Upgrading capacitors

[Bertp]

Hi all,
I have been enjoying my S.E.X. 3.0 for about 2 years. I have installed the C4S. No problems at all use with both with speakers and headphones. Now I would like to change the coupling caps and the inter-stage caps. Want to make sure what values I can use. For example the 1.5 uf 630v can I use 2uf 600 volt. And .1 uf 400 volt is it ok to go a little higher or lower in voltage

Thanks
Albert

 

[Paul Joppa]

For the parafeed cap, you can use as low as 600 volts - we've never seen a problem with that voltage - though I would still prefer an 800v rating on theoretical grounds. The calculated value is 1.25uF, but anything from 0.62 t0 2.7uF is quite reasonable - the performance does not change much over that range.

For the interstage cap, a 400v rating is probably OK with a metalized-film cap, since they are self-healing to some degree. For other types I would be more cautious unless I knew a lot more about the particular cap - I'd use a 600v cap, myself. The rest of the Bottlehead team will likely agree that I am cautious ...  :^)  The value of 0.1uF gives a bass cut that is down 3dB at 6.3Hz, -1dB at 12.5Hz. If you go below 0.047uF you will likely hear the loss of deep bass, and if you go much larger (say, more than 0.22uF) the recovery from momentary overload will take longer and may become audibly objectionable.

If you are contemplating capacitance values outside those general ranges, I always suggest using decent but affordable caps until you settle on a value that works for you, before investing too much money on fancy boutique cap$. Different values won't cause damage.

 

[Paul Birkeland]

I would not recommend going lower in voltage rating on the 0.1uF/400V cap. 

 

[kgoss]

I have one rule when substituting any part in a Bottlehead kit. I always use the same or higher voltage rated part.  I am not qualified to electrically modify any Bottlehead circuit and I appreciate the fact that the designers build in headroom for the parts they include. 

If I can’t afford the same voltage rated part i will happily use the stock part because i know its a quality piece and it will actually deliver the designer’s desired sound quality.  I have no desire to run any part at the ragged edge of its specification.

I know Doc occasionally posts about blindly substituting “upgraded” parts and how you never know its an improvement to (to your ears alone) unless you listen to the stock parts first.  Modding is fun and one reason Bottlehead kits are so popular but i see too many posts asking if they can get away with a lower voltage part.

My 2 cents anyway.