opamp with/without buffer....???

tbla · 12th September 2003, 03:48 PM

will an opamp sound /function at its best with or without a buffer in the feedback loop...?
and how about using a constant current source - to bias the opamp - and a buffer in the loop at the same time...?

PMA · 12th September 2003, 05:46 PM

OpAmp without buffer:

YES - for OpAmps on the PCB inside signal path and not heavy loaded.

NO - for OpAmps trying to drive signal cable, any kind.

tbla · 13th September 2003, 07:46 AM

good morning......

what you are saying is that a "buf in the loop" always degrades the sound but sometimes its needed.....?

PMA · 13th September 2003, 07:55 AM

Quote:

Originally posted by tbla
good morning......

what you are saying is that a "buf in the loop" always degrades the sound but sometimes its needed.....?

Oh no

. What I am saying is that OpAmps without buffers do a good job inside the circuit on the PCB, but fail as output devices of CD players or preamplifiers. Then OpAmp with buffer inside feedback loop is a perfect solution, not degrading the sound.

Pavel

tbla · 13th September 2003, 08:41 AM

.....but what if the opa is followed by a 10k load, would there be any benifits of including a buf in the loop....? (both are on same pcb)
i would expect a quicker and cleaner sound....but perhaps there will be a degradation of sound because of the extra component....?

Pjotr · 13th September 2003, 09:49 AM

Hi,

Be careful with IC buffers. Many of them are biased slightly in class-C. These are intend to drive motors and absolutely not suitable for audio.

If you implement a buffer take care that it is biased in class-A. A simple emitter follower loaded with a current source will do the job quite well. On the other hand most audio opa’s will drive a 600 ohms load easily. To avoid stability problems driving cables it is a good habit to put a 100 – 470 ohms resistor between the output of the opa and the cable for audio purposes.

Cheers

tbla · 13th September 2003, 10:55 AM

...yes but...

has anybody tried to use a buffer in the loop in a circuit were its normal to use opa only.....?

PMA · 13th September 2003, 11:15 AM

Quote:

Originally posted by tbla
.....but what if the opa is followed by a 10k load, would there be any benifits of including a buf in the loop....? (both are on same pcb)

Then you have no reason to use buffer.

Quote:

Originally posted by Pjotr
Hi,

Be careful with IC buffers. Many of them are biased slightly in class-C. These are intend to drive motors and absolutely not suitable for audio.

If you implement a buffer take care that it is biased in class-A. On the other hand most audio opa’s will drive a 600 ohms load easily. To avoid stability problems driving cables it is a good habit to put a 100 – 470 ohms resistor between the output of the opa and the cable for audio purposes.

Cheers

Quiescent current of BUF634 can be adjusted by external resistor from some 2mA to 15mA.

100-470R resistor works, but the question is how high quality solution you are trying to reach.

Quote:

Originally posted by tbla
...yes but...

has anybody tried to use a buffer in the loop in a circuit were its normal to use opa only.....?

It makes no sense.

tbla · 13th September 2003, 03:00 PM

sure, i get the point.....but it doesn't make sense either if you have an amplifier rated 50 watts with a 300 VA trafo, and then you change it for a 500 VA trafo.....it will definately sound better...! but why....?

JOE DIRT® · 13th September 2003, 03:06 PM

Quote:

Originally posted by tbla
sure, i get the point.....but it doesn't make sense either if you have an amplifier rated 50 watts with a 300 VA trafo, and then you change it for a 500 VA trafo.....it will definately sound better...! but why....?

If you have a 4 cylinder engine and put in a 8 cylinder will your car go faster?

12th September 2003, 03:48 PM	#1
tbla diyAudio Member Join Date: Jul 2002 Location: denmark	opamp with/without buffer....??? will an opamp sound /function at its best with or without a buffer in the feedback loop...? and how about using a constant current source - to bias the opamp - and a buffer in the loop at the same time...?

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12th September 2003, 05:46 PM	#2
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	OpAmp without buffer: YES - for OpAmps on the PCB inside signal path and not heavy loaded. NO - for OpAmps trying to drive signal cable, any kind.

13th September 2003, 07:46 AM	#3
tbla diyAudio Member Join Date: Jul 2002 Location: denmark	good morning...... what you are saying is that a "buf in the loop" always degrades the sound but sometimes its needed.....?

13th September 2003, 08:41 AM	#5
tbla diyAudio Member Join Date: Jul 2002 Location: denmark	.....but what if the opa is followed by a 10k load, would there be any benifits of including a buf in the loop....? (both are on same pcb) i would expect a quicker and cleaner sound....but perhaps there will be a degradation of sound because of the extra component....?

13th September 2003, 09:49 AM	#6
Pjotr diyAudio Member Join Date: Nov 2002 Location: Netherlands	Hi, Be careful with IC buffers. Many of them are biased slightly in class-C. These are intend to drive motors and absolutely not suitable for audio. If you implement a buffer take care that it is biased in class-A. A simple emitter follower loaded with a current source will do the job quite well. On the other hand most audio opa’s will drive a 600 ohms load easily. To avoid stability problems driving cables it is a good habit to put a 100 – 470 ohms resistor between the output of the opa and the cable for audio purposes. Cheers

13th September 2003, 10:55 AM	#7
tbla diyAudio Member Join Date: Jul 2002 Location: denmark	...yes but... has anybody tried to use a buffer in the loop in a circuit were its normal to use opa only.....?

13th September 2003, 03:00 PM	#9
tbla diyAudio Member Join Date: Jul 2002 Location: denmark	sure, i get the point.....but it doesn't make sense either if you have an amplifier rated 50 watts with a 300 VA trafo, and then you change it for a 500 VA trafo.....it will definately sound better...! but why....?