John Curl's Blowtorch preamplifier part II

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#55,741
Interesting how people have such a thing about noise - provided it doesn't modulate with the signal I have zero problems with such being part of the picture. What was the "uh-oh" moment in the review was:

As the melody ascended there was also the slightest reduction of the upper-frequency glare that would sometimes slip into the picture with the JC 3.
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That's what I would be chasing, there's the remanents of the real demon, for me at least ...
 
#55,749
They emphasize the overload margin (although at 1kHz only) of this pre and I find this correct.
How is it that even today there are phono preamplifier specs that do not include max (*) input voltage (or overload margin ref some V).

George

(*)In the past, max input voltage was the voltage just before clipping, 1% to 3% THD area.
 
#55,751
If you are using opamp type +-15V rails, there are severe compromises if you go for passive, or split (ie equalization over two stages) approaches.

On the one hand you have noise, and the other overload capability.

A single feedback equalization stage on +-15 volts gets you to 42 dB OLM ref 3mV in and 150 mV out across the audio BW - so not just T 1 kHz which is what a lot of passive or split designs quote. Of course you can trade this OLM for greater gain and higher output, but either way, > 30 dB is easily achievable. Passive and split schemes sacrifice up to 18 dB OLM.

For tube based systems with their very high supply voltages, passive makes mores sense in my view.
 
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#55,756
godfrey said:
There's more info here and here about the negative inductance trick KSTR used in that thread he linked - theory, calculations etc. Don't be put off by the time machines and flux capacitors in the first link - it's just a bit of humour along the way, he gets to the point eventually.
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That's funny. If you want to publish something useful but don't want educated people reading it and stealing your ideas, you can just add a few pages of flux capacitors and time machines before the important part and they won't even read the rest of the page.

I'll have to remember that trick. It was really funny how he turned the flux capacitor into the inductance canceling thing though.

The part I like best is how he made that SMD cap - that's got to be the most expedient way of doing it I've seen, and looks so elegant.

I know of one way I might be able to make a negative inductor or negative capacitor using a few super-low-capacitance transistors, though it will require a small circuit and power.
 
#55,757
keantoken said:
That's funny. If you want to publish something useful but don't want educated people reading it and stealing your ideas, you can just add a few pages of flux capacitors and time machines before the important part and they won't even read the rest of the page.
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Indeed! I first saw that first link posted in a thread on the short lived DIY Audio Engineering forum. None of the "serious" engineers there took it seriously. Typical comments were along the lines of "That's obviously rubbish, everyone knows there's no such thing as negative inductance. The bit about flux capacitors is a dead giveaway it's a hoax".

I read it all the way through and learned something. They didn't. Funny how life works.
😀
 
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