[Bjornboy81]

Quote:

Originally Posted by Pars /img/forum/go_quote.gif Slew rate or pulse slope (dV/dT) is a spec applied to film caps that I don't see in electrolytic datasheets. Normally specified in V/uS.

Are these good specs for an input cap?

Polypropylene Film Capacitor
ESR (mOhms) = 5
ESL (nH)= 26
dV/dt (V/uS) = 856
Ipeak (A) = 402
Irms (A) = 10.6

 

[nikongod]

Quote:

Originally Posted by NelsonVandal /img/forum/go_quote.gif Have any of you actually done a blind test with power caps? Or have you tried add/remove them live? I have, and I couldn't for my life tell the difference in an amp with active ground channel.

who is talking about an amp with active ground channel? who is even specifying thus far what type of amp they are using it in. the questions at hand are regarding the theoretical benefits of various aspects of a cap. for all YOU or any of us know, the application could VERY well be a simple triode based amp with PSU rejection numbers you have long scoffed off in favor of a "superior" overcomplicated op-amp based amp...

perhaps some advice on what the benefits of various aspects of a cap are as opposed to the statement that they make no difference in ONE amp would be beneficial to the forums.
Quote:

Originally Posted by Bjornboy81 /img/forum/go_quote.gif Are these good specs for an input cap? blaah blaah

the key is how it sounds. ignore the numbers when you are in the signal path.

it is not dificult for a skilled designer to make a cap that operates like a dream under narrow frequency band test conditions... good luck getting one that is uniform across the audible range.

 

[JeffL]

Quote:

Originally Posted by nikongod /img/forum/go_quote.gif the key is how it sounds. ignore the numbers when you are in the signal path.

Bad idea!

The numbers are there for a reason. You can't just ignore objective measurements when designing something. If you do, I guarantee you will subjectively agree with me anyway. But disagree as you will, ignorance is bliss.

 

[nikongod]

Quote:

Originally Posted by JeffL /img/forum/go_quote.gif Bad idea! The numbers are there for a reason. You can't just ignore objective measurements when designing something. If you do, I guarantee you will subjectively agree with me anyway. But disagree as you will, ignorance is bliss.

to an extent i agree with what you are saying, to an extent i disagree.

i was incorrect in leaving my statement above so open ended. stipulations of "basic quality thresholds" should have been made, i do agree.

however i dont totally agree on the idea of blindly (deafly?) following the specs. it is far too easy for a designer to build a cap (or any component) that measures absolutely perfectly in a narrow frequency band if she chooses to ignore everything else. the market is LITTERED with caps that are REALLY excelent for applications with digital noise and switching power supplies, but sadly lacking in ones that are exceptionally linear across the WHOLE audio band.

 

[Bjornboy81]

I understand that it all comes down to how it sounds...that's the point after all. However, I was asking if the specs looked in line for a decent inline cap. From what I can tell (and I'm a noob at this) it has all the traits of a decent audio cap, but before I go start hacking circuits I want to know if it's even worth it or if I should get something better to start with.

thanks for the input though...I'm learning quite a bit about this stuff everyday.

 

[AudioCats]

when I said faster, I was talking about the ESR rating.

Yes I have done power reservoir cap test before, two channel headphone amp no active ground, when using CDE low esp caps (two 680uf/40v, so 1360uF per channel), the bass is much better than 12000uF generic LUX per channel. It was not a blind test, but the CDE's cost me $0.15 each while the LUX cost me $2 each, so there was no reason for me to wish the LUX to lose. The sonic difference was un-deniable.

 

[aych]

how do you tell esr rating? is it written on the caps? i noticed u said uF and Volts, but didn't mention any number regarding esr.

 

[Pars]

Look up the datasheet for the particular cap series...

 

[ericj]

What's funny is that boutique audio capacitors seem to say less and less in the datasheet as the price goes up.

 

[kipman725]

Quote:

Originally Posted by nikongod /img/forum/go_quote.gif scoffed off in favor of a "superior" overcomplicated op-amp based amp...

opamps have diffirential inputs and the 50/60Hz mains hum is common mode and so is greatly attenuated! designing amps to use this type of input is a very good idea it just uses more semiconductors or valves so costs more.

 

[Pars]

Quote:

Originally Posted by ericj /img/forum/go_quote.gif What's funny is that boutique audio capacitors seem to say less and less in the datasheet as the price goes up.

If you can even find a datasheet.. anyone have one for Elna Cerafines (particularly the discontinued 350V and 500V ones)? Blackgates? I haven't seen one...

 

[00940]

for the cerafines, here is all I could get... not much :
http://www.elna.co.jp/en/capacitor/a...og/pdf/roa.pdf

 

[AudioCats]

Quote:

Originally Posted by aych /img/forum/go_quote.gif how do you tell esr rating? is it written on the caps? i noticed u said uF and Volts, but didn't mention any number regarding esr.

you will have to go to the manufacturer's web site and get the info from them. Extra low ESR aluminum electrolytics usually have about the same ESR as the tantalum caps, (30% of a equal size generic aluminum electrolytic). so if you can't find extra low esr aluminum in the size you need, just use tantalum.


But tantalum caps are not cheap at all.....

 

[ericj]

but the electrolytic, unlike the tantalum, is incapable of exploding and shorting out your power supply.

 

[nikongod]

Quote:

Originally Posted by ericj /img/forum/go_quote.gif but the electrolytic, unlike the tantalum, is incapable of exploding and shorting out your power supply.

they blow up plenty good still, and do all manner of fun things when they do.

the reason you see very few tantalum caps in audio circuits is their absolute lack of linearity and typpically worthless performance in the audio band. they make great caps for decoupling HF noise from fast opamps and for stuff with digital noise, but building an amp EXCLUSIVELY with tantalum caps is a only one notch better than putting a functional rudder&propeller on a bicycle.