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WIGGLING 'LITE' IN GUEST MODE

heptaphasis - 3HP 7-phase LFO
MUFF WIGGLER Forum Index -> Music Tech DIY Goto page Previous  1, 2 [all]
Author heptaphasis - 3HP 7-phase LFO
charonme
I found out what the problem is: I tested T8 on a breadboard with 2N3906 and it worked perfectly, but for the PCB I used BC857. I soldered some legs to a BC857 and tried it on the breadboard instead of 2N3906 and now it behaves the same (broken) way as the PCB.

On mouser I noticed there are versions of the 2N3906 with different values of VCEO, VCBO, VEBO, Collector-Emitter Saturation Voltage and Maximum DC Collector Current. I have no idea what these are and which version I have

But when I add the original 1n4148 diode in series with the 10Ohm R38 it seems to be working fine. I originally had that diode there because it somehow seemed intuitively logical to me, but it was working (with 2n3906) even wihout it, so I removed it from the design d'oh!

I replaced the 10Ohm R38 on the PCB with a LL4148 and it works now, except at very low frequencies it starts noticeably interfering with the oscillation and introduces an offset. I'm considering completely removing this part of the circuit and lengthen the increased startup frequency by using a higher value cap for C24
guest
yeah, you were getting reverse leakage through the transistor (Vbe breakdown), and the diode acted as a backup to this.
charonme

guest
looks good!
cackland
Very nice smile

Couldn't see the LL4148 on the pcb...

A few questions:

- so you removed R38, R39, C21 and T8 and it still works? Wasn't this sub circuit of components meant to help with the initial voltage start up?

When you started it up in your video, why did it act the way it did if the circuit was removed?

Also, why would polyster through hole caps work over smd mlcc caps you replaced?
charonme
the 4148 was a temporary fix of the subcircuit around T8 which I finally removed because it still affected the oscillations, caused an offset etc. The T9 subcircuit that causes a temporary rise of the frequency at the beginning is still there, I just prolonged the period during which the freq is maxed out so that there is enough time for the amplitude to stabilize. However it still isn't ideal because if you turn it off and back on again the 10uF cap is still charged and the freq.rise period is too short for it to work, so you need to manually increase the frequency with the pot. In rev2 I might add a jfet that would discharge the cap when power is removed

cackland wrote:
why would polyster through hole caps work over smd mlcc caps you replaced?


turns out mlccs have some technological imperfections that make them unsuitable for this kind of application (for "timing caps"). I did often see in various DIY build documents and BOMs a note like "timing cap - use a good one", but I didn't know which are the "good ones" nor that there is such a huge difference in practice. Perhaps there even is a thread about this somewhere here or on electro-music

some info might be here:
https://www.muffwiggler.com/forum/viewtopic.php?t=82443
https://www.muffwiggler.com/forum/viewtopic.php?t=142469
http://electro-music.com/forum/topic-41821.html
I'd be interested in any other good info on this
charonme
frijitz
charonme wrote:
the 4148 was a temporary fix of the subcircuit around T8 which I finally removed because it still affected the oscillations, caused an offset etc.

Yeah, I never understood that one. Seems to me it forces the system into a non-quadrature state. What would be good about that?
Quote:
turns out mlccs have some technological imperfections that make them unsuitable for this kind of application (for "timing caps"). I did often see in various DIY build documents and BOMs a note like "timing cap - use a good one", but I didn't know which are the "good ones" nor that there is such a huge difference in practice. Perhaps there even is a thread about this somewhere here or on electro-music

It's pretty standard to use silver micas for timing caps. What "technological imperfections" are you refering to?

Ian
charonme
frijitz wrote:
it forces the system into a non-quadrature state
it just introduced a nanosecond disturbance that was supposed to instantly make the circuit to oscillate at a higher amplitude like this:
it worked well at some specific conditions, but created other problems because the transistor leaked even after it was shut off.


frijitz wrote:
What "technological imperfections" are you refering to?

nothing specific, I don't know anything about caps as was clearly demonstrated when I assumed the SMD caps I bought would work smile I just referred to the fact that it didn't work there properly and not because it would be a faulty product
charonme
frijitz wrote:
This design has pretty low distortion. I just measured it again

how did you measure it and what circuit exactly did you measure? I'd like to measure the distortion of the one I have here, but the frequencies are well below what my scope's spectrum analyzer could display nor do I have a dc coupled computer interface
frijitz
charonme wrote:
frijitz wrote:
This design has pretty low distortion. I just measured it again

how did you measure it and what circuit exactly did you measure? I'd like to measure the distortion of the one I have here, but the frequencies are well below what my scope's spectrum analyzer could display nor do I have a dc coupled computer interface

It was the original design with manual control — the one Yves modified. I recorded it at a couple hundred Hz and analyzed it with software.
EATyourGUITAR
I think it would be way more punk if you named it "hepatitis" and put it on a rusty iron panel SlayerBadger!
charonme
lol yes, but it would be much harder to google it wink
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