DEFX Lola Phase: LFO question

[spacekid71]

Hi everyone,

I have built the DEFX Lola Phase (https://drive.google.com/file/d/1WDIcJKwfED5GuEUQh-Zo87qZaRinuMxV/view) and initially I had some problems with the power supply part of the circuit but I have been able to resolve that. I had put 12K instead of 12R resistors, and I also fried the 7815 while investigating...

Now the square green LEDs turn on so that seems good but I thought that they would always flash based on the RATE and DEPTH pots... The phasing also doesn't work so I am suspecting that the Sweep Generators/LFOs don't work.

Any help would be great, I can provide more information if needed.

Thanks!

Martijn

[Kevin Mitchell]

Is the LFOA rate switch in the up position for internal modulation or is down for pedal mode?

[spacekid71]

The Rate Control switch is in Manual mode (UP) but the green LED is not flashing.

[Kevin Mitchell]

Okay just checking! Always have to ask the silly questions first.
With a voltmeter on pin 1 of IC45 do you see any oscillation? May have to turn the rate CCW and the depth CW for best observation.

Do any of the LFO control effect the LEDs?

Also feel free to post a photo of the boards. I have a working unit - still need to finish it up and do a build report but I can eye the values for you - which is easier than verifying them one by one. Wrong values are more typical than bad parts.

[spacekid71]

So I had a look at IC45 and it seems totally off... I measured the following:

IC45
1:    0.03V
2:   -0.03V
3:   -0.02V
4:   -1.26V
5:    0.00V
6:    0.01V
7:    0.01V
8:    0.64V

Pin 4 should be -15VD and pin 8 should be 15VD according to the DEFX schematics...

I checked that the middle header has -15, GND, +15 and it does...

Anyway I am adding some photos of the boards so you can have a look at them as well.

[bluebunny]

You need to trace through the +/-15V power lines until you find where they cut out.  Perhaps a short, perhaps a bad solder joint.  Without power, that IC will do nothing. 

[spacekid71]

Okay so the +/-15V on the header is taken directly from the power supply section that has the voltage regulators on the control PCB.

On both the control PCB and the effect PCB it then gets changed to +/-15VD. There are two 12 Ohm resistors in this section and I put 12K resistors in both sections.... This is why I am currently having problems with the effect PCB still. I will be replacing the 12K resistors with the 12R resistors and see if the pedal starts working.

I would be interested in knowing what 15VD means compared to 15V.

Thanks for the help so far!

[ElectricDruid]

On both the control PCB and the effect PCB it then gets changed to +/-15VD. There are two 12 Ohm resistors in this section and I put 12K resistors in both sections.... This is why I am currently having problems with the effect PCB still. I will be replacing the 12K resistors with the 12R resistors and see if the pedal starts working.

Yep, that'd probably do it!! So you need to swap the 12K's to 12R's on both boards, right? (you said you put 12Ks "in both sections").

I would be interested in knowing what 15VD means compared to 15V.

The "VD" supplies are a filtered version of the main 15V supplies, and they've provided separate filtered supplies on each board. R1/C5/C7 and R2/C6/C8 are lowpass filters. This is usually done to keep noise created in one part of the circuit out of other parts of the circuit. In this case, the LFOs would be a likely source of ticking noises, so they have their own filtered supply. I'm not sure why they bothered for the page with the CV input on it, but presumably they had a reason. I also can't explain why they chose to call it "VD", but I suppose it's as good a name as any!

HTH

[bluebunny]

Those two 12R resistors are probably playing the role of fuses.  You could short them out temporarily until you can replace them.  (Do you have any other low-value resistors to hand?)

[spacekid71]

Thanks for the explanation ElectricDruid and bluebunny, I understand better now how the whole circuit works.

Just for clarity, I had put 12K resistors in place of all 12R resistors so I have to swap them out. What's even worse is that I had bought the 12R resistors but just didn't use them!

[ElectricDruid]

Those two 12R resistors are probably playing the role of fuses.  You could short them out temporarily until you can replace them.  (Do you have any other low-value resistors to hand?)

Given that I just worked out the cutoff and it comes out at 282Hz, I think I agree! Those values aren't really doing a whole lot of filtering (especially not of LFO frequencies, although LFO ticking will be mostly higher harmonics).

[spacekid71]

I swapped the resistors and now the pedal is working! Thanks again ElectricDruid, Bluebunny, and Kevin Mitchell for the help on this one.

Last night I tried it out and it sounds awesome. I will be calibrating the pedal using the procedure in the DEFX build instructions and also building out the expression pedal now.

Other than that I was wondering if there is a mod available where a LED flashes at the rate and depth of the LFO/pedal sweeping. Maybe it has been done before?

[bluebunny]

Good news!