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Playing With Panasonic Strain Gauge Cartridges (And A Dedicated Phono Stage)
Playing With Panasonic Strain Gauge Cartridges (And A Dedicated Phono Stage)
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Old 14th May 2017, 09:21 PM   #1
kevinkr is offline kevinkr  United States
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Playing With Panasonic Strain Gauge Cartridges (And A Dedicated Phono Stage)
Default Playing With Panasonic Strain Gauge Cartridges (And A Dedicated Phono Stage)

So a friend has asked me to design a strain gauge phono pre-amp based on the Panasonic strain gauge cartridges.

I've got an EPC-460C and an EPC-465C on hand along with two NOS replacement styli.

(Even better I get to keep one of the cartridges when the project is done.)

I have spent several days reading VE and AK threads about these cartridges and how to amplify them.

Many people seem to like them without any sort of EQ, but based on measurements posted on VE and elsewhere this doesn't seem correct to me. Reviews back in the day show FR plots that by today's standards look pretty bad.

I might mention I have heard several modern strain gauge cartridges and thought they sounded absolutely terrible. I also heard a Panasonic with some limited EQ that didn't.

To be fair my frame of reference are a couple of Ortofon Per Windfelds. I have several others including a couple of SPUs, but I feel the PW is the most accurate cartridge I own.

From extensive study it seems like the following might be true..

  • HPF at 50Hz
  • Shelving HPF filter between 500Hz - 2.21kHz
  • As yet undetermined rolloff between 2.21kHz and 10kHz..
All subject to change as I figure this out.
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Old 14th May 2017, 09:37 PM   #2
kevinkr is offline kevinkr  United States
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Playing With Panasonic Strain Gauge Cartridges (And A Dedicated Phono Stage)
Well both seem to be electrically good..

460C 900 ohms DCR

465C 869 ohms DCR

In both cases the channel to channel match is within an ohm or so using my Keithley 2002 bench meter.

I am planning on about 3mA of current through the elements as this is a value I have seen frequently recommended. Higher currents have been advocated, but self heating may be an issue so I won't go there.

The two channels are inverted relative to one another, Panasonic accommodated for this in their CD-4 demodulators by adding an inverting stage on I think the left channel. (I need to check)

Since my line stage and that of my friend can invert polarity independently on each channel I may just not bother to address the polarity issue at this point in this design. Given my design proclivities this might be best addressed in a phono stage with output transformers.
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Old 14th May 2017, 09:39 PM   #3
kevinkr is offline kevinkr  United States
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Playing With Panasonic Strain Gauge Cartridges (And A Dedicated Phono Stage)
Note that both NOS and brand new (Jico) shibata equipped styli are still available for the full line. Compared to what I am used to they are cheap as dirt!

https://www.turntableneedles.com/EPS...DQ_p_1278.html
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Old 14th May 2017, 10:45 PM   #4
billshurv is online now billshurv  United Kingdom
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Playing With Panasonic Strain Gauge Cartridges (And A Dedicated Phono Stage)
I hope you are planning to put a couple of dials on the front, one for VTF and one for anti-skate (assuming it's final destination is for a pivoted arm).
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Old 15th May 2017, 06:07 AM   #5
hazard500 is offline hazard500  Australia
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Quote:
Originally Posted by kevinkr View Post
I have spent several days reading VE and AK threads about these cartridges and how to amplify them.
Hi Kevin, have you searched DIYAudio? There is some good info in this thread.

Strain Gauge jFET Pre-amp

Quote:
Originally Posted by kevinkr View Post
  • HPF at 50Hz
  • Shelving HPF filter between 500Hz - 2.21kHz
  • As yet undetermined rolloff between 2.21kHz and 10kHz..
.
My latest design includes HPF at 50Hz. As you correctly state, theory says that there should be a shelf between 500 and 2.1kHz (with 12dB gain), in practice my WIN strain gauge sounds fine without this, but my EPC460 sounds shy on treble. I have recorded an LP played with EPC460 via EMU sound card, and playing around in Sound Forge, I find that a boost of 4 to 6 dB gives a pleasant response. Although theory states that it should be 12dB, applying this much gain results in a very shrill response. So clearly, neither the WIN nor Panasonic are perfectly linear strain gauges, and it is not possible to derive one standard response curve that will will suit all. Unfortunately it seems that we have to tailor the eq to suit individual cartridges

My audio friend has a EPC451, we recorded his test record (white noise) and a spectrogram did indeed show a drop in response from 500 to 2.1kHz. However once again, equalising in sound forge showed that about 6dB lift provided the preferred presentation.

Why do you want a roll-off between 2.1 and 10k? There are no poles or zeroes in the RIAA standard to correct for, in fact the natural response of the Pana (based on whit noise analysis) seems to drop off after 10k so if anything a boost may be needed.

At the moment I am playing with a Lyra Skala so I haven't listened to either strain gauge in a short while. But they are very rewarding if you get them running properly, with my clear preference being for the WIN.

Regards,
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Old 15th May 2017, 07:56 PM   #6
AVWERK is offline AVWERK  United States
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There was an Electro Research EK-1 strain gauge / preamp back in the early 80,s and each strain gauge pick up required specific frequency compensation. No plug and play unless you wanted wild frequency response swings...,

I believe Gordon Holt reviewed in Stereophile and loved it back then and it was over 3k+ for the system
Alot of money in the early 80,s
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Old 15th May 2017, 11:11 PM   #7
jplesset is offline jplesset  United States
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And before that was the Euphonics cart. '70s perhaps? maybe late '60s? Used it for a while.
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Old 16th May 2017, 01:40 AM   #8
hazard500 is offline hazard500  Australia
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Quote:
Originally Posted by AVWERK View Post
There was an Electro Research EK-1 strain gauge / preamp back in the early 80,s and each strain gauge pick up required specific frequency compensation. No plug and play unless you wanted wild frequency response swings...,

I believe Gordon Holt reviewed in Stereophile and loved it back then and it was over 3k+ for the system
Alot of money in the early 80,s
That's interesting, I have not heard of the Electro Research before but it certainly confirms my own observations ie each cartridge needs its own eq.

Actually just done a bit more research and here is an interesting article

Audio Investigations: Equalizing the strain gauge

This blog references the EK1 phono system, and also mentions that he prefers 6dB of eq between 500 and 2.12k, which is very close to my own experience.
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Old 16th May 2017, 03:47 AM   #9
kevinkr is offline kevinkr  United States
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Playing With Panasonic Strain Gauge Cartridges (And A Dedicated Phono Stage)
Interestingly I installed the 465C on one of my Southers and added about 5gms of mass to the too light arm wand so I could use a 6gm counterweight to apply a tracking force of 3.5gms.

I modified my Muscovite Mini and added 6dB of boost between 500Hz - 2.1kHz, did nothing above that, but it strikes me it can be a bit bright on some material. VTA definitely plays a role.

Surrounds surprising good. My line stage allows me to invert outputs independently of each other.
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Old 16th May 2017, 03:53 AM   #10
kevinkr is offline kevinkr  United States
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Playing With Panasonic Strain Gauge Cartridges (And A Dedicated Phono Stage)
Quote:
Originally Posted by hazard500 View Post
Hi Kevin, have you searched DIYAudio? There is some good info in this thread.

Strain Gauge jFET Pre-amp


My latest design includes HPF at 50Hz. As you correctly state, theory says that there should be a shelf between 500 and 2.1kHz (with 12dB gain), in practice my WIN strain gauge sounds fine without this, but my EPC460 sounds shy on treble. I have recorded an LP played with EPC460 via EMU sound card, and playing around in Sound Forge, I find that a boost of 4 to 6 dB gives a pleasant response. Although theory states that it should be 12dB, applying this much gain results in a very shrill response. So clearly, neither the WIN nor Panasonic are perfectly linear strain gauges, and it is not possible to derive one standard response curve that will will suit all. Unfortunately it seems that we have to tailor the eq to suit individual cartridges

My audio friend has a EPC451, we recorded his test record (white noise) and a spectrogram did indeed show a drop in response from 500 to 2.1kHz. However once again, equalising in sound forge showed that about 6dB lift provided the preferred presentation.

Why do you want a roll-off between 2.1 and 10k? There are no poles or zeroes in the RIAA standard to correct for, in fact the natural response of the Pana (based on whit noise analysis) seems to drop off after 10k so if anything a boost may be needed.

At the moment I am playing with a Lyra Skala so I haven't listened to either strain gauge in a short while. But they are very rewarding if you get them running properly, with my clear preference being for the WIN.

Regards,
I did a search on google but the diyA thread did not come up immediately. I'll have a look.. (Edit: I take that back, having just taken a look I did indeed read your thread.. )

Using cascode 6DJ8 in front end, cartridge is currently providing cathode bias to the amplifier circuit. Current is ~ 2.5mA which is a bit low. Eventually I design something specific with about 4mA of bias current for the cartridge.

The EQ reduces gain in the pre-amp by about 10dB overall giving me about 48dB of gain which given my system gain budget is quite a bit shy of what I need. (I design for redbook CD levels to +3dB or so)
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