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Flanger issues
MUFF WIGGLER Forum Index -> Oakley Sound Systems  
Author Flanger issues
Leverkusen
I just finished the Flanger built but have difficulties getting it to work.

I tried to calibrate it and failed at the first level (probably somewhere earlier...) cause adjusting the TUNE trimmer does not change the frequency measured at pin 6 of U7. I get something between pulse and trapezoid waveform there, stable at a frequency of about 60 Hz. I am not sure how to properly do this with an analog scope I mainly have for watching waveforms but there should be change when I move the trimmer, shouldn't it?

When I patch in audio and an LFO I get something like flanging but no feedback. Also the switches have no effect. The CV2 pot seems to do what it should and while Drive does not sound very pronounced it affects bot LEDs - first green then red.

What I messed up during the build was the direction of half the diodes. I think D14
D19, D20, D10, D13, D9 were wrong. I carefully desoldered them and turned them around. After this the LEDs started working.

Any ideas what I could look after regarding the HFVCO which seems to be more of an LFVCO in my case?

It looks like this btw:

Synthbuilder
Check pin 8 of U2. That should be oscillating at the high frequency. If not then the core of the HFVCO is dead.

Definitely check D1 is around the right way. Check too that pin 16 is at 9V - put your probe on the IC pin itself to check. Make sure that Q1 and Q2 are the right parts, Q1 is a BC560 and Q2 is a BC550.

U2 is a 4069UBE. These are highly static sensitive and can be damaged if suitable precautions haven't been taken.

Actually, check pin 7 of U2 is at 0V with your scope. If you get the 60Hz (maybe its 50Hz?) signal there you may just have a bad ground/0V connection somewhere.

Tony
Leverkusen
Synthbuilder wrote:
Check pin 8 of U2. That should be oscillating at the high frequency. If not then the core of the HFVCO is dead.

Definitely check D1 is around the right way. Check too that pin 16 is at 9V - put your probe on the IC pin itself to check. Make sure that Q1 and Q2 are the right parts, Q1 is a BC560 and Q2 is a BC550.

U2 is a 4069UBE. These are highly static sensitive and can be damaged if suitable precautions haven't been taken.

Actually, check pin 7 of U2 is at 0V with your scope. If you get the 60Hz (maybe its 50Hz?) signal there you may just have a bad ground/0V connection somewhere.

Tony


Thanks Tony!

Now with a new probe I eventually found the oscillation, adjusted it to about 33k (as precise as I could get by converting cm on the display to Hz - I might need better measuring tools for things like this). Also I think I have both NULL trimmers set.

Now, while I get a sawtooth at R32 that is gently reacting to OFF2, on R45 I only get a spike waveform that is not reacting to OFF1.

Also adjusting FBK is not provoking any reaction while turning the panel pot does turn the auxiliary Feedback input on or off as expected. The overall flanging effect is very shy yet. It is somehow working and I get nice FM sounds out of the delay out with audiorate modulation but it sounds as if there is not enough delayed audio mixed back in the dry signal for a nice effect. Also when I patch a signal only into the feedback input the Mix Out is significant quiter than the Delay Output.

So could it be that there is something wrong the non inverting BBD line? In a way that the overall delayed signal is to weak for a pronounced flanging effect and feedback?
Leverkusen
...I worked myself through the schematic with the oscilloscope and found that the non inverted signal got lost between pin 5 and 7 of U8. It also looked suspicious there and after reflowing that part it sounds much better now and I get feedback. SlayerBadger!

I still might have to calibrate a bit, not sure about the 33kHz thing and the offset controls still don't do anything, no clipping either so I don't know if it is important. The CV2 input seems a little weak compared to CV1 though...
Leverkusen
Right, I found two more mistakes I made. CV2 was weak because U17 wasn't properly soldered and the Offset trimmers were 20R instead of 20k. d'oh!

While fixing this I somehow managed to kill the 4069 and had to replace it. d'oh! d'oh!

Plus my oscilloscope just died in between while doing nothing and I had to get a new one for the calibration routine (got me one of those cheap DSO 138 display-on-naked-PCB thingies nuts ).

Now the Flanger does work as expected and I am very happy with it. love

It was a bit adventurous to build after having done just a few digital eurorack modules with much smaller parts but not as many of them. I also learned a lot again though and it really sounds great! Also looking at it and knowing that I have build this feels good!

If there was a delay coming that sounds as nice and has those nifty Oakley features I most certainly would do it again.

Thanks Tony for all the work and dedication going into this...

we're not worthy
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