Pass Discrete Opamp in DIP-8 Package - Page 4

jacco vermeulen · 9th April 2008, 10:30 AM

6 nV/√Hz ?

EUVL · 10th April 2008, 01:09 PM

We have done some more simulation and testing. Basically you can get stability for almost any gain other than +1 (unity gain buffer). But then for unity gain buffer, one might just as well use a pair of BF862 without any feedback.

For gain of -1 (unity gain inverting), we found that it is best not to use the compensation cap but just a cap in parallel the feedback resistor. Bandwidth is never a problem, always way above 200kHz.

We plan to test this in a Buffer-Filter-Buffer phono preamp with single stage gain of 100. Will take a while. Need to make and trim 4 new ones.

Patrick

flg · 10th April 2008, 11:11 PM

EUVL · 20th April 2008, 06:33 AM

> We plan to test this in a Buffer-Filter-Buffer phono preamp

While waiting for potting compound ....

Patrick

EUVL · 20th April 2008, 06:35 AM

One more ....

Justcallmedad · 20th April 2008, 04:59 PM

Bravo Patrick !!! Congratulations !!! Very very nice job really !

EUVL · 20th April 2008, 05:53 PM

Thanks Richard.
Was an interesting challenge and real fun to realise the design.
Hope to report on listening test in a month or so.

Patrick

peranders · 21st April 2008, 08:39 AM

Nice work

but what the positive results be

compared to using a high performance opamp? Have you ever considered to make a current feedback "opamp"? You can make those rather simple and compact also.

bays_9a5tt · 21st April 2008, 09:41 AM

Quote:

Originally posted by EUVL
One more ....

I love the shape of top layer - reminds me of '70s hand-drawn PCBs, just inverted :-)
Nice work, BTW

AndrewT · 21st April 2008, 09:41 AM

Quote:

Originally posted by EUVL
But then for unity gain buffer, one might just as well use a pair of BF862 without any feedback.

is that a FET follower fed from a CCS that you're suggesting?
or a cascoded FET?
or what?

9th April 2008, 10:30 AM	#31
jacco vermeulen diyAudio Member Join Date: Oct 2004 Location: At the sea front, just under Rotterdam	6 nV/√Hz ? __________________ Looks like Sponge Bob has killed another thread.

20th April 2008, 04:59 PM	#36
Justcallmedad diyAudio Member Join Date: Jun 2004 Location: Paris	Waouhhh Bravo Patrick !!! Congratulations !!! Very very nice job really ! __________________ Richard Perez

21st April 2008, 08:39 AM	#38
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	Nice work but what the positive results be compared to using a high performance opamp? Have you ever considered to make a current feedback "opamp"? You can make those rather simple and compact also. __________________ /Per-Anders (my first name) or P-A as my friends call me

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10th April 2008, 01:09 PM	#32
EUVL diyAudio Member Join Date: Oct 2003	We have done some more simulation and testing. Basically you can get stability for almost any gain other than +1 (unity gain buffer). But then for unity gain buffer, one might just as well use a pair of BF862 without any feedback. For gain of -1 (unity gain inverting), we found that it is best not to use the compensation cap but just a cap in parallel the feedback resistor. Bandwidth is never a problem, always way above 200kHz. We plan to test this in a Buffer-Filter-Buffer phono preamp with single stage gain of 100. Will take a while. Need to make and trim 4 new ones. Patrick

10th April 2008, 11:11 PM	#33
flg diyAudio Member Join Date: Jul 2005 Location: North East

20th April 2008, 05:53 PM	#37
EUVL diyAudio Member Join Date: Oct 2003	Thanks Richard. Was an interesting challenge and real fun to realise the design. Hope to report on listening test in a month or so. Patrick

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