John Curl's Blowtorch preamplifier part II

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#44,263
SY said:
Yes, the Hitachi ones (I think someone else took over production and I haven't tried the newer ones). The consistency of Vth is not good, but that's universal among MOSFETs, not just these particular ones.
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Renessas(sp?) now. Seem the same as Hitachis.
Then perhaps my standards aren't as high.
Or you got a bunch of someones rejects 🙁
Probably the former. I only make sure there is
no visible crossover or to much idle.
AND
Even if Vth were to vary, the negative tempco
(in my experience) pretty much adjusts for it....
(they do run warm (but nicely))
 
#44,264
john curl said:
Edde, your schematic is a 'updated' version of an SCP2-A, with a 'C' mod. Where did you get this schematic? Not from me, for sure.
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From:

1) Never born projects and many diagrams !

2) diyaudio " A real Vendetta ? " thread.

3) Tips from you ( about exchange MOSFETs to Jfets at second stage ; lower parts of cascodes ).

4) Some modifications from me during simulations.

Attached follows sch with BIAS and little "clearing".
 

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#44,266
simon7000 said:
If you have a noise level of 100 dB at 25 hertz from mechanical noises in your listening space you will still be able to hear a tone of 3000 hertz at 0 dB. It will actually be perceived as if it were the same volume!

Now you you look at each tone with a flat frequency response meter you really will see a 100 dB difference.

Now it is quite unlikely you could reproduce 100 dB at 25 hertz with a sound system. But it is not beyond current technology to record the signal.
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These are very extreme conditions Ed, and I can't think of any circumstance you'd have a sound system to cope with that. And even with these extreme conditions I don't agree with you.
Coincidentally, the October aX has an Oppo BD-105 review by Gary Galo who also addresses these issues but more realistically, and I fully agree with his conclusions.

Jan
 
#44,268
Jan, Outdoors with lightning at a distance you can get way above 100 dB at frequencies well below 25 hertz. As to 100 dB at 25 hertz, you can get that in a building with an old freight elevator where the winch drum is not quite round, near a trolley or train track where the wheels have flat spots and even on a top floor near an air conditioning compressor.

SY, An NC20 space will allow you to hear 3kHz at 0 dba!

A quiet small town house will meet that requirement.
 
#44,270
SY said:
All I need is a small, quiet townhouse...😀
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i did have one project where the plant created noise that was in the crickets' mating chirp range. As a result the cricket noise was lower than normal so the plant noise stood out. All of this was below NC35 levels outdoor. A thin wall will reduce that by 20 dB.

I also had one where a neighbor to a minor league ball park complained of the noise. He got a Radio Shack sound level meter and would point out whenever it went above 85 dB. Of course the noise was not from the ballpark. it was from trucks on the highway a bit of a distance past the ballpark.

Playing with a decent meter will surprise you as to how much noise there really is.
 
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#44,272
simon7000 said:
Jan, Outdoors with lightning at a distance you can get way above 100 dB at frequencies well below 25 hertz. As to 100 dB at 25 hertz, you can get that in a building with an old freight elevator where the winch drum is not quite round, near a trolley or train track where the wheels have flat spots and even on a top floor near an air conditioning compressor.

SY, An NC20 space will allow you to hear 3kHz at 0 dba!

A quiet small town house will meet that requirement.
Click to expand...

Yeah, I once had a woman who talked like that. Also irrelevant 🙂
 
#44,273
I make my own film caps using cat 6 or kynar insulated wrapping wire as twisted pairs when I want values less that 10pF. Getting down to 1pF is doable but 1aF ( or whatever it was ) would be quite a challenge.

I guess if anyone has made values like that someone on this thread would know about it.

come on - amaze me 🙂
 
#44,277
I think I'll just leave it as this. Yet another arrangement of JFET's that sort of looks like a traditional op-amp with the right values for all the resistors.
 

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