mki x es.EDU VCO

[fosimoor]

Also I think it's possible i blew one of the ICs (TL074). I thought I heard a pop, and it got really hot. Is there a way of testing if it's still good?

Unfortunately, the chip getting hot is often a surefire sign you connected the power backwards (i.e. you connected + to - and vice versa)

[thecrimpmaster]

Welcome to ModWiggler, thecrimpmaster!

Very first time builder here, and a bit lost. Apologies for the basic questions. I'm trying to put together the very first step on a breadboard but I can't hear any sound at all. Are there any tips on how to trouble shoot a circuit, where/what/how should I test with a multimeter?

First make sure the power pins are correct and the voltages are also correct. Some whiteboards are crap. Try moving the circuit to a different part of the breadboard.

Also I think it's possible i blew one of the ICs (TL074). I thought I heard a pop, and it got really hot. Is there a way of testing if it's still good?

Look online for the pinout of the '074. What you'll find are power pins in the middle of each row, with the remaining 12 pins grouped so each 3 pin 'corner' group has an op amp with positive input, negative input and output pin.

The simplest circuit to test is a buffer. That means you connect the minus and output pins together. Then you put some voltage or signal on the positive input pin. What you put in should be what you see-hear at the output. 1V in, 1V out. 5V in 5V out. Saw in, saw out. Audio signal in, audio signal out. Since there is no external IC pin for GND in this setup you get the GND-0V for your meter and inputs, outputs from your dual power supply.

Do this for each group of three pins and you'll know if the part is still working!

Be sure you have the power supply -pins 4 and 11- connected according to the pinput-drawing you saw on the net or in the 074 datasheet.

Dual and single op amps can be tested the same way. Identify the power pins. Identify the three -primary- pins of the op amp or op amps in the package.

Dual op amps will have two power pins and two groups of three pins.
Single op amps will have the three pins and power pins, but not in the same locations.

The 'extra' pins -beyond the 3+2- are used in various ways depending on the actual type of op amp. They are not needed for a basic functional test.

Hey KSS, thank you very much for the welcome and the reply. I found a few of my mistakes after posting. And I also learned about continuity :-) It turns out the breadboard I bought didn't have a continuous power rail (but had no markings to indicate this!).

I bought a couple of more ICs, a new breadboard and a more careful eye on the diagrams (not upside-down IC placement) and I've managed to get to the end of the breadboard build with close to what was described (I need to buy a sequencer now too to fully test). I also ordered my solder equipment for the next step :fingerscrossed:

When I pull apart my circuit on the breadboard I'm going to go through the steps you listed on how to test the IC (even though I know it's definitely broken). Thanks again for the reply, it'll really help me in the future

[thecrimpmaster]

Also I think it's possible i blew one of the ICs (TL074). I thought I heard a pop, and it got really hot. Is there a way of testing if it's still good?

Unfortunately, the chip getting hot is often a surefire sign you connected the power backwards (i.e. you connected + to - and vice versa)

Yep, didn't pay close enough attention to the dot on the diagram and put it in upside-down

Ordered a replacement and got something working though (as the post above), so on to the full build.

Thanks for the reply and confirmation of my mistake!

[Whatthevolt]

hi all

Module soldered and sounds all good.
However the chips get really hot. too hot to touch really.

Wondering if that’s normal, or if anyone has any advice?
The notches align with the notches on the board so they’re aligned correctly.

[Mickleman]

I have managed to complete the module but once power was put through it the two 10 ohm resistors (R14 & 15) started to smoke. I found out this could be caused by a short or something put in or soldered in the wrong way around. Turns out that one of my IC's was put in incorrectly, I rectified this and once the module was powered up again I had sound....but way too high! What ever I do either with the trimmer pot or the course tuner I cannot move the pitch of either the saw tooth or pulse wave down to any where close to C0. I have used an SQ1, an Arturia Keystep Pro and a Doepfer Darktime, no change - too high. I have checked the soldering and re-soldered some joins, I have checked the values of placed components, against the placement diagrams on p.50 of manual. Nothing - still too high. Could I have damaged either one of the IC's? Could this damage cause the pitch to be too high? I am at a lost and feel that I cannot move forward at the moment with this project. If anyone here has any ideas please let me know, I don't want to give up yet.

[KSS]

Module soldered and sounds all good.
However the chips get really hot. too hot to touch really.

Wondering if that’s normal, or if anyone has any advice?

In an analog synth circuit I would not consider too hot to touch to be normal normal outside of inverters used as amplifiers. Seen in the 4069 VCO of Rene Schmitz and a few others.

Best to ask the mki x es.EDU designers.

And welcome to ModWiggler!

[KSS]

I have managed to complete the module but once power was put through it the two 10 ohm resistors (R14 & 15) started to smoke. I found out this could be caused by a short or something put in or soldered in the wrong way around. Turns out that one of my IC's was put in incorrectly, I rectified this and once the module was powered up again I had sound....but way too high! What ever I do either with the trimmer pot or the course tuner I cannot move the pitch of either the saw tooth or pulse wave down to any where close to C0. I have used an SQ1, an Arturia Keystep Pro and a Doepfer Darktime, no change - too high. I have checked the soldering and re-soldered some joins, I have checked the values of placed components, against the placement diagrams on p.50 of manual. Nothing - still too high. Could I have damaged either one of the IC's? Could this damage cause the pitch to be too high? I am at a lost and feel that I cannot move forward at the moment with this project. If anyone here has any ideas please let me know, I don't want to give up yet.

First and foremost, Welcome to ModWiggler -and SDIY!- Mickleman!

You're right not to give up. Such things as you're dealing with have happened to all of us at some point and getting past them is part of the process.

Yes, there is probably something else damaged -not necessarily an IC- and yes it could be causing the pitch to be too high. Possible suspects are low value resistors -which can change their value or burn out, and depending on their function in the circuit can be causing the response change. Or hurting some other component. Capacitors of film type can definitely be ruined or have their values changed by excessive heat from reversed rails. <--The capacitor itself is not harmed -unless a polarized type like Tantalum or electrolytic- but the circuit around it may be placing too much stress upon it during the mistaken IC direction. Check the electrolytic caps first and look for the effects of over-heating for all components. Brown, burned, something that looks like spit out goo..

Trim pots are another candidate to be altered or wrecked by a reverse voltage situation. Again, it's not that they cannot take reverse voltage, they can. But during the time it was powered up with the chip incorrect, the circuit is doing things unexpected and some trims -like a V-oct trim will have a low value. Low value resistors are always more susceptible to over-voltage faults due to Ohms law. It's much worse and more likely today due to vastly reduced watt rating for pots of all types. This means your coarse and fine panel pots can also be a potential risk. <--But less than the others listed so far. In most cases. <--This is REALLY important. Most cases means exactly that. You can't 'assume' anything is or isn't the problem only by guess and by golly. Doing that will very quickly lead to chasing your own tail.

Work through the circuit and look carefully at the PCB for clues. But it does make sense that if one IC was burned from reverse voltage that another might have also been altered or ruined. <--In this case you have a clear reason to suspect the remaining chips. What you want to avoid is getting in a habit of 'blaming' the ICs. Too many do this because if they've used sockets they figure, WTH, I'll just replace it and see. Normally I'd *strongly suggest not dong that. Here, in *this* case, you might want to try the other IC too. But check the other suggestions above first.

Take a photo with your phone and put it on the biggest screen you have to look with 'new' perspective. Post the photos here for others to help look.

[Mickleman]

Hey KSS, thanks for the very informative and prompt reply. I was also thinking that I might have messed up the transistors, they are in the right place but soldered very poorly, I attempted to solder them again from the front panel but no change to the high pitch. I have include photos of the front and back of the module, I am a bit ashamed of the back panel photo as the soldering is so poor and this may be a contributing factor. I know....practice, practice, practice!

VCO Front panel

VCO Back Panel

Great tip about enlarging it on screen, now back to trouble shooting the board. Thanks again.

Realised that the titles of the photos are the wrong way around , front should be back and so on!

[Whatthevolt]

Yet another question..

Checking continuity between the solder points on the jacks and the power pins.

There is continuity between ground and various headphone jack pins - more than I had anticipated. It’s there between all pins of the input jacks. but just the bottom ones of the output jacks. Does that make sense and sound correct..?

[Whatthevolt]

Hey KSS, thanks for the very informative and prompt reply. I was also thinking that I might have messed up the transistors, they are in the right place but soldered very poorly, I attempted to solder them again from the front panel but no change to the high pitch. I have include photos of the front and back of the module, I am a bit ashamed of the back panel photo as the soldering is so poor and this may be a contributing factor. I know....practice, practice, practice!
VCO fron panel.jpg VCO back panel.jpg
Great tip about enlarging it on screen, now back to trouble shooting the board. Thanks again.

Realised that the titles of the photos are the wrong way around , front should be back and so on!

Soldering in general seems like it could do with another go - there are joints that don’t look great there, especially on the bottom of the ICs and jacks? I’m not an expert at all (hence me posting here myself!) but I think it might need more solder and more heat..?

[KSS]

I wouldn't suggest more heat or soldering. It's not terrible fora beginner and mostly ok. The specific obvious trouble areas are:
-some GND pins 3,4,5,6,7,8 of the power connector. <--Pin duplication means this probably still works.
-Pin 10 of the IC closest to the metal shaft pot.<--This is the only one that appears in *need* of re-soldering.
-melted housing of the blue box film cap next to C6. C3?

The bigger issue is the flux and spatter. That's easily capable of causing a problem like that described. Get a toothbrush and some high purity isopropyl alcohol. All those specs of solder need to be gone. Looks like spray from prior rework clearing holes. Or an iron that was WAY too hot. But probably rework.

The blue box cap is quite likely the VCOs timing cap and the heat that melted-damaged its case could have easily 'adjuated' its value too.

[Whatthevolt]

hi all

Module soldered and sounds all good.
However the chips get really hot. too hot to touch really.

Wondering if that’s normal, or if anyone has any advice?
The notches align with the notches on the board so they’re aligned correctly.

Just an update in case anyone else is looking..

The hot chip was the 40106.

I’ve swapped it for another 40106 (I got some from eBay for breadboard tinkering) and this one is fine. Doesn’t seem to get perceptibly warm at all in the same time frame the other one became lava.

I guess I got a faulty chip..

[Mickleman]

I wouldn't suggest more heat or soldering. It's not terrible fora beginner and mostly ok. The specific obvious trouble areas are:
-some GND pins 3,4,5,6,7,8 of the power connector. <--Pin duplication means this probably still works.
-Pin 10 of the IC closest to the metal shaft pot.<--This is the only one that appears in *need* of re-soldering.
-melted housing of the blue box film cap next to C6. C3?

The bigger issue is the flux and spatter. That's easily capable of causing a problem like that described. Get a toothbrush and some high purity isopropyl alcohol. All those specs of solder need to be gone. Looks like spray from prior rework clearing holes. Or an iron that was WAY too hot. But probably rework.

The blue box cap is quite likely the VCOs timing cap and the heat that melted-damaged its case could have easily 'adjuated' its value too.

I set the iron to 330c after reading comments from other contributors maybe could go down to 320c. I accidently touched the 1uf film cap with my iron while re-soldering. I did quite a bit of rework so that's probably the cause of the excess flux. Will touch up pin 10 of the TL074, clean the board and touch up the suggested GND pins of the power connector. If the pitch is still too high then I have probably gubbed the film cap. Thinking that I might get another VCO kit from Erica Synths and try again, but it would still be good to get this module working.

[msegarra]

I’ve looked but can’t figure it out do these modules work with standard Eurorack power buses? Or do they only work on their .edu case?

[Mickleman]

I’ve looked but can’t figure it out do these modules work with standard Eurorack power buses? Or do they only work on their .edu case?

I have powered up this module in an .edu case and Eurorack power bus (Doepfer), same problem but am now tackling tasks set out by KSS, hopefully will do the trick

[Whatthevolt]

I’ve looked but can’t figure it out do these modules work with standard Eurorack power buses? Or do they only work on their .edu case?

Standard Eurorack power supply- they can live alongside other modules. I’ve got mine in a Rackbrute. I figured I’d want a little expansion after finishing the set. Wasn’t sure on the best approach to take, whether to get the EDU case and treat it as a single instrument or not.. but I want to try some other DIY modules!

[Whatthevolt]

I wouldn't suggest more heat or soldering. It's not terrible fora beginner and mostly ok. The specific obvious trouble areas are:
-some GND pins 3,4,5,6,7,8 of the power connector. <--Pin duplication means this probably still works.
-Pin 10 of the IC closest to the metal shaft pot.<--This is the only one that appears in *need* of re-soldering.
-melted housing of the blue box film cap next to C6. C3?

The bigger issue is the flux and spatter. That's easily capable of causing a problem like that described. Get a toothbrush and some high purity isopropyl alcohol. All those specs of solder need to be gone. Looks like spray from prior rework clearing holes. Or an iron that was WAY too hot. But probably rework.

The blue box cap is quite likely the VCOs timing cap and the heat that melted-damaged its case could have easily 'adjuated' its value too.

I set the iron to 330c after reading comments from other contributors maybe could go down to 320c. I accidently touched the 1uf film cap with my iron while re-soldering. I did quite a bit of rework so that's probably the cause of the excess flux. Will touch up pin 10 of the TL074, clean the board and touch up the suggested GND pins of the power connector. If the pitch is still too high then I have probably gubbed the film cap. Thinking that I might get another VCO kit from Erica Synths and try again, but it would still be good to get this module working.

I reckon you can rescue it honestly. You can get spares parts from eBay easily enough to replace those that you suspect have died.

I got myself some prototyping board and general cheap components to get a feel for soldering first and I’m glad I did..!

[msegarra]

I’ve looked but can’t figure it out do these modules work with standard Eurorack power buses? Or do they only work on their .edu case?

Standard Eurorack power supply- they can live alongside other modules. I’ve got mine in a Rackbrute. I figured I’d want a little expansion after finishing the set. Wasn’t sure on the best approach to take, whether to get the EDU case and treat it as a single instrument or not.. but I want to try some other DIY modules!

Awesome thanks!

[Mickleman]

I wouldn't suggest more heat or soldering. It's not terrible fora beginner and mostly ok. The specific obvious trouble areas are:
-some GND pins 3,4,5,6,7,8 of the power connector. <--Pin duplication means this probably still works.
-Pin 10 of the IC closest to the metal shaft pot.<--This is the only one that appears in *need* of re-soldering.
-melted housing of the blue box film cap next to C6. C3?

The bigger issue is the flux and spatter. That's easily capable of causing a problem like that described. Get a toothbrush and some high purity isopropyl alcohol. All those specs of solder need to be gone. Looks like spray from prior rework clearing holes. Or an iron that was WAY too hot. But probably rework.

The blue box cap is quite likely the VCOs timing cap and the heat that melted-damaged its case could have easily 'adjuated' its value too.

I set the iron to 330c after reading comments from other contributors maybe could go down to 320c. I accidently touched the 1uf film cap with my iron while re-soldering. I did quite a bit of rework so that's probably the cause of the excess flux. Will touch up pin 10 of the TL074, clean the board and touch up the suggested GND pins of the power connector. If the pitch is still too high then I have probably gubbed the film cap. Thinking that I might get another VCO kit from Erica Synths and try again, but it would still be good to get this module working.

I reckon you can rescue it honestly. You can get spares parts from eBay easily enough to replace those that you suspect have died.

I got myself some prototyping board and general cheap components to get a feel for soldering first and I’m glad I did..!

Thanks for the encouragement, got to clean the board yet then maybe get a new film cap (if that's the problem). Definitely will practice on a test board before the next module, I'm afraid the old enemy, impatience, got hold of me

[patternmusic]

Synth DIY Guy points out in his envelope build video that you are going to need two envelopes for the full kit. (Plus you may want two VCOs.)


A note on Erica's page for the Envelope kit points this out too.

NB! The full EDU DIY system is designed to have 2 EG modules, therefore everyone aiming to build the whole system will need 2 kits.

https://www.ericasynths.lv/news/edu-diy-eg/

[TheAnswerIsYes]

I'm a little behind, but I finally built the VCO after breadboarding. Have started on the VCA, and have the case and 2 x envelopes come next. What a great entry point for people interested in Eurorack.

[Matariel]

Hi guys, having built a bunch of DIY gear before, I dove right into the build without breadboarding, which might've been a mistake as the only signal I get is a constant ~+4v out of the square that switches to -4v when I turn up the PWM, and similar "popping" to some others earlier in the thread.
No magic smoke or overheating of components, but after reading some advice from previous posts, I'll get some alocohol and scrub the flux off the board and give the test points a measure.
I think I'll breadboard future EDU DIY builds first from now on haha...

[c0rt3x]

Hi guys, having built a bunch of DIY gear before, I dove right into the build without breadboarding, which might've been a mistake as the only signal I get is a constant ~+4v out of the square that switches to -4v when I turn up the PWM, and similar "popping" to some others earlier in the thread.
No magic smoke or overheating of components, but after reading some advice from previous posts, I'll get some alocohol and scrub the flux off the board and give the test points a measure.
I think I'll breadboard future EDU DIY builds first from now on haha...

Not really sure. My routine would be to first check all solder points for cold joints or bridges. Then I check all resistors for their value with the multimeter. Then I check all caps with the multimeter, if they get charged (measuring their resistance charges them with the battery of the multimeter).

I also had a lot of problems with potentiometers: In my first builds, I applied heat too long for soldering them. This is damaging the potentiometer in a way, that it looks like a loose connection or having a constant very high resistance. The solution to prevent this is just to turn up heat and apply the soldering iron for a maximum time of 2 seconds. However, I measure all pots in all different positions and the multimeter pins connected in different ways to also detect this tricky 'loose connection' faults.

The last thing would be measuring under voltage the points in the circuit you know the target voltage and if there are any deviations.

[KSS]

I also had a lot of problems with potentiometers: In my first builds, I applied heat too long for soldering them. This is damaging the potentiometer in a way, that it looks like a loose connection or having a constant very high resistance. The solution to prevent this is just to turn up heat and apply the soldering iron for a maximum time of 2 seconds. However, I measure all pots in all different positions and the multimeter pins connected in different ways to also detect this tricky 'loose connection' faults.

Nobody seems to take the time now to use an old-school solution; a clip-on heatsink. With many electronic components today using thermoplastic resins where once only thermosets were used -AKA pot and switch body plastic- these inexpensive little soldering aids shold be seen *more* often. not less!

Thermoplastic melts and sets by cooling. A reusable plastic.
Thermosets don't melt -but can be burned- and set by chemical reaction. Requires special consideration for re-use and not always even possible.

Surgical clamps aka hemostats can be used but are not as effective as the little aluminum types due to stainless steel material. Don't use Hemostats with serrated jaws! They'll bite and make weak points in the component leads. Just waiting for some road vibration to ruin your day with an odd and hard to find problem at a gig.

[Matariel]

Not really sure. My routine would be to first check all solder points for cold joints or bridges. Then I check all resistors for their value with the multimeter. Then I check all caps with the multimeter, if they get charged (measuring their resistance charges them with the battery of the multimeter).

I also had a lot of problems with potentiometers: In my first builds, I applied heat too long for soldering them. This is damaging the potentiometer in a way, that it looks like a loose connection or having a constant very high resistance. The solution to prevent this is just to turn up heat and apply the soldering iron for a maximum time of 2 seconds. However, I measure all pots in all different positions and the multimeter pins connected in different ways to also detect this tricky 'loose connection' faults.

The last thing would be measuring under voltage the points in the circuit you know the target voltage and if there are any deviations.

Thanks for the tips, haven't had time to dive into troubleshooting yet, but melted pots is definitely a possibility. I use an older hand-me-down soldering iron that doesn't have temperature adjustment so I have no idea what it's running at, and I've never used those type of pots before. It definitely took longer to solder in the ground tabs than most components, so they could've gotten cooked in the process.
I have an electronics store literally down the road from me, so I'll pick up some extra parts to try.
There's a second VCO module kit on the way to me as well, gotta work out the bugs and learn so I can build the second without any trouble.