DC offset figures

johnm · 4th February 2004, 11:21 AM

Hi everyone!!

Could someone please tell me what the max. level of DC offset from a source (in my instance a CD player) can be before the DC input cap is really necessary in the Gainclone?

Usign my multi-metre I put one probe inside the phono socket of my cd player, and the other touching the outside of the socket, with the player on, but no CD. measured about 0.54mv on both sockets. Is this acceptable, or should I use the 4.7uF input cap?

Thank you,

- John.

P.S. Nuuk i have read the section on DC offset on your site, but this is with a built Gainclone. I onyl want to build my gainclone once, so need to have the circuit/parts worked out before building. Cheers.

Richard C · 4th February 2004, 11:44 AM

Seems ok, you'll probably get an additional 10-20mV at the output of the amp which is quite acceptable IMO.

GregGC · 4th February 2004, 02:08 PM

Quote:

Originally posted by johnm
Hi everyone!!

Could someone please tell me what the max. level of DC offset from a source (in my instance a CD player) can be before the DC input cap is really necessary in the Gainclone?

Usign my multi-metre I put one probe inside the phono socket of my cd player, and the other touching the outside of the socket, with the player on, but no CD. measured about 0.54mv on both sockets. Is this acceptable, or should I use the 4.7uF input cap?

Thank you,

- John.

Did you measure it when the player was playing or when in stop mode? I think you should be fine using DC coupled GC.

Peter Daniel · 4th February 2004, 05:19 PM

Connect your source to the amp (with speakers disconnected and CD in PLAY) and then measure it on the amp. If it's less than 80mV (or so) it should be fine.

johnm · 5th February 2004, 10:35 AM

Thanks for all the advice guys! So - if I've understood this correctly - in order to measure DC offset properly the CD player MUST be connected to an amp, and must also be playing a CD then? can I not just measure the DC directly from the phono sockets on the CD player?

li_gangyi · 5th February 2004, 10:56 AM

it is possilbe because the player has some DC out...if it's low then u don't need a DC blocking cap in front...however with an amp...the voltage will rise...due to gain and of course the opamp itself itself will have a little Offset...so you have to test for offset at the outputs as well to determine if your amp is working properly...but you wun need the DC blocking capacitor (usually 4.7uF) in front as your CD player seems to have low offset...

johnm · 6th February 2004, 12:51 PM

Hmmm.... I think I'll go without the input cap then. I'll just make damn sure to test it with an old pair of speakers first

I doubt - when all's said and done - that there can be a day and night difference between using either the cap, or the input resistor instead. when I've saved up more money I'll build a second one and try it with the input cap and compare the sound. So I gues it comes down to what sounds best - a 220r 2w carbon film resistor, or a 4.7uF Black Gate non-polar cap...

sss · 6th February 2004, 01:01 PM

dont forget that the amplifier will amplify the offset of your cd player

4th February 2004, 11:21 AM	#1
johnm diyAudio Member Join Date: Sep 2003 Location: Hampshire	DC offset figures Hi everyone!! Could someone please tell me what the max. level of DC offset from a source (in my instance a CD player) can be before the DC input cap is really necessary in the Gainclone? Usign my multi-metre I put one probe inside the phono socket of my cd player, and the other touching the outside of the socket, with the player on, but no CD. measured about 0.54mv on both sockets. Is this acceptable, or should I use the 4.7uF input cap? Thank you, - John. P.S. Nuuk i have read the section on DC offset on your site, but this is with a built Gainclone. I onyl want to build my gainclone once, so need to have the circuit/parts worked out before building. Cheers.

5th February 2004, 10:56 AM	#6
li_gangyi diyAudio Member Join Date: Jun 2003 Location: Woodlands Circle	it is possilbe because the player has some DC out...if it's low then u don't need a DC blocking cap in front...however with an amp...the voltage will rise...due to gain and of course the opamp itself itself will have a little Offset...so you have to test for offset at the outputs as well to determine if your amp is working properly...but you wun need the DC blocking capacitor (usually 4.7uF) in front as your CD player seems to have low offset... __________________ Kids in the back seat cause accidents...Accidents in the back seat cause kids...

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4th February 2004, 11:44 AM	#2
Richard C diyAudio Member Join Date: Jul 2003 Location: Nottingham, England	Seems ok, you'll probably get an additional 10-20mV at the output of the amp which is quite acceptable IMO.

4th February 2004, 05:19 PM	#4
Peter Daniel diyAudio Member Join Date: Jul 2002 Location: Toronto, Canada	Connect your source to the amp (with speakers disconnected and CD in PLAY) and then measure it on the amp. If it's less than 80mV (or so) it should be fine.

5th February 2004, 10:35 AM	#5
johnm diyAudio Member Join Date: Sep 2003 Location: Hampshire	Thanks for all the advice guys! So - if I've understood this correctly - in order to measure DC offset properly the CD player MUST be connected to an amp, and must also be playing a CD then? can I not just measure the DC directly from the phono sockets on the CD player?

6th February 2004, 12:51 PM	#7
johnm diyAudio Member Join Date: Sep 2003 Location: Hampshire	Hmmm.... I think I'll go without the input cap then. I'll just make damn sure to test it with an old pair of speakers first I doubt - when all's said and done - that there can be a day and night difference between using either the cap, or the input resistor instead. when I've saved up more money I'll build a second one and try it with the input cap and compare the sound. So I gues it comes down to what sounds best - a 220r 2w carbon film resistor, or a 4.7uF Black Gate non-polar cap...

6th February 2004, 01:01 PM	#8
sss diyAudio Member Join Date: Jul 2003 Location: Israel , haifa	dont forget that the amplifier will amplify the offset of your cd player