Adding a PSU to a turntable

Hi All,
As some of you are aware, I have an old Sony Midi system complete with turn tables.
In recent years, the only thing I’ve used the main boxy bit for, is to provide 12V to drive the turntable. I’d like to feed it from something a bit more compact. But as usual, have zero budget.
I’ve taken the bottom of the turntable and discovered It has a 9 point Something volt motor (it also has an auto Arm liftty and Putty away mechanism).
I checked the power out from the big box, and it’s a little over 12 V. I had a dig in my PSU box and the nearest I’ve got claims to be 13.1 V.
Does the team think that’s near enough? Or do I need to get I? ?d down? If so, could I get away with adding a diode (and resistor (valu e?)?) in series?
If not, could I add a 12V regulator? Or would I need more than 13V to feed the regulator?
TIA
Chris
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On Tuesday, 16 April 2019 07:32:16 UTC+1, snipped-for-privacy@o2.co.uk wrote:

rntables.

is to provide 12V to drive the turntable. I’d like to feed it fro m something a bit more compact. But as usual, have zero budget.

12V. I had a dig in my PSU box and the nearest I’ve got claims to be 13.1 V.

??d down? If so, could I get away with adding a diode (and resistor (v alue?)?) in series?

d the regulator?

A diode would do it.
NT
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On 16/04/2019 07:32, snipped-for-privacy@o2.co.uk wrote:

I'd *expect* it to be OK, but would be tempted to try to measure the voltage from the original PSU on-load, and see if it's 12v then, and get a PSU as close to that as possible, or use a higher PSU and a regulator. Apparrently you'll need at least 14.5v to drive a typical 12v regulator and *guarantee* 12v:
https://electronics.stackexchange.com/questions/7463/7812-minimum-input-voltage
I'd expect the motor drive to be regulated in the turntable, so I'd expect the main problem is not burning that up :-)
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The latter sounds feasible but you need to know the current drain when its running under max load and of course you need to measure the voltage supplied under max load too, it might not be a regulated supply. If you opt for an external psu, put it as far away as you can to prevent any inductive pick up, on the other hand by a turntable and donate the old working system to somebody else.
Brian
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On 16/04/2019 07:32, snipped-for-privacy@o2.co.uk wrote:

One silicon diode and one Shottky diode in series will drop a shade under a volt which should be fine. It is unlikely that something that is old and designed for a crude bridge rectifier PSU would be particularly voltage sensitive. The PSU voltage of the original is quite likely to be load dependant and higher when not spinning up the turntable.
The main thing you need to know is how much current does the turntable draw at 12v.

Although low dropout regulators are available the most common ones need a couple of volts headroom.
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Martin Brown
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Hi All,
Thanks for the reply’s. I will try and get more info.
Someone spoke of it probably being regulated in the turntable.
There is no evidence of this.
The wires carrying 12.1 volts come in, go to a tiny PCB with no components on either side, and then goes off to Power the motor (small round can with 9V written on it) and also the arm twidly mechanism.
I do have an 8V PSU kicking about, maybe I should check what that appears t o be putting out, and if it’s around the 9V mark, see what the turn table does with that.
Otherwise, I might go back to driving it with the big box.
Best regards
Chris
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Have you looked for a schematic of the amp online? Should show you the PS, and perhaps test voltages, etc.
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*I didn't say it was your fault, I said I was blaming you.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On Tuesday, 16 April 2019 13:45:50 UTC+1, snipped-for-privacy@o2.co.uk wrote:

s on either side, and then goes off to

to be putting out, and if it’s around the 9V mark, see what the tu rntable does with that.
That probably would work.
NT

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On 16/04/2019 13:45, snipped-for-privacy@o2.co.uk wrote:

Is the motor AC or DC?
It's quite possibly AC, so the turntable speed is synchronised to the mains.
Andy
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Hi All,
I measured the original supply voltage on load, and it was a shade under 12 V (it’s a very lightweight turntable).
I had another dig in my spare PSU box and found a couple of 12V SMPUs. One of which measured 12.2V off load.
I decided to go for it.
The turntable played fine 11::^*>>)).
I don’t think I checked the on load voltage, as I assumed it would be the same with such a negligible load.
I listened to about a track and a half of an LP, and none of the magic blac k smoke escaped.
Thanks for all the advice.
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On Tuesday, 16 April 2019 22:45:49 UTC+1, snipped-for-privacy@o2.co.uk wrote:

12V (it’s a very lightweight turntable).

ne of which measured 12.2V off load.

d be the same with such a negligible load.

ack smoke escaped.

Good job. If you find a 9v wallwart change over to that, it'll avoid cookin g the motor regulator.
NT
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Hi,
The only 9V Wallwart I Have is DC. I do have an 8V, but I imagine that would be too low.
What would the motor regulator consist of? (Thinking about it, there is a small screw accessible from underneath to adjust each of the two speeds (which may or may not be something to do with a motor regulator, or maybe an alternative method??)
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On Tuesday, 16 April 2019 23:29:46 UTC+1, snipped-for-privacy@o2.co.uk wrote:

why not use the 9v one? 8v would probably work too.

pass transistor, preset pot & a few other bits

they usually have a bit of slotted rubber covering a hole. Poke a jeweller's screwdriver in to adjust the preset pot, but don't short it to the case. A plastic tweaker is better. They seldom need adjustment.
NT
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Let’s try what I meant to say!....
The only 9V I have is AC.
I will give the 8V one a measure, and give it a try.
Thanks again
Chris
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On Wednesday, 17 April 2019 15:09:45 UTC+1, snipped-for-privacy@o2.co.uk wrote:

right. Even if rectified & smoothed it would then be the wrong voltage.

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I seem to have invented perpetual motion!
The 8V wallwart (rated at 230 milliamp) showed about 0.5V off load. I cut i ts plug of and tried again on the bare wires. 15V!
I thought, what the heck, it’ll probably drop when it’s on load.
Turned the turntable on, and it span at what looked to be about 33 1/3.
Checked the V on load 19!
Switched off quick, and will wire the 12V beast back in tomorrow.
Ta muchly for all the advice.
Best regards
Chris
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On Wednesday, 17 April 2019 23:12:35 UTC+1, snipped-for-privacy@o2.co.uk wrote:

its plug of and tried again on the bare wires. 15V!

n load.

they're not normally that bad :/. A 12v heavy type wart will often give 19v off load, dropping to 12 at max load.
NT
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Back together with the 12V PSU now.
Having had another gander at the motor (a fine product of the matsushita co rp. it is marked 9,12V.
By which I now think they must mean “Anything between 9 and 12 V or thereabouts is fine round here.
Alls well that ends well!
Now to install it back in my bar, where it will probably gather dust unlove d and unused for the next 20 years (It previously came in very handy digitising a few LOs which were made of U nibtainium-Digitallis.
Although, as it happens I’ve found a couple of them online since.
Chris
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On Tuesday, 16 April 2019 21:16:48 UTC+1, Vir Campestris wrote:

nts on either side, and then goes off to

rs to be putting out, and if it’s around the 9V mark, see what the turntable does with that.

ns.

Mains TT motors use the mains frequency for control, low v ones are dc moto rs with a negative impedance speed regulator.
NT
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On Tuesday, 16 April 2019 09:53:39 UTC+1, Martin Brown wrote:
r 12V.

13.1

Silicon diodes drop 0.65v at very low current, 1-2v at full whack. A single si diode will be fine.

Ideally you want 9v, but it's been ok on 12.

an amp at most, but more when starting. A 3A diode should be ok.
Of course the 13.1v psu might deliver much more, if it's heavy especially. That would complicate things. Measure it.
NT
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