X0xb0x - problems with octave range

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ddoak55
 
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X0xb0x - problems with octave range

Post by ddoak55 »

Hallo,

This is my first post. I bought the Mode Machines XOXBOX 2 from someone and I am having big problems setting up octaves. For some brief moments I can get ok octave using the TM5 trimmer but then it jumps in pitch much higher and the octave sound as octave between C1-D2 (or up to E2 at the other end of the trimmer range). I replaced the whole 200k resistor network, resoldered all joints around the VCO but the problem persists. Its like some part is unstable or malfunctioning since as I said randomly it puts out good octave (accordig to the plugin, my tuner and my ears) and even the scale sounds ok . The 5,33 V and 12 V are OK. Otherwise it works (makes sound, filter, env etc all works. Please help, I dont know what to look for.

Thank you for any help
David

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antto
 
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Re: X0xb0x - problems with octave range

Post by antto »

how exactly do you tune it?
you mentioned a plugin - what plugin?

ddoak55
 
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Re: X0xb0x - problems with octave range

Post by ddoak55 »

I used the AS_x0x_tune VST according to the tutorial and also my guitar tuner (or roughly by ear). I pluged midi out of my MPC1000 to midi in, switched xox to midi play and made short sequence of alternating tones (C1-C2). Also played by hand slowly. This way I found that when moving the TM5 I was unable to get to full octave when playing C1-C2. But when I played C1-D2 it was almost perfect. When I moved the TM5 to the other extreme I had to play C1-E2 to get the full octave. The actual frequencies varied but the interval worked this way. However sometimes - when I touched the trimpot with my screwdriver it suddenly completely changed (pitch dropped quite alot) and I got perfect octave where it should be. And then it mysteriously changed again back to the error. I thought it is the trimpot so I removed it, measured - it seemed to be ok. So I returned it back (didnt have a replacement at the moment) and for a while it all worked, octave was correct. And the it changed back to the error again. Then I measured the trimpot in the circuit and it shows correct values. I also measured the resistors around and all seem to have correct values.

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antto
 
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Re: X0xb0x - problems with octave range

Post by antto »

the note when you program "c" (the lower one) without any transpose - that's C2
for AS_x0x_tune you have to use C3 and C4 alternating, so program high-C and high-C+UP

now, in your case, i guess you should have replaced the trimpot with a new one
the pitch shouldn't just move around

ddoak55
 
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Re: X0xb0x - problems with octave range

Post by ddoak55 »

Thank you, ok I will try different trimpot.

ddoak55
 
Posts: 5
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Re: X0xb0x - problems with octave range

Post by ddoak55 »

So I replaced the trimpot with a multiturn one but the problem persists. The best I can get using the VST tuning plugin (C3-C4) is between 1.035 and 1.873. The other extreme is 1.072 and 1.764.

Thanks for any help
David

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antto
 
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Re: X0xb0x - problems with octave range

Post by antto »

okay.. maybe some of the surrounding resistors is of the wrong value
check all resistors in the VCO (including the two trimpots) if they are the right values

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mmm
 
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Re: X0xb0x - problems with octave range

Post by mmm »

My guess is that R106 has a wrong value (probably 27k instead of 24k) and/or there's a problem with R100A/R100B (or a cold solder joint).

ddoak55
 
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Re: X0xb0x - problems with octave range

Post by ddoak55 »

R 106 = 26.5k (in circuit)
however I found the culprit - it was the pin 8 of the IC9 - there was a cold solder joint. I followed advice of Malte from MM looking for the proper 1V/oct at pin 7 of IC11 (it was wrong) and while measuring I just tried various grounds and touched the pin 8 of the IC9 which resulted in instant pitch drop and correct octave behavior. So I resoldered it and now it seems to work ok. But the R106 value seems to be wrong. I should replace it too, I guess?

Thank you very much for your assistance!
Best regards
David

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