[IN STOCK] Eurorack 4hp THAT2180-based Audio VCA

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zrknlzr
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Post by zrknlzr » Wed Dec 16, 2015 3:59 am

Thanks for your response. Also no changes when i turn the offset. I double checked my multimeter but it's a cheap one and i did check all orientation relevant parts.
VCA doesn't affect the signal at all don't matter which pot i turn it all goes clean in and out.
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Post by AndrewM » Fri Jan 01, 2016 9:31 pm

negativspace wrote:A regular 0805 1k resistor will work just fine as a substitute.
Phew!

I received my kit from Synthcube (PCB v1.2) and it came with an 0402 PTC thermistor (a Murata PRF15BD102RB6RC from Mouser). It was going to be a definite challenge to solder that one - and I had thought that the 0805 caps were bad!

Alas, as I was removing the resistor from the tape, the flap of plastic managed to sproing the resistor... well, somewhere. Definitely not into the dish I was trying to drop it into, nor on my desk either. :doh:

Rather than sift through every piece of dust near my desk, I think I'll just pick up an 0805 1k resistor from the local electronics shop instead.

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Post by billieblaze » Sun Jan 03, 2016 9:17 pm

I got one of these from SythCube, v1.2. fired it up before seeing the mods, noticed the smaller opamp was warm - not hot. no sounds in or out.

If anyone has any immediate ideas or things to check, I'd love to hear them!

I'll try to trace through the schematic a bit with a scope and see if i can find where it drops off.

EDIT: I don't get much of anything just after the 20k resistor.. what in the world?!

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Post by Sleipnir » Tue Jan 19, 2016 2:44 am

I just finished my MA VCA kit from Thonk.
Great kit, fairly easy build. :tu:
I'm having some minor issues though, and wondering if my experience matches any others.
1. Even after calibration, no signal comes out until the Offset knob is around 2:00, then it ramps up quickly. Not just using ears, but a scope.
2. There is a small ultrasonic output, even with Offset/cv zeroed. I can't hear anything, but am slightly concerned about artifacts once it's part of a mix.

Just wondering if the knob thing is normal, and if the oscillation is my screwup and if there are any pointers for troubleshooting.
Still makes an awesome AM module :nana:
Edit: added scope pics

~1khz sine from a Dixie, through mavca, offset @ max:
Image

Zoomed *way* in on the sine curve:
Image

Maxfreq of Dixie (18khz?) sine. You can see the individual wiggles now. Something like 120+kHz?
Image

Reference maxfreq Dixie output, bypassing mavca
Image

:despair:

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Post by neil.johnson » Thu Feb 11, 2016 10:07 am

It would help if you could post the scope timebase setting.
Also your exact test setup - do you have any cables plugged into the output for example?
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Post by negativspace » Thu Feb 11, 2016 4:21 pm

The only way I've ever been able to get one of these to oscillate is by omitting the SMT bypass cap nearest the 2180. That one's critical.

The control curve also sounds way off, it should respond more or less like any other audio/log VCA. (From full CCW to ~9:00 it may not produce much sound but then it'll come in gradually from there.)

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Post by DJMaytag » Sat Mar 05, 2016 11:38 pm

Sourcing isn't my forte either. Just checking on a couple things since this BOM was made up:

Would this 0.1uF ceramic disc cap work instead of the one in the cart above? Looks like there's a minimum requirement of 200 0.1uF caps?

Also, LME49710NA/NOPB is saying it's nearing EOL. What might be a suitable replacement?
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Post by mskala » Mon Mar 07, 2016 3:07 am

DJMaytag wrote:Also, LME49710NA/NOPB is saying it's nearing EOL. What might be a suitable replacement?
The metal can version seems to be still in active production. Same pinout, and you can bend the legs to fit in a DIP socket without too much trouble. http://www.digikey.com/product-search/e ... 0HA%2FNOPB
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Post by DJMaytag » Mon Mar 07, 2016 9:03 am

Damn those are pricey!
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Post by negativspace » Mon Mar 07, 2016 1:33 pm

No harm in a TL071, really. Maybe a NE5534? I wouldn't bother with the metal can 49710, that's a bit insane. :doh:

I may address this by converting that chip over to a dual opamp, leaving a lot more possibilities open. Would probably transition to an OP275 in that case. Could possibly add an attenuverter to CV2 that way, too.

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Post by DJMaytag » Tue Mar 08, 2016 3:34 pm

negativspace wrote:No harm in a TL071, really. Maybe a NE5534? I wouldn't bother with the metal can 49710, that's a bit insane. :doh:

I may address this by converting that chip over to a dual opamp, leaving a lot more possibilities open. Would probably transition to an OP275 in that case. Could possibly add an attenuverter to CV2 that way, too.
Mouser still has the original part, but I'll look into other projects I'm looking at that probably need TL071's.

What about this part: https://www.mouser.com/Search/ProductDe ... U5-104M-RC

It says the minimum quantity is 200, and I really don't want to buy $28 worth of caps to only use 3 of 200! Any suitable replacement, or should I buy elsewhere on this one?
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Post by DJMaytag » Tue Mar 08, 2016 5:36 pm

Would a TDK FG26C0G1H104JNT06 MLCC C0G work?

I searched for 0.1uF caps, and filtered by voltage rating (50VDC), termination (radial), lead spacing (5mm) and found just a few caps available. I then filtered by C0G caps, as I'd seen caps with that dielectric in a lot of other BOM's and recommendation.

Would these work? Would they be close enough?
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Post by DJMaytag » Mon Mar 14, 2016 1:16 pm

Are these the pots that will work, or should I be ordering from elsewhere?

http://smallbear-electronics.mybigcomme ... -pc-mount/

Since this is an audio VCA, should I be selecting the audio taper pots?
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Post by negativspace » Mon Mar 14, 2016 5:41 pm

Errrrp, been building hard this past week, missed some posts.

On the 0.1uF ceramics, those are just for supply rail decoupling so you don't need anything fancy. The TDK part you linked will work fine but might be overkill. I use Vishay part# K104K15X7RF53H5.

Don't dismiss the thought of buying a hundred or two of these things. They're common in many, many projects as decoupling caps. If you're planning to build a bunch of stuff over the next couple of years you might very well go through more than you expect... and you'll get a price break if you don't buy them 2 at a time.

On the pots, yes, those are correct. Erthenvar also carries them, but SB stocks the C50k I like on the offset control so for this project I'd send you there. The 2180 chip has a log response so in this case you want an antilog pot (C taper) for a roughly-linear panel control and a linear (B taper) for an "audio" taper control. Like I said, I like C50k in the offset location and B50k for the CV inputs. But all 3 B50k would also be fine.

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Post by DJMaytag » Tue Mar 15, 2016 9:05 am

negativspace wrote:Errrrp, been building hard this past week, missed some posts.
No big deal. Keep on churning out great products! :)
negativspace wrote:On the 0.1uF ceramics, those are just for supply rail decoupling so you don't need anything fancy. The TDK part you linked will work fine but might be overkill. I use Vishay part# K104K15X7RF53H5.

Don't dismiss the thought of buying a hundred or two of these things. They're common in many, many projects as decoupling caps. If you're planning to build a bunch of stuff over the next couple of years you might very well go through more than you expect... and you'll get a price break if you don't buy them 2 at a time.
Buying 100 or 200 is a lot more palatable when the cost is $4, and I'll be buying at least 100 of that Vishay part. The original part in the cart linked in this thread would be $28 at the MOQ, and that's more that the rest of the parts combined at Mouser!
negativspace wrote:On the pots, yes, those are correct. Erthenvar also carries them, but SB stocks the C50k I like on the offset control so for this project I'd send you there. The 2180 chip has a log response so in this case you want an antilog pot (C taper) for a roughly-linear panel control and a linear (B taper) for an "audio" taper control. Like I said, I like C50k in the offset location and B50k for the CV inputs. But all 3 B50k would also be fine.
Is there a FAQ or guide of some sort to these Alpha knobs? I've searched and read a ton of threads on here, and I'm just as confused. I don't ask this because I'm anti-Thonk or anything like that, but why is it that their version of the jacks are what everyone uses? Why doesn't Mouser carry them? Is Smaller the best price on these?

Sorry if these things are bit much to answer, but I'm just not clear on what the deal is with these pots and why everyone uses them?
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Post by DJMaytag » Tue Mar 15, 2016 9:18 am

negativspace wrote:antilog pot (C taper)
Forgot to ask... are these the "reverse audio" pots listed on Smallbear?
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Post by negativspace » Tue Mar 15, 2016 8:24 pm

Yes, C-taper is reverse audio. :tu:

The deal with these pots is that they're small, relatively inexpensive, durable (metal shaft), available in many values, and of reasonably high quality. An ideal part for a Eurorack module. I don't know why Mouser doesn't stock them, perhaps they're not popular outside our little Eurorack microcosm.

Best price is going to be Erthenvar but Nick only stocks a few of the more common values. Small Bear has by far the best selection but you pay a few cents more per pot unless you're ordering a large quantity. Thonk sells the same stuff, and Steve's prices and selection are good, but you're better off ordering from one of the American shops given your location.

(Which is too bad - Thonk has them made without the little locator tab molded in and that is a FANTASTIC feature. If it made sense from a business perspective I'd source them all from Steve...)

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Post by AndrewM » Sat Mar 26, 2016 8:28 pm

Finally got around to finishing off my MA VCA. While I remembered to cut the traces on my V1.2 PCB, when I attached the pots I had forgotten to connect the jumper to the offset pot. During calibration I was wondering why I couldn't hit +305mV, but then it all became clear when I remembered that I had missed the jumper.

Soldered that up and everything seems to be working fine. Great sound - and I like how it's easy to dial in a bit of overdrive as well!

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schem

Post by daniel.fiction » Tue Apr 05, 2016 3:00 am

thanks for posting the schematic!

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Post by pulsepsycle » Wed Apr 06, 2016 11:12 pm

The PCB + Panel sets are Out Of Stock at Thonk. :cry: Any other sellers in Europe? I want 4.

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oscillation!

Post by daniel.fiction » Tue May 03, 2016 5:21 pm

Oh I just figured I'd report something. I was playing around on my bench, with a 2162 for the VCA, and an LM837 for the control scheme. I found significant oscillation, but everything improved as soon as I removed the 1.5nF and 100R parallel network.

fyi!

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Post by pulsepsycle » Sat May 14, 2016 10:29 pm

I didn't have a SMT Tempco for the MA That VCA so did it this way.

Image

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Post by ronski » Thu Jun 09, 2016 8:28 am

I might need one as well, any UK or Europe stock?
pulsepsycle wrote:The PCB + Panel sets are Out Of Stock at Thonk. :cry: Any other sellers in Europe? I want 4.

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Post by negativspace » Thu Jun 09, 2016 11:05 am

If you guys don't mind ordering directly from me, I have plenty here. :tu:

Unfortunately (and I truly mean that) I'm not in Europe.

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Post by woodster » Thu Jun 09, 2016 11:18 am

a single panel and pcb should sneak under the import duty threshold, multiples not so much.

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