Somewhat OT Buzz on an Hofner Clavinet D6

[tomtom]

It's really important, I have to lay down a track so I borrowed a friend's Clavinet, it's magic... Like a Rodes, it uses a pseudo guitar pickup with cords and it rocks.

The mic senses strings movement and a very long shielded cable send the signal to a tiny cicuit to select coil arrangement and voice (quite like wha wha filtering with inductors), it work on a 9v battery !!

The box is made out of wood so no shielding. It sounds great but with a single coil like hum. I don't know what to do... I only noticed that the first capacitor on the signal path just before a transistor makes a pretty efficient antenna, amplifying hum as my finger approach it.

Any idea ? It's not a typical FX box or guitar so I'm quite afraid to work on it and srew it up...

Thanks.
Tom

[downweverything]

yes those things are awesome, how old is it (i know some of those have been around for decades), may be due for a recap

[Paul Perry (Frostwave)]

I think these things are intrinsically hummy, maybe orientation will help.
I'm sure it isn't a cap problem. Google gives over 400 hits for claviner + hum, so plenty of people have struck this before.
maybe (if you have channels to spare) record the clav separate & try to remove hum via software?

[tomtom]

It's a D6 from 1978 or alike, all wood with six "tone" switches and a vol pot on the left and a mute knob on the right.

I was thinking about that same treatment you may give to a strat to avoid grounds loops, ie shielding the inside of the box, put the circuit in a metal case and use star grounding. Maybe too much...

My main guess is that this so sensible cap may be a transistor problem or one with the shielded cable...

[drew]

My home studio is intrinsically "hummy"... 80-year-old building with horrible wiring, not a formula for success, but the biggest place I could find with my budget.

Anyway. I've found that mics can be turned certain ways and my guitars, when facing the right way, can avoid the hum. Take the clavinet and set it on a stool and listen to the output turned all the way up, and turn it around on the stool. There should be angles where you have less hum, and angles where you have more.

Then try this in various locations in the room. It sounds like voodoo but I bet you'll be able to find a spot that's not so hummy. I may have to play my telecaster facing the closet door, but hey, if I can get a sound that's not hummy, I'll do it...


drew
www.toothpastefordinner.com

[Tim Escobedo]

They came with a single coil pickup, IIRC. There is a aftermarket mum canceller available for these things, believe it or not.

Other things to look for might be poor ground connections, poor shielding, the stuff you might associate more with electric guitar.

I've thought some about active hum cancellation. Don't know how well it'd work. Here's the idea. Run a plain single coil pickup into a gain stage with variable attenuation. Also run the output of the clav into a buffer. Sum both signals. Orient the single coil pickup so that hum is cancelled, and fix it into place. The gain would probably need to be tweaked. Also, the single coil pickup need not be magnetically loaded. The idea is that the single coil pickup becomes a dummy coil. Might be a interesting experiment.