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Chikara
21-07-2009, 01:26 PM
Hi all,

For a while, I've been copying some old audio cassettes onto my PC.
I've been using a portable walkman tape player, as I actually found it gave clearer sound than my larger, normal stereo.
Anyway, that has been working fine. But as the walkman is battery powered, I didn't want to keep switching and re-charging batteries each time I use it, so I've just bought a power adapter.

Now, when the walkman is plugged into the power adapter, I get a constant, quite loud humming noise from the PC speakers. This never happened with the batteries.
But the strange thing is, the hum is only present when the power is plugged in but the tape is *not* playing. As soon as I press play, the hum stops completely. The hum stops even if there is no tape in there, as long as the play button is pressed. So, it's not the sound of any music just drowning out the hum.

I've tried different power points, it hasn't made any difference. The voltage and polarity are correct.

Any ideas what's causing the humming and how I can stop it?
Thanks in advance...

pctek
21-07-2009, 02:51 PM
Interference.

Chikara
21-07-2009, 03:07 PM
Interference.

Thanks, but could you please explain more - how do I troubleshoot it?

If it was interference, why does it only do it when the walkman is not playing, but it stops as soon as I press play?? :confused:

Terry Porritt
21-07-2009, 03:51 PM
Here's my take on it, but I expect Billy T will have a better explanation and a better resolution.

First of all, plug packs are not earthed, and wherever you have a mains supply or device there is the potential for 50Hz "mains hum".

When the Walkman is switched off, the plug pack output is looking at high impedance, that is, there is no DC current flow. This means that 50Hz "interference" or very very low value of AC voltage will be present at the output and can be transmitted into the walkman via capacitive or inductive coupling. Even when "off" there will most likely be a connection from one side of the plugpack connector if the switch is single pole.

When the Walkman is switched on, then the plugpack is supplying power and it "sees" a low impedance, and the hum is shorted out.

The cure is not easy, you would need to connect a bleeder resistance across the plugpack output, say 100 ohms, or a value by trial and error.

Chikara
21-07-2009, 04:49 PM
Thanks for the reply, gosh it sounds complicated, especially for someone who has very little knowledge about electrical circuits like me!!

Terry Porritt
21-07-2009, 05:19 PM
Since there is no hum when you are actually recording, does it matter that there is when the Walkman is switched off ? Could you live with that
?

Chikara
21-07-2009, 06:56 PM
Yeah, I can live with it I guess...it's a pain because when I'm recording on the PC from there, as soon as I stop the tape I get the hum..but, the main thing is, it is not present on the actual recording itself which is the most important thing. I'd be keen to fix it if I can, but I can live with the way it is...

linw
21-07-2009, 10:44 PM
A suitable capacitor in the right place should get rid of it. But you would need to get at the walkman circuitry and experiment a bit with what value cap and location.

Not for someone who knows nothing about electronics, unfortunately, unless you wanted to start with googling "mains hum removal" or somesuch and spending hours on an education!

feersumendjinn
21-07-2009, 11:52 PM
Oops, double post :)

feersumendjinn
21-07-2009, 11:57 PM
Is it a regulated plug pack like this one?
http://www.dse.co.nz/dse.shop/en/product/M9927
Or an unregulated one, as these can cause hum.
Alternatively, you could make a battery adapter like this (should be easyish to do :p )
http://www.dse.co.nz/dse.shop/en/catalog/CTG0000178
with a large battery or series of batteries to get the correct voltage for your Walkman wired to the correct adapter plug, you wont have hum problems with that.
I would recommend using alkaline cells (they last about 4 times longer than standard).

Chikara
22-07-2009, 12:03 AM
Is it a regulated plug pack like this one?
http://www.dse.co.nz/dse.shop/en/product/M9927
Or an unregulated one, as these can cause hum.
Alternatively, you could make a battery adapter like this (should be easyish to do :p )
http://www.dse.co.nz/dse.shop/en/catalog/CTG0000178
with a large battery or series of batteries to get the correct voltage for your Walkman wired to the correct adapter plug, you wont have hum problems with that.
I would recommend using alkaline cells (they last about 4 times longer than standard).

Yep, that one in the first DSE link is the exact same one I bought.

Thanks for the link about the battery holder, I suppose it may reduce the hum, but in that case I may as well just go back to using the batteries in the Walkman itself (which is what I previously used to do) - they never caused hum, but it was a pain to keep swapping batteries over and recharging them, that's why I bought a power adapter!

feersumendjinn
22-07-2009, 12:46 AM
My point was/is that using larger (and I recommend alkaline) batteries (C or D size) would last a lot longer than the AA or AAA size you have in the Walkman, plus you will have no hum (which was your original gripe) :D.

WalOne
22-07-2009, 04:48 PM
I think you have a bug somewhere. A humbug :banana

(sorry, someone had to say it :o )