Grounding an ungrounded rhythm box

[publicradio]

I recently purchased a Search Rhythm-Matic II from eBay. The one I bought has a built-in speaker and I like it a lot. I could only find , which isn't great. But even in that video, you can hear that there's a hum as soon as he turns the unit on.

Mine hums pretty loudly, too. The hum is so loud, it almost competes with the rhythm itself. And when I turn up the volume, the hum goes up, too.

I opened up the back of the unit, and I've attached an image if that's useful. I'm wondering if there's a place where I can run a wire from the unit to the ground slot in my outlet. My assumption is that it just needs to be grounded, but I could be mistaken. If anyone knows for sure, and how to fix this problem, please let me know. Thanks.

[BertKoor]

Your best bet with least effort is to disconnect its power unit and use a well-designed no-hum power adapter (of the right voltage and amperage) because this is very likely the cause. A "balancing" act won't help much then.

Replacing all the electrolytic condensers might make the hum bearable again as well. These tyipically don't age well.

[publicradio]

That's a good answer. It sounds like you're saying I would need to disconnect this transformer, the one pictured behind the lamp cord in the photo. I would replace this with a new power supply and this might make it better, but that the age of this drum machine is likely the main factor.

I was hoping I could just take a single strand wire, touch one end to something in the unit, and touch the other end to a ground outlet. If I have to replace components, then I don't think it's worth it and I'll just enjoy my rhythm box the way it is. Thanks!

[BBFG#]

Has it always "hummed" or just recently? If the latter, then maybe it's RF as much as grounding. Try fixing a layer of aluminum foil with adhesive to the inside box itself. Something I did way back when I had a Clavinet. I perhaps was a bit pedantic and actually gutted the components to line every mm of it. However, I had seen others doing less and getting almost as good results.

[publicradio]

I only just bought it, but lining it with foil seems like a very easy task and I'll be sure to try it out, and report back with the results.

[BertKoor]

No, not just the mains transformer. Near it is the stuff that makes up the power section which converts 110 or 220V Alternating Current to whatever the designers thought best Decent Current. Typically something between 5 and 25 V, using condensers and a rectifier (4 diodes). You might want to gut that section out completely.

Using an oscilloscope you can probe what happens where. Studying the thing closely will reveal what the power rails to all the stuff is.

If you have no experience with electronics then either educate yourself further or stop right here.

[lfm]

Watch circuit boards for printed voltages, that is often the case.
Maybe even test points saying a voltage.

Old stuff often have transformers that start acting out making noise, even mechanical. Vibrating iron core plates and such. Some types have nuts and bolts to tie as well.

I have an hifi amp that has major mechanical noise when it gets warm. Not so much in audio as mechanical though.

Search hi and low for service manual. Contact Hammond repair shops and whatnot, which ever unit was from Hammond.

[publicradio]

Thanks for the replies. I tried the foil, but it didn't help. I tried spraying everything down with contact spray, and it didn't change anything. I think I'm OK with this unit the way it is. It doesn't have an aux out, so I'm not going to be recording with it. It's just a rhythm accompaniment tool, and it's fine. Thanks for the help!