Strain Gauge catridges

[Pio1980]

They seem to fall in between 600^ and 1200^. My EPC-450C-II is ca 1200^ internal element resistance per channel and the EPC-451C ca 750^ per. For your custom pre we will want to choose the value of the current limiting loading resistors to keep the current at ca 4 ma per channel.

For the e-Bay board preamp SG mod, the current limiting resistors are chosen to provide ca 4mA thru each channel of the cart at the 15 volts provided, so the total resistance for each channel should be 3750^. For my EPC-405C-II at 1200^ per channel, 2500^-2700^ loading/limiting should do it. For our EPC-451C, 3K is the loading/current limiting resistor value for 4mA. Use lo-noise 1/4W metal film type for these resistors.

The values I posted earlier were incorrect tho' harmless to the carts. Those postings have been corrected AFAIK.

 

[Qilin]

Latest update,
Yesterday I got the DIY preamp running, with great thanks to Pio1980 for all of the fantastic help!
Unfortunately, the channels are still unbalanced by about 6dB (left channel low output). It seems to me that the unbalanced L-R channels are due to something within the cartridge, as evidenced by the different resistances I measured and reported in an earlier post.
I would say that based on the right channel (the stronger one), the sound quality is excellent, better than the SE-405. Pio1980, you are right!
Question is where to go from here...
Pio1980 suggested replacing two 1K resistors with a 2K 10-turn trimpot to equalize the channels. That's my plan! More to come, later...
Best regards, DM

 

[Pio1980]

I don't know why it's imbalanced, the cart's resistances aren't really that far off. What is your tracking force? 2.5g seems to work well for pre-loading the cart's components for good performance. The trimpot should nonetheless give you a balance control for this cart/pre combo..

 

[Qilin]

I don't know why it's imbalanced, the cart's resistances aren't really that far off. What is your tracking force? 2.5g seems to work well for pre-loading the cart's components for good performance. The trimpot should nonetheless give you a balance control for this cart/pre combo..

Hello Pio1980,
I am tracking at 2.5g VTF.
When I get the trimpot, I will post again!
Best regards, DM

 

[Pio1980]

Very good! E-mail sent.

 

[Qilin]

I wanted to update this thread to the latest status of my DIY preamp project for the Panasonic strain gage cartridge.
First of all, I would like to acknowledge the tremendous help that AK member Pio1980 has provided to me, to get the project up and running.
I have hooked up the DIY preamp assembled from a Chinese kit, with mods by Pio1980. Due to an issue with the cartridge, *not* the Pio1980 preamp, the left channel level is lower than the right channel level by approx 6dB, resulting in an off-center stereo image to the right. As a temporary fix, I have installed a volume pot to reduce the level of the right channel and balance the stereo image to the center. The temporary fix has allowed me to focus on evaluating the sound quality.
And I am really pleased with the sound quality of the cartridge/DIY preamp combo! I think it's better than any other cartridge+preamps that I have evaluated (all of them were MM type).
MM Cartridges - Jico MM-1, Tonar 555, Astatic MF-200, Grado, various others.
Preamps - Cambridge 640P, Bellari VP129+Mullard, Yaqin MS-12B, Panasonic SE-405 (either in MM or Strain Gage mode).
Admittedly I have not listened to MC cartridges, nor any higher-budget gear.
My next step will be to get a more permanent fix for the unbalanced channel levels.
Thanks again Pio1980!
Cheers! DM

 

[flavio81]

The circuit I use is fully symmetrical, short, and simple. Thanks goes to Flavio Egoavil of Lima Peru for introducing me to the topology I've adapted for the convenient and very economical e-Bay board kit.

Flavio here!! Hi fellas!!

For the ones who just arrived to the thread and need a quick and dirty preamp:

NOTE: This preamp is to be powered using 9V batteries. Do not use a power supply since if something fails in the power supply and the voltage goes way up, or there is a power surge... bye bye strain-gauge elements!!

Note the "15Hz hi-pass section" has been wrongly calculated by me. And thus it is seriouly lacking in the bass department. Change the resistor or the capacitor to a higher value (for example 2X the value). Experiment.

Of course it needs more improvements. Suggested:
- Another "balance" control (for the other channel)
- Have both strain gauge elements conected to the same +V supply and invert one of the channels using an additional opamp.

It works OK with TL072 and TL082 opamps. Noise is not intrusive.
Sound quality is good and clear as a strain gauge cartridge should sound (once you correct the "hi pass filter" for better bass). Satisfaction guaranteed.

I'm pretty sorry i cannot draw an updated schematic, i've been very busy lately. But i promise i will draw a better preamp... at least within this year

 

[flavio81]

And I am really pleased with the sound quality of the cartridge/DIY preamp combo! I think it's better than any other cartridge+preamps that I have evaluated (all of them were MM type).
MM Cartridges - Jico MM-1

If it's sounding better than Jico's "SAS MM-1" cartridge then consider it a great achievement. I've read nothing but unbriddled passionate praise for the MM-1; it's users elevate it to the level of "best cartridge ever." We have a thread on it on vinylengine.

 

[kcc123]

Hi Flavio,

Welcome to this forum! Some strain gauge cartridge owners would like to hear more from you.

 

[flavio81]

Hi Flavio,

Welcome to this forum! Some strain gauge cartridge owners would like to hear more from you.

Ok, what do you want me to sing?

 

[Pio1980]

Hi Flavio, Welcome!!
As previously posted, I give Flavio credit for the topology for the SG mod to the e-bay preamp board project. Elegant!!

Some suggestions; Try increasing the LF roll-off resistor loading to ca 33k-39k with precision trimpots, with the wiper into the chip to provide balance correction independent of FB.
If offset is low enuff, sub the 1k output resistor and 0.1uF blocking capacitor with a 100^ 1/2W resistor. The best capacitor is no capacitor and this app gives no charge coupling advantage, unlike the input blocking/LF roll-off cap which does.

 

[kcc123]

Hi Flavio,

Heheh! I have heard more than enough from you on vinylengine, so let the others be your audience.

 

[flavio81]

If offset is low enuff, sub the 1k output resistor and 0.1uF blocking capacitor with a 100^ 1/2W resistor. The best capacitor is no capacitor and this app gives no charge coupling advantage, unlike the input blocking/LF roll-off cap which does.

An interesting variation for this schematic would be to use single opamps (1 opamp per chip, like the TL071 for example) and then use the "offset null" adjustment to bring offset to zero. And then have a capacitor-less output. But i think it's not necessary if the capacitor is of good quality.

 

[Qilin]

If it's sounding better than Jico's "SAS MM-1" cartridge then consider it a great achievement. I've read nothing but unbriddled passionate praise for the MM-1; it's users elevate it to the level of "best cartridge ever." We have a thread on it on vinylengine.

Hello Flavio81,
Thanks for the comment! I still stand behind my evaluation. But as a matter of fact, the Jico MM-1 is clearly the best of the MM cartridges that I have. Keep in mind that my evaluation is Jico MM-1 + Cambridge 640P Preamp system versus EPC-451C + DIY preamp system. The MM-1 cannot be played through the DIY preamp, and the 451C cannot be played through the Cambridge 640P! So it's not truly a straight-up cartridge versus cartridge direct comparison. Maybe this is stating the obvious, though!
Best regards, DM

 

[Pio1980]

An interesting variation for this schematic would be to use single opamps (1 opamp per chip, like the TL071 for example) and then use the "offset null" adjustment to bring offset to zero. And then have a capacitor-less output. But i think it's not necessary if the capacitor is of good quality.

The enhanced version you propose sounds worth persuing.
The kits I'm using come with blue 1.0 uF polyprop film output blocking caps, I've built 3 of them, one without the caps for 80^ resistors. While they all sound terrific I do prefer the one with resistors subbing the caps, and the output offset is a couple mV only which my system tolerates. I also don't run an active line stage, instead direct-driving the power amp thru a passive selector/attenuator controller. The cart is so 'open', dynamic, and natural sounding that anything that gets in it's way is obvious by elimination. 'Daisy-chaining' unnecessary/inferior gear and interconnects with this phono system is audibly counter-productive, I honestly can't imagine a system too 'good' for this set-up.

 

[Susurus]

What a cool forum. My Japanese WIN cart might become threaded to a Lima Peru design. Truly international.

Cheers!

 

[Pio1980]

Recieved this info from Professor Bizzt to pass on to the group;

From original Panasonic literature for recommended tracking force range on the following cartridges:

EPC-450C 1.7 to 2.3 grams
EPC-450C-II 1.5 to 2.5 grams
EPC-450CM4-P 1.7 to 2.3 grams
EPC-451C 2.0 to 3.0 grams
EPC-460CM4 3.0 to 4.0 grams

He states;
"I think it should be considered that these mid-seventies recommendations were taking into account that these cartridges would probably be used in less than great tonearms. Using them in a very good tonearm should reduce the tracking force requirements a bit."

I might add that using them in a good LT arm would probably apply to the rec.

 

[flavio81]

Recieved this info from Professor Bizzt to pass on to the group;

From original Panasonic literature for recommended tracking force range on the following cartridges:

EPC-450C 1.7 to 2.3 grams
EPC-450C-II 1.5 to 2.5 grams
EPC-450CM4-P 1.7 to 2.3 grams
EPC-451C 2.0 to 3.0 grams
EPC-460CM4 3.0 to 4.0 grams

He states;
"I think it should be considered that these mid-seventies recommendations were taking into account that these cartridges would probably be used in less than great tonearms. Using them in a very good tonearm should reduce the tracking force requirements a bit."

I might add that using them in a good LT arm would probably apply to the rec.

Who is Professor Bizzt? Anyway, send greetings to him and a deep thanks for summarizing the information.

The left-right channel separation is done by the doughnut shaped "resolver" at the cantilever and i would guess it would require a certain minimum VTF to properly separate the channels.

 

[Pio1980]

My thinking is that the elastomerics need a certain amount of pre-load above what the stylus will actually track well in order for the system to operate properly. One difference between model versions seems to be the distance between the pivot damper and resolver ring on the stylus and the leverage may have something to do with tracking pressure as well.

 

[flavio81]

My thinking is that the elastomerics need a certain amount of pre-load above what the stylus will actually track well in order for the system to operate properly. One difference between model versions seems to be the distance between the pivot damper and resolver ring on the stylus and the leverage may have something to do with tracking pressure as well.

Most probably.

So who is Professor. Bizzt? Can you invite him to AK?