Real Men Don't Use Opamps

[AndrewT]

Hi Bonsai,
I can't see any detail and many of the connections are deleted at your resolution.

 

[Bonsai]

Andrew, att is an LTC file - you should be able to open it with LTC spice

 

[AndrewT]

But I can see post181 clearly.
It's post200 that is partially deleted.

 

[KBK]

The Burson thingie looks quite ridiculous. Won't even comment on the price as it looks like it would cost ten bucks max to clone.

Has anyone actually heard it?

If it cost $10 to clone and then $10 for someone to stuff the boards and package it, then it is a very, very fair retail price.

Nothing unusual there.

 

[tiefbassuebertr]

I found the datasheet online - vertical dielectric isolated op amp in 1975??

Datasheets & application notes - Datasheet Archive Search Engine

the datasheet schematic shows a quasi-comp output stage with a lower "pnp" cfp follower - I guess the pnp must still not have equaled the npn in that process

the frightening thing for audio quality is the 500 Ohm typ output Z - woefully underbiased Class AB is known to not be the best idea with cfp

negative feedback shouldn't asked to "fix" the expected dynamic deadzone expected when trying to commutate the weakly biased quai-comp output

I would expect to see major improvement from Class A biasing the output

I wouldn't expect significant distortion improvement from just resistively loading the BW pin - but it is possible that "tuning" the loop gain and phase could cause some specific cancellation of a few distortion products

the datasheet isn't longer available, unfortunately.
Who can upload the datasheet ?

 

[tiefbassuebertr]

JCX, the HA-911 is what I found in 1970 as the answer to a good quality audio amp. Independently, Dick Burwen found it as well, and used it in all his designs, including the LMP-2 preamp, that he designed for Mark Levinson. In his case, he screened the op amps for xover distortion and used the rejects for signal processing rather than audio through-path. His selected IC's were pretty darn good, but were ultimately be replaced by discrete op amps and trans amps that I designed.
In any case, it would be first supposed that feedback can fix just about anything, and less feedback would make MORE IM rather then LESS IM.
I think that you are on the right track. It is the beta non-linearity of the output stage and its extremely high drive impedance that made a lower drive impedance (1 meg ohm) better than its nominal drive impedance, even with a reduction in open loop gain at low frequencies.
It is important to point this out, just because 'hard and fast' rules sometimes fail, and you just can't assume everything in advance.
The same thing happens with listening to differences. You just can't always predict what is audible and what is not. We are still scratching our heads about hi feedback op amps, and why they are less than perfect for audio circuits

That is correct. The most difficulty is the fact, that the individual application is very different (e. g. phono stage with high voltage gain factor, inductor replacing in sallen-key active filter stages or unity gain line buffers). In each case other types are the ideal solution - so I think.

In the moment I want to know, which OP-Amp from currently available model spectrum I should prefer for an equalizer (graphic, no parametric one) with constant Q charakter. I would like to enhance additional the sound quality of a RANE GE60 by replace the op-amps through newer versions with better performance. A discrete solution isn't possible, because the space on the PC-board isn't enough.
Schematic of this model is here:
http://www.rane.com/pdf/old/ge60sch.pdf
and from the monaural Version RE27 go to
http://www.rane.com/pdf/old/ge27sch.pdf
Currently an extremly wide range of types for audio are available at many manufacturers like Analog devices, TI (National Semiconductor), Linear Technology and many more.
Thank you very much for advices.