is .18uF too small for input cap?
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 29th August 2003, 11:36 PM #1 travis diyAudio Member   Join Date: Apr 2002 Location: orange ca is .18uF too small for input cap? i'm assuming yes. its the biggest non-polarized cap i have here. i am using this circuit for guitar, so... no matters as much. (to me?) __________________ donuts
 30th August 2003, 12:00 AM #2 OliverD   diyAudio Member     Join Date: Nov 2002 Location: Germany Depends on what the signal sees after the input cap. Typical values are no less than 1 µF.
 30th August 2003, 08:01 AM #3 peranders   Electrons are yellow and more is better! diyAudio Member     Join Date: Apr 2002 Location: Göteborg, Sweden It depends of the input impedance of the amp. f = 1/(2*pi*R*C) => 0.18uF and 100 kohms = 8.8 Hz How low bass do you want? __________________ /Per-Anders (my first name) or P-A as my friends call me Group buy: DCT03 DC trap for big toroidal transformers. Sign up for interest HERE. 27 pcb's in interest.
travis
diyAudio Member

Join Date: Apr 2002
Location: orange ca
Quote:
 Originally posted by peranders It depends of the input impedance of the amp. f = 1/(2*pi*R*C) => 0.18uF and 100 kohms = 8.8 Hz How low bass do you want?
I'm using a 10k volume pot

i put it together with no input cap. i hope i don't have to get back in there.
__________________
donuts

patriz
diyAudio Member

Join Date: Apr 2002
Quote:
 Originally posted by peranders It depends of the input impedance of the amp. f = 1/(2*pi*R*C) => 0.18uF and 100 kohms = 8.8 Hz How low bass do you want?
So in the IGC the input impedance is 18K with 1uF result in 8,8Hz, that I think is low enough why others forum members are suggesting higher value?

 1st September 2003, 12:41 PM #6 peranders   Electrons are yellow and more is better! diyAudio Member     Join Date: Apr 2002 Location: Göteborg, Sweden It's about taste. If 8.8 Hz is OK for you, that's fine. My personal taste is below 15 Hz at least. __________________ /Per-Anders (my first name) or P-A as my friends call me Group buy: DCT03 DC trap for big toroidal transformers. Sign up for interest HERE. 27 pcb's in interest.
 1st September 2003, 12:45 PM #7 AKSA   diyAudio Member   Join Date: Sep 2001 Location: Melbourne, Australia Hmmm. Lowest note on a bass guitar is around 43Hz - I think. If you are playing a bass guitar, and input impedance is 10K, then you'd want a corner frequency no more than 20Hz to avoid too much phase shift. This would be 0.82uF, say 1uF nearest preferred value. If you are using it for rhythym or lead, frequencies are much higher, and likely 0.18uF would be just adequate. Cheers, Hugh __________________ Aspen Amplifiers P/L (Australia) www.aksaonline.com
 1st September 2003, 12:54 PM #8 peranders   Electrons are yellow and more is better! diyAudio Member     Join Date: Apr 2002 Location: Göteborg, Sweden I didn't read so closely. I was referring to hifi. Guitar isn't very bass demanding and I'll guess you won't use a sub to your bass amp. 20-30 Hz is very good bass peformance to be a guitar amp. __________________ /Per-Anders (my first name) or P-A as my friends call me Group buy: DCT03 DC trap for big toroidal transformers. Sign up for interest HERE. 27 pcb's in interest.
PMA
diyAudio Member

Join Date: Apr 2002
Location: Prague
Quote:
 Originally posted by travis I'm using a 10k volume pot i put it together with no input cap. i hope i don't have to get back in there.
In case you use 10k input pot I would recommend input cap of 4.7 uF at least. The reason is phase characteristics, that is influenced up to 10x higher frequency than -3dB low frequency limit.

Pavel

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