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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 17th May 2017, 01:44 PM   #11
kevinkr is offline kevinkr  United States
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Playing With Panasonic Strain Gauge Cartridges (And A Dedicated Phono Stage)
Seems like partially correcting the region between 500Hz and 2122Hz works better than the more aggressive approach I initially took because the highs above 10kHz are not boosted as much.

From 6.5dB shelving HPF I went to 3.5dB and it seems to be better overall.

So far I have not established a need for cut below 50Hz..

I still think the response may need to be knocked down a bit above 10kHz.

Debating on whether a new Jico stylus would provided superior performance to the NOS shibata. It has improved considerably with use but after an indeterminate number of years I find it hard to believe that the rubber components have not hardened significantly.

One thing that is evident is that there is a lot of detail, and they track HF well. Quite sensitive to VTA (SRA). Sometimes it sounds a bit artificial and HIFI, have not decided whether this is a cartridge artifact or the material. Bass response is quite good as well.

Tonight I will share graphs of the EQ tried so far.

They are sensitive to the quality of the arm and effective mass needs to align properly with the cartridge's rather low compliance. Tracking the 465C at 3.5gms currently.

A phono stage design will ultimately come out of this which I will share here. I have not yet decided on any of the details other than it will utilize vacuum tubes for gain.

A lot of design iterations are shared in this thread, please look for the very last design for the one you should build if you are considering building anything at all. Not all of these iterations sound particularly good, you have been warned.
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Old 17th May 2017, 03:28 PM   #12
Pano is offline Pano  United States
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Playing With Panasonic Strain Gauge Cartridges (And A Dedicated Phono Stage)
Interesting topic. Thanks Kevin, I'll watch to see what you come up with.
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Old 20th May 2017, 12:44 AM   #13
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Kevin, Any new development? We Texas boys are anticipating!
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Old 20th May 2017, 12:59 AM   #14
GTHICM is offline GTHICM  United States
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The eyes of Texas are upon you, Kevin. Let's listen to your progress tomorrow. It sounds like you are well along the way to sussing out the mysteries of this cartridge.
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Old 20th May 2017, 01:07 AM   #15
kevinkr is offline kevinkr  United States
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Playing With Panasonic Strain Gauge Cartridges (And A Dedicated Phono Stage)
Hi Shooter, You aren't part of the Dallas crew I know perchance?

I haven't figured out how to do a 3dB/octave filter, but some EQ appears to be needed.

Currently I have a very simplistic EQ with about 3.7dB of boost between 500Hz - 2122Hz which means the area above 10kHz is not excessively boosted, but doesn't fully compensate for the trough.
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Old 20th May 2017, 01:13 AM   #16
shooter is offline shooter  United States
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Yes Kevin, I am the one with the Rullit horns.
Getting my soldering iron ready!

Last edited by shooter; 20th May 2017 at 01:34 AM.
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Old 20th May 2017, 02:59 PM   #17
kevinkr is offline kevinkr  United States
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Playing With Panasonic Strain Gauge Cartridges (And A Dedicated Phono Stage)
I wasn't sure if it was you or not. I hope you will find what I have come up with interesting. There will be more gain, mid band, and LF correction (optional) and the topology itself deals with the HF peak above 10kHz. Output impedance will be much lower making for good compatibility with your TVCs.
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Old 21st May 2017, 01:57 AM   #18
kevinkr is offline kevinkr  United States
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Playing With Panasonic Strain Gauge Cartridges (And A Dedicated Phono Stage)
Default Version 1 Schematic Design

As I've remarked before I design phono stages with deliberately high output levels in order to integrate well with systems with digital sources with maximum output levels of 2.0Vrms @ 0dBFS.

With approximately 57dB of gain @ 1kHz the maximum output level of this combination of EPC-465C and strain gauge phono stage should result in approximately 2.1Vrms @ 5cms/sec at 1kHz.

Detailed description:

The first stage is nothing more than a 6DJ8 mu follower although the battery bias scheme may make that less than obvious. The batteries last many years and allow me to establish an operating point that is more than usually independent of the tube's slope of transconductance. In this case I have chosen 4mA as the target current as this is the value Panasonic mentions in the specification for these cartridges.. This yields a gain of approximately 30dB in the first stage and the follower provides an output impedance to the network of < 1K ohm.

Something less obvious is the input stage is non-inverting and provides bias to the cartridge.

The second stage is a hybrid mu-follower using a DN2540 as the upper element, again battery bias is applied, this reduces dependence to operating current on fet threshold voltage, it also allows for fairly large source resistance which improves the performance of the follower. The follower will drive transformers effectively output impedance is < 200 ohms.

A Salas SSHV set for approximately 200 - 220V would make a good power source for this design. Local decoupling is a must.

You will note that there are a lot of 47/100 ohm resistors, unless you want a VHF oscillator you will not omit these. These particular resistors need to be placed right at the socket.

Yes, I like batteries, they're cheap and quiet sources of bias. There are two A23 12V batteries and a single AA per channel.

Note that at your discretion I might recommend the use of a 5.1V low capacitance TVS diode on the cathode of each channel to protect the cartridge in the event of a tube or other component failure.

This version is currently in use here at home with an EPC-465C.

**Note** C1 may be increased to 0.1uF if LF roll off is not desired. (This is what I am currently using)

No provisions have been made to invert one channel relative to the other, you will need to invert at the speaker or if using transformers on the outputs invert one relative to the other. My line stage provides the ability to invert either or both channels as desired right from the front panel.

The design is shared with the explicit understanding it is for personal use only.

Edit: Please see POST # 73 for the updated design. (Major improvement)
Attached Images
File Type: png Strain_Gauge_Phono_V1.PNG (57.2 KB, 451 views)
File Type: png Gain and phase Strain Gauge Phono V1.PNG (72.3 KB, 444 views)
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Old 21st May 2017, 02:02 AM   #19
kevinkr is offline kevinkr  United States
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Playing With Panasonic Strain Gauge Cartridges (And A Dedicated Phono Stage)
GTHICM was here today, but did not get to hear the newest iteration of the front end design.

The improvement over what he heard is substantial; it is much more dynamic and quicker. Gain is 10dB higher, which results in better integration with the rest of the system.

It is also very quiet with a low subjective noise floor which I have not yet measured.
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Old 21st May 2017, 02:17 AM   #20
GTHICM is offline GTHICM  United States
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Yes, I did hear the previous iteration this morning and it did sound promising. But as observed, the dynamics were not quite there to my liking. The sound was what could be described as polite, but interesting with good imaging, nonetheless. Unfortunately, I will not be able to hear this latest iteration for several months because of overseas travel plans. This however confirms that this rather unique cartridge holds quite a bit of promise. Not bad at all for a relatively meager cost, with the benefit of replaceable styli.
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