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Old 1st October 2012, 10:32 PM   #11
wanders is offline wanders  United States
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I'd appreciate suggestions on how to test the cart. If it's damaged, I need to know; if it's ok, I need to be more careful.

Audibly, the sound quality from the m/c-phonostage is commendable, but with more hum than from any other source. The separate tonearm motor is extremely noisy (amplified) when in operation.

Thanks,
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Old 1st October 2012, 11:12 PM   #12
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Your tonearm has a motor...?
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Old 5th October 2012, 04:54 PM   #13
kevinkr is offline kevinkr  United States
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What sort of turntable is the Denon mounted on? Lift motor assemblies are probably not the friendliest neighbor for a cartridge with a typical maximum output of 250uV. Strikes me that the arm and other cartridge wiring may not be that suitable for an LOMC. This thing doesn't also happen to have a mute switch that shorts the cartridge when lifting and returning to home position?

Does the hum vary depending on proximity to the platter?
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Old 5th October 2012, 06:59 PM   #14
wanders is offline wanders  United States
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Quote:
Originally Posted by kevinkr View Post
What sort of turntable is the Denon mounted on? Lift motor assemblies are probably not the friendliest neighbor for a cartridge with a typical maximum output of 250uV. Strikes me that the arm and other cartridge wiring may not be that suitable for an LOMC. This thing doesn't also happen to have a mute switch that shorts the cartridge when lifting and returning to home position?

Does the hum vary depending on proximity to the platter?
I use a mid 70’s vintage Pioneer PL-570, fully automatic table with a medium-high mass, s-shaped tone arm. Among vintage vinyl users, the PL-570/DL-103R (m/c) combo is thought to be highly desirable. There are two dc motors, a direct drive motor for the platter and a separate motor to drive the tonearm during automatic functions. The tonearm motor operates only to move the tonearm to and from the record. The mechanical functions were considered leading-edge at the time and are pretty complex. There is a muting switch that triggers off a cam driven by the tonearm motor. The switch shorts both channles (i.e., the cart) – at the muting switch – during the entire period that the tonearm is in motion. All mechanical functions and the muting switch work properly.

Using the m/c setup (cart to phono amp to preamp aux), there is hum that is not present from any other input source possibility: like cd to aux; or m/m to the preamp phono circuit. The m/c hum is not audible with sound present; but it is audible with no signal in the circuit or during dead space on a record. However, the hum is very loud during tonearm operations. A note, the tonearm (Warren) motor is a weak spot in this turntable. They are NLA from any source and difficult to repair. There’s a guy on eBay who specializes in repairing these small PL-570 motors and he repaired mine. It now works properly, but is noisier than it was designed to be.

It was suggested that there is a grounding problem in the table which is exacerbated by the very high gain phonostage and I’ve been probing and testing to try to it. I was stumped because on the bench, the muting switch always tested properly. When I reassembled the table, it tested fine with the m/m cart, but not with the m/c cart. That was the reason for my op. The hum does not vary relative to proximity, it varies directly with preamp volume.

Appreciate your interest.
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Old 6th October 2012, 12:31 AM   #15
kevinkr is offline kevinkr  United States
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The likely issue is pick up in all of tone arm wiring, bear in mind that the DL-103R has about 20 - 26dB less output than the typical MM cartridge, but noise pick up should in theory be somewhat mitigated by the very low output impedance of this cartridge.

You should probably verify that the phono stage is sufficiently quiet with the phono cables disconnected and the inputs shorted, from there you can determine what the exact source of pick up might be.

I suspect the large exposed loop area of the typical Japanese tone arm muting switch and wiring may be the culprit here. I'm sure that shorting switch was probably put there in order to deal with EMI from the tone arm cuing motor and worked fine with a good motor and MM cartridge.
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Old 6th October 2012, 02:57 PM   #16
wanders is offline wanders  United States
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The likely issue is pick up in all of tone arm wiring ... .
That makes sense. I doubt the cart is damaged, or there is a bad ground connection, or any other quick fix. I'll start with the phonostage and work back from there. I'll post when I learn more.

Thanks again
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Old 6th October 2012, 09:24 PM   #17
kevinkr is offline kevinkr  United States
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Good luck! Report back when ready...
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Old 7th October 2012, 12:17 AM   #18
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by kevinkr View Post
The likely issue is pick up in all of tone arm wiring, bear in mind that the DL-103R has about 20 - 26dB less output than the typical MM cartridge, but noise pick up should in theory be somewhat mitigated by the very low output impedance of this cartridge.

You should probably verify that the phono stage is sufficiently quiet with the phono cables disconnected and the inputs shorted, from there you can determine what the exact source of pick up might be.

I suspect the large exposed loop area of the typical Japanese tone arm muting switch and wiring may be the culprit here. I'm sure that shorting switch was probably put there in order to deal with EMI from the tone arm cuing motor and worked fine with a good motor and MM cartridge.
One of the reasons why i tend to stay away from low output cartridges , pre-preamp is very sketchy and requires a lot of patience...
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Old 7th October 2012, 12:29 AM   #19
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Are you using a pre-preamp or input transformer for your low output MC?

Mike
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Old 7th October 2012, 12:31 AM   #20
kevinkr is offline kevinkr  United States
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I've got two Ortofon SPUs and a Denon DL-103D, which are used with various SUTs, and no problems at all with noise on my various arms. The common thread is that everything is well shielded and there is no electronics in proximity to the arms.

In a case like this the whole arm will probably need to be rewired without that mute switch connected. Good idea to check and make sure the arm tube is grounded as well, this has caused me some mischief in the past.
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