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John Curl's Blowtorch preamplifier part II
John Curl's Blowtorch preamplifier part II
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Old 30th November 2011, 06:59 AM   #18531
ThorstenL is offline ThorstenL  Germany
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John,

Quote:
Originally Posted by john curl View Post
Thorsten, could you put up the schematic for the TAA761? I am having trouble finding it. I suspect that Studer used something like this with an output stage in 1973, for there A80 MK 1 master recorder.
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
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Old 30th November 2011, 07:08 AM   #18532
john curl is offline john curl  United States
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The schematic looks pretty marginal without an output stage added. Too little current available.
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Old 30th November 2011, 08:48 AM   #18533
Joao@AltheaMusica is offline Joao@AltheaMusica  Switzerland
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Quote:
Originally Posted by zinsula View Post
That works best for me too.

Unfortunately, for development purposes, this is not an efficient way to evaluate designs and components, I'd need years with my limited spare time..
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?
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Old 30th November 2011, 09:34 AM   #18534
ThorstenL is offline ThorstenL  Germany
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John,

Quote:
Originally Posted by john curl View Post
The schematic looks pretty marginal without an output stage added. Too little current available.
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
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Old 30th November 2011, 09:49 AM   #18535
PMA is offline PMA  Europe
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John Curl's Blowtorch preamplifier part II
Nostalgia for "Ossie" times?

I strongly hope not.
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Old 30th November 2011, 10:27 AM   #18536
scott wurcer is online now scott wurcer  United States
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John Curl's Blowtorch preamplifier part II
Quote:
Originally Posted by john curl View Post
The schematic looks pretty marginal without an output stage added. Too little current available.
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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Last edited by scott wurcer; 30th November 2011 at 10:31 AM.
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Old 30th November 2011, 11:59 AM   #18537
Joachim Gerhard is offline Joachim Gerhard  Germany
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Siemens clones ?
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Old 30th November 2011, 01:02 PM   #18538
PMA is offline PMA  Europe
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John Curl's Blowtorch preamplifier part II
Quote:
Originally Posted by scott wurcer View Post
The PNP in those days was BAD,
Definitely, in the monolithic ICs technology.
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Old 30th November 2011, 01:51 PM   #18539
scott wurcer is online now scott wurcer  United States
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John Curl's Blowtorch preamplifier part II
Quote:
Originally Posted by PMA View Post
Definitely, in the monolithic ICs technology.
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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Last edited by scott wurcer; 30th November 2011 at 01:54 PM.
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Old 30th November 2011, 02:27 PM   #18540
ThorstenL is offline ThorstenL  Germany
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Hi,

Quote:
Originally Posted by PMA View Post
Nostalgia for "Ossie" times?
No Ostalgia.

The original Chip was a Thompson Semi Part anyway, not East German.

Ciao T
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