Unusual phono preamp

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Yesterday I have idea to make one transistor
low noise preamp. I had intended to
use it for mid class phono in my living room.
I decided to make one transistor preamp with
paralel feedback (for damping moving magnet pick-up resonances
noiselessly). - then I decided to use current leaks in RIAA equalising
capacitor to the ground to do this work.
After six hours of work I have preamp and its sound is nice.
Preamp have some unusual topology which allows me
to use only one 9V battery for power. It is mid-class preamp
for mid-class chassis

Schemo is here:
http://radio.feld.cvut.cz/~vlk/vlkal.gif

Have somebody comments (or improvement :)) ?

Have a fun,
xvlk
 
It is unusual indeed.

The input termination is certainly unconventional. A voltage gain of -20x fed back to input 1M will give nominal 47K termination MM carts expect. I don't see how this delivers the nominal termination capacitance.

Output impedance of pre will interact with following stage, but perhaps OK for specialized app.

Looks like a little too much current consumption for good battery life.

Interesting.

JR
 
[quote author="JohnRoberts"]
The input termination is certainly unconventional. A voltage gain of -20x fed back to input 1M will give nominal 47K termination MM carts expect. I don't see how this delivers the nominal termination capacitance.
[/quote]
... Yes, like 47 KOhms at temperature 30K :) Richard Burwen
had used it for electrostatic microphone in 1977.

Nominal termination capacitance... Is mainly Miller capacitance,
but capacitive correction network in FET drain reduces its amount
to small level in my topology, without using cascode :). But for all variable reluctance pick ups - input capacitance need to be minimal and controlled by input cable.
[quote author="JohnRoberts"]
Output impedance of pre will interact with following stage, but perhaps OK for specialized app.
[/quote]

It is intention. Followers have bad distortion profile
[quote author="JohnRoberts"]
Looks like a little too much current consumption for good battery life.
Interesting.
JR[/quote]

Hmm. I play on it for a second afternoon for two 4.5V batts. For my using batteries are enough.
 
Some ballasting R's in the current source emitters would improve noise performance substantially. Also, positive voltage swing is fairly limited at the collector of the cooled termination amp section.
 
[quote author="xvlk"] Is mainly Miller capacitance,
but capacitive correction network in FET drain reduces its amount
to small level in my topology, without using cascode :) [/quote]

It is almost cascode (without 680 Ohm resistor it would be a complete folded cascode) :grin:
 
[quote author="Wavebourn"]
It is almost cascode (without 680 Ohm resistor it would be a complete folded cascode) [/quote]
For "cooled termination" it is cascode, but for output it is
(capacitor controlled) common source amp.
[quote author="Bcarso"]
Some ballasting R's in the current source emitters would improve noise performance substantially. Also, positive voltage swing is fairly limited at the collector of the cooled termination amp section.
[/quote]
Balasts in current mirrors affects transilinear principle. But O.K. for
higher Vcc.
At my sample - some 4V at the collector of termination amp is presented.
But... Termination amp gain is well defined. It is input transistor transconductance * termination amp collector resistance (for mid and high frequencies) 22mS*1k = 22. Input voltage is 10 mV - output swing 220 mV. Collector voltage reserve (positive swing) = (9 - 0.7 -0.2) - 4 = 4.1 V
Only for headroom (if is in termination amp needed).

Thanx,
Xvlk
Bcarso, by the way, is there used "Cooled termination" for description of
that amps commonly? Only french term "Amortissement du circuit de sortie par contre-réaction" have seen.
 
AFAIK the "inventors" of cooled terminations were those using it for nuclear science apps. Arbel's book has the refs, I've posted them before I believe but I will do it again when I have had some more sleep.

The violation of translinear should not be of any consequence when making current sources, no? For lower distortion stages yes, as amplifiers; or maybe some justification when power supply rejection is considered.
 
[quote author="bcarso"]AFAIK the "inventors" of cooled terminations were those using it for nuclear science apps. Arbel's book has the refs, I've posted them before I believe but I will do it again when I have had some more sleep.
[/quote]
Thanx
[quote author="bcarso"]
The violation of translinear should not be of any consequence when making current sources, no? For lower distortion stages yes, as amplifiers; or maybe some justification when power supply rejection is considered.[/quote]
O.K., there are also much more complicated and
noise better solvings of well known "folded cascode", but adding resistors into emitors makes possible voltage swing of cascode lower in
my low voltage circuit. And also circuit will not be so straightforward.
I mean, that principle of circuit must be visible for first view and
with minimal component used. We can make (and sell) more complicated circuits, but number of components added will not corresponds with
adequate performance enhancement.
It is known law of decreasing marginal costs from oeconomy applied into HiFi electronics.

xvlk


xvlk
 
The paper describing the use of “cooled terminations” is V. Radeka, Signal, noise, and resolution in position-sensitive detectors, IEEE Transactions on Nuclear Science NS18, 1, Feb. 1974, pp.51-64, and is discussed in Arbel, Analog Signal Processing and Instrumentation (1980), ISBN 0 521 22469 1. Well before that Oliver discusses it a little, without calling it such, in his Thermal and Quantum Noise paper we've talked about, but doesn't show examples.

Resistors are cheap*. IMO a little less voltage swing would be well worth the advantages in reducing noise---right now a rough calculation says the input referred voltage noise is about 12nV/sq rt Hz, about 12 times that of the FET. This assumes 30 ohm rbb bipolars; with lower values for those (like with 2SA1316 for example) this would not be so bad.



*They should be low-excess-noise resistors though.
 
> adding resistors into emitors makes possible voltage swing of cascode lower in my low voltage circuit

Yes, but a 20mV difference between junctions makes large output, while even a 200mV drop in a resistor will make nearly no difference on output swing, even at 9V.

OTOH, phono playback noise is mostly about the disk, and pickup, not the amplifier. Starved 12AX7s are pretty "noiseless" once you put the needle down.

My impression is that I can easily find records which will overload a 9V-power preamp. Try the first seconds of Wyman's "Monkey Grip". The alternative is to set phono preamp gain so low that other albums will not play at full volume with normal line-amp sensitivity. Phonodisc recorded levels, at least when a variety of pickups may be used, are much more variable than any other audio source except a microphone.

> AFAIK the "inventors" of cooled terminations were those using it for nuclear science apps

It was also used in the first BBC transistor studio amps. I don't know if this is stolen or parallel invention.

And I don't recall seeing it called that in audio literature; indeed it may not have a good English name?
 
[quote author="bcarso"]V. Radeka, Signal, noise, and resolution in position-sensitive detectors, IEEE Transactions on Nuclear Science NS18, 1, Feb. 1974, pp.51-64, and is discussed in Arbel, Analog Signal Processing and Instrumentation (1980), ISBN 0 521 22469 1. Well before that Oliver discusses it a little, without calling it such, in his Thermal and Quantum Noise paper we've talked about, but doesn't show examples.
[/quote]
I had seen mixing console schemo using it. It was 1930 or 1940 -ies.
Van der Ziel in his "Noise" book from 1950-ies had explained this also.
[quote author="bcarso"]
Resistors are cheap.
[/quote]
Maybe, but think, that there are much more low-noise current sources
without using so much resistors. And that added
resistors could not work optimally. Why not to add transistors like
diodes (C+B) or what about DC servo?
http://radio.feld.cvut.cz/~vlk/miror2.gif
I can not figure out its performance.


xvlk
 
[quote author="PRR"]
OTOH, phono playback noise is mostly about the disk, and pickup, not the amplifier. [/quote]
Yes, "cooled termination" is a way to taming pick-up noise.
[quote author="PRR"]
Starved 12AX7s are pretty "noiseless" once you put the needle down.
[/quote]
Yes, but not at 9V power. But there is some way... But not with triodes,
I had used 9V to power EF80 tube (in electrometric mode) amplifier.
It has some gain, output from first grid, and my colleague was weird.
[quote author="PRR"]
My impression is that I can easily find records which will overload a 9V-power preamp. Try the first seconds of Wyman's "Monkey Grip".
[/quote]
I do not think, that normal acoustic record can
overload my amp, I can try Soviet-Union hymn (it is 5 minutes per one
side LP high level cut )
Of course, some electroacoustical recordings can do everything (i.e
R.I.P Neumann lathe), maybe it generates 1V pp out of pick-up to overload my amp.
O.K., I must construct passive peamp for that records:)

xvlk
 
[quote author="xvlk"]...Van der Ziel in his "Noise" book from 1950-ies had explained this also.
xvlk[/quote]

You are right; it's in Noise, (1954) in the chapter called Noise in Feedback Circuits. And Van der Ziel references what may be the earliest: W. S. Percival, Wireless Engineer, Vol. 16, 237, 1939.

Radeka extended the approach to include other-than-strictly-resistive feedback and achieved additional enhancement. I tried to get him to respond to an email once to no avail, but this is often the way with academics.

EDIT: BTW the Van der Ziel book is great, but bookfinder has only one copy listed as such for a lot of dough. However, in the listings for a different book that comes up when search is used with Van der Ziel and Noise (and hardcover), Noise in Solid-State Devices and Circuits, shows some much more reasonable prices for the 1954 book and the 1956 later printing.
 
[quote author="xvlk"]
Maybe, but think, that there are much more low-noise current sources
without using so much resistors. And that added
resistors could not work optimally. Why not to add transistors like
diodes (C+B) or what about DC servo?
http://radio.feld.cvut.cz/~vlk/miror2.gif
I can not figure out its performance.


xvlk[/quote]

I'm not sure what that is but it doesn't look like a current mirror, more a compound source follower (voltage source).

JR
 
It is a current source on AF with servo, similar to what I used in mic preamps and power amps to load vacuum tube triodes. On DC it is indeed a voltage source.

http://wavebourn.com/images/audio/CS-Load-Servo-Wavebourn.gif
 
BTW just found an excellent discussion of simple (first-order translinear) current mirror noise in Fred Waldhauer's book Feedback (Wiley-Interscience, 1982, ISBN 0-471-05319-8), which corroborates my rough calculations.**

Waldhauer on adding external emitter resistance: "On the surface it seems paradoxical that we can quiet the current mirror by adding resistors that are themselves noisy..." :green:

Someone needs to extend this to Wilson mirrors now, or find the place where someone has.

I was sorely tempted by a bookseller's offering of an inscribed copy of Waldhauer in Fine condition with a NF dust jacket, but Prudence***, my conscience, and knowledge of upcoming IRS-State estimated tax due next month (Support the Troops!!!*) stayed my hand from the order button. I did wonder again though about what my inscribed copy of Bode's classic book might fetch, which I got for a song (well maybe something of a bargain-basement oratorio) on eBay some time ago.


* best left to The Brewery what was to go here

** No, this is not the ONLY thing that makes the discussion "excellent" :razz:

*** aka Fanny, who sent me here with her regards for everyone (apologies to The Band)
 

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