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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
Tube VCA: Troubleshot!
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Peake



Joined: Jun 29, 2007
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PostPosted: Mon May 12, 2008 10:02 pm    Post subject: Tube VCA: Troubleshot! Reply with quote  Mark this post and the followings unread

Edit: One is now working and another awaits a new "second choice" tube. Intestingly, the 1J17B is much less expensive than the 1J24B (at least at the moment). I got ten of them for $18.00, including shipping.

A couple of other folks here state that they are having issues with this circuit. I have two and neither function. I doubt that I've purchased two dead tubes, but have built according to the photo on Ken's web site and checked the schematic. I'm certain that I'm making a simple, obvious mistake. I'm not entirely certain regarding the combinations for rev2 regarding the 330 resistor and the jumper. Both of mine have the resistor in the lower slot, akin to the rev1 board, going to the negative rail. One has the jumper in the dotted slot, the other uses the other slot. Neither work. I've rechecked the parts values and soldering. I've checked the 062s (not using 072s). Voltages are correct to the ICs. The tubes are correctly stuffed.

Please help me to tube-y goodness Very Happy And thanks for being here, Ken.

Last edited by Peake on Wed May 28, 2008 8:23 am; edited 1 time in total
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otherunicorn



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PostPosted: Tue May 13, 2008 1:43 am    Post subject: Reply with quote  Mark this post and the followings unread

You have probably wired the tubes in wrong. It isn't easy to identify which lead is which. Beyond that you aren't giving enough info to help further. I'd suggest you find a friend to look over the tube pin wiring even if they don't know electronics. show them the data and the tube, and see if they can see an error that is invisible to you. And assuming the wiring is right, makes sure none of the tube wires are touching.
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Peake



Joined: Jun 29, 2007
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PostPosted: Tue May 13, 2008 8:04 am    Post subject: Reply with quote  Mark this post and the followings unread

Fun, huh. I've recently troubleshot and repaired an A/DA STD-1 which is easily 10X more complex than this circuit Laughing A dead non-polarized electorolytic was the culprit there.

The tubes are in correctly and no leads are touching. I've confirmed the tube pin sequence with the dot for #1, #6 in the hole between 1/2/3 and 4/5, and the correct placement of 4/5 as well. I've compared to the close-up photo on your site. I've swapped a single tube between two boards and then installed a new tube as well. I had a problem with voltage once before and fried the negative rail 100r resistor, but have swapped 062s etc. in working circuits just fine. I can only think that I may have stuffed the drain LEDs incorrectly

It could be more of those bad jacks which prevented my Mankato from functioning, more info today. The problem is inevitably with me, not the circuit. Bear with me and my error shall be revealed. It sounded good enough in MP3s to inspire purchase and I look forward to using them, especially in the feedback loop of echo effects, with a little inverted envelope following to produce compression. I can't wait to hear what that sounds like. Thanks again for being here and for the projects!
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prophei



Joined: Jan 27, 2007
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PostPosted: Fri May 16, 2008 9:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

i don't know if ken remembers, but at the end of last year, i was actively soliciting help in his yahoo group regarding this same circuit.

he and others were kind enough to patiently go over everything with me a number of times, and it became extremely perplexing as to why it didn't work.

the problem? some resistors i had were labeled incorrectly. i had swapped 220k and 220r resistors in part of the circuit. (i'm pretty sure it was those)

the lesson? sometimes the dumbest crap is the biggest problem Razz
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Peake



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PostPosted: Fri May 16, 2008 11:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've read through and printed out some of that thread and used it already... I'm pretty sure that the bad jacks I've been using are the culprit. They of course work just fine on my Fonik 2044... Thanks. My Fonik 2044 and Mankato work fine...
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guitarfool



Joined: Feb 26, 2007
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PostPosted: Sun May 18, 2008 12:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

Peake wrote:
I had a problem with voltage once before and fried the negative rail 100r resistor, but have swapped 062s etc. in working circuits just fine. I can only think that I may have stuffed the drain LEDs incorrectly


Something besides the ICs must have sucked a lot of current. Possibly the LED's were trashed. Do they still light up? If they don't, then the LED's are gone or in backwards. The cathode heater won't get any current and the tube won't want to work.

Peake wrote:
I'm not entirely certain regarding the combinations for rev2 regarding the 330 resistor and the jumper.


Below are the 2 options for the 330k resistor and jumper. If not correct, it probably won't work.


CGS65_option_2.jpg
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CGS65_option_1.jpg
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Peake



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PostPosted: Sun May 18, 2008 4:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

The LEDs have never lit up. I didn't know that they drew enough to do so. That might be a culprit right there... And thank you very much for the visual reference; I had correctly installed the resistor and jumpers (to keep the distortion at low levels).

Cheers! I appreciate it! I'll change out the LEDs tonight and post results.

Last edited by Peake on Sun May 18, 2008 6:33 pm; edited 1 time in total
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guitarfool



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PostPosted: Sun May 18, 2008 6:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Oh, speaking of which, here's the additional panel wiring I did. There's a switch to select between the 2 bias options (instead of the 2 330k resistor locations and 2 jumpers), plus a positive feedback control. The positive feedback is really worth it. You could also just normal the output to a second audio input instead.


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fluxmonkey



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PostPosted: Sun May 18, 2008 7:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

i just completed a 2nd tube VCA (traded the first one only because i had the parts for the second). the tube pinouts on were confusing, not in a nice circle and just wasnt sure after the heater... but it worked first time, and is a sweet module. as guitarfool said, the feedback pot is well worth it (should be standard issue imo), tho mine is linear not log, seems fine. is there a big difference between the sound of the 2 bias positions?

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Posted Image, might have been reduced in size. Click Image to view fullscreen.


bbob
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Peake



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PostPosted: Sun May 18, 2008 7:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey, nice build!
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guitarfool



Joined: Feb 26, 2007
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PostPosted: Sun May 18, 2008 8:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

Nice layout - I really like the vent!

bbob wrote:
tho mine is linear not log, seems fine.


Most of the good stuff is in the upper half of the range on mine, so a lin pot is probably better anyway. It's not real "touchy" though, so it isn't really critical.

bbob wrote:
is there a big difference between the sound of the 2 bias positions?

Yes. Not earth-shaking, but pretty noticeable.

I normalled the 1st CV jack to V+ and have a 2nd CV in, unattenuated. This gives me an initial gain, or an attenuated CV in, but not both. It was either that or have a very cramped panel if I wanted to stick with a single width. Sad


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PrimateSynthesis



Joined: May 02, 2008
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PostPosted: Wed May 21, 2008 6:07 am    Post subject: Re: Tube VCA Troubleshooting Reply with quote  Mark this post and the followings unread

Peake wrote:
I've checked the 062s (not using 072s). Voltages are correct to the ICs. The tubes are correctly stuffed.


I don't know why you chose TL062's. You can use a TL072 for the audio amp, but you cannot use a TL072 for the CV amp (it will go into phase reversal). You need an op-amp that go to the negative rail such as an LM358 or LT1013.
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Peake



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PostPosted: Tue May 27, 2008 11:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

Lo and behold, it is exactly as I thought- I've received ten of the "second choice" tubes (for a fourth the price of the "standard" tube, on eBay and elsewhere) and the one board I've stuffed it in now works just fine (doesn't sound anything like the Manley gear I've had around, but should that be so very shocking!?). It adds a really nice "blat" to swept resonant filters at max gain and high input, but doesn't add controlled warmth or fullness- it actually reduces dynamic range a bit, and adds a touch of noise (I'll have to try the other board next as it has smaller LEDs- wonder if that'll make any difference). It does seem to add a touch of boost, perhaps in the upper bass region? I've only had a few minutes with the circuit to confirm functionality so I know that there is a sweet spot and I just have to find and exploit it. It does have a specific character. I look forward to getting used to it and making the best use. Great circuit, Ken!

How nice when our suspicions are confirmed. Two dead tubes in a row? I'll have to stuff the other board and see. I apologize to the local surplus supplier of the 1/4" jacks I've been using, and had considered a possibility. It's not their fault. Thank you Ken for being here and for your suggestions (I am a bit better at this than incorrectly installing the tubes, but I -have- pulled similarly boneheaded errors before now...thank you for pointing out the most obvious course of action...)

Sigh. Watching gas prices rise and rise; is there an end in sight, and are we resonsible at any level? Wink

Primate Synthesis: I have 062s around owing to their use in some Buchla circuits (296). 072s are rarer in my parts bins...and the 062 draw less current, correct? Then again Don Buchla himself split up the 259 with 062 AND 082, so there must be a difference in there somewhere aside from current draw... And I took Ken's note seriously about not swapping the 358 (I did swap them between boards to make certain that one wasn't dead). Aside from stuffing the tubes incorrectly, that would be the next obvious answer, so thank you for the tip.
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PrimateSynthesis



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PostPosted: Wed May 28, 2008 8:01 am    Post subject: Reply with quote  Mark this post and the followings unread

Afaik, the 062 is a low-power version of an 082. I have no idea why Buchla used both, but it might have had to do with cost, offset-voltage, input range, etc. That was a long time ago, and today there are many more choices. Regardless, the 072 is better suited for audio -- faster slew rate, lower noise, etc. I used an OP275 in mine. YMMV.

Anyway, I'm surprised that you got that many dead tubes.
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Peake



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PostPosted: Wed May 28, 2008 8:17 am    Post subject: Reply with quote  Mark this post and the followings unread

PrimateSynthesis wrote:
Anyway, I'm surprised that you got that many dead tubes.


It was my first consideration regarding the lack of functionality.

I'm also not surprised at the economy and oil prices. Sadly, such things are intertwined and inextricable. Obviously, it can only go in one direction.
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JoeMorris



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PostPosted: Thu Nov 18, 2010 12:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi, sorry to dredge this old thread up - i just built a tube vca and while the leds light up, I get nothing on the output but hum. Havent had time to do a full debug, but one quick question - are the photos for resistor and jumper positions correct? I have the resistor on the 330k and the jumper on dotted line, i.e. the opposite of what the photos show. I hope its something this easy.
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otherunicorn



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PostPosted: Thu Nov 18, 2010 2:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

JoeMorris wrote:
Hi, sorry to dredge this old thread up - i just built a tube vca and while the leds light up, I get nothing on the output but hum. Havent had time to do a full debug, but one quick question - are the photos for resistor and jumper positions correct? I have the resistor on the 330k and the jumper on dotted line, i.e. the opposite of what the photos show. I hope its something this easy.

The photos above (there are two versions) are not as per what is now stated on my page.
Nonetheless, they are NOT as critical as suggested in the text above. Using a mixed combination would not stop it working.
As such, your parts placement is valid, so look elsewhere for your bug. If you are getting hum, it suggests you are getting amplification, at least at the output buffer, so start working back from there.

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Last edited by otherunicorn on Mon May 14, 2012 5:11 pm; edited 1 time in total
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JoeMorris



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PostPosted: Thu Nov 18, 2010 5:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for clearing that up Ken. And thanks for the great boards, looking forward to getting them all up and running. Had a nasty feeling it wouldnt be that easy. Will have a good thorough look when I get a minute.
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sonicwarrior



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PostPosted: Fri Mar 23, 2012 3:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

guitarfool wrote:
Below are the 2 options for the 330k resistor and jumper. If not correct, it probably won't work.


As these positions are not correct (according to Dragonfly/Bill&Will and the current CGS65 page) and nobody recognized it by now they can't be that important.

I placed it wrong today because I used your picture as a guidance but I will unsolder them tomorrow.

I'm building two Tube VCAs, one with the standard bias position and one with the 'modified' so I may be able to make pictures of the correct positions.
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sonicwarrior



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PostPosted: Sun May 13, 2012 4:05 am    Post subject: Reply with quote  Mark this post and the followings unread

OK, here are pictures of my bias positions:


Ken Stone CGS65 Tube VCA - Bias Settings.jpg
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otherunicorn



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PostPosted: Sun May 13, 2012 8:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

sonicwarrior wrote:
OK, here are pictures of my bias positions:


That is correct according to what is written on my page.
Ken

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sonicwarrior



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PostPosted: Mon May 14, 2012 9:08 am    Post subject: Reply with quote  Mark this post and the followings unread

Great! Thanks! Smile
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