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Hello again, I picked up a lowrey L50 (similar to a Teenie geenie) for free. It sounds great but is picking up some am radio signals. It's not super audible live but I'd like to make some recordings without it. Any tips for trying to chase this down would be much appreciated, thanks!
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You can try an AC line filter in case it's coming in through the power. Also, does the volume pedal have any effect on the RF?
geo -
Thanks geo, it gets louder as I increase the volumeComment
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How close do you live to the stations that you hear?
Is it one station or multiples?Comment
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KC9UDX: it's hard to say what station it is but I performed yesterday across the bay in San Francisco, at home in north Oakland and at my practice space in Berkeley and could hear radio coming in at all locations even though they are miles apartComment
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Maybe try shielding all long wires and ground the shields?Allen 530AComment
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Try to catch an ID (they're required to identify near the top of the hour; but if you listen for a full hour you should be able to hear it). Hopefully it's a legal station. Even the illegal ones tend to identify though. If you find just one station that's interfering, there may be a specific reason for it. T may be a problem at the transmitting station, and there may be a defect in your organ, but this will be hard to find from here.Originally posted by northoak View Post
If you can hear more than one station that will be good to know, too. Also note the times of day that you hear it.
You may want to enlist the help of a local radio amateur (they are plentiful in your area). They tend to be experts in this sort of thing, and willing to help.Comment
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This used to be a problem with certain Lowrey organs back in the 70's and 80's. Also, I had a funeral home with a small 4 channel mixer/PA that picked up a nearby radio station. In all those cases placing a small value capacitor in the right place solved it. In the lowrey's, a capacitor was placed in the expression circuit. That was a photo-cell device with very high impedance. Don't remember the size but used a capacitor decade box to dial it in. In the mixer I placed a capacitor across the input of each channel to ground. Again, use a decade cap box to dial it in. The value should kill the radio without effecting the normal audio. Something like a 0.001uf or similar.
Since it's under expression, I would look at the A B inputs of the preamp and experiment with some caps. Can't hurt anything.
GeoComment
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Hi still experiencing this problem, Would replacing the two prong power cable with a three prong for a more secure ground possibly help?
Geo, I'm not sure where I would put said capacitor?Comment
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Grounding it isn't a bad idea but won't help this problem.Comment
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This kind of repair isn't easy even for a seasoned technician. It's not a repair, it's a modification. You can experiment with hanging a small capacitor from various points in the signal chain to ground. I would try a 0.01uf to start and I would first focus on the expression circuit. It's a very high impedance circuit making it susceptible to radio interference. Find the signal going into the pedal circuit and put the cap from there to ground. If that doesn't work, then you would work backwards in the signal chain toward the first stage(s).Originally posted by northoak View Post
Hanging a small cap like this from anywhere to ground won't hurt anything. If you find a place where it kind of helps but not enough, use a larger value cap. (0.05uf, 0.1uf etc)
The thing to consider is by adding this cap you're adding a low pass filter. This can affect the organ sound if the cutoff frequency is too low. The capacitor value is a balance between getting the radio signal out but not affecting the organ.
GeoComment
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Couldn't adding a cap to ground in the wrong place potentially short something to ground? I'm fairly comfortable working on electronics safely but confess I'm scared of frying a resistor, diode or op amp. I imagine part of my issue is that I'm playing this thing in a LOUD punk band so it's going through a keyboard amp over a drum set and bass. I also get a high pitched whine but all the caps tested fine.Originally posted by geoelectro View Post
going to try ferrite beads on the power cable as well. My power supply does use the photocell u speak of where a light bulb faces the cell.
The expression pedal basically changes the amount of light it receives when you push it up or down. Would I try a cap from one of the leads to the photocell to ground or between the two wires going to the cell?
thanks for the help! Trying to record again soon but really don't want that am radio in the mixComment
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Capacitors only "conduct" AC, almost. A capacitor does always appear as a short circuit for a finite amount of time. You're not going to have an issue with this at all, considering what you're doing. I can't imagine a situation where installing a ceramic disc capacitor is capable of doing any harm. But it's the middle of the night for me so I might be forgetting something.
The worst case is that you'll weaken an intended signal, especially treble.
For your purposes, I think you should always connect one lead of the capacitor to "ground". That is, 0V, chassis ground, common, etc.
By the way, I'm not sure if this is helpful, but you only need to try the capacitor on high impedance circuits. This rogue signal is not coming from a low impedance circuit. I'd start with any long wires near the pedals (expression especially) and manuals, and work your way electrically toward the power amp. Long wires make good antennas, especially for AM broadcast radio.
On one hand, I'm glad that it's broadcast interference, not amateur radio. Too many times the ham gets blamed for poor conditions in the complainer's equipment. On the other hand, if you were getting amateur radio instead of broadcast, you might get some help from the ham. I can't remember if I mentioned this already, but you're in an area with an extremely high ham population. I'd contact an amateur radio club. Many hams would bend over backward to help someone like you with a problem like this.Comment
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One of the things I always try first is installing torrid "snap on chokes" on the input leads and speaker output leads. If that doesn't work I go to the capacitors next. You can buy an assortment of 20 different chokes of various sizes on the bay for about 15 bucks. Allen now puts chokes on all of the leads in their organs.
Good luck
John. WA5JRComment
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I'm over here in my studio right now troubleshooting the organ and it appears that the issue lies in the line out because I can't hear interference with the built in speakers. I tried a couple different amps and cables to rule that out with no luck.Comment
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