TT Hummmm Problem

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MidiMagic

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Oh the hums I have encountered as a service tech. Here are some things to think of:

1. Ungrounded turntable chassis.
2. Too many connections to ground to the same component - a ground loop.
3. Too many ground connections between components - a ground loop.
4. Hum field picked up by the magnetic cartridge (a wall wart transformer or that VARIAC). The hum level might change when you move the arm.
5. Phono to preamp leads are too long. Move the preamp next to the phono.
6. Is rumble being mistaken for hum? If the hum quits when you lift the stylus, it's rumble.
7. Is there some item (e.g. an electric clock (motor), fan, or fish tank pump) that is vibrating the table the turntable is on?
8. The hum was intermittent - it happened only when the house furnace blower was running. It vibrated the floor and the table the turntable was on.
9. This setup had balanced line cables between preamp and powered speakers. But a cell phone charger was next to a balancing transformer.

My favorite hum poser was one where the owner and I were trying everything to get rid of hum in the right channel. Then, after 3 hours of testing, I noticed the hum was still there when the amp was turned off. Someone in the next apartment had hung an electric clock (motor driven) on the other side of the wall.
 
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quadsearcher

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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.
CATV should be grounded before it enters the house.
If there's a ground path between it and the system, disconnect the cable and try. I've seen some strange things with poor ground on cable coming off the pole.
 

gene_stl

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This would be better although a little more money. Try running a wire from the preamp ground terminal to various points on the tt AND reversing the plugs and/or using the preamp AC outlets. (I know you already know to do all that stuff)

Running ground wires DOES sometimes make it worse. Probably increases the hum voltage at the input where there is gain.

Could it have been there all along but earlier you weren't turning the gain up so high???
 

Sonik Wiz

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CATV should be grounded before it enters the house.
If there's a ground path between it and the system, disconnect the cable and try. I've seen some strange things with poor ground on cable coming off the pole.

Right you are & that's how it is. From the pole the CATV coax connects to a terminal block and is directly earth grounded at that point. Then into a 2 way splitter & into the house. No other splitters inside. One split off coax goes to my Motorola SB modem, and the other goes to the only TV in the house in the family viewing. Yup, one TV. We used to have a bunch more but being a retired family of 2, we watch a 55" Sammy OLED for casual viewing. In my Bassment I have a Panasonic projector but no cable box. I sent that back a couple of years ago & switched to an OTA TV tuner. Works very well, 62 chs free. And I only watch real TV a couple of times a year anyway on the big screen so it works out nicely.

At any rate I'm saying CATV ground loops is out of consideration cuz it's out my system.
 

Sonik Wiz

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This would be better although a little more money. Try running a wire from the preamp ground terminal to various points on the tt AND reversing the plugs and/or using the preamp AC outlets. (I know you already know to do all that stuff)

Running ground wires DOES sometimes make it worse. Probably increases the hum voltage at the input where there is gain.

Could it have been there all along but earlier you weren't turning the gain up so high???

I just tried it using the internal pre-amp & the hum is still there! :mad: This time I even bypassed the Adcom pre-amp & plugged the TT direct into the analog inputs on my Anthem. Yup still there. I think if it was a ground loop or external interference it would be there constantly using the TT but is absolutely silent when the TT power is turned off. ????

Maybe the hum was there longer than I thought. In casual listening my Adcom volume would be set about 1:00. This is a good match for the SMv2 with it's input level on max, as suggested by Chucky. Using the Anthem to convert A>D I get good levels in AA 3 when the Adcom is at max, and then I get the hum. It is loud enough I even can see it on AA3 level meters. But then I have copied records to my HDD many times before & didn't notice it. Maybe some sake will help....
 

stobo222

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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.
You need to keep the subjects of cable system grounding and turntable grounding seperate. Your turntable issue is related to the lack of a chassis ground on the turntable itself. This is standard operating procedure for turntables, and yours SHOULD have a seperate turntable chassis ground, and as stated before, the RCA shields should not be connected to the TT chassis. Get back and lemme know!
 

ar surround

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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.
@Sonik Wiz , did you every try checking the cartridge / headshell wiring like both Duncan and I had suggested earlier? Old turntable wiring is notorious for having an incipient problem suddenly manifest itself.
 

Wagonmaster_91

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OK, I know this is a long shot, but it is a really cheap & easy to test and it worked recently for a friend of mine when he set up his TT. Wrap a small piece of aluminum foil around the audio plugs where they plug into the pre-amp. That extra bit of shielding fixed my friend's hum problem. Worth a try.
 

Sonik Wiz

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You need to keep the subjects of cable system grounding and turntable grounding seperate. Your turntable issue is related to the lack of a chassis ground on the turntable itself. This is standard operating procedure for turntables, and yours SHOULD have a seperate turntable chassis ground, and as stated before, the RCA shields should not be connected to the TT chassis. Get back and lemme know!

Yeah, maybe it should have a chassis ground but it doesn't. The base is a heavy weight plastic resin composite. And the top is a sturdy plastic of some sort as well. No mertal chassis ground points. Who knows how the metal tone arm is grounded. I will have to open it up and see what ground points could be used. The only TT I've ever had with a separate ground wire was a Phillips 212 TT.
 

Sonik Wiz

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@Sonik Wiz , did you every try checking the cartridge / headshell wiring like both Duncan and I had suggested earlier? Old turntable wiring is notorious for having an incipient problem suddenly manifest itself.

I am taking a break from this tonight. I will say this about 10 years old, not vintage by any means. I bought it just about the time AT was adding USB outputs to it, that I certainly don't need.
 

Sonik Wiz

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Sonik my old dual 1225 turntable has a ground wire the last time I had it hooked up.

Or you could put the aluminum foil on your head and see if that helps. :unsure:
Of course I've tried aluminum foil on my noggin. Squelch's the rattle and hum in my brain to about -13dB. Doesn't' do anything for the TT.
 

par4ken

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I think that you said that this turntable has a built in RIAA preamp. If that is the case the metal parts are likely grounded there. So no need of the ground wire. If you are bypassing that internal preamp then you would need a ground wire back to your pre-amp/receiver/AVR.
 

Sonik Wiz

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Many thanks to everyone for the insights & advice. I have tried most all of the suggestions but still had that slight hum when power was switched on. So I finally bit the bullet & opened up the turntable for a look around. This is a DC servo-controlled direct drive TT so I knew it was more complex then a simple synchronous motor belt drive, but there was even more 'tronic stuff inside than I anticipated:

TT 1.jpg


The tone arm port is on the lower right side. Immediatley the emerging teeny tiny cartridge wires are shielded & grounded to the green board just above. I noted that it was not 100% shielded but a metal braid. It didn't occour to me to carefully enclose that section with a bit of aluminum foil until I put it back together. Oh well.

The transformer has two secondaries & the only filter caps I could identify were mounted & glued to the actual motor PCB & on the top side of the large PCB on the right of the photo. So I opted for simply adding a real ground wire.

To the left of where the RCA output cables are is a common ground point with a little spring on top. No soldering!

After re-assembly I tried connecting the new ground wire to the pre-amp grounding screw & to a proper earth ground. And.... the hum was even worse!! :confused::mad: Significantly. So now I am back to where I started.

I guess I could try the isolation XFMR Gene suggested but that's a $100 experiment. So maybe no. I think next to try is to turn down the Adcom pre-amp level until the hum is inaudible & then restore gain digitally in my audio editor. Something tells me the hum is there & will be noticeable again whether I set the gain to appropriate level early in the signal chain or after capturing.

Well, bummer. I really can't justify spending $$ on another TT. And I need to get these dozen or so records shipped to a friend. Maybe a sharp 60 Hz notch filter....
 

par4ken

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Many thanks to everyone for the insights & advice. I have tried most all of the suggestions but still had that slight hum when power was switched on. So I finally bit the bullet & opened up the turntable for a look around. This is a DC servo-controlled direct drive TT so I knew it was more complex then a simple synchronous motor belt drive, but there was even more 'tronic stuff inside than I anticipated:

View attachment 78741

The tone arm port is on the lower right side. Immediatley the emerging teeny tiny cartridge wires are shielded & grounded to the green board just above. I noted that it was not 100% shielded but a metal braid. It didn't occour to me to carefully enclose that section with a bit of aluminum foil until I put it back together. Oh well.

The transformer has two secondaries & the only filter caps I could identify were mounted & glued to the actual motor PCB & on the top side of the large PCB on the right of the photo. So I opted for simply adding a real ground wire.

To the left of where the RCA output cables are is a common ground point with a little spring on top. No soldering!

After re-assembly I tried connecting the new ground wire to the pre-amp grounding screw & to a proper earth ground. And.... the hum was even worse!! :confused::mad: Significantly. So now I am back to where I started.

I guess I could try the isolation XFMR Gene suggested but that's a $100 experiment. So maybe no. I think next to try is to turn down the Adcom pre-amp level until the hum is inaudible & then restore gain digitally in my audio editor. Something tells me the hum is there & will be noticeable again whether I set the gain to appropriate level early in the signal chain or after capturing.

Well, bummer. I really can't justify spending $$ on another TT. And I need to get these dozen or so records shipped to a friend. Maybe a sharp 60 Hz notch filter....
I've never been a fan of Japanese turntables, and prefer belt drive as well. I wouldn't rule out looking for another turntable, always lots for sale on eBay. Sadly you don't often find the bargains there that you once did! But it never hurts to keep looking, thrift stores, yard and estate sales as well.

You can always remove the hum in software but it's still best to prevent it in the first place!
 

gene_stl

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Sonik
I have a pal here a young extremely keen audio nut who has LOTS of turntables here in St. Louis. I am sure he would loan you one. I might have one I could loan you in the basement.

The only way to reduce the hum in software is to use a Fourier Transform filter on the files which can pick out a particular frequency and its harmonics.
This sort of thing is done in imaging software to remove things like photo lithography dot patterns. Might be a decent solution and I wouldn't be surprised if you could find something that could do that in Audition. It certainly is in Photoshop.

Is the deck pictured, lunimum or plastic. You could ground it. I would ground it but NOT connect it to the preamp as someone mentioned earlier.
I think you may have leakage developing in that power transformer. It is nice to see that there even IS a power transformer rather than a switching power supply which I love when they work and despise when they don't work. Usually difficult to repair and get lit again.

I don't think the foil trick would work either. I doubt you are picking it up from the fine tonearm wires. try running a ground from the transformer frame screws to earth ground.
 

Sonik Wiz

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I've never been a fan of Japanese turntables, and prefer belt drive as well. I wouldn't rule out looking for another turntable, always lots for sale on eBay. Sadly you don't often find the bargains there that you once did! But it never hurts to keep looking, thrift stores, yard and estate sales as well.

You can always remove the hum in software but it's still best to prevent it in the first place!

Thanks Ken. I can't say I'm so much of a fan of Japanese turntables but I am even less of a fan of belt drive units. The belts wear out. I figure I would have the same luck with replacing as I always have had with R2R belts: By the time I need a new one they are at least very hard to find, maybe impossible.

Having said that one of my favorite TT's from my past was the humble belt drive Phillips 212:

1652375906075.png


The only tone arm adjustment it had was tracking weight & anti-skate, but it competed favorably with the ubiquitous Acoustic Research table of its day. And groovy green touch sensitive switches!
 
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gene_stl

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I liked the Philips stuff. They had a great Preamp that was actually made by CM labs. Great sounding, and good measuring, for a reasonable price.
Those touch buttons were very kewl.

I reccomend opening it again. Hook it up to your system while its open and upside down. try unplugging the blue wires from the motor board and see whether that makes a difference. Do the same with the power wires running to the preamp USB board. The "phono cartridge pass through" may or may not be direct. They may have stuck a buffer in there in which case you won't get any signal if you pull that yellow power line but it may tell you something about the hum.

I do like Japanese turntables. I have three of them.
 
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Sonik Wiz

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Sonik
I have a pal here a young extremely keen audio nut who has LOTS of turntables here in St. Louis. I am sure he would loan you one. I might have one I could loan you in the basement.

The only way to reduce the hum in software is to use a Fourier Transform filter on the files which can pick out a particular frequency and its harmonics.
This sort of thing is done in imaging software to remove things like photo lithography dot patterns. Might be a decent solution and I wouldn't be surprised if you could find something that could do that in Audition. It certainly is in Photoshop.

Is the deck pictured, lunimum or plastic. You could ground it. I would ground it but NOT connect it to the preamp as someone mentioned earlier.
I think you may have leakage developing in that power transformer. It is nice to see that there even IS a power transformer rather than a switching power supply which I love when they work and despise when they don't work. Usually difficult to repair and get lit again.

I don't think the foil trick would work either. I doubt you are picking it up from the fine tonearm wires. try running a ground from the transformer frame screws to earth ground.

Hey Gene
The deck base is some sorta heavy weight faux granite composite stuff. The top part is thick & quite sturdy ABS plastic. There's not much to ground too!

I could try grounding specifically the XFMR. Why not at this point? Now that I've had a look ath TT's interior I think I will try one more thing as a last resort. I will disconnect the phono cart wiring from the internal pre-amp & install higher quality cables to output the signal direct, just like a regular TT. I might try Blue Jean Cables LC-1 low cap audio cables but for 3 feet it's $45. Which if your Ralphie it's dirt cheap but not for me. I have an abundance of Monster Interlink 100 which is 2 conductor twisted pair with shield terminated at one end only. Dunno what the cap is on that. I do have a cap meter so I can check that. These are flying leads out the base so out comes the 'ol soldering gun.
 
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