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texwest
12-15-2009, 04:42 PM
I replaced the cathode bypass caps in my blackface princeton reverb and don't like the sound quite as much. I replaced them with the standard sprague atom 25 uf caps. I measured the capacitance on the original caps and they had all drifted up to about 35 uf. what sound difference would raising this value from 25 to 35 make? I guess, in other words, what does higher capacitance do on the bypass caps?

TweeDLX
12-15-2009, 04:50 PM
Higher values allow more low frequencies through, lower values restrict low frequencies.

Mike

texwest
12-15-2009, 06:55 PM
Would 25 to 35 make that much difference in the cathode bypass caps?

Thanks

Axekisser
12-15-2009, 08:28 PM
Would 25 to 35 make that much difference in the cathode bypass caps?

Thanks

I don't think so. The 25ufs let most everything through anyway. You're probably hearing a new/different cap material. I always tell my customers to let things break-in a bit too.

schmidlin
12-15-2009, 08:46 PM
Found this a while back, and it helps in understanding the hi-pass roll-off of cathode caps. Draw a straight line accross it intersecting the C & R values and it will show the cut off frequency. Add a chart that shows guitar string frequencies and you have yourself a good start.
http://i247.photobucket.com/albums/gg122/darthneighbor/cathodebypass.jpg?t=1260931503

zzmoore
12-15-2009, 10:10 PM
That is an awesome chart. I am going to ask an honest, sincere, question, not being a Smart Ass... Is it accurate/legitimate?
Thank You

texwest
12-15-2009, 10:59 PM
Thanks, I'm wondering if they need to be broken in, so I'm running a loop thru the amp right now. The amp sounds a little brittle and harsh with the new caps. I'm hoping a break in will resolve this. If that chart is correct there shouldn't be that much difference, especially since the frequencies seem to be lower than any note on the guitar.

schmidlin
12-16-2009, 02:16 PM
Accurate? I'm sure there are math formulas that back it up, somewhere. It's a tool, not the answer.

But more importantly, you need to understand that it is a frequency roll-off, not a hard cut. Not sure how sharp the roll-off is, or if this shows where it begins, peaks or ends. You EEs can chime in at any time. ;)

schmidlin
12-16-2009, 03:02 PM
Here you go, too:
http://www.freewebs.com/valvewizard2/OtherStuff.html

zzmoore
12-16-2009, 03:43 PM
Accurate? I'm sure there are math formulas that back it up, somewhere. It's a tool, not the answer.

But more importantly, you need to understand that it is a frequency roll-off, not a hard cut. Not sure how sharp the roll-off is, or if this shows where it begins, peaks or ends. You EEs can chime in at any time. ;)

Thanks -
Those are good observations. I assume the indicated frequency is the cut line (if the number is 100Hz then no lows pass below that). But I never considered the taper or start of the roll.
Just to reiterate, I am wondering if that chart is "generally" accurate. Apparently it is. I have printed it and will keep it for easy, visual reference.
Thank You

Patrick620
12-16-2009, 04:23 PM
This thread is becoming very helpful for me. Thank you, to all who have contributed.