Sound Smith Strain Gauge Phono Preamp - diyAudio
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Old 2nd December 2011, 02:53 PM   #1
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Default Sound Smith Strain Gauge Phono Preamp

Features and Technical Data:

Frequency response, DC to 70 Khz

No "RIAA" filter circuitry is required or used in our preamp - just one ULTRA clean gain stage (this is because the Stgrain Gauge is a "displacement" device, not a "velocity" sensitive device like magnetic cartridges).

Compatible with standard "4 wire" tone arm wiring


This is what is mentioned on their website, and they say that their preamp is just "one ULTRA clean gain stage" which I think is just a load of BS, cause you have to correct for the equalization recorded into the grooves of the record.

The cheapest system is $5000+. But the replaceable styli are not expensive, starting at $150.00.

I'm wondering, does anyone know what is in the phono preamp box. With the correct kind of test LP, one could design and build a phono preamp for the strain gauge stylus.

So, I'm thinking about it. But, also wondering if this system is really better, and if I would be just wasting my time.
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Old 3rd December 2011, 01:28 AM   #2
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Sorry to burst your BS bubble hopes, but the strain gauge principal (constant velocity or constant amplitude, I forget which) pretty much follows the RIAA playback curve so all that is needed is a power supply to power the gauge followed by a linear amplifier. I have heard the cartridge many times and it is truly remarkable. A friend built up his own "front end amplification" for it also.
Stereophile has reviewed it a few times in the past year.

Peter Liebermann is to be congratulated.

Charles

Last edited by stellavox; 3rd December 2011 at 01:32 AM.
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Old 3rd December 2011, 03:04 AM   #3
SY is offline SY  United States
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Quote:
Originally Posted by stellavox View Post
Sorry to burst your BS bubble hopes, but the strain gauge principal (constant velocity or constant amplitude, I forget which) pretty much follows the RIAA playback curve...
...except for some major deviations in the midrange. You need EQ, just a different one than for a velocity-sensitive transducer.
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Old 3rd December 2011, 03:43 AM   #4
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Quote:
Originally Posted by jcx View Post
simple Bode asymptote aproximations: ~ 1:4 zero-pole "flat spot" is going to give ~ 12 dB difference from the expected pure 1st order slope of a uncorrected strain gage cart response
could be viewed as 12 dB mid/high cut or +/- 6 dB at low/high vs 1 kHz matched level
but in any case "celarly audible" by just about anyone in ABX comparison with a accurate RIAA played on the same system - pink noise anyone?

it could be excused on not doing level matched comparisons, by just walking into a demo room with unknown speakers/room frequency response - still I would be suprized that anyone with truely trained ears - even many "lesser trained" ears than recording/mastering engineers, techs wouldn't pick up on that much error even if they weren't sure where to place the blame

red single pole response - I assume even though strain gages give DC response any audio system won't like it so I kept the 50 Hz corner
green RIAA, the curves level matched at 1 KHz

looks like 38 degrees, 3.2 uS phase, time errors - where our hearing is pretty sensitive too
Quote:
Originally Posted by jcx View Post
I pre-emphasized 2mV, 100 Hz + 1 mV, 5 KHz square waves and put them thru the 1st order 50 Hz LP and full RIAA eq

with 1 KHz matched EQ levels for minimum FR error you can see red single pole "uncorrected strain gage cart" response is wrong at both low and high frequencies

but what's +/- 6 dB error as long as there's a good audophile story attached?
Attached Images
File Type: png riaa_1order.png (37.4 KB, 377 views)
File Type: png riaa_1order_sq.png (34.9 KB, 370 views)

Last edited by jcx; 3rd December 2011 at 03:45 AM.
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Old 3rd December 2011, 04:23 AM   #5
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I've also heard it and was impressed. Don't know what's in the box, tho.
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Old 3rd December 2011, 05:06 AM   #6
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Default Hello stellavox

Quote:
Originally Posted by stellavox View Post
Peter Liebermann is to be congratulated. Charles
I am writing this with the utmost respect:
His name is Peter Ledermann.

Sincerely,

Ralf
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Old 3rd December 2011, 02:19 PM   #7
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JCX, thanks for the information.

So, you're saying the strain gauge is just a first order slope. It looks like that first order slope closely matches the first part of the RIAA curve. I mean if you had the low frequency amplitude set the same, you'd have the first pole.

Did you measure a strain gauge cart? It wasn't clear to me from you post.

Anyway, if the response is like that, all one has to do is get rid of the first pole on a standard phono preamp, and the rest is taken care of.

I'd be interested in doing this. I've got my Pearl phono preamp boards stuffed and working, so perhaps I could mod the filter and get rid of the first pole in a way that doesn't affect the rest of the filter response.

I mean if that really is the response of the strain gauge.

Does anyone know of a good test LP, with test frequencies I could use to get the response of the strain gauge cart?

John
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Old 3rd December 2011, 02:26 PM   #8
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In my MPP thread you find enough information to build a strain gauge phono amp based on the Panasonic models. I have also published FRD curves there. Without any correction you get a presence dip and a rise in the upper treble so without any EQ is plays but does not sound optimum. I have shown a way to build an equalizer.
The Ledermann cartridge may behave different but i can not tell. Scanning the web i did not find any reliable information about what he does exactly but i would be surprised if zero EQ is the ticket.
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Old 3rd December 2011, 03:38 PM   #9
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Hi Joachim,

Your thread is pretty long ... you have an idea about where that information is located?

I'll have to buy a SS strain gauge cart and test it, once I am ready to do this. I think this will be a fun project though.
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Old 3rd December 2011, 03:45 PM   #10
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Mpp

I found this with a search, but nothing else.
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