bates wrote:



I have asked Andre about this also. I seem to recall him (or maybe it was
someone else) saying that too much C "slows" an amp down. Perhaps
this could be the subject of a new thread.

Lotsa C speeds up an amp if anything because the PS acts more like a perfect
voltage source
as the amount of C goes up.

If only slow and fast could be defined!

Ppl talk about fast bass. But bass is slow, compared to treble, and treble that
sounds slow is what? Its usually the result of a poorly designed amp stage or
one that has not been serviced
for 40 years, so the triode is on its last legs, and acts like a crummy
compressor.....



To some degree I believe it's refering to the self resonance of
capacitors.

There isn't much resonance in caps within the AF band.

In modern electronics it's common to see
bypassing/decoupling accomplished using capacitors of different types
and typically orders of magnitude different in value. The impedance of
a capacitor acts as a notch filter over frequency. The impedance comes
down due to the capacitance and then at the self resonant point, the
impedance goes back up due to the capacitors self inductance.

I am aware of elcaps having inabilties to bypass radio F.
So add plastic caps to do the shunting for RF.

Different types and different values is an attempt to gain
over-lapping impedance curves to reduce the insertion loss over a
broader bandwidth approaching the ideal voltage source, if you will.
Large value capacitors will usually have larger self inductance and a
low frequency impedance curve. More large capacitors will still suffer
a poor high frequency response as compared to a spread in values such
as 100uF, 1uF, 0.1uF etc. This is very true when you are trying to
decouple high frequncy ringing in typical switching circuits.

Not my experience in audio amps.

The biggest caps i've used were Sprague 100,000 uF for each rail in a 300 watt
ab mosfet based amp. No LF "slowness" or any other problems at LF.
But when testing with a good square wave I found I had to add 1,000 uF elcaps,
0.47 plastic and 0.01 uF at the drains to ensure bypassing of the applied drain
supply up to RF. Square waves would not excite much signal in the rails.
Earth pathing and cap location is critical for RF since any long lead is
inductive, so the smaller caps are placed to bypass the rail close to devices
to shunt the long leads to the larger caps that cannot be located close to the
devices.

The issue of slow/fast sounding is pure conjecture; the solid state amp I have built

along with all the tube ones have never been described as slow, or fast, or awkward,

conjested, embarrassed, sick, or with any negative terminology.

I don't agree that using 8uF in tube preceded with a large choke off the input C
will sound better than 470uF
with a small choke, which is what i use.




So this is kind of how I view or define fast or slow.

I am still looking for text book definitions of fast or slow....

Patrick, along
with your remarks on a poorly designed amp too. Kind of like slew rate
or driving a large grid capacitance without sufficient drive current,
it's too slow to keep up with demand.

Yeah sure, i know all about having adequate driver currents to charge/discharge
stray or miller C.
I now do find that having more than enough current to deal with C is the better
sound path.


The power supply impedance will

rise as frequency rises and it's ability to deliver energy to the
circuit has suffered on the high frequency end.

I routinely bypass elcaps with plastics.
But when i measure amp rails thogh at 20kHz, the placement of 2uF close to the tube
rarely makes the
slightest difference Its just habit I guess, and to stop some imagined
RFinterference...



Do I think I could point this out in a listening session? Probably
not, but that's my 2 cents worth...

Here the ideas cannot be tested; we just get reports from all and sundry about the
sound
without any proof to back it up.

Patrick Turner.


.

Relevant Pages

  • Re: Interesting Electrolytics
    ... Lotsa C speeds up an amp if anything because the PS acts more like a perfect ... To some degree I believe it's refering to the self resonance of ... bypassing/decoupling accomplished using capacitors of different types ... The impedance comes ...
    (rec.audio.tubes)
  • Re: Newby needs stereo amp repair help
    ... >> output transistors have been replaced. ... There are 2 pairs of capacitors ... >> help appreciated as this is a nice amp when working. ... my first suspicion would still be caps. ...
    (sci.electronics.repair)
  • Re: Capacitors
    ... Also, I have a list of all the capacitors needed, ... The low voltage electrolytics in a valve amp would typically ... a severe hum in one channel, and a slight hum in the other. ... dealer I bought it off did say replacing the caps would improve it. ...
    (uk.tech.broadcast)
  • Re: TOT: Capacitors
    ... question about capacitors. ... I've read some marvelous threads on this NG about vintage telly ... Because I was told that with an amp of this vintage, ... all the caps will need replacing. ...
    (uk.tech.broadcast)
  • Re: Capacitors
    ... I need to replace all the caps in a 40 ... Also, I have a list of all the capacitors needed, ... Marky P. ... The low voltage electrolytics in a valve amp would typically ...
    (uk.tech.broadcast)