Output Capacitor Upgrading Questions

[jrihs]

OK, I know nothing about Caps and am not getting what I need from other threads so far. Just more confused....But I am learning bunches! OK Sooo....From reading another post I get the impression that, for the output caps, 100uf/250VDC is fine, but what are you giving up, if thats the right word, with something less than a 650 VDC rating? In other words, would I pick a 100uf/350VDC over a 100uf/250VDC? or try and save a buck (well 5x2 bucks actually)?

My goal is to find something a little nicer than the Solens...without paying hundreds.

There are the obligato 100uf/400VDC which I have heard great reviews on and Mundorfs as well in this range. Has anyone tryed the Obligatos in the Crack (sounds painful). Mundorfs?

Then I saw these on a famous canadian parts purvayor...MUNDORF-72480, 100uf / 550VDC,  M-TubeCap,   50*80 9 ESR (mOhm). Funky connections but when I saw them I thought they might look really cool sticking up through the top of the plate on either side of the cooling slots. Would this cap work?

So far I have:
1) 18 gauge teflon continuous cast copper for the power path.
2) 22.5 gauge silver gold/teflon for the signal path.
3) teflon sockets
4) Silver RCA/s
5) various resistor upgrades-Mills, etc.
and,
A speedball and Goldpoint attenuator on the way.

This is probably going to sound a litte forward and edgy, is my guess...I'll find out this week after I replace the LED I shorted during my Voltage check. Obviously, the caps need to be synergistic/complimentary with these upgrades and should be the finishing touch...did someone say three more film caps in the power path? Five pin XLR plug?

PS...For me its allot about holographic imagery/soundstage/air around the instruments as well as detail and clarity. bass is fine if its accurate. Tubes available now are WE 5998 equivelants and a 50's bugle boy or seimens chrome plate (fav.) 12au7, or a bunch of others including e80cc's...what fun!

[Grainger49]

Let's see...

The value, in microfarads, is going to determine the lowest frequency the amp will produce without attenuating (rolling off) some bass notes.  The stock cap values are always good.  I have tried one half the capacitance and it didn't have a noticeable affect on the bass. 

The voltage rating allows it to work without exploding.  I can't tell you what voltage rating is OK.  Doc or PJ can.  Going over the rating wastes money and makes the cap much bigger.

Obbligato are great "Bang For The Buck" caps.  I have used them often.  I did replace the Obbligatos I was using for the output cap in my FP 2 with a Mundorf Supreme (high bucks for me but the low end of Mundorf) and it was an improvement.  The Mundorf had greater clarity, nicer high frequencies but not as intimate in the midrange.  Head spinning yet?

Let's jump back.  Here is a problem.  Each cap sounds a bit different.  One might bring the voices forward and portray them in a very lifelike manner.  One might give sheen to the high frequencies, another might have tight and extended bass response.  Each shines a light on some aspect of musical reproduction.  No one can tell you what you will like.  Sadly it would take unlimited cash to try them all for yourself.

[2wo]

As a rule, you are not gaining anything by arbitrarily using a higher voltage cap then you need. to get it to stand up to a higher voltage some compromise may need to be made. High voltage caps tend to be larger with  thicker film so they don't arc and die. the larger size leads to more inductance and other stuff your not looking for.

I don't have a Crack, other than original equipment but I have used the Obbligatos and like them...John       

[Maxwell_E]

Does more capacitance mean lower bass notes? I've always wondered how exactly those values are chosen, as it seems there'd be a point where the higher value would be bad for the sound.

[Grainger49]

Yes, but doubling the value will not mean a large audible difference.  The low frequency point is pretty low as it is.  Not that many headphones will respond down to the amp's stock roll off as it is, some yes, many, no.

The real improvement will be in the quality of the sound, after the Speedball, is when replacing the electrolytic output capacitor.

[jrihs]

GREAT input guys!! Thanks mucho.

Say, can you replace a 100uf with 2-50uf's?...not that I would...?

[Grainger49]

Yes, in parallel capacitors add.

[HF9]

If two caps of the same value are setup in series, I know it halves the capacitance, but does it double the max voltage eg.: 100uF 500V + 100uF 500V in series = 50uF 1000V? ...I think that was the case although I have never used it in application.

[Grainger49]

Yes, like in some Bottlehead power supplies, two caps of the same value in series cuts the value in half and doubles the voltage rating.  Bottlehead does it right by putting high (resistance) value resistors in parallel to equalize the voltage across the two capacitors and act as a bleeder so you can work on them faster.

[Maxwell_E]

So would a nicer 100uF cap bypassed with a smaller cap, like about 8-10uF, make any difference? Or would the bypass value be insignificant compared to the larger cap?

[Grainger49]

First, Yes!

"Conventional Wisdom" says that you shouldn't bypass an audio path cap.

I do it quite often and like the results, YMMV.  The whole idea behind audio signal cap bypassing is to impart a percentage of the higher dollar cap to a larger, not as sophisticated cap.  Such as, I have used 2.2uF 630V Obbligato (cheap black PP Film in Oil) caps for output in my Seduction.  Those were bypassed with 0.1uF 200V KK Teflon caps (Teflon broken in as is my custom).  Who could afford a 2.2uF Teflon cap?

There was a distinct improvement in the high frequencies, smoothness and extension, with the Teflon bypass.  The midrange seems a little more natural as well.  I heard no effect on the bass.

I'm not the first to think of this.  Ack! dAck! offers (offered) a "Teflon option" which is a 0.1uF 200V Teflon bypassing the stock 2.2uF 200V Auricap on the output. 

[Maxwell_E]

Hmm, interesting. Is there a magic ratio between the body value and the bypass value? I was looking at a 100uF Solen and maybe some value of a Mundorf Supreme or ESA Clarity Cap between .47-2 uF.

[Paul Joppa]

Two short notes:

1) putting caps in series requires the dividing resistors; otherwise one cap will inevitably hog the voltage until it blows out. However, that means the combination will have leakage current. You can't do this with an output cap such as the 100uF in Crack - you'll get DC current through your headphones.

2) The technical problem with bypassing caps is the possible resonance between the small cap and the parasitic inductance of the large one. If that resonance is damped by the parasitic resistance, you are OK - unfortunately those values are hardly ever specified. If the resonance is well above audible frequencies, you may also be OK - it's been argued both ways. Usually a small resistance (0.1 ohm to 1.0 ohm) in series with the larger cap, with the small cap bypassing the combination, will damp the resonance pretty thoroughly. At least in theory it will...  :^)

[Maxwell_E]

Hmmm, interesting. I may have to run some tests. I've got a couple ClarityCaps in my SEX right now, I could play around with those and come to my own conclusions.

[HF9]

1) putting caps in series requires the dividing resistors; otherwise one cap will inevitably hog the voltage until it blows out. However, that means the combination will have leakage current. You can't do this with an output cap such as the 100uF in Crack - you'll get DC current through your headphones.

Very informative post Paul. Is there a place online that describes how to calculate the dividing resistors? I assume that even with them in place, it effectively changes the circuit so it really shouldn't be used for modifying an existing circuit unless you really know what you're doing.