I thought the LSK line amp from BAF2013 could be used with a Panasonic EPC-450C strain gauge cartridge.
4 mA through the cartridge's strain gauge elements. Opposite polarities on bias to avoid an inverting stage, or swapping cartridge leads.
Any comments?
/RK
4 mA through the cartridge's strain gauge elements. Opposite polarities on bias to avoid an inverting stage, or swapping cartridge leads.
Any comments?
/RK
Attachments
Last edited:
Optimum excitation voltage has a significant effect on strain gauge performance.
Basically you want the highest voltage without overheating the strain gauge. I'll have to refer to my notes. My brain doesn't remember that level of detail anymore.
A Salas shunt reg should make a noticeable improvent for this application.
I'll think about the amp side of things once I remember my strain gauge stuff. I'm no expert about amps but folded cascode definitely gives you high performance.
Basically you want the highest voltage without overheating the strain gauge. I'll have to refer to my notes. My brain doesn't remember that level of detail anymore.
A Salas shunt reg should make a noticeable improvent for this application.
I'll think about the amp side of things once I remember my strain gauge stuff. I'm no expert about amps but folded cascode definitely gives you high performance.
I found this at Vinyl Engine - The Home of the Turntable, thanks to one Flavio.
Postby flavio81 » 13 Jun 2010 05:00
Ok, here's the information i've found:
Here's how you get sound from it, directly from Technics patents:
ImaThe cartridge needs, per channel, 4mA or 5mA of current through it.
The internal resistance of the cartridge is 1000 ohm per channel (= per semiconductor element). When deflecting the needle with my finger, i get around 100 ohm.
Panasonic SE-405 demodulator specs say the input impedance (of that preamplifier) is 4700ohm, which means that for 4mA, they are using around 18 to 22V of bias voltage.
For me, if i want to use 9V of bias tension and 5mA of current for the semiconductor cartridge, the "R" (resistor) value on that diagram would have to be 800 ohm, so the total resistance (1800 ohm) together with the voltage (9V) gives 5mA.
The capacitor is there to filter out the bias voltage (DC). I guess any high enough value will work...
The output in theory would go to the AUX input, no RIAA compensation is required, like if it was a ceramic cartridge!!!
Another additional consideration i've found is that one of the two channels must be reversed in phase to give a correct stereo output. Or you can invert the leads of one of the speaker channels...
Attachments
Elements tweaked for RIAA curve match looks suspicious. A SG is a constant displacement transducer, I can't see the mechanical elements varying their properties at low frequencies. I would think you still need a preamp with a different de-emphasis curve. A ceramic cartridge simply "plows" through the RIAA curve there are considerable errors in doing this.
Yes. I had a discussion with the late Lou Dorren at the QuadraphonicQuad forum some years ago regarding this. I think I found quite some deviation, but I think Lou argued it was not that important (due to other errors if I remember).
I made a simple LTSpice simulation, and I believe I found quite some dBs error. I can probably dig out this again from some harddisk.
I made a simple LTSpice simulation, and I believe I found quite some dBs error. I can probably dig out this again from some harddisk.
Generally speaking a strain gauge should give you an absolutely flat frequency response.
You do have to consider thermal effects in the lead wires though. We use a 3 wire quarter bridge setup.
It is important you understand this document on how to setup the quarter bridge circuit.
http://www.vishaypg.com/docs/11092/tt612.pdf
You do have to consider thermal effects in the lead wires though. We use a 3 wire quarter bridge setup.
It is important you understand this document on how to setup the quarter bridge circuit.
http://www.vishaypg.com/docs/11092/tt612.pdf
No, you are talking about two different issues a strain gauge might very well be a perfect displacement transducer but LP's have been equalized for ideal velocity sensitive transducers of which most cartridges are not due to several factors. There is no way the frequency response is correct without de-emphasis of some kind.
Strain gauges are absolutely flat in frequency response (I'll check on the bandwidth)
I wasn't aware that LPs are recorded with frequency correction.
Does anyone know how much they tweak the frequency response before it is put down on vinyl.
Last edited:
RIAA
https://en.wikipedia.org/wiki/RIAA_equalization
You have a shelf between 500Hz and 2122Hz which is the main frequency response problem when using a strain gauge cartridge.
https://en.wikipedia.org/wiki/RIAA_equalization
You have a shelf between 500Hz and 2122Hz which is the main frequency response problem when using a strain gauge cartridge.
Attachments
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.