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

[jaybird100]

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

Isn't there a switch, somewhere on the turntable (check the back and bottom of the unit) to turn off the power supply? It should be near the CD-4 separation adjustment controls.

 

[DudeRocks]

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.

I've seen mention of people taking out the demodulator for a standalone DIY box. But I haven't stumbled on any instructions yet. With this SL-701 I'm going to have to solder on some new cart connector pins today, never done this before so this is a new project. The ebay seller broke the ones that were on there when he sold the cart separately. This is one of those listings that you see a guy playing a video of it working but they send it to you with missing parts. Sadly the dude inadvertently broke the pin connectors. I testing this out some months ago just rigging up the wires direct to a cheap cart then a quad cart. It took months to get new full tonearm cables sent in as they don't come from in the US, and wound up buying the little pins themselves which took 2 days to come in. Then I spend all my time online looking for answers, rather than testing

 

[Owen Smith]

The ebay seller broke the ones that were on there when he sold the cart separately.

I hate it when sellers split something up like that. They had everything you need, but split it up (presumably thinking they could make more) and broke something in the process. Sigh.

 

[DudeRocks]

Isn't there a switch, somewhere on the turntable (check the back and bottom of the unit) to turn off the power supply? It should be near the CD-4 separation adjustment controls.

I'm looking at the inside for this now, no switch on the outside.

 

[MidiMagic]

I have worked with strain gages in kinesiology labs.

A strain gage is basically a Wheatstone bridge with the strain elements on opposite sides of the bridge. The elements change resistance as their lengths change.

Ours had a 12-volt power supply and elements with a 1000 ohm resistance of the elements. The output then goes to a sensitive DC amplifier.

No matter what kind of cartridge you have, the RIAA de-emphasis must be somewhere in the audio chain to the amp, because the RIAA emphasis is on the record.

Some ceramic cartridges have their ceramic bars cut to provide the equalization. Magnetic cartridges need external de-emphasis. I don't know what the strain gage has, but it must be there.

This might use a form of phantom power similar to that which electret mics and cartridges use.

Replacing the connections to the arm wiring should let you convert it to a regular cartridge.

 

[Doug G.]

That turntable came with a semi-conductor (strain gauge) cartridge so the DC voltage WILL be there at the cartridge terminals. it has to be or the cartridge wouldn't work and there would be NO output from it. If there is no switch present to select a strain gauge cartridge or MM cartridge, it will always be set for a strain gauge cartridge.

As Kirk said, the outboard demodulators from Panasonic or Technics, like the SH-400, have a switch to select between using a strain gauge cartridge or MM cartridge. The DC voltage is switched OUT and the RIAA circuit is switched IN for a MM cartridge.

The warning is there to be sure the switch is set correctly or damage can occur to MM cartridge if the switch is set for a strain gauge cartridge. I have inadvertently left the switch set for a strain gauge cartridge when installing a MM cartridge (I, of course, corrected the error as soon as I realized what I had done) and no harm has happened (it's not that much current) but I guess it COULD happen. Follow the rules/instructions.

A MC cartridge can be used for CD-4. There is no reason for one NOT to work as long as its response is satisfactory and its output is stepped up to be in the MM range before it's fed to the demodulator. I know Linda uses one.

As far as RIAA, a strain gauge cartridge has a response roughly the opposite of that on the record so there is no real need for further correction. The DC voltage is on the same leads as the signal leads to/from the cartridge so it is a phantom supply, although that is really a misnomer.

Doug

 

[MixerRog]

I have a complete CD4 & SQ Pro-Logic playback system with Sony Turntable with installed Strain Gauge cartridge for sale. See my listing at Quad Items

I included details of the Strain Gauge Cartridge in the pictures there also -- see my latest post there for the most pictures including the 2 decoders.

Rog

 

[DudeRocks]

I hate it when sellers split something up like that. They had everything you need, but split it up (presumably thinking they could make more) and broke something in the process. Sigh.

Little soldering and I've got it up and going! I'm kind of back and forth on another thread. Sadly, the best way to find some of these answers is to hijack old threads. Probably drives the older members nuts. I'm trying to get a photo of one of these switches on another Panasonic board to see if maybe it's just not included and crossing my fingers that the circuits might be on the board after all.

 

[DudeRocks]

I have a complete CD4 & SQ Pro-Logic playback system with Sony Turntable with installed Strain Gauge cartridge for sale. See my listing at Quad Items

I included details of the Strain Gauge Cartridge in the pictures there also -- see my latest post there for the most pictures including the 2 decoders.

Rog

Perhaps you might want to purchase this SL-701? I already have a really good turntable and two quadraphonic carts that work well on it. I wasn't expecting this TT to be locked into one specific cart type this way. It's a shame really. Thing works fine otherwise. Full auto too!

 

[aludra]

I believe the Strain Gauge cartridge also has a channel out of phase as well as needing a DC voltage.....Might explain you not getting any bass in the stereo mode

​

 

[kap'n krunch]

that was the first kinda real TT I ever encountered, my stepfather had it but unfortunately, it ran quite faster than normal and there was no way to repair that...

 

[MixerRog]

I believe the Strain Gauge cartridge also has a channel out of phase as well as needing a DC voltage.....Might explain you not getting any bass in the stereo mode

​

Yes, the output of the cartridge is out of phase so the phone preamp must correct for this as shown in the easily built schematic diagram or when using the proper CD4 playback circuit like mine has.

Rog

 

[MixerRog]

Perhaps you might want to purchase this SL-701? I already have a really good turntable and two quadraphonic carts that work well on it. I wasn't expecting this TT to be locked into one specific cart type this way. It's a shame really. Thing works fine otherwise. Full auto too!

I already have plenty of great turntables including a Pioneer PL-630 with my own built in phono preamp so I can record directly to a computer & two Sony PS-LX520 fully automatic, direct drive, quartz lock, linear tracking turntables that was there top model from about 1985 to 1991. You can read about the PS-LX520 at Sony PS-LX520 I also have a cheaper Sony PS-LX250H turntable. I will be selling these Sonys soon after I finish installing new belts that I have for the tone arm drive system.

Rog

 

[MidiMagic]

that was the first kinda real TT I ever encountered, my stepfather had it but unfortunately, it ran quite faster than normal and there was no way to repair that...

The turntable was for 50 Hz power and you were running it on 60 Hz.

I just realized that I have a Panasonic RD-700 with a CD-4 demodulator. But I have no cartridge and no spindles, Is this the same thing? There is a 2-channel output.

 

[DudeRocks]

The turntable was for 50 Hz power and you were running it on 60 Hz.

I just realized that I have a Panasonic RD-700 with a CD-4 demodulator. But I have no cartridge and no spindles, Is this the same thing? There is a 2-channel output.

I did a quick Google search for this and there's too many things that come up that are not turntables. But if you have an internal CD4 do some research on it, they were pretty slick to lock it down to one kind of cart. However, yours may have a switch that will allow a regular cart to work as well. I'm not so lucky with this SL-701.