“Vintage Vibe” Low Voltage 6111 Submini Tube Vibrato

[frequencycentral]

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.

This is how it is on my breadboard right now, I've been tweaking away at it all week and I have to say that I'm pretty pleased with it. As usual, I don't claim to be a whizzbang EE, so any suggestions, improvements, mod, hacks or derision welcome. Theoretically it should also be possible to modify the circuit for phasing - that has so far eluded me - any suggestions?. I'll get some soundclips together over the next few days.

[svstee]

Oh, yeah. Quite nice man, quite nice.

[tranceracer]

WOW!  Very cool ckt!  Looking fwd to the sound clips!   
Keep up the great work and keep us posted on the progress!   

[danielzink]

oh please.....post a schematic using 5672's........please......

Dan

[frequencycentral]

Oh, yeah. Quite nice man, quite nice.

WOW!  Very cool ckt!  Looking fwd to the sound clips!   
Keep up the great work and keep us posted on the progress!  

Thank you gentlemen!

oh please.....post a schematic using 5672's........please......

Dan

Sorry Dan it's not possible to do this with 5672's. The second and third stages are cathodyne phase inverters, the signal at the plate is 180 degrees out of phase with the signal at the cathode. With the 5672 the cathode is internally connected to the heater +ve, which does not allow it to be biased in the same way. Basically the cathode bias of a 5672 is fixed at the +ve heater voltage and inaccessible.

[andrew_k]

Nice one, look forward to hearing it!

[Boogdish]

how's the sound compared to an opamp based phaser?  Have you tried to implenent any feedback, like a resonance control yet?  This is a very cool idea.

[frequencycentral]

how's the sound compared to an opamp based phaser?  Have you tried to implenent any feedback, like a resonance control yet?  This is a very cool idea.

Well, it's not a phaser at the moment, it's a vibrato. The vibrato I would describe as 'wobbly' and 'underwatery' !! As I undestand it, a phaser is a vibrato with the addition of a feedback loop. I've tried a few ways to implement this, and have got tonal change (and whistling!), but nothing I would say is a usable resonance control. Any suggestions?

[Boogdish]

sorry, I meant to say vibrato.  I had just finished reading GEO article on phasers/flangers and had phasers on the brain.

[caress]

wouldn't a phaser just include some feedback and a dry blend?

[frequencycentral]

wouldn't a phaser just include some feedback and a dry blend?

Yeah - I'm having trouble implementing that for some reason. What I though should work doesn't work as I expected. Anyone care to draw me a diagram?

[caress]

all tube - you could use another 6111 as a splitter/buffer stage.  just split the signal and use 1/2 the 6111 for the clean blend, 1/2 to go to vibe section.  resistor/pot passive output mixer.
for resonance you could tap off pin 7 from the second 6111 and send back to pin 7 of the first 6111?  maybe check out the ross phaser schematic, they use an opamp in their feedback loop... not 100% sure why, though.

here's the schem for reference:



a bit BIG!

[frequencycentral]

OK, here's a soundclip: http://www.aronnelson.com/DIYFiles/up/Vintage_Vibe.mp3

Signal path:

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.

I've pretty much decided to build the Vintage Vibe as it is now, without modding it to do phasing too. I'll develop a phaser from it later on and do a seperate pedal - I've had a few hints from a certain 'tubey' gentleman. 

[andrew_k]

Love it! Wish I had time to breadboard it, but it's going to have to wait a month or so unfortunately.

[frequencycentral]

In the middle of my build right now. I'm using 7327 tubes instead of 6111, they are identical functionally. While swapping tubes out on my breadboard I've noticed that some are louder than others, so I think I'm going to have to tweak a couple of resistor values to get unity when I finish my build. Here's the layout I'm using,:

[German]

Parameters of LDR?

[frequencycentral]

Parameters of LDR?

Typical dark resistance = 1M Typical light resistance = 2K - 4K

[frequencycentral]

I've completed both boards and tested the oscillator:





........and here's the prototype on breadboard - sheesh what a mess:



You can see my homemade optocoupler on the right, covered in black foam. The mass of caps and diodes on the left is a MAX1044 charge pump circuit delivering ~70 volts - used in 'other experiments'.

[sweetwilly]

Again, beautiful work Rick.  That rainbow ribbon wire makes me so jealous, but glad the 7327's are working out!

[ralley]

Phew, that breadboard isn't a mess at all - better looking than some of my finished builds!  Your idea of writing the component values on bits of tape like that is sheer genius.  Love all these tube circuits you've come up with, I must source some tubes and start playing.

Rob.