John Curl's Blowtorch preamplifier

[carlosfm]

Output impedance is fixed at 1000 ohms.

 

[carlosfm]

I had a short period of fascination with batteries, however, presently I prefer well designed AC PS over the power from batteries. It simply sounds better.

I use batteries, but well bypassed and snubberized.

 

[jam]

Guys,

My last post was censored..............for your information I had joked with Mr.Curl about the name I had used for a proposed new project. I was not taking a shot at him.

Jam

 

[Cal Weldon]

We realize it was a joke but we felt the humour might be misconstrued so it was removed.

 

[Darry]

Hi,

For to build a symmetrical feeding (+ and -Vcc), I wonder if it is preferable to use 2 positive regulators as LM317 or one LM317 for the positive rail and its negative equivalent as LM337 for the negative rail. Benchmarkses of these 2 regulatiors being slightly different.

Does someone have you it makes comparisons to monitoring?

Darry

 

[Terry Demol]

The specs are not very spectacular. Perhaps .01% distortion at 2V out or so. Output impedance is fixed at 1000 ohms. Input impedance is whatever the volume control pot is.

John,

I am assuming you didn't use a follower on the OP?

If this is the case, may I ask what is the reason?

Cheers,

Terry

 

[Ultima Thule]

John,

first I want to thank you for your input regarding relays and the contact pressure thing etc., it's obvious it's really up to the finest details in your design!

As Terry I wondered myself a bit regarding the output resistance, my Q's is why did you guys chose 1000 Ohm?
My guess is that you have a quite low output impedance on the (current/voltage?)amplifying OP stage with a fixed 1000 Ohm resistor which is much more independent by frequency etc..

Cheers Michael

 

[john curl]

The CTC preamp is a transconductance amp that is current output. 1K ohm was the lowest value that we could use and still get reasonable distortion at a few volts out. There are no followers in this preamp. This was also true in the Levinson JC-2, JC-80, and some other line preamps that I have designed. I do use complementary fet followers in the Parasound JC-2.

 

[Elso Kwak]

Transconductance? I don't think so.......

 

[john curl]

john curl

Transconductance it is, i.e. voltage to current.

 

[Elso Kwak]

Ohm's law states where is voltage is current and vice versa........

 

[john curl]

Please Elso, 'Google' the term"transconductance op amp"

 

[john curl]

john curl

Transconductance it is, i.e. voltage to current.

 

[Bobken]

Save yourself the trouble, John.

The rest of us know what you mean, anyway.

Why anyone would waste time on such a daft 'challenge', I'll never know!

Regards,

 

[Tube_Dude]

Save yourself the trouble, John.

The rest of us know what you mean, anyway.

Yes...I can't understand why some people try to make audio discussions , without knowing basic concepts , as amplifiers types ...

 

[GRollins]

Broadly speaking, you might say it's a current source, as opposed to a voltage source. Both obey Ohm's law, but the implications are different.

Grey

 

[Ultima Thule]

The CTC preamp is a transconductance amp that is current output. 1K ohm was the lowest value that we could use and still get reasonable distortion at a few volts out. There are no followers in this preamp. This was also true in the Levinson JC-2, JC-80, and some other line preamps that I have designed. I do use complementary fet followers in the Parasound JC-2.

Oh I see, that was unexpected, but the 1 kOhm fixed resistor was there anyhow.

What is the advantage to use a transconductance stage instead of the common voltage amplifier as a preamp?

Cheers Michael

 

[Ultima Thule]

What's so strange with a transconductance guys, the 1 kOhm shunt resistor gives it a fixed gain but it depends also on the input impedance of the amplifier?

Cheers Michael

 

[Tube_Dude]

What's so strange with a transconductance guys, the 1 kOhm shunt resistor gives it a fixed gain but it depends also on the input impedance of the amplifier?

Yep...for the same reason , transconductance amplifiers are not disturbed by a short at the output, unlike a voltage or a transresistance amplifier..

 

[Ultima Thule]

...transresistance...

...transimpedance...

Cheers Michael