Tweakers' Asylum

Tube coupling caps reduced from 2.7uF to 1.5uF

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This Post Has Been Edited by the Author

I recently had my 20 year old Rogue Audio Stereo 90 in the shop for repair and decided to have some modifications done to the amp. The amp began life as a Stereo 88, was converted by Rogue to a Stereo 90 about 15 years ago and modified about 10 years ago by a local tech (Dan Santoni RIP) At that time the tube coupling caps were changed to Mundorf Supreme at the original value of 2.7uF.
The current modification included changing these coupling caps to Mundorf Supreme SilverOil caps bypassed by Dynacap .01uF and bypassing the main power supply caps with Multicap PPMFX .068uF.
I got the amp back and was pleased with what I heard. Very clean and detailed sounding, a little light on bass and a little thinner in tone, but I figured the caps need breakin. When I got the invoice, I was very surprised to see that the Mundorf caps used for replacement were 1.5uF, not the 2.7uF caps that were in there. This is the value Rogue uses for these caps.
When I asked why this had been done, I was told that lowering the capacitance would "speed up the sound" of the amp, and that 2.7uF was too much. When I asked about bass response, they said the amp was tested flat to 10Hz and that normal coupling caps were .47uF or lower and that 1.5uF was more than enough for the whole audio spectrum. And finally I was told that the 1.5uF Mundorf Supreme SilverOil were the largest caps of that type that would fit.
So I picked up the phone and called Rogue. Unfortunately Mark O'brien is in Europe , but I spoke to a gentleman who also spoke to one of the techs at Rogue. Both agreed that the change would not harm the amp. They basically said to break in the caps and see if I liked the change. Both agreed that the Mundorf Supreme SilverOil were an excellent choice to use as tube coupling caps. Neither one could offer an explanation as to why Mark had chosen such a high value for these coupling caps (there must be a reason, bigger caps cost more don't they?).
Just wondering what people think about all this.......

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