Hi there,

I finally got around to building a case for my Empeg (MKII) using a docking sled and an ATX power supply. Everything seems to work great except that when I use headphones to listen to the player through my stereo I can hear a high pitched whine.

It's very possible that I don't have the sled connected correctly. I don't really know anything about car stereo installations. I supplied the ignition sense with 12v and used the black wire for ground. Originally I had the permanent power wire supplied with 12v but the empeg would turn off periodically with that wire connected.

Anyone have any ideas? It's probably something silly...

Thanks in advance

Everything seems to work great except that when I use headphones to listen to the player through my stereo I can hear a high pitched whine.

Classic ground loop and/or inductive noise problem. Use the same techniques to eliminate this as you would if it were installed in a car:

http://www.installdr.com/TechDocs/999501.pdf
http://www.installdr.com/TechDocs/999502.pdf
http://www.audiocontrol.com/techpapers/tech1002.pdf


Originally I had the permanent power wire supplied with 12v but the empeg would turn off periodically with that wire connected.

This indicates something wrong with the power supply, or incorrect wiring. Do all your problems go away if you disconnect the AT power supply and feed it from the AC adaptor that came with the Empeg?

___________
Tony Fabris

The whine could be due to the fact the AT supply is an SMPS, rather than the battery based analogue regulated setup you'd get in a car. You should have the in-line power filter supplied in the package fitted to the power line from the supply, as there is no in-case filtering in the empeg head unit.

You are probably hearing artefacts of high frequency, low-amplitude ripple superimposed on the 12v supply line from the SMPS which indicates poor filtering in the power unit itself. Bear in mind that computer power supplies are designed to deliver bulk quantities of 5v current for a main board, and the 12v lines are usually poorly filtered and regulated due to the relative unimportance of this supply voltage to the board (RS232 supplies, hard disks, floppies, etc.) where good regulation is of low importance. In a car, 12v is the primary supply voltage, and usually analogue regulated, so there's rarely any high-frequency stuff in there. Now had you used the supply unit from an old IBM disk pack, then I'd have been cheering you on at this point...

One of the few remaining Mk1 owners... #00015

Uh... that was gonna be the next thing I said.

___________
Tony Fabris

First of all, thank you for the replies. I reconnected the permanent power line with the filter on it and that seems to have eliminated the whine. However, I'm still having the 'power cutting out' problem, which I don't have if the permanent power line is disconnected. The Empeg player behaves normally if I use the regular AC adapter. I've also placed a voltmeter on the wires to see if there is a drop in current when the power thing happens, there isn't. Any ideas on this one?

Thanks!

Don't know if this applies to your powers supply, but most switched
power supplies I've played with wants a load of ~1A on the 5V output
to be stable (or some, to leave any output at all...)


/Michael

Well, since the secondary supplies in the SMPS are usually low-current, it could be that the "power out" you are observing is a thermal cut-out operating in the PSU. Again, it points to the PSU not really being the best choice for this; I would look at the ratings label on the unit and work out what current the 12V is meant to supply (continuous rating) and compare it to what the empeg and associated amp will draw. If it's greater than rated, the PSU will simply cut out to prevent overheating.

One of the few remaining Mk1 owners... #00015

I'm just downright confused. I realize that a computer power supply may not be the best choice for this application, but it's what I had around. Also, it doesn't seem to be exhibiting any unstable behavior.

The label on the side of the PSU says the following (i'm trying to use their formatting):
Max DC output
+12V
0.3A~
9A

Does that mean it puts out between .3 and 9A? I've measured the voltage and current going into the empeg player under every condition I can think of. Here is a table:

standard empeg AC adapter:
15V 0.4A
computer PSU:
11V 0.4A

Both the current and voltage coming from the PSU are very stable. During the 'power failure' the current and voltage remain the same, until the empeg switches back on (it comes back on about 2 seconds after it goes off), then the current jumps to 0.7 amps and then settles back down to 0.4.

Rob, what is the best way to test the PSU to see if the thermal cut-out is happening? If the problem was the PSU wouldn't I see a drop in voltage/current when the 'event' happens?

I appreciate any help, thanks!

Ok, problem solved. I gave up on the computer power supply (as Rob suggested ) and went out and spent the money on a 12v 1.5amp Radio Shack AC adapter. Everything works beautifully now! No noise, no power cut-outs!

Thanks for everyone's help. I learned quite a bit about car stereo installation and power supplies.

Dennis