Re: Stereo cart wired mono - what new, impedance resistance?
It's not a hypercritical value. Normally, you would get an idea of the value from the manufacture's suggestions in the little pamphlet that would accompany the cartridge (or the jukebox). Far more critical are the tone shaping circuits in the amp itself... which compensate for not only cartridge characteristics, but also record characteristics (with RIAA being one of them, after a certain date) and room characteristics (if the amp offers controls for that).
Hi Forum, My first juke restore was an M100C that had been modified with a G amp and a stereo redhead cart wired in parallel to feed the mono amp input. The amp had not been totally rebuilt but did have a few caps replaced (quite some time before). It also had the cartridge impedance resistor changed to 39K from the original 10K. I’ve since learned that the 10K was the appropriate resistor for the original blackhead carts, so when the conversion was made to the stereo redhead this resistor was changed. My question. Is - why 39K?
I know that the redhead expects a 47K resistor. I’ve seen multiple posts suggesting that when using a stereo cart wired in parallel that this resistance should be doubled - or perhaps even a bit more. I would have thought that the resistor should be changed to the equivalent of two 47K resistors in parallel (47K/2). Agree?
Anyone have any insights why 39K? I changed it back to 10K because at the time I just thought it was a mistake and the output level dropped, which makes sense. I am thinking I should change it back but would really like to understand what value I should use. The mods were clearly made by someone who knew what they were doing, so I doubt the 39K was just a mistake.
Thanks! Yeah I saw that the redheads amps/preamps expect 47k, so was thinking for the stereo wired in parallel it should be half that. But I guess it’s just whatever sounds good? I did read that it’s important not to go too low (or let it drop to no load) or the cart can be damaged. Not sure if this is true. I’ll probably put it back to the 39K then. I recall it sounded fine - I just changed it because it was suggested that I restore it to what was in the schematic not appreciating that the stereo mod might make that not the best advice. Thanks, -steve.
On Feb 14, 2026, at 1:31 PM, js--- via Jukebox-list <jukebox-list@lists.netlojix.com> wrote:
It's not a hypercritical value. Normally, you would get an idea of the value from the manufacture's suggestions in the little pamphlet that would accompany the cartridge (or the jukebox).
Far more critical are the tone shaping circuits in the amp itself... which compensate for not only cartridge characteristics, but also record characteristics (with RIAA being one of them, after a certain date) and room characteristics (if the amp offers controls for that).
Hi Forum, My first juke restore was an M100C that had been modified with a G amp and a stereo redhead cart wired in parallel to feed the mono amp input. The amp had not been totally rebuilt but did have a few caps replaced (quite some time before). It also had the cartridge impedance resistor changed to 39K from the original 10K. I’ve since learned that the 10K was the appropriate resistor for the original blackhead carts, so when the conversion was made to the stereo redhead this resistor was changed. My question. Is - why 39K?
I know that the redhead expects a 47K resistor. I’ve seen multiple posts suggesting that when using a stereo cart wired in parallel that this resistance should be doubled - or perhaps even a bit more. I would have thought that the resistor should be changed to the equivalent of two 47K resistors in parallel (47K/2). Agree?
Anyone have any insights why 39K? I changed it back to 10K because at the time I just thought it was a mistake and the output level dropped, which makes sense. I am thinking I should change it back but would really like to understand what value I should use. The mods were clearly made by someone who knew what they were doing, so I doubt the 39K was just a mistake.
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js＠cimmeri.com -
Steve Swaine