Low volume on one stereo channel

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sumo guy
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Low volume on one stereo channel

Post by sumo guy » 21 Jan 2020 19:32

I recently acquired 1964 Fisher D-39 Diplomat II console that when I use the AT6 Mk II turntable in it, I have very low volume on one stereo channel. I have equal volume when using the FM stereo tuner or the stereo aux inputs.

I have swapped the amplifier phono input connections which has resulted in the issue switching sides. This tells me that the issue is not the amplifier or phono inputs.

I then swapped the left and right cartridge connections and the issue switched sides again. This tells me there is not an issue with the turntable's circuitry.

When I swapped connections I cleaned all the connections with DeoxIT D5.
The cartridge wires don't seem to be binding where they exit the tone arm and go down in to the plinth.
The stylus is a new old stock Pfanstiehl 159-DS77. Stylus is flipped with "LP◆" side of the tab facing up.
The stylus' vertical tracking pressure has been set to 3 grams using a digital scale.
I don't have a first surface mirror but with a relatively thin second surface mirror the stylus' azimuth seems to be correct.

At this point I'm thinking I either have a bad ceramic cartridge (Astatic 17) or unequal left-right groove pressure on the stylus. From what I can tell and have been told there is no anti-skate adjustment (mine does not have a "bias compensator" which I assume is what Garrard calls it's anti-skate feature that was added on Mk IIa).

The AT6 Mark II manual refers to a "cone bearing adjustment" screw near the tonearm but does not say what it does or how to adjust it. Does this adjust the lateral friction and drag?

Any way to test or "fix" my cartridge besides swapping it with another one?

Just trying to hit the easy stuff before getting in to buying a new ceramic cartridge, converting to a MM cartridge, or going in to a complete disassembly, cleaning, and lubrication which I know I should do eventually.
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A70BBen
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Re: Low volume on one stereo channel

Post by A70BBen » 22 Jan 2020 00:18

Bad ceramic element in cartridge, or bad internal connection between ceramic element and output pins. Replace cartridge.

Cone bearing adjustment is for the vertical-motion pivots and is not critical as those pivots are spring-loaded ball bearings.

A70BBen
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Re: Low volume on one stereo channel

Post by A70BBen » 22 Jan 2020 02:53

Clarification: the cone bearing adjustment IS critical on EARLY production AT6 which did not have spring loaded vertical.pivots. On your AT6 Mk II it is noncritical

sumo guy
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Re: Low volume on one stereo channel

Post by sumo guy » 23 Jan 2020 16:39

A70BBen wrote:
22 Jan 2020 00:18
Bad ceramic element in cartridge, or bad internal connection between ceramic element and output pins. Replace cartridge.

Cone bearing adjustment is for the vertical-motion pivots and is not critical as those pivots are spring-loaded ball bearings.
First of all, a big Thank You to A70BBen for all your guidance and education.

I looked up my cartridge a saw that good 350MV used ones were running around $100. That got me wondering if I should move to a modern MM cartridge and add a preamp for the same or less money, but I'd need to find out if the Fisher 290-T amp has isolated mains first.

Well I thought I'd give everything a good second time over and started to recheck azimuth, tracking force, etc. Nope, same as first tested. Then in desperation I did something again that I had done before. With a "junk" record on I pressed down on the headshell both vertically and laterally thinking perhaps the 3 gram vertical tracking force I had read my cartridge should use was wrong, i.e. too light. Well, I must have "seated" the needle in the cartridge because it started playing with equal left and right stereo channel volume. \:D/ It sounds great and I can't wait to get listening now.

A70BBen
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Re: Low volume on one stereo channel

Post by A70BBen » 24 Jan 2020 05:30

What you may have actually done is to seat that channel's ceramic element in its electrical connection to its output pins. Whatever, enjoy it!

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