heptaphasis - 3HP 7-phase LFO

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charonme
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Post by charonme » Sat May 25, 2019 2:11 am

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 :doh:

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
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Heptaphasis - DIY 3HP 7-phase quadrature sine LFO

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Post by guest » Sat May 25, 2019 3:09 pm

yeah, you were getting reverse leakage through the transistor (Vbe breakdown), and the diode acted as a backup to this.
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charonme
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Post by charonme » Sun May 26, 2019 5:52 am

[video][/video]
Image
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Heptaphasis - DIY 3HP 7-phase quadrature sine LFO

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Post by guest » Sun May 26, 2019 12:17 pm

looks good!
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Post by cackland » Sun May 26, 2019 1:31 pm

Very nice :)

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?

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Post by charonme » Mon May 27, 2019 12:46 am

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:
viewtopic.php?t=82443
viewtopic.php?t=142469
http://electro-music.com/forum/topic-41821.html
I'd be interested in any other good info on this
Last edited by charonme on Mon May 27, 2019 7:18 am, edited 1 time in total.
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Heptaphasis - DIY 3HP 7-phase quadrature sine LFO

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Post by charonme » Mon May 27, 2019 3:12 am

[video][/video]
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Heptaphasis - DIY 3HP 7-phase quadrature sine LFO

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Post by frijitz » Mon May 27, 2019 7:25 am

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?
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?

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Post by charonme » Mon May 27, 2019 11:07 am

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: Image
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 :) I just referred to the fact that it didn't work there properly and not because it would be a faulty product

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Post by charonme » Mon May 27, 2019 11:38 am

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
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Post by frijitz » Mon May 27, 2019 1:15 pm

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.

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Post by EATyourGUITAR » Tue May 28, 2019 11:41 pm

I think it would be way more punk if you named it "hepatitis" and put it on a rusty iron panel :sb:
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Post by charonme » Wed May 29, 2019 12:51 am

lol yes, but it would be much harder to google it ;)
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Re: heptaphasis - 3HP 7-phase LFO

Post by undress » Sun Jan 19, 2020 1:43 pm

hello, are there any updates to this project?

are the gerbers on the github fully functional?

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Re: heptaphasis - 3HP 7-phase LFO

Post by charonme » Sun May 10, 2020 4:11 am

no update, it works for me :)

I believe those gerbers are probably the ones I uploaded to pcbway to get my PCBs
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Re: heptaphasis - 3HP 7-phase LFO

Post by KittenVillage » Tue Jun 23, 2020 1:06 am

I'm thinking of giving this a run at the end of the summer using the v2 board on charonme's site. Does anyone have a panel layout for this board?


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