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Old 9th Jun 2024, 6:31 pm   #21
Boulevardier
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Default Re: Pioneer PL-12 Ground Wire?

Funny that! I very nearly asked if you'd tried completely disconnecting the turntable from the amplifier to see if the hum was still there when you'd done it.. Never overlook the most basic tests, I suppose.
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Old 9th Jun 2024, 10:33 pm   #22
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Default Re: Pioneer PL-12 Ground Wire?

It's interesting - if I turn on the subwoofer when aux-1 (to phono stage) is selected then the hum returns. If I switch to anything else (CD, tuner) - no hum. Subwoofer off - no hum anywhere. That suggests to me no issue with the connections between amp and subwoofer. I've tried switching plug sockets etc. but no difference. Not a huge deal as TT works well without sub - more curious now than majorly bothered.
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Old 10th Jun 2024, 7:11 am   #23
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Default Re: Pioneer PL-12 Ground Wire?

If you've got a powered subwoofer which is connected to mains earth you may be creating a ground loop. The phono input is by far the most sensitive, which is why there's where you hear the hum
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Old 10th Jun 2024, 8:23 am   #24
Paulietheboy
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Default Re: Pioneer PL-12 Ground Wire?

Quote:
Originally Posted by Gabe001 View Post
If you've got a powered subwoofer which is connected to mains earth you may be creating a ground loop. The phono input is by far the most sensitive, which is why there's where you hear the hum
Thank you, Gabe. Would you be able to suggest a way to reduce/remove it? I read a couple of things about swapping mains plugs around, keeping cables apart etc. but no change as yet. I've also seen something advertised called a ground loop isolator - they seem to range from small change to serious money price wise.

All the constituent parts of my set up are relatively modern - it's only the TT that might be classified as vintage. Is the older mains cabling (i.e. 2 and not 3 and so non-earthed) plug a factor?

Total novice here so forgive the questions.
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Old 10th Jun 2024, 9:55 am   #25
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Default Re: Pioneer PL-12 Ground Wire?

Hi Paul

Until you mentioned that you used a sub, who knew what else might be in the mix.

I thought you would miss the sub working on vinyl and so the problem itself hasn't gone away.

If there is no hum when the pre-amp is switched out of the circuit then the TEAC amp can be excluded from the cause.

May I suggest you go back to basics using post 19 or similar to narrow down where the problem is.

Chris
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Old 10th Jun 2024, 10:10 am   #26
Paulietheboy
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Default Re: Pioneer PL-12 Ground Wire?

Thank you, Chris. I shall do that once the working day is done. Your post makes sense and I need to look before I leap sometimes. Despite being nearly 60 I still suffer from the same mixture of excitement and impatience when setting up new things - you'd think that I'd have learned by now!
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Old 10th Jun 2024, 10:26 am   #27
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Default Re: Pioneer PL-12 Ground Wire?

It would be good if you could post a drawing of what devices you've got connected and indicate which of those have a 2-core and which have 3-core mains cable. I still suspect a ground loop caused by the sub, but there are other possibilities of course
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Old 10th Jun 2024, 10:55 am   #28
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Default Re: Pioneer PL-12 Ground Wire?

I was just about to suggest the above. A drawing of all the parts and how they connect will be very helpful. For a while I've run my TT with a crocodile clip lead from the tonearm base to a case screw on the power amplifier while I work out how the loop is being created!

Theoretically simple (two points that are supposed to be at the same potential of 0V are instead not quite the same, meaning a current flows between them, which is converted by the loudspeakers into sound) as there are so many variations in circuit design and grounding schemes, particularly in home-made equipment, hum can be very difficult indeed to track down. Something as simple as a turntable plugged into one socket with a small current flowing via the shield of the phono leads to the amplifier casing referenced to another socket could cause a ground loop.

If your ground lead has been removed by a previous owner it could well have been their solution to their own hum problem.

There's no need to purchase anything snake-oil related. Incidentally, if you want some solid engineering amusement, have a look at the long-running (178 pages...) 'Audiophoolery Thread' which demolishes any of the crapulous products available to separate fools and their money.

Looking before you leap is good. I'm certainly guilty of posting on here before fully thinking through the problem, finding that the act of typing is a good way to be forced to logically attack it.

Can you post the original jpeg of your tag strip in the turntable? The forum compression software means the 'phone screenshot is too small for me to make it out.
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Old 10th Jun 2024, 12:02 pm   #29
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Default Re: Pioneer PL-12 Ground Wire?

Quote:
Originally Posted by Uncle Bulgaria View Post
I was just about to suggest the above. A drawing of all the parts and how they connect will be very helpful. For a while I've run my TT with a crocodile clip lead from the tonearm base to a case screw on the power amplifier while I work out how the loop is being created!

Theoretically simple (two points that are supposed to be at the same potential of 0V are instead not quite the same, meaning a current flows between them, which is converted by the loudspeakers into sound) as there are so many variations in circuit design and grounding schemes, particularly in home-made equipment, hum can be very difficult indeed to track down. Something as simple as a turntable plugged into one socket with a small current flowing via the shield of the phono leads to the amplifier casing referenced to another socket could cause a ground loop.

If your ground lead has been removed by a previous owner it could well have been their solution to their own hum problem.

There's no need to purchase anything snake-oil related. Incidentally, if you want some solid engineering amusement, have a look at the long-running (178 pages...) 'Audiophoolery Thread' which demolishes any of the crapulous products available to separate fools and their money.

Looking before you leap is good. I'm certainly guilty of posting on here before fully thinking through the problem, finding that the act of typing is a good way to be forced to logically attack it.

Can you post the original jpeg of your tag strip in the turntable? The forum compression software means the 'phone screenshot is too small for me to make it out.
Are these any better?

I'll also post a drawing along the lines of Gabe's post also in a little while.

Thanks again.
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Old 10th Jun 2024, 2:13 pm   #30
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Default Re: Pioneer PL-12 Ground Wire?

Ok - there are 3 pictures attached, showing the set up itself (I've only just moved it so it will be tidied up, speakers properly positioned etc. soon).

TEAC receiver, subwoofer, Pre-Amp, Arylic streaming device and TT are plugged into the same extension lead. Receiver and subwoofer have 3 core mains cables. TT has 2 core. The pre-amp has an AC adapter with a "false" earth pin - see pics 2 and 3. The arylic connects via a USB lead to 3 pin plug adaptor.

TT is connected to TEAC's AUX1 by way of pre-amp. If TEAC selector is in any position other than AUX 1 there is no hum issue at all, regardless of whether sub is on or off. When AUX1 is selected and pre-amp turned on, there is the faintest of hums(and only at high volume) if the sub is off. When playing a record this is not discernible, even in the quietest parts. Turn on the sub and the hum becomes much, much louder and is a distraction to most vinyl playback. Turning off the sub for vinyl playback isn't the end of the world as the speakers are decent on their own (Dali Zensor) but I'd prefer to have the sub as an option across all fronts if possible.

Do please tell me if I've missed anything out!
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Old 10th Jun 2024, 2:36 pm   #31
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Default Re: Pioneer PL-12 Ground Wire?

Have you got a multimeter with a continuity setting so that we can test what's connected to what?

A ground loop between the sub and teac is a possibility. Can you check whether there is continuity between:

1. Teak: The signal ground (outside of aux RCA input) and your mains earth pin in the plug of this device, obviously with system disconnected.

2: sub: the signal ground wire/socket/binding post (usually black) and the mains earth pin in the plug of the same device

Good firm connections are essential

Last edited by Gabe001; 10th Jun 2024 at 2:52 pm.
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Old 10th Jun 2024, 2:49 pm   #32
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Default Re: Pioneer PL-12 Ground Wire?

Quote:
Originally Posted by Gabe001 View Post
Have you got a multimeter with a continuity setting so that we can test what's connected to what?
I don't, Gabe, no.

This kind of thing? I can probably get one soon enough.

https://m.media-amazon.com/images/I/...L._SL1500_.jpg
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Old 11th Jun 2024, 5:39 am   #33
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Default Re: Pioneer PL-12 Ground Wire?

Yes that's a good one. What the Teac's model and has it got a grounding post at the back?
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Old 11th Jun 2024, 11:33 am   #34
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Default Re: Pioneer PL-12 Ground Wire?

Gobe001

The TEAC CD receiver model is shown in post 13 together with the list of connected hardware except for the subwoofer or its model number. The make of the speakers - Dali Zensor is shown but again not the model number.

Chris
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Old 11th Jun 2024, 3:53 pm   #35
Gabe001
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Default Re: Pioneer PL-12 Ground Wire?

Yes it's the CR-H248.

If done correctly, the multimeter will tell us whether audio ground is earthed at 2 points, a single point or none at all. We may need to remove an earth (safely) or add one and link it to AGND at one point only (ideally turntable as it looks from Michael's post that AGND is already bolted to deck). If neither is the case, I'm a bit stuck.

Admittedly the deck of the turntable should be earthed anyway, for safety, but that's a discussion for later. Which means that the only real decision really is whether AGND is bolted to deck or isolated from it. Enough rambling for now. We'll cross that bridge in due course.

Happy to be corrected if I'm barking up he wrong tree, or there is an easier way of doing things. This is based on my own experience with my own amps with different grounding arrangements and what worked best for me. I'm not an expert by any means
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Old 11th Jun 2024, 10:27 pm   #36
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Default Re: Pioneer PL-12 Ground Wire?

Reading through this thread and It strikes me a few obvious things have been missed...........
The hum increases from faint to loud when the subwoofer is turned on. Of course it will, thats the job of the Subwoofer to boost the low frequencies and so I'd expect a low level hum to become more audible.
So given that, and given also that we should be well able to reduce the Hum from the TT to inaudible, we have, to my mind, a fairly simple path to follows
Assuming that there are no faults in the main amplifier input circuitry, ie all line level inputs should not display a hum with a noise free source, then we connect the phono stage and I suggest a couple of shorting plugs in the input sockets. This will do no harm whatsoever.
If the hum occurs at this point then the issue is with the phono preamp.
And heres a thing, I spent days chasing down an annoying low level hum just like this problem of yours and in the end it was as simple as having the phono preamp situated too close to a piece of other mains powered kit and the hum was being picked up off the mains transformer field. Not all phono amps are equally well shielded from this.
So if we've eliminated the amplification stage, that does leave us with the Turntable and here it becomes a matter of elimination again. First, as has been suggested earlier, check the continuity of the connecting leads from the phono plugs to the cartridge pin leads, you should be able to do this with a steady hand and the headshell removed. Also check the tonearm, NOT the metal chassis, is earthed to SIGNAL ground, as there seems to be no separate earth wire to connect to the earth post on the preamp. (this will almost certainly be connected to the signal earth on the phono socket outers).
If the tonearm cables earthy side (screen) isn't connected to the chassis/tonearm then you will need to fit an external earth wire, this is the easy bit. You'll probably find on of the tags under the chassis where the thin tonearm wires are soldered to the screened cable is electrically connected to the tonearm. This is the tag to take the earth wire from.
Now we get to the esoteric issues. I was stting up a nice BSR MP60 for a great nephew and I was well hacked off with ann anooying low level hum. This TT was earthed via the tonearm screens to the preamp. A quick look underneath told me that at some point, possibly original from the first owner/supplier, that instead of running an earth wire fronm the tonearm lead, the screens had been connected to the tonearm earth and also to the TT chassis, this was causing a classic hum loop, easily sorted by cutting the link to chassis and fitting an earthing wire from tone arm to preamp. This is quite normal on most Good quality Turntables, especially those with separate tonearms.
And now if we still have a hum and the wiring seems sound, I would ask what cartridge is fitted as there are some out there that are quite prone to hum especially on decks with AC motors. Grado springs to mind here, I have one here that is unusable on any TT with an AC motor under the platter or near, which is most out there.
The advice about wring your TT with a mains earth is possibly incorrect, if its been designed with a 2 core mains lead and is a double insulated design just like your Project Phonobox then it doesnt need a 3 core mains lead. I'd trust Pioneer on this.
A long post but I hope it illuminates the issue and the importance of a methodical and steady approach to troubleshooting.
I'm certain you'll get a solution.
Andy.
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Old 12th Jun 2024, 8:40 am   #37
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Default Re: Pioneer PL-12 Ground Wire?

Thank you Andy for the very informative post.

I have drawn a schematic of the original pioneer 12d grounding scheme which I've tried to work out from the pictures online and accompanying text from various sources. I'm pretty confident this is correct.

It appears that the OPs turntable has been modified to using 3 tags as MM pointed out in post 16 likely with the rca and cartridge signal ground taken to the centre tag bolted to the turntable chassis. I'm not certain as the what the state of play is regarding the tonearm grounding (2 black leads) and whether there is continuity between tonearm and turntable chassis via the bolts, or between the tag bolt and the chassis itself. I don't own this model. I understand the OP has a multimeter which is arriving today in the post, and these are things worth checking along with everything else suggested.

Andy, would you think returning this to the way pioneer originally intended it is a good idea? Post #16 suggests to me that this may be as good as things get from the turntable end with the current (3 tag) arrangement.
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Old 12th Jun 2024, 8:53 am   #38
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Default Re: Pioneer PL-12 Ground Wire?

Sorry - I've only just now been able to check back in and read all of the further guidance.

A multimeter is due to be delivered today so I should then be able (with some homework first as I've never used one before) to run the test(s) that you have suggested. I can also as Andy writes try resituating the pre-amp to see if that's the culprit.

Willing to try anything that is suggested that is within my capabilities and also willing to learn. I'd not heard of a shorting plug before today - I can get some if necessary? How many might one need?

When I bought the TT it was fitted with a new but fairly basic/generic headshell, cartridge and stylus. It worked but wasn't particularly wonderful. I replaced this with an Audio-Technica AT-VM95E (Green). That certainly sounds better. I should add that the same level of noise remains with either. I'd also like to emphasise that the hum to which I referred when AUX 1 (TT) is selected and the sub is off is very minor - it's only switching in the sub that causes the jump to a noticeable level.
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Old 12th Jun 2024, 9:12 am   #39
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Default Re: Pioneer PL-12 Ground Wire?

Lightbulb moment...

I have a second system - it's a cheapo Currys own brand micro thing into which I have plugged an old DVD player. I use this in my "office" (spare room!) for listening to CDs sometimes. I could plug the phono stage and TT into this and see what happens, hum wise? It does not have a sub woofer output, so may be not ideal for testing purposes, but even so?

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Old 12th Jun 2024, 9:41 am   #40
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Default Re: Pioneer PL-12 Ground Wire?

So Paul

When you unplugged the turntable from the pre amp, first without the power supply to it and then with it, what happened?

Then, when you then plugged in the turntable, did the hum change when you plugged the TT into the mains and or switched it on?

Did the hum change in volume when you placed your hand near the head shell?

Only asking.

Chris
PS I'd leave the lightbulb moment for another day.
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