Spectrum Analyzer Test - 6PS vs 715P Capacitors

[vibratoking]

Well my intention was to answer this question once and for all. Do capacitor types make a difference. However as I didn't measure the values exactly its still not a great test but I personally believe they do.

Please don't take this the wrong way, but your personal conclusion could be very misleading based on the fact that you don't really know or understand what you tested. I am a bit surprised that you are willing to come to a conclusion on your technical experiment while ignoring the technical details. It could be that you don't want to bother to perform the experiment correctly because it takes too much effort? If so, you are in good company because Sozo hasn't done it either. I can understand not wanting to put more time and effort into it, but I can't understand coming to a conclusion based on a failed attempt. I am afraid that this thread will lead others to believe that you conducted an experiment and came to a technical conclusion when, in fact, you did not.

[Littlewyan]

O no I'm still willing to get to the bottom of this. Sorry I'm terrible when it comes to phrasing things. At the moment all we know is I changed the capacitors and my amp sounded very different. Unfortunately I don't have a capacitance meter so can't measure the caps. Also I will say I'm not willing to take these caps out and put the old ones back in for another test as I just haven't got that much spare time. However when I change out the rest of the capacitors I will be more than happy to do another before and after test.

Is there anything you'd like me to do differently in the next test?

[VacuumVoodoo]

Do I understand correctly that you changed ALL capacitors circled in your schematic between the tests?
If so, this invalidates your conclusions as you have no way of knowing where in the circuit the most significant change occurred.
Also, with 10% capacitance tolerance i.e. it can be 10% over or 10% below nominal value, it's only to be expected the amp to sound different when all caps get replaced. Sometimes it's enough to replace just one. It will sound different even if you replace the caps with the same type and make but different batches.

[matt h]

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[Merlinb]

Knowing that an amplifier is set up as a series of, well, amplifiers... it would make sense that the first cap in the signal path is going to have the most influence.
So if you were a/b-ing one cap for another, that's where I'd do it.

The only difference between polyester and other poly' caps is the amount of distortion they produce (mostly third harmonic). The distortion is proportional to the signal voltage across the cap, so if there is any change to be heard, it will be where there is the largest signal voltage across the cap. Most coupling caps are so large that they have negligible signal voltage across them, so they will never sound different. You need a spot where the cut-off frequency lies somewhere in the guitar's register. Even then, I doubt you could detect the difference with all the valve distortion layered on top. The capacitance will have far more effect because it alters both the frequency response and the dynamic bias shifts.

[matt h]

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[Littlewyan]

[/quote]
The only difference between polyester and other poly' caps is the amount of distortion they produce (mostly third harmonic).[/quote]

Would this not coincide with the increase in odd order harmonics within the amp after putting in the Polyester Caps?

Another point I forgot to mention is that the test signal was applied to the input of the amp and was a sine wave, so all distortion was produced by the circuit.

Edit: Just noticed that one of the test results is missing, the 6.1Khz test. I think there is a limit of 5 attachments on each post so will add the missing test tonight.

[Merlinb]

So polyester, does that have more or less third order than the other polys?

Polyester produces mainly third harmonic. Other poly's and silvered-mica produce no distortion at all.

Would this not coincide with the increase in odd order harmonics within the amp after putting in the Polyester Caps?

It would, but I seriously doubt that's what you're seeing here.

[matt h]

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[vibratoking]

Polyester produces mainly third harmonic. Other poly's and silvered-mica produce no distortion at all.

I am not questioning whether this is an accurate statement. Wait, yes I am. With all due respect, how do you know this?

After I wrote the above, I did a search and found this link:
http://sound.westhost.com/articles/capacitors.htm#2.3

There is quite a lot of sound technical information in the article I linked to. I recommend reading the WHOLE thing. Very informative. I am going with this information until convinced there is better information.

[Littlewyan]

Very good read. I won't pretend to have understood all of it , but according to tests there is no difference between different types of capacitors in audio circuits. I do believe that quite often when differences are heard its actually to do with what that person 'wants' to hear and its more of a 'feel good' factor having that nice expensive cap in there. However in my case there definitely was a change in tone which I measured, its just I'm not sure what actually caused the change at this moment in time -_-. Was most likely either a bad capacitor or change in value.

Here are the missing test results, as you can see there is a big difference in the higher frequency harmonics. I have an idea that the change was caused by the new silver mica cap. The silver mica I changed out was an cheap unknown brand from Japan which I think has a tolerance of 5%, although it wasn't quoted to me when I bought it I'm going by an identical cap sound on ebay that is advertised with 5% tolerance. The new silver mica from Cornell Dubilier is definitely 5% tolerance.

The difference between 470pF and 500pF is fairly small and probably not easily noticeable (if at all), however if the 470pF Cap was actually 450pF (within tolerance) and the 500pF was actually 520pF then there would be a difference. Only a small difference, but still a difference nonetheless.

One day I will buy a capacitance meter and will measure the cheap silver micas I bought a while back to see what values they really are. I know that article just explained how cheaper capacitors aren't much different to the more expensive capacitors, but, it didn't account for cheaper capacitors having a lower level of quality control and the sliver micas I bought a while back were pretty dam cheap.

[schaublin65]

Hi,

thanks for trying this out. It's an interesting subject to say the least.

A few assertions have been made about the harmonic distortion produced by different dielectrics.

I understand that Harmonic Distortion is the easiest to measure.

Intermodulation Distortion is rarely discussed in regard to capacitors.

It always seemed to me that simply measuring THD and failing to consider IMD might not give a true picture of the "Device Under Test" and its response to a musical instrument rather than an idealised waveform.

Just thinking.....

Take care

John

[Littlewyan]

One thing which hasn't been mentioned is injecting various different frequencies all at the same time just like a guitar would. My test does do this to an extent as the harmonics are caused by the distortion of the valves and thus various different frequencies are sent through the capacitor all at the same time.

Now I must admit my theory with electronics only goes so far and inter modulation distortion is not something I've yet understood or read much about.

[Merlinb]

Polyester produces mainly third harmonic. Other poly's and silvered-mica produce no distortion at all.

I am not questioning whether this is an accurate statement. Wait, yes I am. With all due respect, how do you know this?

Its very easy to measure the distortion if you have a sensitive analyzer, and the shortcomings of polyester and other dielectrics have been well known to the audio industry for decades. See for example: http://books.google.co.uk/books?id=u249 ... &q&f=false

Be aware, however, that Self only measured 100V caps. Higher-voltage caps show proportionately less distortion, which is another reason why you're not likely to detect it in a guitar amp!

[schaublin65]

Hi,

"One thing which hasn't been mentioned is injecting various different frequencies all at the same time just like a guitar would."

That is what intermodulation distortion is all about. In english.

It's a lot more complex to determine, so it seems possible that there are people who prefer to pretend it doesn't exist.

So you're thinking about the same question as I was asking.

Take care..

John