TWO59 VCO module (Building Thread) by FEEDBACK [UPDATE]

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windspirit
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Post by windspirit » Wed Oct 02, 2019 8:39 pm

Scratch that, I put a J201 in the footprint and first one gave me a pretty decent sine wave. You have to redo the transistors legs the same way as the other FET but it seems to work well.

I just put another 68k in parallel with R2 on the front board, hopefully I can get some 1v/o tracking for now until I can hunt down the other problem.

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windspirit
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Post by windspirit » Mon Nov 18, 2019 8:52 pm

Ok so this oscillator has been working well for me so far BUT the output levels are so much lower than the rest of my oscillator modules, especially the analog ones which are usually 20V peak to peak. All of the outputs on this module are about 2 - 3V peak to peak. I couldn't help but notice the rather unusual output buffer circuitry, mostly the fact that there is no input resistor for the op amps which are set up somewhere between a voltage folllower and an inverting op amp. I managed to increase the amplitude of the sine wave by increasing R17 (I got about 10V p2p with a 68K resistor, Ill probably double the value for 10V p2p) but increasing the feedback resistors of the other buffers resulted in a wave that is a higher amplitude but clamped at the top around 1V. I tried increasing R47 just to see if this would work instead with the unaltered buffer circuit but output is still clamped.

Before I rip out more resistors and solder them back in any suggestions on what parts to tackle to improve this behavior? I don't want to break a trace by repetitive soldering / desoldering.

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Post by NiteEagle » Tue Nov 19, 2019 8:29 am

windspirit wrote:Well, I missed the part about soldering the THAT chip directly to the board but afaik it was just for the spacing because you are supposed to use a large tempco correct?
I did the same thing by default as well. I got some Stackable Headers from Tayda to give the extra space between the boards, but I don't have any depth constraints in my cases.
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Re: TWO59 VCO module (Building Thread) by FEEDBACK

Post by CliffordMilk » Wed Jan 08, 2020 1:25 pm

I built four of these and have been using them for a while. All four have the same issue in that the frequencies are way too high, even with the offset trimmer all the way down. I have checked C6 is correct and as far asI can see so are the values of r1-r30.

I built all four at the same time so must have made an error on all with an incorrect component.

I’d really like to get them correct so has anyone had the same experience and managed to solve it? Any ideas?

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Re: TWO59 VCO module (Building Thread) by FEEDBACK [UPDATE]

Post by strat-1 » Tue May 12, 2020 2:11 am

[UPDATE]
LM301 Through Hole version, was pulled out of production. It became very hard to find.
I use the SMD variant, which is very easy to find. Here is how the SMD version is looking after installing.
Image

FLOz
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Re: TWO59 VCO module (Building Thread) by FEEDBACK [UPDATE]

Post by FLOz » Sun May 31, 2020 2:45 pm

I have built 2 VCOs. As minimum frequency with the offset at the end of the stroke I get 28,4 and 30,5Hz. Is that bad?

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Re: TWO59 VCO module (Building Thread) by FEEDBACK [UPDATE]

Post by strat-1 » Sat Jun 06, 2020 6:49 am

We made a stock of LM301 THT version and we included it in KIT2 and KIT3 without changing the price of the kits.

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Re: TWO59 VCO module (Building Thread) by FEEDBACK [UPDATE]

Post by strat-1 » Sat Jun 06, 2020 6:52 am

FLOz wrote:
Sun May 31, 2020 2:45 pm
I have built 2 VCOs. As minimum frequency with the offset at the end of the stroke I get 28,4 and 30,5Hz. Is that bad?
If the V/OCT tracking is OK, than it is no problem if the freq at CCW of the FREQ pot is a bit higher.

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Re: TWO59 VCO module (Building Thread) by FEEDBACK [UPDATE]

Post by Zensac » Mon Aug 17, 2020 7:49 am

I have built two TWO59 VCO's and taken my time to measure all components before stuffing, using 1/2W resistors were suggested, correct polarity of caps, etc., but none the less, I'm blowing the fuse of my (test) PSU every time I connect either of the ctrl PCBs (have a rev1.1 and a rev 1.2) to either of the main PCB's. That is, both of the Main PCBs can be connected to my test PSU and I can measure correct +12/-12V on the board. +5V is also working. I added the errata jumper to connector2, pin9/10 as suggested in the build manual.

As said, the PSU fuse (650mA T) is blowing each time I also connect the CTRL board. Any ideas what could cause this?

I don't have any picture of the boards at the moment, but I have done tons of other builds, SMD included. I'm fairly confident that my soldering is decent (cleaning up with isopropyl and a toothbrush + pads).

How would you go about debugging this? Thanks.

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Re: TWO59 VCO module (Building Thread) by FEEDBACK [UPDATE]

Post by pieter » Mon Aug 17, 2020 9:43 am

Hi Zensac, that sounds like you have a short on the board. The first thing you should check is if the +12V and –12V are connected directly to each other or to the ground when the control PCB is attached to the main PCB. Do not power up the module, but see if the pins of the power connector are shorted with a multimeter (if there is a short, the multimeter should beep when you touch two pins).

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Zensac
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Re: TWO59 VCO module (Building Thread) by FEEDBACK [UPDATE]

Post by Zensac » Mon Aug 17, 2020 1:48 pm

Thanks, Pieter. Good suggestion. No shorting occurs of the rails. I've measured the rail resistance with my Brymen BM687s:

MAIN board without attached CTRL board:
- Resistance from Power Header 0V pins to +12V pins (before 1N5819 Zener): 15.5 kohm (16 kohm for the 2nd build of MAIN/CTRL pcb)
- Resistance from Power Header 0V pins to -12V pins: (before 1N5819 Zener): Approx. 1Mohm (approx 400kohm and rising)

With the CTRL board attached to the MAIN board:
- Resistance from Power Header 0V pins to +12V pins (before 1N5819 Zener): 6.1 kohm (and slowly falling) (8.7 kohm for the 2nd combo of MAIN/CTRL)
- Resistance from Power Header 0V pins to -12V pins: (before 1N5819 Zener): Approx. 800 kohm (slowly rising) (427 kohm and slowly falling for the 2nd combo)

Can anyone explain the resistance differences? Both between the pos and neg rails, but also the difference in the 0-NEG measurement between the two builds? Is this a matter of capacitor charging?

I have a bench power supply with current limiting, but don't really have any experience using this (surplus that I got for free). Would this be handy in debugging? I'm thinking that I could set the bench supply to a low current limit (like 50-100mA) and then power the modules up. This would allow me to poke around on the boards, measure voltages and see if something gets hot, right?

I have attached some picture of the two MAIN and CTRL pcbs. As can be seen on the MAIN_BACK picture, I had to mount a few of the 0.5W resistors on the back of the PCB.
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Zensac
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Re: TWO59 VCO module (Building Thread) by FEEDBACK [UPDATE]

Post by Zensac » Mon Aug 17, 2020 3:04 pm

Doh... I just realized I should measure the rails from the euro header 0V to AFTER the 10 ohm resistors and not before the Zeners.
It seems like I do have a short at the +12V rail. I will continue the debugging.

Again, I appreciate the suggestions, Pieter.

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Re: TWO59 VCO module (Building Thread) by FEEDBACK [UPDATE]

Post by mightycoco » Thu Oct 22, 2020 2:14 am

Can i substitute the 5K9 with something similar? 5K6 or 6K? I don't find a place selling 5K9... Ali, Mouser, local stores, nada :/

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pieter
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Re: TWO59 VCO module (Building Thread) by FEEDBACK [UPDATE]

Post by pieter » Thu Oct 22, 2020 2:26 am

You can put two resistors in series that sum to 5K9 or two in parallel that inversely sum to 5K9.

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Re: TWO59 VCO module (Building Thread) by FEEDBACK [UPDATE]

Post by finalplane » Mon Nov 16, 2020 4:00 pm

I finished one of my VCOs and it seems to be working quite well!

One question - on the 1.2rev PCB, do I still need to solder pins 9 and 10 of con2 together?
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pieter
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Re: TWO59 VCO module (Building Thread) by FEEDBACK [UPDATE]

Post by pieter » Mon Nov 16, 2020 6:10 pm

I don't think so. I didn't and mine works fine.

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