Another Capacitor question

[pvannest]

OK

I have read quite a few of the threads regarding output caps and have a few questions.  I am trying to really understand the role of the capacitor as it relates to my EROS.  As I understand it, the stock output cap that is in the Eros is the Solen  1uF 630 Volt cap.    The two in my preamp are working just fine and I have about 50 Hours worth of break in time as of today.  I have read that you could install caps going down to .47 uF with various voltages.  I have looked at possible caps to roll and am interested in trying some of the Mundorf's discussed in other threads.  Either the Silver/Gold/Oil or the Silver/Oil.  I can find both of these at what I consider reasonable prices, but they are not an exact match for what is installed.    1 uF is not an issue but they are only rated at 450 Volts.    I assume this is not a problem but would like to know what roll the voltage really plays.    I have also found 1 uF caps that are rated at 1,000 Volts.    Would they be ok as well?  I am not an engineer by any stretch but am having a great time learning and listening.  :

 

[Grainger49]

The Eros output stage is the same as the last stage of the Seduction, now discontinued.  The Seduction used a 0.47uF DC blocking output capacitor.  So the Eros will respond to very low frequencies with a 0.47uF capacitor.

The Solen was a stock part that Bottlehead used elsewhere, a larger value and greater voltage rating, and the Solen is an upgrade over the Seduction metalized PP film cap.  That is to say the Solen sounds better and exceeds the value and voltage rating needed.

When I built my Eros I broke it in and then rolled a number of capacitors as outputs.  I had bought 2 pair of 0.22uF Kommie Kap Teflon capacitors.  The intention was to parallel them for a 0.44uF cap.  Paul Joppa had encouraged me to try one 0.22uF and I did.  My impressions were that a single cap sounded better than the parallel pair of caps.  The bass was indistinguishable between the two but the imaging was sharper with only one cap there.

As for voltage ratings, Paul Burkeland has posted that 400V or greater is suitable for the Eros.  The voltage needs to be greater than the highest voltage the capacitor will be subjected to.

I have ended up with one 0.47uF Mundorf Silver/Oil in my Eros.

More than you asked but I think it is all relevant. 

 

[pvannest]

Actually it does help but leads to another question.    Why would you have only one Cap instead of two?

"I have ended up with one 0.47uF Mundorf Silver/Oil in my Eros"

 

[Grainger49]

The point, made poorly, was that 1) the value of 0.22uF was essentially the same as 0.44uF as far as bass response is concerned and 2) that having two capacitors smeared the sound.

On that smearing the sound thing, two parallel current paths can delay the sound in one path relative to the other.  Rather than being coherent it is smeared.

If you are asking if I have one capacitor and not one for each channel.  I have one for each channel; but not two for each channel.

Maybe I ended up with one 0.22uF in the Eros.  I will have to check.

 

[pvannest]

That makes sense.  I think you could expect some, even if insignificant signal degradation due to even the slightest difference in composition or length of lead.  That is a big assumption on my part but at least is seems logical.

 

[Paul Joppa]

Grainger has given an excellent summary of the practical aspects, so I'll try to summarize just the technical ones.

When the preamp is first turned on, and before the tubes heat up and begin conducting, the is exposed to a very high voltage, as much as 350vDC. Therefor it must be rated to withstand this voltage without damage. A higher maximum voltage is never a problem (except for physical size and cost).

The low frequency response depends mostly on the capacitance and the input impedance of the next device in the chain, usually the preamp or integrated amp. The input impedance of preamps and power amps varies greatly. Eros (and Reduction, the current version of Seduction) are specified for 30,000 ohms or greater, at which value a 1uF cap is down 3dB at 5Hz, which is far below any actual musical content, or anything a real-world speaker can produce. A 0.47uF cap would be closer to 10Hz, still very low. At higher impedances the low frequency rolloff happens even lower. So why do I spec such large capacitors?

I have to thank long-time Bottlehead and occasional poster VoltSecond, who first brought this to my attention. The output interconnect is exposed to electromagnetic fields, many of which can impose hum through capacitive coupling. Thus hum is reduced when the impedance of a conductor is low, so a rational criterion is that the impedance of the output capacitor should be no greater than the output impedance of the source at 120Hz, the most common (non-magnetic) hum frequency. The output (source) impedance of Seduction/Reduction and Eros is around 4000 ohms, so doing the numbers we get 0.33uF. That's why Seduction uses a 0.47uF cap. The Seduction cap is a 250v part, so we need a different part anyhow, and the 1uF/630v part was in inventory for the then-current version of the SEX amp - that's how it got into the Eros.

Bottom line - the minimum voltage rating is 400 volts, and the minimum capacitance is 0.47uF. A higher rating ion either variable will not hurt, but it will not buy you any technical (performance or longevity) benefit. That's not to say it won't buy more subtle subjective benefits - if we truly understood those, they would be technical benefits, but they are not there yet.

 

[pvannest]

Thanks Paul

Between you and Granger, all of my questions and then some were answered....

 

[Grainger49]

 

[Atom Shop]

Thanks Paul

Between you and Granger, all of my questions and then some were answered....

I like Grainger49's take on single caps and Paul really nailed it with his Eros output cap explanation. BUT, if you wanna make your head swim (or explode! ) as to what might be an option in the cap rolling department, check these out.

http://www.humblehomemadehifi.com/Cap.html
http://www.v-cap.com/pdf-files/21capacitorshootout.pdf
http://www.enjoythemusic.com/diy/0708/capacitor1.htm - parts 1, 2 and 3
https://www.head-fi.org/t/284863/orgy-of-capacitors-the-cap-thread - very length-y
http://diy.ecpaudio.com/p/some-notes-on-coupling-capacitors.html
http://tech.juaneda.com/en/articles/electrolyticcapacitors.html - electrolytics
http://www.laventure.net/tourist/caps.htm

Even though some of this stuff may be appear dated the results make for some interesting debate, discussion, arguments, etc. My personal experience with some of the Russian goodies has been very rewarding.

 

[2wo]

Maybe make that a sticky, every time someone ask, "whats the best cap"

Here go read this ...John