TT Hummmm Problem

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Sonik Wiz

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I am doing some LP ripping of a dozen or so discs in prep for sending them off to a friend. I was re-checking balance & levels last night when I noticed that too familiar 60 Hz hum, about -40 dB below max level. That's definitely high enough to interfere on the low levels of an analog disc.

I am using an AT-PL120 TT with an AT 440 cart, and plugging into my Adcom GFP 555 pre-amp. I am not using the cheapo built in AT pre-amp. Plenty of stuff on the web about hum using that approach.

For those unfamiliar with the AT-PL120 it has two on-off functions on it.
1651594424020.png


The first is he actual power switch, the round knob on the left side. Then there is the square button that starts/stops the turntable rotation. The hum starts when the power switch is turned on, it doesn't matter if the turntable is going or not.

I first suspected a ground loop so I tried different outlets and no change. I have a good earth ground wire available that hooking to the pre-amp chassis ground made it a bit louder. I don't have a proper isolation XFMR but I do have a Variac XFMR that should provide the same purpose. No change.

The hum doesn't come from the pre-amp as it only occurs when the TT power is switched on. It doesn't come from an external magnetic field because if so the hum would be there with the TT switched off.

I have no idea when this problem started. When listening to LP the system is TT> pre-amp> Surround Master> Anthem pre-pro. I'm using the Anthem's internal ADC at 24/48 & sending over SPDIF to my Delta 1010 digital input. For proper levels the pre-amp must be cranked almost all the way up to make the Anthem happy. Normally the Adcom level would be quite a bit lower when just listening to records, and the hum is not noticeable. I have ripped several LP recently and looking at it close between tracks in AA3 the hum is indeed there.

The PL-120 is a good not great TT. The TT & cart combo is about all I can justify cost wise when this is far from my primary audio source. I would like to keep it. Right now I'm considering a power supply cap might be bad. But really this is not a vintage piece of gear. And I don't like working on turntables.

I'm usually good at trouble shooting my systems problems but this one has got me frustrated. At least I know where to go for good tech support! Any fresh ideas is most appreciated.
 

4-earredwonder

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Interesting, SW, that your TT has a detachable power cord but the RCA output cables are fixed which precludes upgrading them to better cables. Could those be the culprit? They probably offer little if any insulation from external 'sources.'

I've always been a champion of upgraded interconnect cables even though some surmise ... they have little, if ANY, effect on the sound. I disagree wholeheartedly....MOST especially apparent on separate components.

As a last resort, you might might to try a 'cheater' plug on your TT power cord. They're not recommended as a rule but might offer a temporary fix.

Good luck ......
 

kap'n krunch

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The screwed up part is that I am sure that it had been working perfectly until it didn't, so I would go through all of the troubleshooting possible and if nothing works I'd get a Technics Linear Tracker (I know I sound like a broken record) like mine, the SL-QL1, they are built like tanks and maintenance is fairly easy---hell, if I can do it, most anyone can!
 

4-earredwonder

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Interesting, SW, that your TT has a detachable power cord but the RCA output cables are fixed which precludes upgrading them to better cables. Could those be the culprit? They probably offer little if any insulation from external 'sources.'

I've always been a champion of upgraded interconnect cables even though some surmise ... they have little, if ANY, effect on the sound. I disagree wholeheartedly....MOST especially apparent on separate components.

As a last resort, you might might to try a 'cheater' plug on your TT power cord. They're not recommended as a rule but might offer a temporary fix.

Good luck ......
Wish I could help bro, but the only time I had hum, was when I tried to use a longer cable and the extra length introduced considerable hum. Once I shortened the cables, it went away. (RCA)
The screwed up part is that I am sure that it had been working perfectly until it didn't, so I would go through all of the troubleshooting possible and if nothing works I'd get a Technics Linear Tracker (I know I sound like a broken record) like mine, the SL-QL1, they are built like tanks and maintenance is fairly easy---hell, if I can do it, most anyone can!

$150 PER HOUR for the free[?] advice ..... split three ways, SW!
 

LuvMyQuad

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Is the hum in both channels?

It seems like it may have to do with the internal pre amp. If you do use the internal pre amp is the hum still there? Is it worse?
 

Soundfield

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Right now I'm considering a power supply cap might be bad. But really this is not a vintage piece of gear. And I don't like working on turntables.
Given the things that you’ve already eliminated that was my first reaction as well (assuming it has an internal RIAA preamp of course –if not, I’m baffled).
 

ar surround

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Did you try checking the wire connections at the cartridge? The tone arm gets moved around when you cue up records, and something may have gone amiss.

The end of my vinyl days occurred when I suddenly developed a ground loop in the phono circuit. I happened out of the blue and I never was able to fix it. Might have been the cartridge or the tonearm wiring as everything else checked out OK. That's when I threw the thing in the trash and sold my LPs. Simply no longer worth the effort.
 

4-earredwonder

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Did you try checking the wire connections at the cartridge? The tone arm gets moved around when you cue up records, and something may have gone amiss.

The end of my vinyl days occurred when I suddenly developed a ground loop in the phono circuit. I happened out of the blue and I never was able to fix it. Might have been the cartridge or the tonearm wiring as everything else checked out OK. That's when I threw the thing in the trash and sold my LPs. Simply no longer worth the effort.

I couldn't stand those ticks, pops and swishes especially during quiet passages. And I had a very expensive TT set up with a separate power supply and vacuum clamp ....... not every record I owned was 180/200g custom pressings.......FAR FROM IT!
 
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Sonik Wiz

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Interesting, SW, that your TT has a detachable power cord but the RCA output cables are fixed which precludes upgrading them to better cables. Could those be the culprit? They probably offer little if any insulation from external 'sources.'
Yes, detachable power cord like on my Pioneer LD player. But every TT I've owned has had fixed RCA output cables so no way to easily change.

If cheap cables were acting like a hum antenna, it would there whether the power was on or off. Only when power is on.

As a last resort, you might might to try a 'cheater' plug on your TT power cord. They're not recommended as a rule but might offer a temporary fix.

The TT has two prong polarized plug on the power cord. No third prong to cheat! At any rate an isolation/variac XFMR would prvide a superior form of "cheating". I've tried that to no avail.
 

Sonik Wiz

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Wish I could help bro, but the only time I had hum, was when I tried to use a longer cable and the extra length introduced considerable hum. Once I shortened the cables, it went away. (RCA)
Were you talking about extra long cables between the TT & pre-amp/AVR? Yeah I can see how that could be problematic. Now my Bassment room is about 25' long with my PC AV workstation in the rear and my audio gear at the other end. I have 6 chs of line level analog audio (beside SPDIF) running the length to my Anthem up front. No hum no hiss. Over the years my system has been pretty free of gremlins.
 
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Sonik Wiz

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Is the hum in both channels?

It seems like it may have to do with the internal pre amp. If you do use the internal pre amp is the hum still there? Is it worse?

The hum is equal in both chs. I have never used the internal pre-amp since my Adcom is full featured pre-amp of high quality. But now you've got my curiosity up. I may give try the AT internal RIAA pre-amp just to see.

Maybe I will need to surgically remove the TT pre-amp & just hard wire the cartridge connection straight through, no switches, etc.
 

Sonik Wiz

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The screwed up part is that I am sure that it had been working perfectly until it didn't, so I would go through all of the troubleshooting possible and if nothing works I'd get a Technics Linear Tracker (I know I sound like a broken record) like mine, the SL-QL1, they are built like tanks and maintenance is fairly easy---hell, if I can do it, most anyone can!

I had a roommate at one time that had a Harman Kardon straight line tracking TT. Boy did I covet that beauty. Then at one point I had a cheap JVC straight line TT that I don't think was worth the $150.00 I paid for it at World Radio. P mount cartridge. Phhhtt.

My AT PL-120 was purchased specifically for a small project I did for a co-worker. He found 4 of those old WW II by his father of records that the soldiers would record on (direct to disc!) & send home to their families. His mom was blind & so this would mean a lot to her. I didn't want some super craptastic Crossley, at least get something good enough I wouldn't be ashamed to play my records on. I got the AT 440 cart & a =nother AT cart with spherical stylus made for playing old timey mono records. The project turned out great & it allowed me to make use again of a rather large & unquie record collection I have. Umm, large is relative. I've seen some of the mega-collections members have on the forum...
 
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DuncanS

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Try detaching the cartridge/headshell, it looks like it should come off easily. Have a check of the wires going to the cartridge, if there are solder joints do they look dull/tarnished? However, it is most likely crimp connectors to the cartridge, hopefully they & the wires look ok. Then re-attach. If the hum is still there, I'd say there is a dry solder joint somewhere, they have a habit of rearing their head suddenly, so in the TT wiring, cartridge, or possibly even in your pre-amp. Sadly not easy to find.
 

gene_stl

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95% of variacs are not isolation transformers. There are some more expensive ones that do have isolation but mostly they just provide variability.
And they will usually brag about it on the label or part number.

Have you run ground wires between the chasis, and reversed the AC line cord (which may be a headache if it is polarized.)? Is the TT plugged into the preamp.
Finally have you opened it and looked to see if there is any capacitor between between each of the two AC lines and the chassis (sometimes called the death capacitor)?

Sometimes removing that will cure such hums.

If it starts when you turn the TT power on and is in both channels , and varies with the preamp volume control, you have some kind of ground loop going to the tonearm cables. See if using the cheapo internal preamp makes it better. I bet it will.
 
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stobo222

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I am doing some LP ripping of a dozen or so discs in prep for sending them off to a friend. I was re-checking balance & levels last night when I noticed that too familiar 60 Hz hum, about -40 dB below max level. That's definitely high enough to interfere on the low levels of an analog disc.

I am using an AT-PL120 TT with an AT 440 cart, and plugging into my Adcom GFP 555 pre-amp. I am not using the cheapo built in AT pre-amp. Plenty of stuff on the web about hum using that approach.

For those unfamiliar with the AT-PL120 it has two on-off functions on it.
View attachment 78512

The first is he actual power switch, the round knob on the left side. Then there is the square button that starts/stops the turntable rotation. The hum starts when the power switch is turned on, it doesn't matter if the turntable is going or not.

I first suspected a ground loop so I tried different outlets and no change. I have a good earth ground wire available that hooking to the pre-amp chassis ground made it a bit louder. I don't have a proper isolation XFMR but I do have a Variac XFMR that should provide the same purpose. No change.

The hum doesn't come from the pre-amp as it only occurs when the TT power is switched on. It doesn't come from an external magnetic field because if so the hum would be there with the TT switched off.

I have no idea when this problem started. When listening to LP the system is TT> pre-amp> Surround Master> Anthem pre-pro. I'm using the Anthem's internal ADC at 24/48 & sending over SPDIF to my Delta 1010 digital input. For proper levels the pre-amp must be cranked almost all the way up to make the Anthem happy. Normally the Adcom level would be quite a bit lower when just listening to records, and the hum is not noticeable. I have ripped several LP recently and looking at it close between tracks in AA3 the hum is indeed there.

The PL-120 is a good not great TT. The TT & cart combo is about all I can justify cost wise when this is far from my primary audio source. I would like to keep it. Right now I'm considering a power supply cap might be bad. But really this is not a vintage piece of gear. And I don't like working on turntables.

I'm usually good at trouble shooting my systems problems but this one has got me frustrated. At least I know where to go for good tech support! Any fresh ideas is most appreciated.
I would check DC resistance between the ground wire and the two RCA cable shields. They should be infinite resistance-an open circuit. In otherwords, the cartridge (-) terminals should only go to the RCA shields, nowhere else. Also, the ground wire should be tied to the preamp's ground terminal, not the outlet-but it seems that you already tried that. If those two checks don't cure the issue, I'd like to know.
 

Sonik Wiz

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I would check DC resistance between the ground wire and the two RCA cable shields. They should be infinite resistance-an open circuit. In otherwords, the cartridge (-) terminals should only go to the RCA shields, nowhere else. Also, the ground wire should be tied to the preamp's ground terminal, not the outlet-but it seems that you already tried that. If those two checks don't cure the issue, I'd like to know.

I can see how my wording in the OP could be confusing. The TT does not have a dedicated ground wire coming from it. I do have a earth ground wire sourced from a cold water pipe connection. It has come in handy sometimes repairing & bench testing to reduce hum/noise when PCB's are out of their metal enclosures.

When I first set up my audio gear yearz 'n yearz ago, I had it connected to the set up & it didn't seem to help or hinder. Then when we switched to digital cable (also a long time ago) I got a hum from I think a ground loop caused by the cable ground. I removed my wire & it was good.

So I took my H2O water pipe ground & attached it to various points in my system trying to eliminate the TT hum. All it did was make it worse haha etc.
 

Sonik Wiz

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Thanks for the reply Pappa Gene.

95% of variacs are not isolation transformers.

So I went looking for isolation XFMR's and the cheapest most bare bones one I could find is this for $50:

Only 850mA output but the TT is only 13 watts. I haven't done the math but it should work. The next step up XFMR has AC plug & socket on it but costs almost double. Either way it's pretty expensive experiment just to see if it works. What do ya think?

Have you run ground wires between the chasis, and reversed the AC line cord (which may be a headache if it is polarized.)? Is the TT plugged into the preamp.

See above about the ground wire. I have plugged the power cord into various other basement outlets assuming somewhere I might be plugging into the same or different leg of 120 V. It made no difference. It is a polarized plug & I haven't trimmed it to switch around yet. I might. The TT was originally plugged into the switched outlet on the Adcom pre-amp. But changing that still made no change.

I haven't opened it up yet... first I will try the internal pre-amp & see what happens.
 

GOS

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The irony of this thread...

Last night I decided I wanted to rip my Peter Frampton Band vinyl. Get Audacity all set up, fire up the TT, and bam. I have feedback. I'm like, huh? Spent 30 minutes doing this and that. Finally, I grabbed my little Soundblaster and moved it about 4 inches, and the feedback went away. WTF was that all about? And, why did it just happen after months of using it with no issues? Odd.

Anyway, back to your regularly scheduled programming....
 
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