John Curl's Blowtorch preamplifier part II

[john curl]

Anyone can reduce distortion with global negative feedback with gain supplied by an IC. This is just a technical fact. In the old days, 25 years ago, I did not want to make a small power amp that could adequately drive the 25 ohm load (or so) that my design would have required. Therefore, I designed the first stage, open loop, and relied on Class A, and AC balance for low distortion. The noise was essentially the same as any design, today, especially with a minor resistor change.

[syn08]

Originally Posted by john curl

Anyone can reduce distortion with global negative feedback with gain supplied by an IC. This is just a technical fact. In the old days, 25 years ago, I did not want to make a small power amp that could adequately drive the 25 ohm load (or so) that my design would have required. Therefore, I designed the first stage, open loop, and relied on Class A, and AC balance for low distortion. The noise was essentially the same as any design, today, especially with a minor resistor change.

Well, 25 years passed; and now we have high speed high voltage JFET input opamps, able to deliver high current into 25 ohm load, for $3 a pop.

You couldn't do such for the money, 25 years ago. Isn't this amazing?

I should add that the Vendetta phono preamp is indeed an amazing phono stage, for the technology level of the early 80's, but obviously outdated today, at least in terms of distortions and dynamic range (headroom).

[Andre Visser]

Originally Posted by syn08

Well, 25 years passed; and now we have high speed high voltage JFET input opamps, able to deliver high current into 25 ohm load, for $3 a pop.

And after 25 years they still can't match a good discrete stage in sonics.

[syn08]

Originally Posted by Andre Visser

And after 25 years they still can't match a good discrete stage in sonics.

Prove it. Wait, no, you have to prove first the audibility of speaker cables.

[john curl]

No, Syn08, I would have added a 2 transistor output stage to the IC op amp, to get the peak current, 25 years ago. Oh Joy! What a break-through in solid state design.

[syn08]

Originally Posted by john curl

No, Syn08, I would have added a 2 transistor output stage to the IC op amp, to get the peak current, 25 years ago.

Performance wise, that would be a very bad idea.

[john curl]

I bet I could have done as well as you are doing today.

[syn08]

Originally Posted by john curl

I bet I could have done as well as you are doing today.

Don't think so, but at least you could do it today better than 25 years ago.

[john curl]

I don't think so. I will stick to open loop.

[syn08]

Originally Posted by john curl

I don't think so. I will stick to open loop.

Then it will be no better than 25 years ago. Moreover, given that those JFET devices are still unobtanium (according to your own measurements) it will actually be worse than 25 years ago.