My turntable hates subwoofers

[Chrispy]

It’s an odd problem and seems the obvious tests have been done. Vintage turntables are not complicated I’d open it up and see what’s going on inside.

Good grief what would looking at the turntable do when you get proper 2.0 signal? Or is the OP not saying that it sounds right in 2.0 either? Not sure, but thinking the 2.0 signal would be "special" and involve exam of the tt or cartridge just seems a bit insane to me.

 

[Dure16]

Thank you for all the feedback. I’ll try to answer all the questions here:

@Labhound - your idea about a phase issue seems plausible. If the TT sends the two channels out of phase, would the Denon then sum them to zero for the low frequencies? I’m not sure what kind of wiring mismatch inside the TT would cause that, or how to identify it.

Other answers:

• I can swap the two TTs back and forth and the Technics works every time, while the Realistic never works properly, so I would be surprised if the issue is related to any component other than the Realistic TT. But I’m trying to explore all possibilities.
• The Shure cartridge is only used on the Realistic as my particular Technics uses a different P-mount. So the cartridge is indeed a potential culprit.
• No, I unfortunately was not able to confirm operation with the previous owner.
• Yes, I am sure nothing else in the setup is changing.
• Yes, I am sure I’m using stereo decoding rather than direct or pure direct.

 

[AaronJ]

Good grief what would looking at the turntable do when you get proper 2.0 signal? Or is the OP not saying that it sounds right in 2.0 either? Not sure, but thinking the 2.0 signal would be "special" and involve exam of the tt or cartridge just seems a bit insane to me.

You’re right about something in this thread being insane.

 

[Laika2]

Thank you for all the feedback. I’ll try to answer all the questions here:

@Labhound - your idea about a phase issue seems plausible. If the TT sends the two channels out of phase, would the Denon then sum them to zero for the low frequencies? I’m not sure what kind of wiring mismatch inside the TT would cause that, or how to identify it.

Other answers:

• I can swap the two TTs back and forth and the Technics works every time, while the Realistic never works properly, so I would be surprised if the issue is related to any component other than the Realistic TT. But I’m trying to explore all possibilities.
• The Shure cartridge is only used on the Realistic as my particular Technics uses a different P-mount. So the cartridge is indeed a potential culprit.
• No, I unfortunately was not able to confirm operation with the previous owner.
• Yes, I am sure nothing else in the setup is changing.
• Yes, I am sure I’m using stereo decoding rather than direct or pure direct.

Google turntable cartridge wired out of phase. Endless posts. Seems it drops bass like a rock. Easy fix if that's the issue. Credit to the posters above that brought it up as a possibility. (I was very skeptical) Hope it works.

 

[kyuu]

Google turntable cartridge wired out of phase. Endless posts. Seems it drops bass like a rock. Easy fix if that's the issue. Credit to the posters above that brought it up as a possibility. (I was very skeptical) Hope it works.

Right, makes sense. Bass is generally mono or at least highly correlated between channels, whereas higher frequencies are more likely to be uncorrelated. Therefore, being out of phase affects bass the most. At least, that's my recollection of why phase issues generally affect bass most prominently.

 

[Labhound]

Thank you for all the feedback. I’ll try to answer all the questions here:

@Labhound - your idea about a phase issue seems plausible. If the TT sends the two channels out of phase, would the Denon then sum them to zero for the low frequencies? I’m not sure what kind of wiring mismatch inside the TT would cause that, or how to identify it.

Other answers:

• I can swap the two TTs back and forth and the Technics works every time, while the Realistic never works properly, so I would be surprised if the issue is related to any component other than the Realistic TT. But I’m trying to explore all possibilities.
• The Shure cartridge is only used on the Realistic as my particular Technics uses a different P-mount. So the cartridge is indeed a potential culprit.
• No, I unfortunately was not able to confirm operation with the previous owner.
• Yes, I am sure nothing else in the setup is changing.
• Yes, I am sure I’m using stereo decoding rather than direct or pure direct.

The R47XT is reported to be the RS version of the Shure M95ED. Here's a diagram of the wiring for the M95ED. You could try swapping the cartridge connections on one channel at the head shell and see if that fixes it. If you haven't pulled head shell wires off a cartridge it is delicate work.

 

[raindance]

The cartridge (stylus/cantilever) suspension could have hardened or it is tracking far too light. From what you've posted it's pretty logical that the issue is originating with the turntable, so I don't understand all the rabbit holes.

The challenge with troubleshooting is that it is apples and oranges; two different turntables with two different cartridges.

 

[Dure16]

Problem fixed. I redid the cartridge/headshell wiring with a different diagram than I had used before, and it completely fixed the issue. The bass has returned.

The two TT channels must have been out of phase, and then the Denon was summing the low frequencies to zero for subwoofer output.

Thank you to everyone who jumped in to help. I appreciate it!

 

[Chrispy]

You’re right about something in this thread being insane.

What the OP not describing his situation well or not knowing how to wire the cartridge? I guess that's a bit insane....

 

[Osvaldo de Garay]

Some subwoofers I repaired, adds bothe channels via a low pass filter. So, if one but no both audio inputs are reversed in phase, this add will be destructive, and little or no output will be available. Did you check it?

 

[Balle Clorin]

A am glad OP issue was solved by correcting channel phase.

Do not forget that a subwoofer will amplify a lot of low frequency garbage if the RIAA is not applying a subsonic filter, like this. Every RIAA should have a steep subsonic filter