Learning to debug Frequency Central XVCO2 build

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DanaFo
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Re: Learning to debug Frequency Central XVCO2 build

Post by DanaFo » Sat Jan 16, 2021 1:21 am

guest wrote:
Sat Jan 16, 2021 1:02 am
ok, that actually doesnt seem too bad. did you try an extrnal CV? it looks like its beeing driven really hard into the subaudio range. pin2 should go +/-100mV.

the difference between the base and emitter voltages is about 0.6-0.9 on most of them.
oh right I meant to ask, what pin would I measure to see what the external cv would be affecting? I'm guessing the many mv range readings indicate the subaudio range you mentioned?

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Re: Learning to debug Frequency Central XVCO2 build

Post by guest » Sat Jan 16, 2021 1:42 am

so, if you plug in the module and apply an external CV (or turn the tune knob) you should see pin2 go up and down by 18mV per octave.
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Re: Learning to debug Frequency Central XVCO2 build

Post by DanaFo » Sat Jan 16, 2021 1:52 am

guest wrote:
Sat Jan 16, 2021 1:42 am
so, if you plug in the module and apply an external CV (or turn the tune knob) you should see pin2 go up and down by 18mV per octave.
noted, will give this a go tmrw morning, thanks again

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Re: Learning to debug Frequency Central XVCO2 build

Post by DanaFo » Sun Jan 17, 2021 2:04 am

DanaFo wrote:
Sat Jan 16, 2021 1:52 am
guest wrote:
Sat Jan 16, 2021 1:42 am
so, if you plug in the module and apply an external CV (or turn the tune knob) you should see pin2 go up and down by 18mV per octave.
noted, will give this a go tmrw morning, thanks again
Well I went ahead did a ton of reflow, replaced the 1k trimmer, replaced some film caps with any marks on them and now I'm getting about 2.5 volts at the test point with the trimmer no longer seeming to have effect.
Fine tuning changes the pin 2 reading min:137mv to 107mv.

Ive already ordered a replacement pcb. I'm not sure the quality of this one can really handle component replacement as the holes appear to be thinly foiled Teflon. It's literally impossible to remove a lead without some damage to the hole.

If I'm going to have to literally retest every connection I might as well start from scratch.

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Re: Learning to debug Frequency Central XVCO2 build

Post by DanaFo » Sun Feb 07, 2021 10:47 pm

Alright, so I threw my hands up, rebought the pcb. I did a very very careful build, the soldering is super clean, I reflowed anything that looked slightly out of line.

All my outputs are fine, the knobs work, the LFO works, the FM works. But I'm getting 2.5v at the 0.65v test site and (thus?) everything is pitched down quite a bit, I think the highest I get is maybe a middle C.

This is the schematic attached, where would I dig into to manage this weird frequency offset/division?

Cheers,
XVCO TWO Schematic.pdf
(221.08 KiB) Downloaded 9 times

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Re: Learning to debug Frequency Central XVCO2 build

Post by DanaFo » Mon Feb 08, 2021 11:36 pm

guest wrote:
Sat Jan 16, 2021 1:42 am
so, if you plug in the module and apply an external CV (or turn the tune knob) you should see pin2 go up and down by 18mV per octave.
So i replaced the original 3046 and the test points all test perfectly. But the frequency of the output is at least 2-3 octaves too low. All knobs and outputs and switches work. Any idea what could be the issue?

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Re: Learning to debug Frequency Central XVCO2 build

Post by guest » Mon Feb 08, 2021 11:37 pm

ha, i was just in the middle or writing a reply:

what are the voltages on all pins of the 3046? if its supposed to 0.63 and youre seeing 2.5V, then the 3046 might be blown.
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Re: Learning to debug Frequency Central XVCO2 build

Post by guest » Mon Feb 08, 2021 11:38 pm

do the pitches move at 1V/octave, but are just shifted down a bunch, or is the scale off as well?
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Re: Learning to debug Frequency Central XVCO2 build

Post by DanaFo » Tue Feb 09, 2021 12:11 am

guest wrote:
Mon Feb 08, 2021 11:38 pm
do the pitches move at 1V/octave, but are just shifted down a bunch, or is the scale off as well?
I appreciate your response let me set this up tomorrow the bench is a mess for sequencing atm. Will reply then. Have a good night!

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Re: Learning to debug Frequency Central XVCO2 build

Post by DanaFo » Tue Feb 09, 2021 1:18 pm

guest wrote:
Mon Feb 08, 2021 11:38 pm
do the pitches move at 1V/octave, but are just shifted down a bunch, or is the scale off as well?
Ok so I blindly threw it into a vco tuner app via midi->doepfer darklink and it seems to track much much higher than the octave dial allows?
What I don't understand is when the v/oct in is unplugged the basic output is super low frequency, at the 2' position on the dial I think it's about C2, but plug the cable in, adjust to 8' position and it goes 34-1335hz (c-2 to c3) midi->darklink. With the test app it goes through a much higher range I think.

Maybe it's not broken at all? I have no way of knowing being a noob.

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Re: Learning to debug Frequency Central XVCO2 build

Post by DanaFo » Tue Feb 09, 2021 1:21 pm

also it appears the tracking gets exponentially worse as the pitch increases :P

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Re: Learning to debug Frequency Central XVCO2 build

Post by DanaFo » Tue Feb 09, 2021 1:37 pm

Ah no, it's way too low still, I have to crank the scale and freq trimmers to get somewhat near normal frequencies to the note value.

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Re: Learning to debug Frequency Central XVCO2 build

Post by guest » Tue Feb 09, 2021 2:37 pm

ok, if you plug in an external CV, and put in 1V and then 2V, does the frequency output double? does it more than double?

the scale being off with higher pitches is normal, and can be trimmed with one of the onboard trimmers.

measure pin1 of IC1 as you turn the pitch knob from min to max, what are the min/max values?
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Re: Learning to debug Frequency Central XVCO2 build

Post by fitzgreyve » Tue Feb 09, 2021 2:48 pm

I've built four of the original version of the XVCO and never had any significant problems ( I designed the add-on heater PCB for the original version).

I have a supply of NOS RCA 3046's (and that I can test in a fully working xvco) if needed, but you do now seem to have a basically working VCO, just too low in pitch ?

Various thoughts:

The 0.63V at test point 1 sets the heater temperature to above ambient. The 3046 should feel warm, but not "hot". If you still can't get this, I would check the resistor values around the heater circuit - have you checked your resistor values with a meter? if you get problems like this "assume nothing". (NB remember that once in circuit they will not read correctly). If the heater is not working it can make it difficult to get the thing to accurately track 1v/oct, but that shouldn't account for the very low frequency you are getting.

Are all the resisitors around the CV summing node correct values (measured?) - particularly R1 and R6. If R1 is too low it will drag the base frequency down.

Is your 2n2 timing capacitor (above the FET) actually 2n2 ?

Ignore anything except the sawtooth output until you get it working, then look at the triangle and pulse. A very slow sawtooth generally just sounds like "clicks", so it does appear to be oscillating ?

Also, Rick's 1v/oct trimming procedure is a bit "terse" - I can send you my more detailed version if that would help.
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Re: Learning to debug Frequency Central XVCO2 build

Post by DanaFo » Tue Feb 09, 2021 2:55 pm

guest wrote:
Tue Feb 09, 2021 2:37 pm
ok, if you plug in an external CV, and put in 1V and then 2V, does the frequency output double? does it more than double?

the scale being off with higher pitches is normal, and can be trimmed with one of the onboard trimmers.

measure pin1 of IC1 as you turn the pitch knob from min to max, what are the min/max values?
I'll have a look and report back thanks!

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Re: Learning to debug Frequency Central XVCO2 build

Post by DanaFo » Tue Feb 09, 2021 4:47 pm

guest wrote:
Tue Feb 09, 2021 2:37 pm
ok, if you plug in an external CV, and put in 1V and then 2V, does the frequency output double? does it more than double?

the scale being off with higher pitches is normal, and can be trimmed with one of the onboard trimmers.

measure pin1 of IC1 as you turn the pitch knob from min to max, what are the min/max values?
0V - 69.8hz
1V- 150.4hz
2V - 324.2hz
3V - 698 hz
4V - 1506 hz
5V - 3247 hz

I didn't see a change on pin1 but on pin 2 the octave switch gives:
211 190 170 150 128 107

So it doesn't look too bad? But I think cv input is overriding the octave input by quite a bit... If I turn off the module, remove the v/oct cable and restart then at 64' I get like 135bpm clicking, at 8' - 31.8hz, 4' - 69, 2' I get 150 hz. So there's something offsetting the frequency controls wise?
fitzgreyve wrote:
Tue Feb 09, 2021 2:48 pm

Are all the resisitors around the CV summing node correct values (measured?) - particularly R1 and R6. If R1 is too low it will drag the base frequency down.

Is your 2n2 timing capacitor (above the FET) actually 2n2 ?

Ignore anything except the sawtooth output until you get it working, then look at the triangle and pulse. A very slow sawtooth generally just sounds like "clicks", so it does appear to be oscillating ?

Also, Rick's 1v/oct trimming procedure is a bit "terse" - I can send you my more detailed version if that would help.
I get the proper test calibration voltages at the test points, the new 3046 is 'barely warm' (the old one was quite a bit warmer and i'm assuming was blown).
is_this_r1.PNG
It looks to be a 2n2... Is this the 100k at R1 you mean?

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Re: Learning to debug Frequency Central XVCO2 build

Post by guest » Tue Feb 09, 2021 5:50 pm

yeah, those pitches seem fine (with some slight adjustment) with the CV input. what did you have the octave switch set at for that test?
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Re: Learning to debug Frequency Central XVCO2 build

Post by guest » Tue Feb 09, 2021 5:58 pm

also, does the pitch change at all if you just plug a cable into the CV in (nothing connected to the other side of the cable)?
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Re: Learning to debug Frequency Central XVCO2 build

Post by guest » Tue Feb 09, 2021 6:01 pm

double check R1 through R5 are the right values.
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Re: Learning to debug Frequency Central XVCO2 build

Post by DanaFo » Tue Feb 09, 2021 6:17 pm

guest wrote:
Tue Feb 09, 2021 5:58 pm
also, does the pitch change at all if you just plug a cable into the CV in (nothing connected to the other side of the cable)?
I had the octave switch cranked at max 2'
There is no change in signal when I plug in an loose cable to the cv in.

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Re: Learning to debug Frequency Central XVCO2 build

Post by guest » Tue Feb 09, 2021 6:34 pm

what is the voltage on pin6 of the TL071 that is connected to the octave switch for the various ranges of the switch?
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Re: Learning to debug Frequency Central XVCO2 build

Post by DanaFo » Tue Feb 09, 2021 7:09 pm

guest wrote:
Tue Feb 09, 2021 6:34 pm
what is the voltage on pin6 of the TL071 that is connected to the octave switch for the various ranges of the switch?
1.6mv~
1.502v
3.004
4.507
6
7.5v

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Re: Learning to debug Frequency Central XVCO2 build

Post by guest » Tue Feb 09, 2021 7:17 pm

when you turn the pitch knob, how far does pitch go up and down? is it around an octave for the full range? does the other CV input give similar 1V/oct results when the attenuation knob is turned full up?

also, all those numbers above look good.
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Re: Learning to debug Frequency Central XVCO2 build

Post by DanaFo » Tue Feb 09, 2021 8:04 pm

guest wrote:
Tue Feb 09, 2021 7:17 pm
when you turn the pitch knob, how far does pitch go up and down? is it around an octave for the full range? does the other CV input give similar 1V/oct results when the attenuation knob is turned full up?

also, all those numbers above look good.
Using the pitch I went from 214hz to 490hz about 1.4ish octaves?
With pitch maxed, I got 51hz,109,231,489,1039,2203. At min I got null,47,101,214,453,962

Playing cv in octaves fiddling with the pitch knob looked pretty ok.

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Re: Learning to debug Frequency Central XVCO2 build

Post by guest » Tue Feb 09, 2021 8:19 pm

what is the frequency spread for min/max on the "freq trim" trimpot?
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