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Old 3rd October 2012, 04:27 AM   #1471
RNMarsh is offline RNMarsh  United States
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Smile Its an OPA - have a cigar !

Its a universal design for high end audio applications; Use it for what ever you need it to be; preamps, cross-overs, EQ/filters. Its a discrete OP-Amp. Just like the forum title says. A fine SW-OPA has emerged. I wanna see pcb's when i get back... I'll be all beat up and tired and shot at ('cause I'm American)... so a nice quiet time doing pcb stuffing will be in order.
-Thx RNM

Last edited by RNMarsh; 3rd October 2012 at 04:39 AM.
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Old 3rd October 2012, 04:46 AM   #1472
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Excellent idea, Scott. Please do.


/S

Quote:
Originally Posted by scott wurcer View Post
Rather than answer questions piecemeal how about I put a device by device description in the articles section, this is a holiday weekend I might have some time.
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Old 3rd October 2012, 04:52 AM   #1473
EUVL is offline EUVL  Europe
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> I wanna see pcb's when i get back...

I'm happy to do a PCB if Scott would send me his definitive schematics including device choices.
Will take quite a few days, since I do not use PCB layout software.
They cannot do what I want to do; to many restrictions.


Patrick
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Old 3rd October 2012, 05:20 AM   #1474
RNMarsh is offline RNMarsh  United States
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[thought I'd just sneek this in: Nice stuff dept -- Did everyone read EDN in July 19,2012 By Dimitri D. called jFET Follower Amp Distortion Cancellation? -RNM]
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Old 3rd October 2012, 05:42 AM   #1475
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We all know Dimitri. He frequently contributes to EDN.
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Old 3rd October 2012, 06:08 AM   #1476
qusp is offline qusp  Australia
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@kgrlee:

oh common! dont put the 'feedback'll'fix everything' amp up as a target. for starters clipping at a standard 2.1v line level input is not something I expect this amp to do.

besides, it would appear destruction/negativity and promotion of an unsustainable business model is what prompted the O2, quite the opposite of this.
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Old 3rd October 2012, 07:52 AM   #1477
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Quote:
Originally Posted by qusp View Post
for starters clipping at a standard 2.1v line level input is not something I expect this amp to do.
Err..rh? Would you like to specify when you expect this (Wurcer) amp to clip if it was configured as a headphone amp like the O2?

This would help us tie down your performance requirements for Guru Wurcer's fine design. Presently the only common thread in all the versions is zillion V/us slew.

You may like to check out why the O2 doesn't have this. We, of course, would welcome your explanation why zillion V/us is necessary.

I think Mr. Wurcer would like to ensure his design at least equals the O2 both objectively & subjectively so its a perfectly valid target for the headphone amp application.

BTW, the O2 isn't a "Feedback fixes everything" design. It's actually quite sparing in its use of this evil sauce. Only enough to meet the performance requirements and everything else must be right too.
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Old 3rd October 2012, 07:57 AM   #1478
fas42 is online now fas42  Australia
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Some pointers to an answer - it appears the JFET models I'm using may need to be better quality; I noted that the inter source resistor R5 on dadod's version was 50R rather than 250R, this made a big difference to stabilising the DC output point. But, reducing the value again triggered instability, more to be done ...

Frank

Last edited by fas42; 3rd October 2012 at 07:59 AM.
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Old 3rd October 2012, 09:14 AM   #1479
dadod is offline dadod  Croatia
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Quote:
Originally Posted by fas42 View Post
Some pointers to an answer - it appears the JFET models I'm using may need to be better quality; I noted that the inter source resistor R5 on dadod's version was 50R rather than 250R, this made a big difference to stabilising the DC output point. But, reducing the value again triggered instability, more to be done ...

Frank
It is not my version, 50R is original Wurzer value.
Why do not start with my simulation file, unzip it in separate directory and you'll have all you need, with the models also.
Only difference, I did, is the compensating cap connected to the left side of 50R resistor instead to the ground, and LED instead two diodes for the cascode. After that you can start to change components, output transistors first.
dado
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Old 3rd October 2012, 11:44 AM   #1480
fas42 is online now fas42  Australia
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Thanks for that, dadod. I've already looked at your verson, and there's no real difference between the two, apart from the LED and single diodes, not sure what you mean about the comp cap. Yet you were getting close to a null DC output, didn't make sense.

Anyway, in the end it came down to the JFETs subcircuit being very sensitive to the source resistors, if you change a single 25R to a 26R say, then your version shows the same symptoms as mine ...

Frank
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