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In Reply to: RE: bank of capacitors posted by audioeyedoc on November 12, 2007 at 20:04:17
As always, depends on your intent, but one of the main benefits of a battery supply, in my opinion and experience, is to banish all of those irritating electrolytic capacitors to the parts bin. If you can, try the battery with just a good sounding film capacitor(s) at the circuit connection point to minimize connection impedance affects. Provided the rest of the circuit is free of bad sounding capacitors, you may be surprised. "Fast" power supplies are really only needed for unstable audio circuits using lots of feedback. Look at the schematic of a good sounding tube preamp sometime. The big electrolytics of common solid state gear are replaced by the copper windings and magnetic circuit of a choke, along with a small amount of quality film caps. And the sound is much better for it.
Follow Ups:
Hi.
Battery NEEDs, repeat needs an audio signal bypass if used to power audio amps. A cap, being an AC passing component, is commonly used as audio signal bypass for any power supply, be it a conventional AC-DC, or simply a battery.
A battery is not a pure DC low ohm (down to milliohms) circuit at all as commonly mistaken.
Like a cap & in fact worse, a battery is a very complex AC network comprising serie & parallel resistance DCR, inductance L & capacitance C plus Warburg impedance (W) which does not exist in a cap.
This is not a smooth highway at all for audio signals. So a bypass by a cap is a must. The battery will take back the used DC return currents while the bypass cap is to provide a smoother bypass for the signal return instead of going thru the impedance of the battery.
The choice of type of caps depends on the audio amp power requirement.
For battery powered phonostages & linestages where the current load from teh battery is not that big. Caps with smaller capacitance will do the job. Here the battery, besides acting as an audio signal bypass, also acts as a small reservoir to store up the electrical energy required by the amps. So small film caps may do the job.
Like the SLA cell (6V5AH) I used to power the heaters of the tubes in my tube phonostage is bypassed with a AC fan cap (7uf250V) parallel with a 0.333uF PP film cap.
Also in my SS phonostage which is also 18V battery powered, I chose a
2uF PE film cap to bypass the battery for each channel (dual mono design).
In fact, I was given advice I should use much larger 'lytic caps for the bypass. I was told by some battery amp experts larger the bypass caps more fluid would be the sound. I don't argue as huge 'lytic caps are being used in those hi-end brandname amps, like the one I posted below.
Filter chokes with smaller caps used in conventional HV tube amp PS is totally another story.
c-J
I just don't think a bank of electrolytic caps sounds as good as a battery with a quality film bypass, applied at the point in the circuit where it is most effective. But we all have different experiences, and there is no right or wrong for everybody :-)
Hi.
Did I say you're wrong? As you already said, it depends on "where is most effective".
But for SLA cells & car batteries, which the orginal poster asked, film capacitors, being too small in value, can't fill the huge shoes of 'lytic caps as a large current load reservoir which a car battery needs.
FYI, I installed PE film caps to replace all the 'lytic caps in my dual-monoral SS phonostage with PE film caps for I/P & O/P coupling. But it was a real pain to squeeze them all in as I have to parallel 5x 2uF PE film caps to give the required 10uF for O/P coupling! Surely film caps sound better than 'lytic caps in signal paths.
For SLA cells & car batteries, we got to use huge size 'lytic caps as a reservoir for large current loads consumed by say, a class B SS power amp, and add film caps as audio signal bypass only.
Film caps can't take the function of a 'lytic caps in this issue.
c-J
The capacitors are there to lower the impedance. I run my whole system without electrolytics, so it can certainly be done. Just a matter of what you want. Most amplifiers don't have a huge bank of capacitors, so they obviously aren't necessary for operation. But if you like the sound better with a bank of electrolytics to further lower the bus impedance, that's completely understandable. I was just mentioning to the OP that there is more than one path, and for some of us that other path with the electrolytics designed out of the audio circuits is the more fulfilling one. The power supply is all in the signal path.
What size film would you recommend?
Mike
Also depends on what you are after, specs or sound quality. Small, tightly wound film caps sound better than bigger ones. Caps with more massive electrodes sound better, ie film and foil. I personally prefer the sound of epoxy impregnated paper caps like the WIMA MP3-X2, but there are many other designer types that sound great. Experiment. But the size and type you ultimately need for your circuit depends on its requirements, as far as stability and other source impedance issues.
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