New Phaser Design - “Causality 4” – Built with you in mind!

[bluebunny]

I'm pretty certain I built a C4 a long time ago using a board from Rick.  You might PM him to see if he has any lying around in the bottom of a drawer?

[FingerBlisters]

Is anyone offering a pcb for the mkII? It seemed like GuitarPCB did for a while but my query never got a response. Maybe someone on the forum can do single order fabs?

I'm working on one now, I'm just worried the pots might be backwards. It'll be for a 1590bb size.

[Will_em_all]

Always late to the party!

Built my lovely C4...except Vbias/Vref is WAY off. 1.8-2v
I've spent hours pouring over this thing and just can't figure it.

The 47k out of pin 14 on the 13700... where is that in the schematic? Pin 14 side, it's 1.8v; Width3 side it's 4.7-5.0v, which is funnily enough where I'd be happy with Vbias being...

Thanks in advance...

Will

[antonis]

Hi and Welcome..

Built my lovely C4...except Vbias/Vref is WAY off. 1.8-2v

There are two obvious reasons:
1. Wrong Vref resistive voltage divider values ratio..
2. Too much current drawn through divider upper resistor..

The 47k out of pin 14 on the 13700... where is that in the schematic?

Do you refer on the schematic below..?

[bluebunny]

I think it might be this one, since Will mentioned a "Width" pot:

[Will_em_all]

Thanks Antonis, Marc,

Yes, it's the mkII with the Width pot.

here are two obvious reasons:
1. Wrong Vref resistive voltage divider values ratio..
2. Too much current drawn through divider upper resistor..

No 1. was my first guess, but I can't find anything that appears to be pulling it down. I originally had the 100k trimmer mod between Vbias and pin 6 of the TL084, but went back to standard to remove as many variables as I can.
With the trimmer at its highest resistance I could get the voltages at the TL084 and 13700 closer, but still not in range, and I presume not operating correctly.

No 2. I've not considered... would a killer blue LED possibly do something like that? I've also got the Speed LED 2 (see vero layout on p.23) which gently increases in brightness with the first LFO cycle, but then never dims...

[antonis]

would a killer blue LED possibly do something like that?

No..
(at least, not without dipping +9V also..)

I've also got the Speed LED 2 (see vero layout on p.23) which gently increases in brightness with the first LFO cycle, but then never dims...

That calls for a permanently "high" LFO output..
(unsurprising 'due to different DC bias levels between inverting and non-inverting inputs..)

[Will_em_all]

That calls for a permanently "high" LFO output..
(unsurprising 'due to different DC bias levels between inverting and non-inverting inputs..)

Yes, that does make sense for the LED behaviour.

Guess I'll triple check the voltage divider values. I've also had a fudged-1M linear pot in for Speed, but can now switch that out for the correct reverse log. Not sure that would affect anything, but who knows at this point! 

[antonis]

First of all, fix that low Vref issue..!!
Unless, of course, your DMM has a very low impedance hence those "faulse" readings doesn't correspond to reality..)

Could you post some pics of your build..??
(items and solder sides..)

[Will_em_all]

Not sure if these work...
Be kind    I know they're rough! When I started it, I couldn't find my 'good' solder! Like doing surgery with a hammer.

[antonis]

RED frame  -> WARNING
GREEN frame -> CAUTION

[Will_em_all]

Thanks!   

Top right is fine, that's pin 1+2 of my trim pot - that I've taken out for now.

I'll check over the others again