mki x es.EDU Output Mixer

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Girts23
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mki x es.EDU Output Mixer

Post by Girts23 »

Hi, guys! Another module in the mki x es.edu series! The Output Mixer essentially is a panning mixer – it takes two mono inputs with adjustable gain and pans them left or right to a stereo output, and an integrated amplifier boosts the signal for use for headphones.
Image
This is slightly different user manual, because the mki x es.edu Output Mixer was developed in collaboration with Maris Zeltins, a teacher in Riga Technical University. So, instead of Moritz’s’ hand drawn breadboard images, we’ll split the schematics of the module in parts and take an academic look on each part and how it contributes to the functionality of the entire module.
The full kit is available from Erica Synths and the best DIY retailers all around the world.
Enjoy!
NanoTramp
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Re: mki x es.EDU Output Mixer

Post by NanoTramp »

First post, be gentle.

I'm a complete novice at this sort of thing but after finishing the build things are not quite what they should be. I can hear both inputs and the level knobs seem to work fine. But the panning is very off on both channels. Setting it to neutral means no sound comes out, but panning to either side increases the volume on both sides. I've clearly messed up somewhere, but was wondering if anybody knew roughly where on the board I should be looking/have any good ways of troubleshooting it.
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KSS
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Re: mki x es.EDU Output Mixer

Post by KSS »

Welcome to ModWiggler, NanoTramp!
Don't feel too bad. This manual really sucks compared to the others in the series.

The first think i'd look at is something often seen in new builders work.

Are the correct values of pots *and* resistors in the correct places.

The 4 around each pan pot and pan pot itself. In both of these you hve pots and resistors that share 1,0 as the first two digits 10K and 100k.
Check those.
NanoTramp
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Re: mki x es.EDU Output Mixer

Post by NanoTramp »

Hey,
I'm back. Thank you for the advice. As an update I have managed to fix it. It turned out it was one of the pins on the power connector had a bad solder joint. Re touching that and it worked as designed!

You're absolutely right about the manual though. I've really enjoyed going through the manuals, learning how the circuits work and building them up piece by piece. With this one being by a more academic author it just flew straight over my head. I'm sure there is an audience for this, but it wasn't me. My breadboards and wires just sat there unloved this time.

Still, not long until the wave folder gets released and then the kit is complete!
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doomcat
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Re: mki x es.EDU Output Mixer

Post by doomcat »

First time poster as well... google shows this as the only place someone reported problems, hoping its ok for me to do the same here.

I've built the power, sequencer and VCO without issue. The Output module is the first one that produced the magic smoke upon hooking up to power. Both R5 and R6 are burning up on power-on. New to modular, but I've been soldering for 35 years - and it looks clean with no cold joints or bridges. I'd put myself at the medium/intermediate level of electronics knowledge.

I've traced the circuit and everything seems it is where it should be. I have also tinned up the connections surrounding that part of the circuit (looks like power/noise conditioning?).

Image

Question. Regarding the voltage lines circled in the picture: even though they are the same voltage as the source, I'm guessing because of the diode that they are now isolated and won't signal continuity back to the original source.

At this point I'm not sure what else I should look at - there are test points, but no docs about how to use them. Other than starting to desolder everything and trying new components, what should I be looking for?
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doomcat
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Re: mki x es.EDU Output Mixer

Post by doomcat »

After a good sleep and a cup of coffee I noticed that I had mistakenly swapped two of the pots of varying resistance. Didn't pay close attention there and assumed they were all the same. I'll update once I get my hands on a better desoldering gun.
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KSS
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Re: mki x es.EDU Output Mixer

Post by KSS »

Welcome to Modwiggler, doomcat!

The diodes will have a drop so the voltage will not be the same. Continuity will depend on the testing voltage of your continuity checker. It has to overcome both the polarity and the forward voltage of these Shottky diodes.

I'd leave them out personally. Jumper them with resistor leads. They're an attempt at reverse polarity protection that comes with issues. The 10ohm resistors have done their 'job' by acting as cheap 'fuses' and again can best be left out once you confirm the build. They've become a cargo cult item often seen -and potentially useful in early stages of neophyte builds- but again will be best shorted out once your module is working correctly.

Between the diodes and the 10R's the designer's taken what's supposed to be a stable supply source and introduced two series elements in the main rails that vary with current draw. Not exactly best practice!.

The Hakko clone of the Denon SC7000 is hard to beat for de-soldering*. If you've been soldering 35 years you'll appreciate it immediately. Not cheap but not crazy expensive either considering what it brings to one's electronic DIY arsenal. You stop feeling like everything needs a socket because you can actually remove ICs -and other parts- quickly with ease and security in the result.

* I have and use the Denon which is significantly more expensive than the Hakko clone. But the reports online for the Hakko from people I trust gives me confidence to recommend it as more than just a cheapie Denon.
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doomcat
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Re: mki x es.EDU Output Mixer

Post by doomcat »

I actually got the Hakko - what a game changer - well worth the spend, so far.

I was able to move the pots to their correct places. This stopped the burn on the +12v line, but there is still a problem on the -12v side. The BD140 on that side gets quite hot, so perhaps I've already burned it out? Will have to research how to test those packages.

In the meantime, I've ordered and built a replacement module - its working just fine. It will serve nicely in troubleshooting, as I'm still determined to learn what went wrong on the original. I will take your advice. Much appreciated!
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