Miasma: Function Generator (DIY PCB based on Befaco Rampage)

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Mindrone
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Post by Mindrone » Tue Jul 09, 2019 4:18 pm

Hey guys, I want to do this build as well, and wondered if anybody has any panel/pcb laying around?

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MatrixModulator
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Re: diodes

Post by MatrixModulator » Wed Jul 24, 2019 7:51 pm

funkytransport wrote:what way around do the 4148 diodes go? the markings on the PCB arent obvious..
Download Kicad it's free you will see it, but there is a longer line on the diode silkscreen on the pcb, thats the line on the diode itself.
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MatrixModulator
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Post by MatrixModulator » Wed Jul 24, 2019 7:52 pm

okelk wrote:I have a problem with my build ( on both channels ).

They don't cycle. The timing cap only charges up to approx. 8.6V. So it never reaches the 10v reference voltage.

Any ideas what the problem could be?

Thanks!
Check your resistors near the bottom corners of the IO Pcb i had the same issue on one of mine. I was using the wrong value and it wasnt able to retriger.
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Sin_Phi
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Post by Sin_Phi » Mon Aug 26, 2019 12:19 am

I did a quick update to the IO board to fix the backwards pot. Files have been updated on the site. Note I updated my KiCAD so it is in a recovered state for the IO board.

No new insights on cycling issues from me. May give some of yall's fixes a try on my paperweights.

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MatrixModulator
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Post by MatrixModulator » Mon Aug 26, 2019 5:24 pm

Sin_Phi wrote:I did a quick update to the IO board to fix the backwards pot. Files have been updated on the site. Note I updated my KiCAD so it is in a recovered state for the IO board.

No new insights on cycling issues from me. May give some of yall's fixes a try on my paperweights.
Nice, thanks for the update. I was wondering if that reverse pots fix was just rewiring the pots pins or if you changed things around, not just the pots?
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Sin_Phi
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Post by Sin_Phi » Mon Aug 26, 2019 5:37 pm

It was literally flipping the pot in the schematic file and a bit of rerouting on the board file. Very simple fix that could be done with trace cutting on old boards. a simple verification step is to check that all 4 attenuverters have the ground pin in the same position.

I didn't want to do any major edits as I am not planning on building more to test in the near term.

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MatrixModulator
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Post by MatrixModulator » Mon Aug 26, 2019 5:56 pm

Sin_Phi wrote:It was literally flipping the pot in the schematic file and a bit of rerouting on the board file. Very simple fix that could be done with trace cutting on old boards. a simple verification step is to check that all 4 attenuverters have the ground pin in the same position.

I didn't want to do any major edits as I am not planning on building more to test in the near term.
Cool thanks, i'll rewire my pots :)
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Post by OIP » Mon Aug 26, 2019 6:41 pm

sounds like a good fix, thanks.

i snipped the pot legs and rewired to the traces on one of my builds and it works fine. been too lazy to do it to the other build yet.

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Post by squarewavesurfer » Mon Aug 26, 2019 8:32 pm

Sin_Phi wrote:It was literally flipping the pot in the schematic file and a bit of rerouting on the board file. Very simple fix that could be done with trace cutting on old boards. a simple verification step is to check that all 4 attenuverters have the ground pin in the same position.

I didn't want to do any major edits as I am not planning on building more to test in the near term.
Which pot was flipped? Was it the left side's rise attenuverter? Any others?




Also, has anyone played around with the mod mentioned below by jakobprogsch? It's one that I am interested in as I prefer the immediate cycle function of Maths as opposed to the 2 step process (cycle ON then trig ON) of miasma and rampage . Any risks or downsides associated with the suggested changes below? I'm also not sure how to replicate this on the miasma (which caps/resistors to bridge/remove).
jakobprogsch wrote:I had issues with EOC triggering external stuff when fall speed was set to low values on my Rampage. The fix, or rather alternative build, was to replace C23 and C24 with wires and remove R89 and R90 (in the Rampage schematic). This way you get a more Math like EOC that is always on if the EG isn't "doing something" instead of the pulse that default Rampage produces. It also results in it cycling the moment you flick the switch without first having to press the trigger. Maybe that would also help in this case?
Last edited by squarewavesurfer on Mon Nov 11, 2019 9:01 pm, edited 1 time in total.

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Sin_Phi
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Post by Sin_Phi » Tue Aug 27, 2019 3:33 am

C23 and C24 on the Rampage are the 100nf in the EOC detector, so C5 and C6 on the Miasma. R89 and R90 is the 1k pull down in the EOC detector of the Rampage, so R85 and R86 on the Miasma.

This mod won't hurt anything if it doesn't work. I don't see a downside really, just a different behavior. As long as whatever your triggering from EOC works on the rising edge I think you will be fine.

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Post by Nucleo » Fri Sep 13, 2019 1:25 am

Hi all. I've got a couple of Miasmas built(thanks to Sin Phi for the design!) which appear to be working fine but I'm unsure of one thing that I've just picked up. If I connect the OUT to my ST Modular CHAINS att/mult/mixer, the output appears to be unipolar. (Compared to if I plug my PEAKS into the CHAINS you can see it's a bipolar signal going by the LED color.)

I could stick it on the CRO but I'm guessing it won't show any different.

Is this normal? Reading the spec, it seems the OUT should be bipolar.

Thanks for any help!

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Post by MatrixModulator » Wed Sep 25, 2019 7:07 pm

So just before i start doing it on my 4 builds, can someone confirm that the reverse behavior of the attenuverters was only the left first chanel rise attenuverter? Fall seems ok on the first chanel and on second right chanel both rise and fall seems ok.

Basicly just need to rewire reversed the pins 1 and 3 of the first left channel rise attenuverter pot?

Thanks :)
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Post by OIP » Wed Sep 25, 2019 10:19 pm

i can check later tonight when at home to confirm but yes from memory that's the one. it's definitely only one pot. you can test the behaviour at audio rates, pitch goes down when it should go up etc. and / or a quick touch with a multimeter and the schematic will confirm it.

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Post by johndifool » Wed Oct 02, 2019 5:44 am

just finished building the Miasma. Sadly, there is something wrong with my build: it seems, that the 10R resistor on the negative rail, right after the power header, gets very hot! So i can measure the correct voltage just before it and the PSU is fine. but everything measured after that resistor is showing something around -1.5V. one thing i found out is, that it probably was not such a good idea, to use 1/10 Watt 0603 resistors all over, instead of 1/8W 0805, as in the BOM...?

so i did swap this resistor several times for a higher wattage one, but still the same problem. what could cause a behaviour like this? my guess would be a damaged 074 or the AD633, causing something weird on the power rail. Or could it be the wattage of the other resistors used!

apreciate any help! thx!

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Post by Altitude909 » Wed Oct 02, 2019 5:48 am

johndifool wrote:just finished building the Miasma. Sadly, there is something wrong with my build: it seems, that the 10R resistor on the negative rail, right after the power header, gets very hot! So i can measure the correct voltage just before it and the PSU is fine. but everything measured after that resistor is showing something around -1.5V. one thing i found out is, that it probably was not such a good idea, to use 1/10 Watt 0603 resistors all over, instead of 1/8W 0805, as in the BOM...?

so i did swap this resistor several times for a higher wattage one, but still the same problem. what could cause a behaviour like this? my guess would be a damaged 074 or the AD633, causing something weird on the power rail. Or could it be the wattage of the other resistors used!

apreciate any help! thx!
Power rail short. Check IC orientation/solder bridges

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Post by johndifool » Thu Oct 03, 2019 1:57 am

Yes, it was a bad AD633 (cheap chinese fake)!
Now its up and working fine, except for the Sum Output.
I did remove the AD, soldered R78 (100k), changed R67 to 100k and put in the Jumper on P7.
Is there anything else i should do, to make the Sum output working?
Any idea, where to look?
thx!

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Bran
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Post by Bran » Thu Oct 10, 2019 3:50 pm

Anybody happen to have a mouser cart they could share?

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Post by OIP » Thu Oct 10, 2019 8:06 pm

here's one from a while back, not sure if it's still good but hopefully somewhat useful
OIP wrote:not sure how much this helps but i have it so maybe better than nothing -
it's the caps, diodes, and ICs other than the matched transistor pairs:

https://au.mouser.com/ProjectManager/Pr ... bb10fab0ab

i got the resistors from tayda aside from the 23.7k. so this needs resistors, pots + jacks, LEDs, switches, matched transistors, headers, spacers.

100n caps are also out of stock in the last week but i just picked whatever was in stock.

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mouser cart incomplete

Post by gbel » Sun Oct 13, 2019 6:55 pm

Bran wrote:Anybody happen to have a mouser cart they could share?
Here is one I did, its missing some parts I sourced somewhere else. Tayda most likely. Also quantities are for more than one build.
It has all the resistors and caps. A very good start for sure.

https://www.mouser.ca/ProjectManager/Pr ... b3ad36ecc7

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Post by wtk » Sun Nov 03, 2019 7:16 am

Sin_Phi wrote:C23 and C24 on the Rampage are the 100nf in the EOC detector, so C5 and C6 on the Miasma. R89 and R90 is the 1k pull down in the EOC detector of the Rampage, so R85 and R86 on the Miasma.

This mod won't hurt anything if it doesn't work. I don't see a downside really, just a different behavior. As long as whatever your triggering from EOC works on the rising edge I think you will be fine.
can confirm, at my build it did not work triggering of other sides by eoc, despite eoc out worked for triggering other modules and also being able to trigger the miasma from other modules (which was really confusing), and after doing this it finally works as i would expect:)

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Post by KT » Thu Nov 28, 2019 8:14 am

Can somebody elaborate a bit on how to patch if I want to explore that four quadrant multiplier ? thanks

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squarewavesurfer
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Post by squarewavesurfer » Thu Nov 28, 2019 8:40 am

wtk wrote:
Sin_Phi wrote:C23 and C24 on the Rampage are the 100nf in the EOC detector, so C5 and C6 on the Miasma. R89 and R90 is the 1k pull down in the EOC detector of the Rampage, so R85 and R86 on the Miasma.

This mod won't hurt anything if it doesn't work. I don't see a downside really, just a different behavior. As long as whatever your triggering from EOC works on the rising edge I think you will be fine.
can confirm, at my build it did not work triggering of other sides by eoc, despite eoc out worked for triggering other modules and also being able to trigger the miasma from other modules (which was really confusing), and after doing this it finally works as i would expect:)
I finally got around to fixing the reversed rise attenuverter pot and did the cap/resistor mod and it works great. being used to maths I prefer this behaviour. I tested the EOC output with a few of my other modules and it triggers fine.

Thanks Sin_Phi!

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Post by OIP » Thu Nov 28, 2019 5:24 pm

that EOC mod means it just shoots up rather than being a trigger? i will do that this weekend.

i'm also interested in any suggestions for patching the 4Q multiplier! at the moment i've experimented with it briefly as a ring mod but that's it.

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shiny saw
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4Qx vs Inv Sum

Post by shiny saw » Mon Dec 02, 2019 8:30 pm

Hi,

could you guys share your impressions about the usability in practical terms of either the 4 Quadrant multiplier or Inverted Sum options?

Also, perhaps direct question to @Shi_Phi: I guess 'Inverted Sum' means the sum is inverted, I mean a negative version of L+R. Is this right? What exactly is the purpose of it being inverted?

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Post by mafouka » Sun Dec 15, 2019 4:39 pm

anybody got a Miasma FS? :goo:
這一生中有多少人擦肩而過?而朋友是多麼可貴啊

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