[time-nuts] Effect of EFC noise on phase noise
bruce.griffiths at xtra.co.nz
Tue Aug 2 03:14:06 EDT 2016
Gerhard, please send me the LTspice files, so I can compare it with some of my circuits.
The Groner preamp uses feedback to adjust the dc input at the input (paralleled) FET gate(s) to adjust the dc output to zero. It uses a small value input coupling capactor with a high value resistor to bias the JFET (parallled BF862's). I had simulated a similar preamp architecture some years before the Groner article.
I suggested a similar preamp architecture on EEVBlog but the responses indicated that most of the respondents appear incapable of rational analysis and just regurgitate the conventional approach.
On Tuesday, 2 August 2016 6:19 PM, Alex Pummer <alex at pcscons.com> wrote:
Ja Gerhard, bitte schicke mir den LTSpice file,
Danke im Voraus und
On 8/1/2016 6:34 PM, Gerhard Hoffmann wrote:
> Am 02.08.2016 um 02:42 schrieb Bruce Griffiths:
>> /"I'm working on a new amplifier based on IF3602 or BF862 FETs that can
>> use 10u foil only."/
>> Similar to that published by Groner in Linear Audio?
> I know that Groner exists from some web site, but had no personal
> Also I don't read Linear Audio other than 2 articles from Scott Wurcer
> that I've bought.
> I highly regard Scott, he's the father of the AD797 after all and AD
> I also had some conversations with him on that.
> The preamp will be classical. Some JFETs in parallel, no source
> resistors except
> half an Ohm for feedback, more would add to the input noise voltage.
> Cascode with a Zetex bipolar (or whatever they are called now).
> OP37 for loop gain. feedback from OP37 output for 50 or 60 dB gain.
> Post amplifier to 80 db or so.
> Without the cascode, the 1 MHz is not possible. It does not help that
> the feedback limits the voltage excursions on the drain.
> I'm not yet sure about the effective input capacitance. I get abt. 1
> or 1.5 MHz
> bandwidth from a low impedance source. A few nF on the input capacitance
> would be ok, in the end I want it after a ring mixer for phase noise
> but I get unreasonably more in simulation, depending on if I measure
> it from
> upper frequency corner with a larger input resistor or the resonance
> with an added inductor.
> You can get the LTspice file if you like.
> regards, Gerhard
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