Bypassing input cap on IGC?

Dumbass · 12th October 2005, 07:57 PM

I use my IGC with a Bottlehead Foreplay pre-amp, which has a 2uF output cap. I recently upgraded the output caps in the Foreplay, so it seems like a good idea to bypass the IGC input caps, as they seem to be redundant.

Am I missing something here?

Also, in the IGC there is a 22K resistor to ground between the input and the cap, I assume I should get rid of that as well?

Netlist · 12th October 2005, 08:23 PM

Measure the output offset without the cap.
If all is within specs you can leave it out. Not so for the 22k.

/Hugo

Dumbass · 12th October 2005, 08:35 PM

Quote:

Originally posted by Netlist
Measure the output offset without the cap.
If all is within specs you can leave it out. Not so for the 22k.

/Hugo

Thanks for the response.

What is the purpose of the 22K? (Just to make certain, R4 in the following schematic: http://www.platenspeler.com/diy/amps...5_inverted.gif.)

Netlist · 12th October 2005, 08:55 PM

R4 determines the input impedance of the circuit.

/Hugo

Dumbass · 12th October 2005, 08:57 PM

Quote:

Originally posted by Netlist
R4 determines the input impedance of the circuit.

/Hugo

Gotcha. Thanks again.

TwoSpoons · 13th October 2005, 01:51 AM

R4 in parallel with R1 determines input impedance. R4 provides DC bypass.

digi01 · 13th October 2005, 03:19 AM

I think the input caps can be remove like nigc.I have try it with my inv3886 pcb.it works fine.
dc offset is a issue,add a 220K trim at active terminal to ground is helpful.

Zang

12th October 2005, 07:57 PM	#1
Dumbass diyAudio Member Join Date: Mar 2003 Location: British Antarctic Territory	Bypassing input cap on IGC? I use my IGC with a Bottlehead Foreplay pre-amp, which has a 2uF output cap. I recently upgraded the output caps in the Foreplay, so it seems like a good idea to bypass the IGC input caps, as they seem to be redundant. Am I missing something here? Also, in the IGC there is a 22K resistor to ground between the input and the cap, I assume I should get rid of that as well?

13th October 2005, 03:19 AM	#7
digi01 diyAudio Member Join Date: Mar 2003 Location: BEIJING	I think the input caps can be remove like nigc.I have try it with my inv3886 pcb.it works fine. dc offset is a issue,add a 220K trim at active terminal to ground is helpful. Zang __________________ 2010 DIY ALBUM UPDATED UCPv1(preamp) & DUAL(power supply)

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12th October 2005, 08:23 PM	#2
Netlist diyAudio Moderator Join Date: Jan 2003	Measure the output offset without the cap. If all is within specs you can leave it out. Not so for the 22k. /Hugo

12th October 2005, 08:55 PM	#4
Netlist diyAudio Moderator Join Date: Jan 2003	R4 determines the input impedance of the circuit. /Hugo

13th October 2005, 01:51 AM	#6
TwoSpoons diyAudio Member Join Date: Oct 2004	R4 in parallel with R1 determines input impedance. R4 provides DC bypass.

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