Firstly, lets get the terminology right – this is a vibrato (pitch modulation), not a tremolo (amplitude modulation). Tube vibrato is not an original concept, similar schematics proliferate in vintage tube amps. I was also inspired by mac’s ‘Fet Phaser Idea’ DIY Stompboxes thread
, Rick Campbell’s ‘Possible Start On a Tube Phaser/Vibrato Pedal Project’ AX84 thread
and R.G.’s The technology of phase shifters and flangers at GEOFEX
So I thought I’d try something similar using two 6111 submini tubes at 12 volts. This allows for only two stages of phase shift, but the effect is very pleasing and useable. More stages could be added for a deeper effect. The advantage of using just two tubes is that it keeps the milliamp requirements down - it’s quite logical to run the two tubes’ heaters in series from 12 volts, keeping the current draw down to just ~300ma (!!). I dare say that the 6111’s could be replaced with 12AU7 without too much trouble, or indeed with 6021 or 7327 subminis.
The LFO is modified from the one I used in my Vibracaster
(which was actually a tremolo – confusing huh?). I’ve added a ‘Range’ switch to give more control over the speed. I made my own little vactrol using a 3mm red LED and two LDRs which I filtched from a kid’s toy (sorry kid). They are all soldered to a little piece of perf and light insulated.
Here's a soundclip: http://www.aronnelson.com/DIYFiles/up/Vintage_Vibe.mp3
Squier Telecaster Custom (HB) > Vintage Vibe > Roland Bolt 60 watt tube combo > Shure SM58 > Event Echo Gina 24 soundcard > Wavelab
No other processing. It's a montage of a few different settings. There are a few crackles because it's a breadboard not a pedal.
After I've built my Vintage Vibe I'm planning on developing a phaser based on the same concepts.