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 Post subject: Strapping A Ceramic Stereo Cartridge for Monaural Use
PostPosted: Oct Sat 26, 2019 3:49 pm 
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Joined: Jan Mon 16, 2012 4:15 pm
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Location: Near Brandon, Iowa
I have a 1941 Zenith 10S599 radio/phono console and have just completed the electrical restoration of the radio chassis. It sounds great. Somewhere over the course of the past eight decades, the set lost its original 78 RPM-only changer and acquired what appears to be a 1960s-era V-M style 4-speed turntable. The "new" changer is in pristine shape and functions well (after cleaning/relubing) but the cartridge is dead. Whoever performed the "upgrade" simply tied the left and right outputs of the cartridge together to feed into the (monaural, of course) radio amp.

I have a ceramic stereo cartridge on order which I expect will work OK (the dead cart in the replacement changer was ceramic, although the original mono pickup was probably a salt crystal) but am questioning the way in which the two output channels are merged: by simply tying the left and right cartridge output pins together, could this cause audio distortion due to backdriving? After all, a ceramic cart is a two-way piezo transducer: mechanical motion produces an electrical signal, and vice versa.

My first thought was that a stereo preamp is needed that drives a resistor combiner network- this would prevent the two channels from electrically interacting with one another inside the cartridge. But of course I'd rather not go this route if it turns out it is not necessary. Has anyone merely connected the two cartridge channel output pins together and obtained satisfactory operation?


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 Post subject: Re: Strapping A Ceramic Stereo Cartridge for Monaural Use
PostPosted: Oct Sat 26, 2019 4:45 pm 
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Joined: Jan Mon 18, 2010 2:13 am
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Location: Dayton Ohio
Another option, which will lessen the effect of one driving the other and get higher volt output would be to wire the two in series.

Granted observing phase relationship.

-Steve

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 Post subject: Re: Strapping A Ceramic Stereo Cartridge for Monaural Use
PostPosted: Oct Sat 26, 2019 10:46 pm 
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Joined: Jan Mon 16, 2012 4:15 pm
Posts: 5908
Location: Near Brandon, Iowa
azenithnut wrote:
Another option, which will lessen the effect of one driving the other and get higher volt output would be to wire the two in series.

Granted observing phase relationship.

-Steve


That's an interesting idea... but I don't think that it will work in my case, since the (inexpensive) replacement cartridge that I purchased has the two "signal return" pins electrically tied together inside the cart- so, no possibility for "stacking" the two channels.


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 Post subject: Re: Strapping A Ceramic Stereo Cartridge for Monaural Use
PostPosted: Oct Sun 27, 2019 12:08 am 
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Joined: Jan Mon 18, 2010 2:13 am
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Location: Dayton Ohio
Ahh, yeah, some were manufactured like that.

In that case, I would try two 1000 ohm resistors, one from each channel tied together.
With the high impedance input of the radio's amplifier, it shouldn't diminish the output much if any.
As I recall, the volume control is 2.5 meg ohm.

-Steve

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Radio Interests
-Zenith
-Sparton
-Pre-War FM
Consoles and floor models, the bigger, the better!


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 Post subject: Re: Strapping A Ceramic Stereo Cartridge for Monaural Use
PostPosted: Oct Mon 28, 2019 2:38 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Boston, MA USA
We generally strap the L&R hot leads together for the mono signal hot, and the L&R grounds together for mono ground. We do this for ceramic and magnetic cartridges.

-David


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 Post subject: Re: Strapping A Ceramic Stereo Cartridge for Monaural Use
PostPosted: Oct Mon 28, 2019 12:22 pm 
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Joined: Jan Mon 16, 2012 4:15 pm
Posts: 5908
Location: Near Brandon, Iowa
dberman51 wrote:
We generally strap the L&R hot leads together for the mono signal hot, and the L&R grounds together for mono ground. We do this for ceramic and magnetic cartridges.

-David

That's the way the cartridge was wired when I received the unit. Apparently it worked OK for the previous owner. I'll try it that way when I get the new cartridge and report back on the results. Thanks for the info.


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