Playing With Panasonic Strain Gauge Cartridges (And A Dedicated Phono Stage)

I have edited my previous post, please read the added comments, as wired it is DANGEROUS.

I thought I wired the switch correctly on L side, not neutral N side. :( Anyway, I corrected it. Thank you again!
 

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Super
You should twist all AC wiring and keep it against the chassis.
On mine I ran the AC line thru a copper tube grounded to earth on one end only and covered all the transformer AC leads in braid grounded also to one end.
Probably doesn't do much but mine was a tight build unlike the open build of others and had to remove the trans housing to fit inside my extrusion.
The transformer itself should be chassis grounded as Kevin suggests also.

Remember that all 3 pcbs float seperate from the chassis and only connect to earth thru the 10 ohm/ diode combo (used 15 ohm as I had it already)

You will want to put a heat sink on that hot running bridge if you want to make it live a long life.
I ended up using a copper sandwich and bolting it to the aluminum side with plenty of thermal compound.
It takes a little longer to come up to a stable temp but worth it I think.

Regards
David
 
David,

So, I should add a resistor and two diodes and connect them as in the image. Do I just connect them inline with a wire loosely? Since I have separate chassis for phono, I need to do the same for phono also if I understand it correctly.

I have some copper shield tape and will cover the ac wire with the tape and ground them.

Jim
 

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I checked the cartridge this morning. The epoxy is completely cured. The stylus fits very tightly and I don’t think it is necessary to add a external brace to hold the stylus down firmly. I am thinking to add a very thin layer of silicone to both legs( please see the image) to further reduce possible resonance.
 

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David,

So, I should add a resistor and two diodes and connect them as in the image. Do I just connect them inline with a wire loosely? Since I have separate chassis for phono, I need to do the same for phono also if I understand it correctly.

I have some copper shield tape and will cover the ac wire with the tape and ground them.

Jim

Yes that is the right circuit, but you only need one in the PSU between the chassis and the PSU board. You can connect the audio supply ground to the chassis in the audio chassis or run a separate ground wire which could be connected to the chassis in the PSU. (No connection between audio power ground and chassis in the audio chassis if you do this.)

Note also that only ONE ground pad on each of the pre-amp cards should be connected to the PSU. I use the one associated with the 300V supply.

Finally the ground loop breaker goes between the PSU chassis and the PSU ground.
 
Yes that is the right circuit, but you only need one in the PSU between the chassis and the PSU board. You can connect the audio supply ground to the chassis in the audio chassis or run a separate ground wire which could be connected to the chassis in the PSU. (No connection between audio power ground and chassis in the audio chassis if you do this.)

Note also that only ONE ground pad on each of the pre-amp cards should be connected to the PSU. I use the one associated with the 300V supply.

Finally the ground loop breaker goes between the PSU chassis and the PSU ground.

I got it. Thanks!
 

ra7

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After recently reading up on strain gauge cartridges (actually, it was one of Kevin's posts that piqued my interest, so thanks Kevin!!), I pulled the trigger on an ebay offering of Panasonic EP451C and the matching demodulator to go with it. When it arrived, it was in absolutely mint condition. It even came with a Walco diamond stylus.

I just got it hooked up last night and it was quite impressive. The response still needs some shaping. I'd say it is pretty close to the attached image, which is the response of the cartridge itself. I put a shelf of -6 db, Q of 1, at 15 kHz. That cleaned up the etched sound at the top. Left the bottom end as it is, which was quite pronounced and probably needs a cut also.

My system is a Technics SL1200 with a DL103 and a Dyna 10X5. The 10X5 is superior to the DL103, and I'd say the 451C was not far behind the 10X5. It definitely calls for more experimentation.

I haven't looked at the circuit of the demodulator, but it does not appear to compensate for the cartridge response. It did sound fine otherwise, so, it must compensate for the RIAA plus inherent SG response. How can one run a frequency response sweep? Might be time to invest in a test LP.

I feel like this technology has a higher ceiling than the MC cartridges and probably at a fraction of the cost. Apart from the tonal response, the imaging was very good, and there was a general sense of ease about the sound.

I'm going to try to build Hazard's JFET preamp to see what it can do, and might even try Kevin's circuit, though I don't have any experience with tubes. I think another viable approach is to just provide gain and do the correction digitally, for example, using a miniDSP. That would make it flexible so that you can correct the cartridge's response together with all the other correction.
 

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We have a get together today to listen to the new strain gauge preamp, everyone that knows my system were impressed with the improvement over the old and commented the sound was the best my system ever sounded! I end up using .12 uf vitamin q and 1 uf polycarbonate as coupling caps. Very happy with the sound! Very quiet as well.
Kevin really did an outstanding job designing this preamp, for those that are on board for the build you won't be disappointed!