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Cary SLP-05 Output Capacitor Question

Is the KimberCap .33uF and MultiCap 1.0uF combination on the SLP-05 the output capacitor between the tube and the output? I am using a Marchand XM126 crossover with a 1,000,000 ohm imput impedence. The V-Cap output capacitor calculator indicates I can use a .08uF cap with a 2hz low frequency cutoff. I have previously reduced the .33 and 1.0 combination to a single 2.2uf Mundorf S/G/O cap but hope to be able to reduce those to .1uF V-Cap CUTF caps.
Any answer or advice would be appreciated. Mike
mberrync
hifigeek1
770 posts
 
The only thing you are potentially doing is raising the frequency of the -3dB down point in the low end.
almarg's avatar
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almarg
9,670 posts
 
I was very surprised that the conventional formula upon which the V-Cap calculator is based on resulted in such a great reduction in the outlet cap's value. This small a cap means I can afford to use CUTF caps which must be the intent of the calculator. Hopefully someone who has replaced a much larger cap with a much smaller one can share their experience.
The experience of others won't be relevant unless the load impedance they were driving approaches the 1 Megohm input impedance of your active crossover, which is an exceptionally high value. As you probably realize, that figure is why the calculator indicates 0.08 uf as being acceptable. A more typical load impedance of 50K, which is 20 times less, would raise the 0.08 uf by a factor of 20, to about 1.6 uf for the same 2 Hz corner frequency.

Good luck with your project! Regards,
-- Al
mberrync OP
3 posts
 
Thank you for the responses. I did want to clarify for any XM126 owners that Phil has indicated that the input impedence for the XM126 is 500K Ohms and not 1M. This is still a very useful value if one is attempting to upgrade capacitors efficiently.
jeffreybehr's avatar
jeffreybehr
805 posts
 
M, understand that all the tubed circuits with coupling caps that I've seen have a shunt resistor following the cap, and that value is in parallel with the input impedance of the device the preamp's driving. Be careful to include that value in your calcs, and if you value high-quality low bass, don't let the filter point get above 2Hz.
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atmasphere's avatar
atmasphere
11,807 posts
 
You can assume that the shunt value Jeffreybehr mentions to be around 1Mohm, if you can't find it. This is used to prevent the output cap from having a charge on it that could damage an amplifier input.

That would make your total driving impedance to be only 500K, meaning that you will want about 0.2uf. Knowing that shunt value could be important.
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