Tube Bandpass

Ken Stone sasami at
Tue Jul 28 01:13:47 CEST 1998

Stage 1 of my tube bandpass VCF has been completed. Eric's design of course. 

A photo of the module as it stands (basic chassis) is at

Input and output jacks have been removed for the photo, as they were only
tacked on. Building it was relatively straight forward, and a pleasant
change from printed circuits. A six way tag strip salvaged from my SH-5
coupled with the tube socket and pot tags provided sufficient mounting points.

Still to go are the voltage control stuff and the panel and case. Components
generally are a mix of old and new. The 5 pin din is for power - nothing
else I have uses this sort of plug :)

I've tried it out on square waves, both, static and swept. Hardly NATA
testing, but that was what was to hand. 

Personal feelings-

The effect of the filter is a little weak with the Q down, but bringing it
up makes it quite satisfactory. Eric does mention this in his notes,
suggesting  two stages may be required for those that require a stronger effect.

My only comment so far is to make sure you put a bleed capacitor across the
150V filter capacitors of the power supply. This resistor will gradually
drain the capacitor when you power down. A neon lamp wouldn't hurt either,
as it will give you some idea of how much charge is left.  Not only will
this reduce the chance of you zapping yourself, but more importantly, it
stops you really making a mess of your tools when you accidently short out
the rails :)

Thanks Eric.


Ken Stone   sasami at  
Catgirl Paradise <>
Australian Miniature Horses & Ponies <>

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