Buffer pre-amp - Page 2

Joachim Gerhard · 31st August 2010, 07:56 AM

Great ! I think this is the first time somebody does that in public. I always try to avoid common mode distortion in my designs but actually i measure and did not do listening tests other then checking the finished circuit.

AndrewT · 31st August 2010, 10:32 AM

is the cancellation resistor a resistance in the normally seen shorting link of the opamp as (non-inverting) unity gain follower?

Normally we see Output connected to -IN as a direct short.

This has come up in a couple of other threads recently.

sandyK · 31st August 2010, 11:12 AM

Quote:

Originally Posted by AndrewT

is the cancellation resistor a resistance in the normally seen shorting link of the opamp as (non-inverting) unity gain follower?

Normally we see Output connected to -IN as a direct short.

This has come up in a couple of other threads recently.

Andrew

This was done by Silicon Chip magazine in their Studio Series Preamplifier of October 2005 with an OPA2134.(P.29)

SandyK

panson_hk · 31st August 2010, 12:43 PM

Quote:

Originally Posted by AndrewT

is the cancellation resistor a resistance in the normally seen shorting link of the opamp as (non-inverting) unity gain follower?

Normally we see Output connected to -IN as a direct short.

This has come up in a couple of other threads recently.

Yes, this is a resistor between output and -IN.

panson_hk · 1st September 2010, 03:34 AM

Quote:

Originally Posted by Joachim Gerhard

Great ! I think this is the first time somebody does that in public.

Do you ware of the Samuel Groner opamp distortion report? http://www.sg-acoustics.ch/analogue_...distortion.pdf

panson_hk · 1st September 2010, 03:36 AM

One more test data for CM distortion in voltage follower. The opamp under test is AD8620. Again, 12 k cancellation resistor seems to be a good choice.

Joachim Gerhard · 1st September 2010, 10:57 AM

Yes. I know Groners work and of cause i know what Dougas Self has to say about it. Sofar i have only seen and done measurement and a listening test whould be really interesting.

panson_hk · 9th September 2010, 02:05 AM

Listening test is tough this comparison ... taking much longer time. I am still working on it.

rabbitz · 22nd September 2010, 06:07 AM

Silicon Chip mentioned in their article to use a resistor that's the same value as the wiper to ground resistance on the pot at your normal listening level. On my buffers I just tend to use 10% of the pot value.

31st August 2010, 10:32 AM	#12
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	opamp follower is the cancellation resistor a resistance in the normally seen shorting link of the opamp as (non-inverting) unity gain follower? Normally we see Output connected to -IN as a direct short. This has come up in a couple of other threads recently. __________________ regards Andrew T.

22nd September 2010, 06:07 AM	#19
rabbitz diyAudio Member Join Date: Jul 2003 Location: Newcastle, Australia	Silicon Chip mentioned in their article to use a resistor that's the same value as the wiper to ground resistance on the pot at your normal listening level. On my buffers I just tend to use 10% of the pot value. __________________ No longer DIY active

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31st August 2010, 07:56 AM	#11
Joachim Gerhard diyAudio Member Join Date: Mar 2009	Great ! I think this is the first time somebody does that in public. I always try to avoid common mode distortion in my designs but actually i measure and did not do listening tests other then checking the finished circuit.

1st September 2010, 10:57 AM	#17
Joachim Gerhard diyAudio Member Join Date: Mar 2009	Yes. I know Groners work and of cause i know what Dougas Self has to say about it. Sofar i have only seen and done measurement and a listening test whould be really interesting.

9th September 2010, 02:05 AM	#18
panson_hk :) diyAudio Member Join Date: Aug 2005 Blog Entries: 10	Listening test is tough this comparison ... taking much longer time. I am still working on it.

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