|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
50.84.144.34
In Reply to: RE: I wasn't discussing what you hear posted by Tre' on February 11, 2016 at 09:21:28
"Theoretically, in the absence of R, the larger the cap value the more HF/RF."With no R in the circuit (except a fraction of an ohm at the 60 Hz source so SPICE will run, and the load resistor), increasing capacitance appears to consistently create narrower pulse widths in transformer and diode current. However, even then, HF energy does not increase at the output of the supply. FFT analysis indicates decreased HF energy with larger value capacitors. My hypothesis is that the reduced impedance from larger capacitors is much more effective at attenuating HF energy than the narrowing of the pulses is at generating it.
Also, note that the series resistance after (and in) the secondary of the transformer has to be absolutely zero for the conduction angle to consistently decrease. Even five or 10 ohms in the winding defeats the theory. We can't get even close to that in real world amplifiers.
--------------------------
Buy Chinese. Bury freedom.
Edits: 02/11/16Follow Ups:
Thank you for that analysis.
The last thing I want to understand is whether or not the RF can be broadcast through the air to the circuit even though it's being attenuating on the line by the cap.
This is something Lynn Olsen has spoken of.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Tre', an FFT plot of diode current pulses does not reveal any RF. Energy even at 20 kHz is 70 dB below the 60 Hz spike. I really think this issue has been blown way out of proportion by audiophiles looking for a way to explain what they hear. With a 20,000 uF capacitor in the circuit I posted, current pulses through the diodes are still nearly 1mS wide. In addition, their corners aren't sharp, probably due to the slope I mentioned previously. This just isn't RF territory.
--------------------------
Buy Chinese. Bury freedom.
OK, I wonder what Lynn was getting at?
Scroll down to "Power Supplies and Noise Spectra"
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
If I were to re-title that section, I would call it "Deficiencies of Poorly Designed Power Supplies." In my opinion - and I say this with considerable respect for much of Lynn's work - this particular lecture borders on fear-mongering. Nearly every caveat and doomsday scenario is based on one small area of the piece, specifically the following:
"...both spikes [wide and narrow] yield a comb spectra going out to at least 100 kHz or more, depending on the residual inductance of the first power-supply capacitor."
Just to be clear, Lynn is saying that undesired energy of consequence will extend to 100 kHz even if the first capacitor exhibits zero inductance. That is categorically untrue. I'm sure it's possible to create a supply that performs so poorly in this regard, but modern parts and general audio design principles make it highly unlikely that anyone would. FWIW, I've also analyzed many power supplies, and I've done so with Lynn's favorite instrument - spectrum analyzers. You can believe that if any of the typical analog supplies behaved in this manner, I'd be blowing the horn on this topic myself.
--------------------------
Buy Chinese. Bury freedom.
TK, Thanks for all your time on this.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: