The ASV is AWESOME (Was: ASV filter problem)

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The ASV is AWESOME (Was: ASV filter problem)

Post by oozitron » Thu Mar 14, 2019 9:58 pm

My first ASV is working well except for the filter. (VCOs, EGs, LFO all work fine)

The only way I get audio through the VCF is to turn the Shape all the way CW to "HP". I can then hear the VCOs. Turning the Frequency & Resonance has *no* effect at all on the sound.

When I turn the Shape knob just a small amount CCW from the max (HP), the audio disappears. The audio that comes through does not sound like it is being filtered at all.

I have double-checked my chip orientations and polarized components.
I have a basic voltmeter, a basic brain and a somewhat helpful cat.

Any suggestions on things I can check?

thanks so much,
Andrew
Last edited by oozitron on Wed Mar 20, 2019 5:48 pm, edited 1 time in total.
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Post by oozitron » Thu Mar 14, 2019 10:18 pm

Also, I have spares of all chips if it sounds like one might be faulty...
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Post by Synthbuilder » Fri Mar 15, 2019 5:01 am

Does putting the filter into BP mode work at all? I'm guessing not. But if it does, suspect the circuitry/solder joints around U5 on the pot board.

Is the VCO1 triangle wave working? This bypasses the VCF so even if the filter is dead you should still be able to play notes using the triangle wave output.

So if it is just the filter: Turn down the VCOs, including the sub-octave and triangle wave, and listen to the main output very carefully. Make the module turn on by turning up the VCA ADSR's sustain control to max and putting an active gate into the module. The gate LED should light. Turn up the resonance and wiggle the filter frequency pot. Can you hear any hissy noise changing with the filter frequency. If so, the filter is probably working and it may be a problem with the routing of the signal from the mixer on the pot board to the input of the filter. This is a normalised connection when using the sockets. If you can't hear the hiss changing tone then the filter probably isn't working and the problems will be around that section in the top left of the main board.

The filter is one of the more complex parts of the board. ICs are rarely dead on arrival - unless they are fakes - so the most common fault is either wrong resistors or solder shorts on the underside. If all is apparently well then the next thing is to try swapping out some of the ICs. The LM13700 is probably the first one to try. The J201 transistors could well worth a look too. They are quite expensive these days and fake ones are probably out there. I buy mine from Mouser which are the newly re-manufactured ones.

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Post by oozitron » Fri Mar 15, 2019 5:45 am

Thanks Tony! All the components came fresh from Mouser (except for 3310 & THAT chips).

The "unfiltered" VCO1 Triangle does work just fine.

The only (known) goof I made when building was that I put J201 parts in for the J112. I carefully removed the two J201 and put the two J112 in. I checked for continuity to the J112's neighbors and it checked out ok. (this was long before a power-up)

I appreciate the help!

Andrew
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Post by oozitron » Fri Mar 15, 2019 4:28 pm

Argh... only other possible clue: if I turn up the VCOs in the mixer then turn the Shape knob all the way CW, the (unfiltered) VCOs can be heard. If I twist the Shape knob back and forth, there is a distinct "scrtch" at the two extremes of the pot.

So far I can't find anything suspicious, but there's a lot of parts...

EDIT - Ok, I just wired up the jacks on my *second* ASV and they both have the exact same problem. There must be a component issue; this is too coincidental to be something like a stray cold solder joint.
EDIT2 - I swapped out the LM13700 chips with an older set I had; no change. This is bumming me out... I'm hosting our 20th annual synth get together tomorrow and I was hoping to have these going. So close :-\

Andrew
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Post by Synthbuilder » Sat Mar 16, 2019 6:48 am

Did you try listening to the hiss of the filter in high resonance and see if that changes with filter frequency? You'll need your monitor amp turned up quite a bit, so be careful.

Are you sure you have the audio from the mixer section reaching the filter? That's a normalised connection on the socket board in a standard build. If I remember rightly your build doesn't have the socket board. I'm not at work so I don't have access to the schematics but there should be an additional wired connection from the mixer out to the filter. It may be worth double checking this even if you have made the connection.

It will also be worth hooking a socket up to the mixer output and seeing if the mixer is working OK. The mixer is on the pot board but its output is available from one of the headers on the main board.

What's the voltage (with respect to 0V/Ground) on pin 1 and pin 7 of U10? With the VCO levels turned down both the voltages should be close to 0V.

Tony

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Post by oozitron » Sat Mar 16, 2019 7:19 am

Even with the amp cranked up, no hiss from the filter. There's that "chiff" when you get to min or max on the Shape control, and the VCOs coming thru when Shape is totally CW.

I have triple-check my normalized "patch" wires, but I will try the direct outs and see what I get (and check the U10 volts).

I'm taking basic tools to the synth meet, and there are plenty of people coming who are geniuses in this area so maybe they can spot my error. I have no doubt it's something stupid :doh:

Andrew
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Post by oozitron » Sun Mar 17, 2019 2:30 pm

Had several smart people look at my filter yesterday. Have confirmed that Q3, Q4, Q5 & Q6 are correct components. Swapped in a different 13700 with no change. I have set all 4 VCF trimmers to middle of their range.

I have cut my normal connection between the MIXER_OUT_A & VCF_IN_SK (and turned down all three mixer pots to zero). So VCF is getting no input.

Shape is set to LP; Freq=0, Res=0; EG Amt=0, VCF mods=0

U10 Pin #1 = +0.65v
U10 Pin #7 = -3.35v

and U6 Pin#1 = +3.3v (which one helper found "suspicious")

Andrew

BTW, I did get to spend some time with a friend's Obie 4VS yesterday which was good inspiration to solve this VCF problem!

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Post by Synthbuilder » Mon Mar 18, 2019 3:54 am

oozitron wrote: U10 Pin #1 = +0.65v
U10 Pin #7 = -3.35v

and U6 Pin#1 = +3.3v (which one helper found "suspicious")
Suspicious it is. U6 is probably behaving itself though since that +3.3V is a result of the -3.3V on pin 7 of U10. And it's that -3.3V I don't like. Really the worst it should be is +/-1V.

Try adjusting F_OFF1 and see if you can bring that pin 7 voltage down to 0.00V. But I think it is looking likely there is a fault in the filter section somewhere.

What worries me is that both boards display the same problem. That pretty much rules out faulty components and board shorts. It could be that a component value is wrong somewhere but that would mean you made the same error twice. Did you build the two ASV main boards together? If so, that could be a picking error, ie. for example all your 220R resistors are actually 2K2.

Actually, what's the voltage on the + of C32, and the - of C35. They should be close to + and - 15V respectively. If not check R79 and R80.

Tony

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Post by oozitron » Mon Mar 18, 2019 6:18 am

Yeah C32 & C35 have the correct volts, and R79 & R80 are definitely 22R

What voltage should be at R34?

My trimmers look upside down compared to your picture in the builder's guide. If the "F_SCL" trimmer was indeed backwards, could that be causing this problem?

Andrew
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Post by Synthbuilder » Mon Mar 18, 2019 8:20 am

oozitron wrote:What voltage should be at R34?
The end that is connected to the base of Q3 (middle pin) should be close to 0V.

What's the voltages on pin 1 and pin 16 of the LM13700, U14. They both should be the same and be just slightly less than -15V.

Also what is the voltage on the top pin of Q4. This should vary with cut-off frequency - going from -15V towards 0V with higher frequencies.
My trimmers look upside down compared to your picture in the builder's guide. If the "F_SCL" trimmer was indeed backwards, could that be causing this problem?
I don't think so. I'm guessing you may have used a different type of trimmer. Mine are Bourns 3386F types - but I've never come across any modern trimmers that don't use the same pin out orientation, ie. middle pin will be the wiper.

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Post by oozitron » Mon Mar 18, 2019 8:42 pm

Middle Pin of Q3 = +0.26
U14 Pin 1 = +13.9
U14 Pin 16 = +13.9

*However*, I found that the VCF_CONTROL (CN8 Pin9) is always at +14.19

This is with all the VCF controls set to 0 (EG, Keytrack, FM1, FM2) and the VCF frequency set to any value min~max.

I think maybe my Pot Board has the problem... Would a constant +14.19 at VCF_CONTROL cause all these other problems?

your patience with me is greatly appreciated,
Andrew
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Post by Synthbuilder » Tue Mar 19, 2019 2:59 am

oozitron wrote:Would a constant +14.19 at VCF_CONTROL cause all these other problems?
Quite possibly. +14.19 is about as high as you can get which means the filter's cut-off frequency is turned to as low as it can get. This could well be source of the problems.

You going to need to get access to the pot board - which means removing the front panel. Thankfully, the PCB stack can be used without the panel in place.

U4a (pins 1, 2 and 3) is clearly in saturation. That would suggest that R12 is either too high or R8 too low. I would also be interested to know the voltage on pin 8 of U4 and see if that is the same as pin 1. If it is there may be a short to +15V on the pot board somewhere.

Tony

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Post by oozitron » Tue Mar 19, 2019 9:18 pm

AH HA!!!

There are four resistors on the Pot Board that are *supposed* to be 470K

I used 470R :bang:

I will replace them tomorrow after work when I am 1,000 times more awake.

This is why I love your projects... super nice board layouts, excellent documentation, and awesome & friendly help when needed.

thank you again,
Andrew
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Post by oozitron » Wed Mar 20, 2019 5:40 pm

WOO HOO - WORKING! :banana:

And it sounds better than I had dreamed. A wonderful electronic sound, just what I wanted. I am so happy!!!

Again, thank you Tony. If I was the pope I'd make you a saint!

Andrew
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Post by Synthbuilder » Thu Mar 21, 2019 2:55 am

:banana: :bananaguitar: :banana: :yay:

Good to hear that you got them working.

:tu:

I would love to see some pictures once it's all done.

Tony

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Post by Pav » Fri Mar 22, 2019 8:47 am

Good to see this fixed, and a happy user #Oozitron.
Ive been watching as I have this build to look forward to.
Just received panel from Schaeffer but the pots are on back order from Banzai.
rgds Pav

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Post by Synthbuilder » Fri Mar 22, 2019 9:10 am

Pav wrote:... but the pots are on back order from Banzai.
Those pots have been on back order for ages. I ordered some in November and I still haven't got mine yet. I have badgered them about it and supposedly they were in last week and will be sent out to customers shortly.

I gave up in the end and got mine from Musikding.

https://www.musikding.de/Alpha-pot-angl ... nt-50k-lin

Arrived within four days.

Tony

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Post by Pav » Fri Mar 22, 2019 9:37 am

That link will be useful, as Banzai do not seem to improve delivery times. They did not even tell me they were on back order until i poked them. They just took the money and didnt ship. Did get an apology though, so not all bad.
rgds Pav

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Post by eggpie » Fri Mar 22, 2019 2:32 pm

Congrats Oozitron. Glad you got it working. I too have been waiting for pots and AS3310s from Banzai since late December!
I got my pots the other day after a few emails to them, so I'm surprised you're (Tony) still waiting.
I had some Coolaudio V3207s on order too, for the Flanger. I gave up in the end and cancelled the order. At least I got an email from Accounts telling me I will be refunded. It's a shame because I've not had these issues with Banzai before. Perhaps there's too many people building Oakley ASVs!
Can't wait to finish it now.

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Post by oozitron » Fri Mar 22, 2019 7:25 pm

Image

I am having a ball just playing with them in drone mode, hard panned L & R with a long delay on them. At some point I need to quit noodling and calibrate them :roll:

I did leave a resistor (R67) out so that only VCO2 is FM'd by the LFO and I'm very pleased with that. With Sync on and a slow LFO moving just VCO2 up and down gives you some great timbre shifting.

Those are lexan panels. Cheap to make and easy to add holes to if I want to make some changes. At some point I'll get some aluminum ones made.

I got my pots at Mammoth (super prices) and the 3310 chips at Modular Addict. Both are in the US though...

Andrew
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Post by oozitron » Sun Mar 24, 2019 1:02 pm

Some drone noddles...



Andrew
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Post by Schlumpfhut » Mon Mar 25, 2019 12:52 pm

oozitron wrote:

I did leave a resistor (R67) out so that only VCO2 is FM'd by the LFO and I'm very pleased with that.
Andrew
If one dont mind the hassle to put in a hole for a Switch on the FPD file or later you could make this mod optional for different modes of operation

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Post by Pav » Mon Mar 25, 2019 3:19 pm

For me it's too late to mod my panel but not too late to have an expander panel adjacent. Any other mod suggestions that pass Tonys opinion re no side effects or issues would be useful to know.
rgds Pav

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Post by oozitron » Mon Mar 25, 2019 6:59 pm

I was thinking it might be cool to have a way for VCO1 to be FModded by VCO2.

Having VCO2 FModded by VCO1 would be much easier to do, but I think the Fine Tune control would better to have on the modulator. Plus you could sweep VCO2's pitch with the envelope and then mod VCO1 with it. That's something that worked really well on the ARP 2600.

I suppose I could wire that in using one of the holes from my empty R67 position... a pot, a resistor and a little wire.

Andrew
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