John Curl's Blowtorch preamplifier part II - Page 3798 - diyAudio
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Old 12th April 2013, 02:30 PM   #37971
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Quote:
Originally Posted by jan.didden View Post
One gripe I have in general will 'passive preamps' is that they have a largish Zout which opens up de power amp to all kinds of source-impedance-related non-linearities. It's a typical case of isolated thinking, instead of looking at a systems perspective.
OTOH, it's a handy way to demonstrate audible differences between pre- and power amps so in that sense it may actually have an important function in the marketplace.

jan
I thought it was to sell multi-$1000 interconnects.
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Old 12th April 2013, 02:35 PM   #37972
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I was thinking matched pairs of those.
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Old 12th April 2013, 02:50 PM   #37973
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Well,

One of the educational projects around here was to build mic preamps. I let the guys come up with the schematics and I added a few. Built so far is a Langevin from the Cinemag website using their transformers and an inshop built 220 mH inductor and to be fair one from the Jensen website that uses their input transformer and no output transformer, along with a similar design using a Lundahl input transformer and a 5534 as a two stage amplifier. Also constructed a copy of an API from a bad web schematic using a Lundahl 1:2 input transformer and a Triad on the output and then a class A FET design from the web in two versions. One was made with a pot for the gain control and a Triad output transformer, the other used a stepped attenuator and no output transformer, both used a Lundahl input transformer at 1/5.

The listening panel picked the FET version with input and output transformers as the favorite.

Attached is the schematic of the amplifies section.
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Old 12th April 2013, 03:04 PM   #37974
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Well,
If the listening panel is still available, it would be educational too to have the chosen circuit supplied from different PSUs.

George
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Old 12th April 2013, 03:33 PM   #37975
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Originally Posted by gpapag View Post
If the listening panel is still available, it would be educational too to have the chosen circuit supplied from different PSUs.

George
Yes, that was done with lead acid batteries. On my list is to build a proper power supply. The RCA and Langevin designs assume a poor power supply in their design.
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Old 12th April 2013, 03:51 PM   #37976
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Quote:
Originally Posted by jan.didden View Post
One gripe I have in general will 'passive preamps' is that they have a largish Zout which opens up de power amp to all kinds of source-impedance-related non-linearities. It's a typical case of isolated thinking, instead of looking at a systems perspective.
That's how I saw it back in the late 80's when the passives became so popular. So I took the idea of no gain and added an output buffer. It was the basis for Corey Greenberg's Aunt Corey's Homemade Buffered Passive Preamp (Corey never mentioned that in his article, but if you've ever read it, I'm Elvis).

se
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Old 12th April 2013, 04:06 PM   #37977
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Originally Posted by simon7000 View Post
Yes, that was done with lead acid batteries. On my list is to build a proper power supply. The RCA and Langevin designs assume a poor power supply in their design.
What were the rail voltages?
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Old 12th April 2013, 04:17 PM   #37978
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What were the rail voltages?
12.8v
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Old 12th April 2013, 04:38 PM   #37979
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Quote:
Originally Posted by gpapag View Post
SY and Jan
Thinking with the cold side of our brain, we all agree on all these.

But there are two issues .
Tell me one diyer here who settles with an integrated amp he built for more than a few @#!!% months, no matter how much satisfied he is with his creation.

You can not beat overload/recovery characteristics of a passive.

George
George, there is a universum of solutions between a 'passive preamp' and an integrated amp, I'm sure you are aware

jan
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Old 12th April 2013, 04:42 PM   #37980
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Originally Posted by PMA View Post
Yes Jan, but 10k stepped attenuator would have <= 2.5k output impedance if driven from low impedance sound source. This is the worst case, and at standard volume it would have something like 50 - 200 ohm. Compare to CTC Blowtorch with its constant 1kohm output impedance, or with tube preamplifiers.

Passive stepped 10k attenuator (like Danish DACT, for example) is the component that affects resulting sound in the smallest possible way. All the active preamps have much more of its own "sound", and the Blowtorch will be no exception.
Interestingly, many here insist on the very, very best, unless someone disagrees with their solution and then 'reasonable' is good enough.
Wish you would make up your minds..

jan
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