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Upgrading coupling caps - which ones first?

I have been experimenting with different coupling caps on the output of my amp.  I now want to try some more expensive caps (Vcap, etc), but cannot afford to replace every coupling capacitor in my system.  Therefore I want to place the best capacitors where they will make the most difference.

For each channel of my amp, I have one coupling cap between the driver and phase splitter stages, and a pair between the phase splitter and output tubes.  There are also output coupling caps on my DAC that feeds the amp which I am thinking about upgrading as well.  Which ones benefit the most from an upgrade that should be targeted first?
solman989
almarg's avatar
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almarg
9,670 posts
 
It may be helpful if you could let us know the capacitance values and the voltage ratings of the three pairs of capacitors, and also the input impedance of the amp. If the amp has lowish input impedance (although it probably doesn’t, given that it is a tube amp) it would tend to increase the criticality of the coupling cap at the output of the DAC. And I’m thinking that as a rough rule of thumb, and everything else being equal, it is probably reasonable to expect that higher values of capacitance and voltage rating will tend to correlate with less ideal behavior of a capacitor.

Regards,
-- Al

solman989 OP
44 posts
 
The caps in the amp are .1 and .47 uF at 600V, and the output caps in the DAC are 3.3uF 200V. 

it is probably reasonable to expect that higher values of capacitance and voltage rating will tend to correlate with less ideal behavior of a capacitor.

My thoughts also.  Amp input impedance is about 70k which means I could get by with a much smaller ~1 uF cap on the DAC without any frequency rolloff.
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almarg
9,670 posts
 
Sounds good re the change to 1 uF.  As you may already have calculated, in conjunction with the amp's 70K input impedance that will result in a 3 db bandwidth extending down to 2.3 Hz, and only about 6.5 degrees of phase shift at 20 Hz.

Based on that and on the values you supplied, and without knowing anything further about the design of the amp, what seems likely to be the most optimal prioritization would be doing that pair of caps first, then the 0.47 uF caps, then the 0.1 uF caps.

Good luck.  Regards,
-- Al
  
grannyring's avatar
grannyring
6,537 posts
 
The best place to start is your source as the whole system will benefit! ! Start with your dac's output caps. Please let me know what brand they are and what sound change or difference you want. I am very versed on what various caps sound like in dac's and amps being a chronic cap roller:)

Dont  try to change too much, but rather start here and give it time to settle into your system and mind. Some caps sound fuller, some warmer, some darker, some more focused on the upper mids and highs etc... 


charles1dad's avatar
charles1dad
10,250 posts
 
I support the concept of  beginning at the upstream  position  (source) and then progressively moving  down the audio signal pathway. Replacing the  output  coupling capacitors in my DAC yielded more impact than changing the  input  coupling  caps in my amplifier. Now I'll admit that changing the  single tweeter cap in my speaker's crossover was a very noticeable  upgrade without question. I used Duelund CAST in the DAC and speaker and Jupiter copper foil in my amplifier. I can recommend  either brand enthusiastically.
Charles,
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