Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[coldcity]

Hi all,

I'm been having fun modding an old 7" B&W TV into a "wobblevision" oscilloscope as an on-stage visual effect as per this thread.

I've left the vertical drive circuit intact, allowing me to control horizontal deflection through an audio input. This lets me get full deflection from a 1V-peak signal.

It's really cool but I'm wondering if there's a way I can better match an audio input to the impedance of the horizontal deflection coil. I expect an opamp-based buffer circuit would help here but I could use some advice on the specifics. Since others have used audio amp circuits for this purpose, I'm wondering if a simple LM386-based circuit would suffice. I mean, speakers have coils - and I want to drive a coil!

Many thanks for any help you can offer.

Best regards,
Iain

[coldcity]

Just to say, I found out from the good folks here that a simple 2W audio amp will do - so all good

[Circuitbenders]

Any chance you can put together a simple wiring diagram of what you've managed to put together for this as i'm sure there are a lot of people who would be interested in this mod.

What kind of deflection do you get with a 2W amp? I'm thinking that running it flat out to get a full screen deflection might prove rather terminal for the amp. You might also find that the horizontal and vertical coils have completely different impedances, which i'm assuming is why you don't get a perfect circle on screen instead of an elipse when you run both coils.

I think i measured an old amber screen monitor a while back that had about 8ohms on the vertical coil but only about 1.5ohms on the horizontal, but then that one went up in smoke about an hour later so that could mean anything.