Interesting someone sent me an article by Dick Burwen today, he feels about the direct opposite. FWIW you can go a long way in audio following your rules, sometimes we cross precision instrumentation with audio. Playing an LP is not the same as weighing something to 6 digits.
Hi,
Funny story.
Back at that small east german maker of studio electronics I worked at in the 80's we used to do bypass tests with various sets of components or complete cassettes. One bypass test used four or six of our transformers in series (connected for unity gain of course) and at least in our test setup, based on Schulze Studio Monitors, we felt we were unable to tell these four or six transformers reliably.
But we could tell the insertion of a single B761/TAA761 (a german Audio Op-Amp, quite interresting, open collector output, SE Class A output, input differential folded cascode somewhat similar to what JC does, 85dB OLG with around 10KHz OLG Bandwidth, externally compensated, actually, a quite good Audio Op-Amp for the times I would say)...
Ciao T
Funny story.
Back at that small east german maker of studio electronics I worked at in the 80's we used to do bypass tests with various sets of components or complete cassettes. One bypass test used four or six of our transformers in series (connected for unity gain of course) and at least in our test setup, based on Schulze Studio Monitors, we felt we were unable to tell these four or six transformers reliably.
But we could tell the insertion of a single B761/TAA761 (a german Audio Op-Amp, quite interresting, open collector output, SE Class A output, input differential folded cascode somewhat similar to what JC does, 85dB OLG with around 10KHz OLG Bandwidth, externally compensated, actually, a quite good Audio Op-Amp for the times I would say)...
Ciao T
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Dick Burwen taught Mark Levinson about quality parts, soldering, and wire. He worked for Mark as a consultant for 1 or 2 years before I did. After I was hired, we replaced virtually every op amp module with one of my own design, at Mark's insistence.
Later, when I was long gone and Levinson was effectively sold to HK, Mark commissioned Dick Burwen to make the equalizer, and it is perhaps one of the best equalizers ever made. The only unit that I have experience with that might be better is an early Sontec (sp) unit made in the mid-70's, and designed by George Massenburg.
Later, when I was long gone and Levinson was effectively sold to HK, Mark commissioned Dick Burwen to make the equalizer, and it is perhaps one of the best equalizers ever made. The only unit that I have experience with that might be better is an early Sontec (sp) unit made in the mid-70's, and designed by George Massenburg.
B611D - operaèní zesilovaè, TTL výstup, datasheet
One can buy them on-line
http://www.denkl.cz/eshop/b-611-d-8788
One can buy them on-line
http://www.denkl.cz/eshop/b-611-d-8788
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John,
Others beat me to posting the Info, as you can see, in some ways a quite interesting IC concept for an Audio Grade Op-Amp (compared to example to NE5534).
I personally would have liked a bit of emitter degeneration or even FET Inputs.
But as it stands these where not bad. Still, I designed a whole new channel Cassette replacing discrete circuits with these and it sounded bad...
When we mixed the old discrete Mike Pre's and such with tunable gyrators using these Op-Amp as semi-parametric tone control and used these OPA's as buffers for non-critical buses (FX, Monitor etc.) we got a good compromise between functionality required and sound quality though.
Ciao T
Others beat me to posting the Info, as you can see, in some ways a quite interesting IC concept for an Audio Grade Op-Amp (compared to example to NE5534).
I personally would have liked a bit of emitter degeneration or even FET Inputs.
But as it stands these where not bad. Still, I designed a whole new channel Cassette replacing discrete circuits with these and it sounded bad...
When we mixed the old discrete Mike Pre's and such with tunable gyrators using these Op-Amp as semi-parametric tone control and used these OPA's as buffers for non-critical buses (FX, Monitor etc.) we got a good compromise between functionality required and sound quality though.
Ciao T
Zinsula
thanks for the reply. We live in the same country so what about to get in touch, if you like we can have a phone call or meet us?
John,
To add an external output, I used to add diodes and a little extra resistor in series with the main load resistor (2k) and then BD139/BD140 complementary pair on heatsinks, you can run quite a bit of current that way.
But for many applications the 6mA or so peak output current where more than enough...
Ciao T
To add an external output, I used to add diodes and a little extra resistor in series with the main load resistor (2k) and then BD139/BD140 complementary pair on heatsinks, you can run quite a bit of current that way.
But for many applications the 6mA or so peak output current where more than enough...
Ciao T
The PNP in those days was BAD, thus the use of only one. If that's a lateral pnp there is a parasitic collector not shown and the ft would only be a couple of MHz.
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I was assuming these were early IC's. The AD744 allows an external pnp to be directly paralleled. I forgot about the decompensation feature (an extension of OLBW). John only complains about the noise of early bi-FETs, but not all circuits are preamps. There were not many IC's that could do 225kHz at G = 1000.
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