is .18uF too small for input cap? - diyAudio
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Old 29th August 2003, 10:36 PM   #1
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Default 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?)
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Old 29th August 2003, 11:00 PM   #2
OliverD is offline OliverD  Germany
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Depends on what the signal sees after the input cap.

Typical values are no less than 1 µF.
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Old 30th August 2003, 07:01 AM   #3
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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?
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Old 30th August 2003, 09:19 PM   #4
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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.
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Old 1st September 2003, 11:22 AM   #5
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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?
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Old 1st September 2003, 11:41 AM   #6
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It's about taste. If 8.8 Hz is OK for you, that's fine.

My personal taste is below 15 Hz at least.
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Old 1st September 2003, 11:45 AM   #7
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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.

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Old 1st September 2003, 11:54 AM   #8
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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.
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Old 1st September 2003, 02:35 PM   #9
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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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