Output on little transistor organ, loud hum

[XstaticNoiz]

Hi there,

This is my first post here so I hope this is the right place to ask.

I bought an inexpensive analog transistor based organ. It's a Gracia (Armon) Charlie 37. It was in bad shape; noisy pots, lots of dust, paint + sharpie markings + stickers on the keys. I totally cleaned it up and it looks like this now:

100_1271_zpse8e8bffc.jpg Photo by AJDbass | Photobucket

It has a build in speaker. I wanted an line out to amplify the organ so I could use it for rehearsels with the band. There was a jack input for a pedal wich was missing, so I pulled out this jack and replaced it for a line out-jack. I found the pcb which contains the power supply and the power amp. I bypassed the white wire which goes to the input of the power amp. The white wire now goes from the output jack to the power amp. If a cable is inserted the signal to the input of the amp is broken.

100_1277_zpsf708911c.jpg Photo by AJDbass | Photobucket

The level of the line out is perfect for a guitar amp and I can control it with te volume control on the organ. The problem is that when there's a cable in the output and there is no signal to the poweramp of the organ, the internal speaker gives a loud hum.

I don't really know how to eliminate this hum. I don't have a schematic. I was hoping someone could give me some tips... I am kind of stuck. Thanks.

[g1]

You need to replace your jack with a type that has another switch contact which will ground the input of the power amp when you use the line out.

[Jazz P Bass]

Something like this: Fender Jack Switchcraft 13A Transfer 0041701000

[52 Bill]

Something like this: Fender Jack Switchcraft 13A Transfer 0041701000

I don't think that that one would work.

I looked up the Switchcraft numbers. A #54A might do it.

Or use a 3 conductor jack with closed circuit contacts. Wire the tip to the signal output, the tip NC contact to the power amp input and also to the ring contact. When a mono plug is inserted the ring contact (power amp in) will be grounded through the sleeve of the mono plug.

[XstaticNoiz]

Thanks everyone! Grounding the input did the trick, works perfectly! No hum and noise from the internal speaker and no hum on the line out.

I connected the input from the amp with the 'ring' contact from the stereo jack I already used, like 52 bill suggested.

Can't wait to use it on the next rehearsel!