To eliminate a coupling cap or two? Really?
After a lot of playing around and listening, I've come to the conclusion that most audiophilia nervosa about caps is because of experience with truly poor quality caps or caps used inappropriately. It is not difficult to design in RC coupling that is sonically inert as long as the listener is unaware of their existence.
I read it as: You can make a c coupled system adequately transparent but don't let them know that maybe more to squeeze, so they may be get caught in angst, find it & remove it ,and go fry their Wilsons sooner or later. So lets rephrase the best capacitor is no capacitor cult. Best capacitor is invisible capacitor.
Quince said:
You'd have to put a few more assumptions into that. For example, if the overload recovery is changed because of the cap, the amp will sound different when used in real-world rather than laboratory conditions. Of course, this will give the audiophile lots of fodder for discussion about how that capacitor utterly ruined the sound of his system and maybe if it were only a niobium foil beta-crosslinked polyethylene superluminal TachyCap, things would be much better. He might even try one, note how hideously expensive they are, and choose a smaller value (hey, f3 is still only 10Hz...), introducing yet another variable...
There's nothing complicated here, just basic engineering.
I've made many of the same measurements Rod Elliot describes. I have far more sensitive equipment, and also work in a field where subtle differences in capacitor characteristics are fairly important, though it is unrelated to audio. IMHO, Rod reaches the same conclusions I have, states the situation very clearly, and bases everything on solid well understood engineering principals.
I have the greatest respect for Walt Jung, and his Op-amp Cookbook is one of the best. Still, some of his articles in Audio Amateur left me a bit bewildered. Like many audiophiles, he can get caught up in the belief system, without making clear what principles support the beliefs. Or at least the science behind his designs wasn't included in what I read.
Some personal observations on building a variety of amplifiers and related audio equipment over the years- completely random, but maybe food for thought-
1) Audio people are not typically RF people, and RF in the audio system can be a real troublemaker. Hopefully the contribution of rectifier diodes is well known by now, but does everybody choose the right kind of diodes with the correct bypassing?
2) Any time I've built an amplifier that sounded different than another amplifier, there was something wrong with it. Often subtle, and often not visible except under certain conditions, but flawed none-the-less. After enough time on the bench, the flaws will come to light, be corrected, and the amp will sound like any other correctly functioning amp. The flaws are usually related to stability under real operating conditions- how many people bother to bench test with full lengths of speaker cable and real drivers, along with the usual standard loads?
3) Uneducated use of low dissipation film caps is asking for trouble. Combined with circuit inductance, it's easy to create ringing resonant circuits. One reason tantalum caps make nice bypass caps is that they have a medium and predictable DF, and tend not to ring. HF bypass caps belong at the circuit, not across the PS filter caps many inches away. You can't turn a "bad" capacitor into a "good" one by bypassing it with anything.
4) Most power amps use a little zobel network at the output for HF stability. If you have a sensitive enough analyzer, try different types of inductor- you'll find that anything other than an air core inductor will increase distortion. What's in your amp?
5) If you can hear it, I can measure it. I have *never* found a difference between two pieces of audio gear that didn't turn out to be some easily understood phenomena of RF, stability, or simple response due to well understood lumped circuit constants. IMO, most people give up too soon and attribute sound qualities to particular designs or pieces of equipment or components. Components have no knowledge of how much they cost or what label they carry. They simply have their own set of properties, and obey the laws of physics every time.
I have the greatest respect for Walt Jung, and his Op-amp Cookbook is one of the best. Still, some of his articles in Audio Amateur left me a bit bewildered. Like many audiophiles, he can get caught up in the belief system, without making clear what principles support the beliefs. Or at least the science behind his designs wasn't included in what I read.
Some personal observations on building a variety of amplifiers and related audio equipment over the years- completely random, but maybe food for thought-
1) Audio people are not typically RF people, and RF in the audio system can be a real troublemaker. Hopefully the contribution of rectifier diodes is well known by now, but does everybody choose the right kind of diodes with the correct bypassing?
2) Any time I've built an amplifier that sounded different than another amplifier, there was something wrong with it. Often subtle, and often not visible except under certain conditions, but flawed none-the-less. After enough time on the bench, the flaws will come to light, be corrected, and the amp will sound like any other correctly functioning amp. The flaws are usually related to stability under real operating conditions- how many people bother to bench test with full lengths of speaker cable and real drivers, along with the usual standard loads?
3) Uneducated use of low dissipation film caps is asking for trouble. Combined with circuit inductance, it's easy to create ringing resonant circuits. One reason tantalum caps make nice bypass caps is that they have a medium and predictable DF, and tend not to ring. HF bypass caps belong at the circuit, not across the PS filter caps many inches away. You can't turn a "bad" capacitor into a "good" one by bypassing it with anything.
4) Most power amps use a little zobel network at the output for HF stability. If you have a sensitive enough analyzer, try different types of inductor- you'll find that anything other than an air core inductor will increase distortion. What's in your amp?
5) If you can hear it, I can measure it. I have *never* found a difference between two pieces of audio gear that didn't turn out to be some easily understood phenomena of RF, stability, or simple response due to well understood lumped circuit constants. IMO, most people give up too soon and attribute sound qualities to particular designs or pieces of equipment or components. Components have no knowledge of how much they cost or what label they carry. They simply have their own set of properties, and obey the laws of physics every time.
By all means experiment with your capacitator selections.
I always listen carefully to my caps, but holding them up to my ears doesn't work as well as smashing a few samples with a hammer, which is how I find out which types sound the best. I find that most electrolytics sound squishy, with a few "pops" here and there, whereas ceramics sound more crisp with lots of crunch. This is also a great method for testing separation, but you gotta whack them sumbltches jist right.
One last tip: Don't pick your tumor son, or it'll never heal.
I always listen carefully to my caps, but holding them up to my ears doesn't work as well as smashing a few samples with a hammer, which is how I find out which types sound the best. I find that most electrolytics sound squishy, with a few "pops" here and there, whereas ceramics sound more crisp with lots of crunch. This is also a great method for testing separation, but you gotta whack them sumbltches jist right.
One last tip: Don't pick your tumor son, or it'll never heal.
There's no question one can build a bad amp; goodness knows I've done it myself many times
My point is that the differences are invariably due to well understood phenomena. I suspect that most people building commercial products can't put sound quality at the absolute top of the list. A few high end vendors certainly, but time is money and at some point, usually too soon, management will say "it's competitive with the rest" and put the product on the market. There was another thread about why the many very knowledgeable people here don't go into business for themselves. IMO, a person with sufficient business skills to succeed in the audio market is probably too valuable to be designing and auditioning circuits, and if you devote enough time to the latter, you certainly wouldn't have time to devote to the former. IMO, the dedicated amateur can beat the financially motivated every time.On the original cap topic, I wanted to mention something for people who like to do simulations. Most real capacitors will display a somewhat constant dissipation factor over a wide frequency range. By definition, that means that the series R (or parallel R if you use that model- I think) is *not* constant with frequency. Thus, you can't just go putting in a series R in the simulator, but have to enter it as DF or a frequency variable resistor. That wasn't clear from Rod's article, but he obviously understands it and didn't want to clutter things up.
juergenk said:
An easily forgotten point.
The power supply if it's a simple big capacitor or 2 type will act as a capacitor in series with the loudspeaker to some extent. Not entirely, as the rectifiers would feed some of the power for a steady state DC output signal.
If the power supply is active then it forms part of the amplifier signal path in the same way. Nothing's simple.
I don't have much to offer on caps, but more on that in a sec. One easy example is an amp I built that seemed excellent in every way on the test bench- distortion was low, bandwidth was wide, just great, except it was a bit muddy sounding. On closer examination, there was a minuscule amount of fuzz on the peak of waveforms. Near impossible to see, but the amp was unstable under real world conditions. If I remember right, the value of the output zobel inductor was a bit low. Fixing that removed the fuzz, and the sound cleaned right up.
As for caps, I wanted to suggest some simple passive test that anybody could perform and that would produce consistent results for anybody that tried it, but I'm not sure what it would be. If such a thing exists, somebody speak up! Meanwhile I'd suggest that capacitors are not wires, and comparing them to such is fraught with problems. It might be better to compare two caps, a reference cap, say a low dissipation polystyrene, to some other type, an electrolytic for example. Included is a first guess at a possible circuit based on a simple /2 voltage divider and X2 amplifier. It should have a pass-thru gain of one, and you can alter the caps and series resistors as desired. The idea is to put it in the music chain and change the test cap to various types, including another reference cap, then look for *differences* between the caps that result in changes in the sound, not differences due to the admittedly non-purist circuit itself.
I'm tossing this out as a starting point for discussion- hopefully more methods or some improvements to that one will result, as I find the topic interesting, but useful test results few and far between.
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Conrad Hoffman said:
I feel a bit cheated with the 'easiness' of the example. If that's the best example you can come up with, it really confirms the subjecivist claim: nothing but the most trivial audible phenomena is readily measurable.
Just kidding. I know all amps sound the same. Unless there's something wrong with them
Such phenomena to be positively explored, scientifically modeled and explained, need a MIT qualified research team doing systematic work for as long as it takes. High end audio and DIY is a small whimsical market. I guess that the private sector will never assemble such a team. Only if sonics was the mightiest weapon as in DUNE we could get such a team improving it and researching its glitches. Till then, lets use whatever material sounds better by trial on error.
You don't want easy, but the fact is most of the things that affect sound *are* easy. You wanna talk about stray RF from slow bridge rectifiers getting into the audio circuitry and creating distortion- probably not. Too easy, yet we're not to a point where 100% of amplifiers built address the problem. You think stability under real world load conditions is easy? My hat is off to you, because I can induce instability in just about any amp, given the right load and signals. BTW, not everybody has a spectrum analyzer to find such things quickly. My personal favorite is probably layout and ground strategy. It's well covered by Self, Ott, and others, but I still see amps that don't get it right. The real enemy to ever settling any of this stuff is the mind. The biases of observers, like amplifiers, are well understood, yet controlled experiments that take them into account are rejected for any number of reasons. MIT's best can study the problem forever (actually the AES has been at it for a while already), but the answers keep coming up the same, so are continuously rejected. Why do you think the serious engineering community has little interest in the topic at this point? Not all amps sound the same, but all amps with the same response, running within their limits, in blind tests run to date, sound the same.
Let me throw out an idea. It's probably fundamental to agreeing or disagreeing on anything. If two signal sources produce the same (let's say within .005%) voltage into a given (complex) load when driven by the same signal (let's choose music of some sort), they will sound identical.
Where does everybody stand on that?
Let me throw out an idea. It's probably fundamental to agreeing or disagreeing on anything. If two signal sources produce the same (let's say within .005%) voltage into a given (complex) load when driven by the same signal (let's choose music of some sort), they will sound identical.
Where does everybody stand on that?
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