Panasonic strain gauge cartridge and amp

[robnec]

Hello. I always wanted to try strain gauge cartridge in my system. It took a lot of time but because of this my monetary investment was low. First I got a cartridge then stylus and today Fedex had brought sl701 turntable. I removed the preamp board only to find out that power transformer was dead. Luckily I had small 6.3v one in my spare box. It is playing now Jeff Beck half speed Blow by blow and I want more of that sound. I would like to make seperate preamp for this cartridge, tubes if possible. Interested only in stereo playback.
What are my options? Thank you. Robert.

 

[Pio1980]

Hello. I always wanted to try strain gauge cartridge in my system. It took a lot of time but because of this my monetary investment was low. First I got a cartridge then stylus and today Fedex had brought sl701 turntable. I removed the preamp board only to find out that power transformer was dead. Luckily I had small 6.3v one in my spare box. It is playing now Jeff Beck half speed Blow by blow and I want more of that sound. I would like to make seperate preamp for this cartridge, tubes if possible. Interested only in stereo playback.
What are my options? Thank you. Robert.View attachment 1354101 View attachment 1354102 View attachment 1354103

Fairly simple, a fairly high gain low noise stereo linear preamp stage with bipolar "ghost" power to the cartridge.
There used to be a $20 diy kit on the 'Bay that could be easily built mod'ed as a pretty decent simple SG cart interface preamp, but I haven't seen it lately.
I've done maybe half a dozen in the past.

 

[JP]

Even though displacement some EQ is still needed to get flat response.

 

[Pio1980]

Even though displacement some EQ is still needed to get flat response.

That may be true, but it does complicate things tho' the results may be sublime when EQed for the individual cart and stylus. Fwiw, Peter Ledermann at Soundsmith didn't EQ his SG carts, last time I checked.

 

[robnec]

Hello. Thank you for your input.
Pio. I did my home work and read your posts. There is a long and old thread at diy audio forum with some schematics. I really want to build something high quality tubes preferred. Even after only few hours of listening to it I think this cartridge deserves the best pre. Robert.

 

[Pio1980]

A tube magnetic mic amp with a low noise regulated +/- ghost power supply for the cart would work.

 

[JP]

That may be true, but it does complicate things tho' the results may be sublime when EQed for the individual cart and stylus. Fwiw, Peter Ledermann at Soundsmith didn't EQ his SG carts, last time I checked.

He didn’t but I heard latter ones he did, but that could be false. Regardless, and though not offensively so, response with displacement is not flat and does not fully compensate RIAA.

 

[Pio1980]

He didn’t but I heard latter ones he did, but that could be false. Regardless, and though not offensively so, response with displacement is not flat and does not fully compensate RIAA.

Flavio81(who should be credited for the simple IC interface) had a work in progress for a general EQ for the IC interface, but afaik, it hasn't advanced in the last few years. Experimentally, a parametric EQ with the simple interface might be interesting research. I moved on before I got around to trying that.

 

[JP]

Ya Kevin at diya did a tube based and a fair number of EQ tweaks - latest effort I’ve seen. I’ve moved to instrumentation amp and DSP RIAA and have been meaning to adapt that setup to SG. Rather deep on the project list ATM.

Fun to play with without compensation though - still a pleasant listen. My first foray was your adaptation of the Chinese board from eBay.

 

[Pio1980]

The problem with the EQ is applying it without complicating the signal path and losing the advantage of simplicity. So, finding a way to use the feedback loop in the interface preamp to apply it would preserve simplicity without additional stages in a tube application.

 

[Pio1980]

Ya Kevin at diya did a tube based and a fair number of EQ tweaks - latest effort I’ve seen. I’ve moved to instrumentation amp and DSP RIAA and have been meaning to adapt that setup to SG. Rather deep on the project list ATM.

Fun to play with without compensation though - still a pleasant listen. My first foray was your adaptation of the Chinese board from eBay.

Very interesting! I've moved on and away from fooling with them but still have a couple of the carts, an interface board, and several various stylii for the later post EPC-450 mk1 series carts.

 

[robnec]

Hello.
JP. This is a schematic I was thinking about. What is your opinion about building it? I have built a universal power supply for tube preamplifiers /have around six so far/ so it would not be a big problem to do it. Robert.

 

[Nashou66]

I have these on my HD from somewhere, Might be from this forum.

I have the same cart as you and the Panasonic SE-405 Demodulator that was made for our cartridge.

Nashou

 

[JP]

@robnec I've no direct experience with it, but wouldn't hesitate to build a design by Kevin, especially one he's invested so much time in tweaking. @Pio1980's board modification is a super easy way to try things out as well, sans EQ.

 

[robnec]

Hello.
JP. I checked this schematic again and it seems it would be the right one to build. Thank you.
Nashou. Thank you for files, may be useful in the meantime. I started building an amp so the rest has to wait.
PS. Did you decided to get a sut or head pre for your cartridge?
Robert.

 

[Pio1980]

What's the consensus on current source vs simple current limiter?

 

[Mark Cermak]

Looking for a Quad EPC-450c cartridge only. I have a new stylus all ready. Any have one for sale?

Thanks

 

[Pio1980]

Looking for a Quad EPC-450c cartridge only. I have a new stylus all ready. Any have one for sale?

Thanks

Check with member @Orthodynamic.

 

[vinyl1]

Hmmm.....don't strain gauge cartridges need equalization that is completely different from MM and MC cartridges? Every one I've seen comes with its own custom phono stage, just for this reason.

I once went to a presentation at the Connecticut Audio Society on phono preamp design, where the theory and required circuit was explained. It was way over my head, but the gist of it is that a strain gauge cartridge responds to a different aspect of the groove than a conventional cartridge, and produces a very different signal.

 

[Pio1980]

Hmmm.....don't strain gauge cartridges need equalization that is completely different from MM and MC cartridges? Every one I've seen comes with its own custom phono stage, just for this reason.

I once went to a presentation at the Connecticut Audio Society on phono preamp design, where the theory and required circuit was explained. It was way over my head, but the gist of it is that a strain gauge cartridge responds to a different aspect of the groove than a conventional cartridge, and produces a very different signal.

It's sort of self-equalizing like piezo-ceramic carts, but imperfectly so. Some higher end preamps made especially for them were individually eq'ed for the specific cart and stylus provided with them. These carts are piezo-resistive, with response from DC to supersonic freqs.
Dave Slagle had some matching transformers for them to simplify the signal path, but I don't know if he eq'ed them.