Strain Gauge Replaced with MM/MC... Cause Cart Electrical Damage?

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DudeRocks

Well-known Member
Joined
Feb 15, 2023
Messages
157
Location
St.Louis
I recently picked up a Panasonic SL-701 with a built in CD4 demodulator. I do not have the EPC-451C & EPS451QD Strain Guage cart that originally came with it. I don't want one, but I do want to use another cart like a shiny new MM or a vintage AT15Sa. Rumor has it the strain guage required some electrical current to flow into the cartridge for it to work. I was warned not to put that expensive vintage AT15SA on this because the electrical current could cause damage to the cart. I would assume any cart that weighs properly on that dinky lil arm would work to play a record, or a fancy high hz CD4 capable cart to play quad. I would also assume the other models like the SL-505, SL-721, and SL-800 would operate similarly, and if there's any other turntables that came with one of those carts. I assume these things, because if I'm here posting I already spent way too much time googling this and did not find answers, and figure we could pull out some awesome people with knowledge on this.

My question on this particular turntable... Will using a non strain gauge cart fry out the cart? Is there really electricity being fed into the cart from such a turntable?

Little details on the strain gauge.
https://www.sound-smith.com/faq/wha...5VnfmaZPqtMwmhJ4PtAYb2uBfquChkpC_o_2YImH1ioUQ
 
DudeRocks said:
I recently picked up a Panasonic SL-701 with a built in CD4 demodulator. I do not have the EPC-451C & EPS451QD Strain Guage cart that originally came with it. I don't want one, but I do want to use another cart like a shiny new MM or a vintage AT15Sa. Rumor has it the strain guage required some electrical current to flow into the cartridge for it to work. I was warned not to put that expensive vintage AT15SA on this because the electrical current could cause damage to the cart. I would assume any cart that weighs properly on that dinky lil arm would work to play a record, or a fancy high hz CD4 capable cart to play quad. I would also assume the other models like the SL-505, SL-721, and SL-800 would operate similarly, and if there's any other turntables that came with one of those carts. I assume these things, because if I'm here posting I already spent way too much time googling this and did not find answers, and figure we could pull out some awesome people with knowledge on this.

My question on this particular turntable... Will using a non strain gauge cart fry out the cart? Is there really electricity being fed into the cart from such a turntable?

Little details on the strain gauge.
https://www.sound-smith.com/faq/wha...5VnfmaZPqtMwmhJ4PtAYb2uBfquChkpC_o_2YImH1ioUQ
Click to expand...
I would assume there is some DC "bias" on the strain gauge cart. You should be able to check this with a voltmeter across the cart contacts. But if you are planning to go to a MM/MC cart, you can't use the strain gauge preamp anyway because it has no RIAA compensation. And if you are going to play CD4 discs, you need to be sure you have response to at least 40KHz. So you may have to replace the tone arm wiring to low capacitance wire out to jacks for an external preamp.
 
If there's no switch for Moving Magnet carts, then it is only good for SG carts.
Not just the extra voltage (which can't be good), but also different EQ. Strain gauge preamps do not have RIAA equalization do they?
Without RIAA eq a MM cart is all tinny sounding, no bass.
 
https://www.lpgear.com/product/TSTSL0701.html
I've never used or heard a strain gauge phono cartridge, but they are said to provide excellent CD-4 decoding performance, maybe just buy a new stylus and keep using the SL-701.

My Technics SH-400 CD-4 demoulator has a switch and special power supply for strain gauge phono carts, a quick Google search indicated the SL-701 isn't switchable, the strain gauge power can't be turn off.


Kirk Bayne
 
audiomaster said:
I would assume there is some DC "bias" on the strain gauge cart. You should be able to check this with a voltmeter across the cart contacts. But if you are planning to go to a MM/MC cart, you can't use the strain gauge preamp anyway because it has no RIAA compensation. And if you are going to play CD4 discs, you need to be sure you have response to at least 40KHz. So you may have to replace the tone arm wiring to low capacitance wire out to jacks for an external preamp.
Click to expand...
Good idea, I'll check it out with a voltmeter and see if it's pushing any voltage back up at the cart. I do not plan to use a cart that does not support under 50 KHz. I had a AT33SA on there to test (goes to 50KHz) for appx 60 seconds. Radar light came on!
 
kfbkfb said:
https://www.lpgear.com/product/TSTSL0701.html
I've never used or heard a strain gauge phono cartridge, but they are said to provide excellent CD-4 decoding performance, maybe just buy a new stylus and keep using the SL-701.

My Technics SH-400 CD-4 demoulator has a switch and special power supply for strain gauge phono carts, a quick Google search indicated the SL-701 isn't switchable, the strain gauge power can't be turn off.


Kirk Bayne
Click to expand...
But do we know in this particular turntable, does it actually push a little bit of electricity into the cart? We are going by assumptions only until I have time to try it with a voltmeter, as I have not been able to find anything about this online. I really don't want to blow out a cart if it can be damaged this way, in which case I will have a great working SL-701 headed for goodwill! lol. But does it push juice and does that juice damage a cart?
 
From my quick Google check, the SL-701 always supplies power for a strain gauge/semiconductor phono cart, the Technics SH-400 CD-4 demodulator manual says this about the SC/MAG switch on it:

"Be careful if the selector is set wrongly. It will damage the cartridge"

The power for a strain gauge cart must be off to use a regular cartridge.


Kirk Bayne
 
kfbkfb said:
From my quick Google check, the SL-701 always supplies power for a strain gauge/semiconductor phono cart, the Technics SH-400 CD-4 demodulator manual says this about the SC/MAG switch on it:

"Be careful if the selector is set wrongly. It will damage the cartridge"

The power for a strain gauge cart must be off to use a regular cartridge.


Kirk Bayne
Click to expand...
Do you mind to share that quick google search, the link you found that from? My google doesn't seem to work as well as your google. Is the Technics SH-400 CD-4 what is included inside the SL-701?
 
kfbkfb said:
I downloaded the manual for the Technics SH-400 (I use a MM cart with my SH-400 so I researched this issue a while ago):

https://www.vinylengine.com/library/technics/sh-400.shtml
I don't know much about the all-in-1 CD-4 turntable/demodulators, but a few posts in other audio discussion forums said the power for the strain gauge cart was always on in the SL-701.

https://www.vinylengine.com/turntable_forum/viewtopic.php?t=73570

Kirk Bayne
Click to expand...
I didn't see anything specific about strain gauge power. They're talking about a muting circuit. Is that what this is?
 
audiomaster said:
if you are planning to go to a MM/MC cart, you can't use the strain gauge preamp anyway because it has no RIAA compensation.
Click to expand...
quadsearcher said:
Without RIAA eq a MM cart is all tinny sounding, no bass.
Click to expand...
DudeRocks, did you read these portions of the above posts?
Tinny sound with no bass would make other issues moot, would it not?
DudeRocks said:
I had a AT33SA on there to test (goes to 50KHz) for appx 60 seconds. Radar light came on!
Click to expand...
How did it sound for those 60 seconds?

I've always wanted to find one of these built-for-CD4 systems to see if it really is plug-and-play, so I'm curious about it. Being that the original cartridge was part of the system design, though, I'd no longer expect it to be so simple without it.
 
quadsearcher said:
DudeRocks, did you read these portions of the above posts?
Tinny sound with no bass would make other issues moot, would it not?

How did it sound for those 60 seconds?

I've always wanted to find one of these built-for-CD4 systems to see if it really is plug-and-play, so I'm curious about it. Being that the original cartridge was part of the system design, though, I'd no longer expect it to be so simple without it.
Click to expand...
You could also say the same about using a coil cartridge. I've heard similar ramblings that you can't use a coil cartridge with a vintage system because they didn't have them back then and it would have tiny sound and no bass yet it sure sounds great on my Lafayette.

I am hopeful that in this thread we will come up with an actual article or someone with experience if it runs juice through that tone arm into the cartridge, and if it does run juice will the juice melt your cartridge? It could very well do no damage at all. Who says it does damage? That's what we should find is moot or not. We are here to learn about this and in the process salvage vintage equipment. 🤷
 
I check the forum on a break from work, or after work. It is fun, interesting, and (usually) relaxing. Now it is 94 degrees here and high humidity, Friday after a tough week, and I'm being argumentative. This is not like me, and I am sorry all. Carry on.
 
DudeRocks said:
You could also say the same about using a coil cartridge.
Click to expand...
But, no, and I do mean no, one could not say the same about a coil cartridge, certainly I would not. One could not. Yes the output is lower with MC compared to MM, and yes this can be compensated. Perhaps perceived as a similar sound when both MM and MC carts have RIAA equalization. But not the same sound at all as when a MM or MC cart is used without RIAA.
.
MovingCoil and MovingMagnet both require RIAA eq. SG does not. Different things are different.

I'm off the rails. wtf.
I wonder if ssully can counsel me.
 
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I recommend buying the Panasonic SL-701 service manual:

https://www.analogalley.com/osccart/product_info.php?products_id=2678
I doubt of the power for the Strain Gauge phono cart can be turned off on the SL-701.

If the Panasonic SL-701 turntable + built in CD-4 demodulator are both working, I suggest just buying a $30 replacement stylus for the Panasonic Strain Gauge phono cart (see an above post for a link).

(I can try to answer more questions about CD-4 also)


Kirk Bayne
 
In the first post DudeRocks said he doesn't have the cartridge, so it's not just a new stylus that is required. Still, finding the right cartridge even if it then needs a new stylus might be the simplest way forwards.
 
If you’re feeling particularly DIY, you can block the DC to the cartridge with a capacitor. The value would depend on the input impedance of the preamp, but a bit of experimentation could be fun and a learning experience.

I undersand if such things aren’t on the list of stuff you’re willing to try, though.
 
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