Accented notes are just short pops!

[r.odent]

First off, this is a pre-built Mode Machines x0xb0x. I wish I'd looked some things up before getting one.

On accented notes it sounds like the filter envelope cuts short (as it should be, I think) but I never get the "wow" sound. Turning the accent knob up I think has a very subtle effect on the cutoff frequency -- the attack and decay are both still very short, nothing like what a 303 sounds like in my experience. Any accented not just turns into a short percussive pop (makes for nice toms!).

The effect on amplitude of turning the accent knob all the way up on seems fine, though. The accented notes are definitely louder.

I don't have access to any measurement tools for a couple of days. I just wanted to throw this out there in case it's a common problem with a simple solution. I'll make a recording of it tomorrow, though.

[antto]

i suspect it's the filter envelope generator, it's a RC decay, so probably either the resistor or capacitor (or both) is wrong value making the minimum decay shorter than it should

what happens to normal notes when you set the decay knob to 0?
if i'm right then the filter envelope on normal notes would be as short as on accented notes

filter envelope is R138 and C62 (decay pot also gets added to the RC via some switching but it only makes the RC time slower, so it cannot be responsible for this issue)

[r.odent]

Thank you! That's right, bottoming decay results in decay on normal notes that sound identical to accented ones. I got a multimeter today, so I will be able to make some measurements, but I really don't know what to look for. I'll start by looking for obvious faults in the filter EG section.

Here's a page I found that describes how the accent works: http://www.firstpr.com.au/rwi/dfish/303-unique.html

[r.odent]

I just noted that if I put an accent on a rested note, have the accent and decay knobs above middle, a note will still be played quietly (at the same pitch as the last non-rested note), no matter the env. mod setting. I don't know if this is relevant or maybe even normal operation.

I found another reference to the "sweep circuit" here: http://alphazone1.com/x0xi0/user/io_user.html (search for swp. out). Resonance in my unit seems not to affect the accent behavior at all, which it looks like it should from that page.

[MMM]

Thank you! That's right, bottoming decay results in decay on normal notes that sound identical to accented ones. I got a multimeter today, so I will be able to make some measurements, but I really don't know what to look for. I'll start by looking for obvious faults in the filter EG section.

This sounds like normal behaviour for the filter EG. Since you also mentioned that you get proper loudness accents I wouldn't expect any faults in the filter EG itself then (the loudness accent IS the short filter EG).

[antto]

MMM: uhm.. what?!
i thought the loudness of accented notes comes from another place, not the cutoff envelope (C62/R138)
lemme see, iirc it's somewhere R119 and C36

the problem he has (according to what he describes) must be the cutoff envelope minimum decay time being too short which is C62/R138, the loudness comes from another place thus it works fine, the accent sweep (C13) is based on the cutoff envelope and making the decay any shorter will reduce the acc. sweep and make it inaudiable

[MMM]

MMM: uhm.. what?!
i thought the loudness of accented notes comes from another place, not the cutoff envelope (C62/R138)
lemme see, iirc it's somewhere R119 and C36

Nope; it's actually the (short) filter envelope passing through R119 (and being slightly smoothed by C36). Just trace it backwards from R119:

- the point where part of the accent signal is split through D24 to the resonance pot
- the wiper of the accent pot
- pin 2 of IC12
- pin 1 of IC12

And on pin 1 you'll find the filter envelope (or its short version for accented notes).

the problem he has (according to what he describes) must be the cutoff envelope minimum decay time being too short which is C62/R138, the loudness comes from another place thus it works fine, the accent sweep (C13) is based on the cutoff envelope and making the decay any shorter will reduce the acc. sweep and make it inaudiable

That's not how I read it. As far as I understand him the shortest time for non-accented notes (Decay fully counterclockwise) is identical to the accented notes:

That's right, bottoming decay results in decay on normal notes that sound identical to accented ones.

[antto]

well that minimum decay time as far as i understand on his x0x is far shorter than it should be, thus the acc. sweep cannot accumulate enough to make the "wow" sound
or it could be something else wrong (since there's no audio recording i could hear)

r.odent: if possible make an audio recording and post it so we can hear exactly what happens, it would help

[MMM]

well that minimum decay time as far as i understand on his x0x is far shorter than it should be, thus the acc. sweep cannot accumulate enough to make the "wow" sound
or it could be something else wrong (since there's no audio recording i could hear)

Well, if the minimum decay time (non accented) is ok and the accented decay time is identical...

I agree, we need a recording.

[r.odent]

Thanks for the input! I recorded a demo and uploaded it here.

First part is resonance all the way up, env mod and accent knobs all the way down, and some tweaking of the decay knob.

Second part has max decay, accent bottomed and I tweak the env mod knob. You can hear the effect of the accent on the decay time, and so far I guess this is how it is supposed to sound. In the end I lower the decay so you can hear that accented notes sound the same as normal notes with no decay at this point.

Third part I begin with accent all the way up, no env mod. You can hear the effect of the accents on amplitude. Then I raise the env mod and lower the decay, and as I just noticed now, you can hear that there IS an effect on the filter when accents are applied, but it's just a short zap.

[antto]

yes, as i expected, the problem is the filter envelope's decay time is far shorter than it should be
(the accent sweep circuit should be fine)
so check the resistor and capacitor there, and maybe also the decay pot (should be 1MegaOhm)

[r.odent]

Thank you for the advice! I will look into it soon. Is there a good way to figure out which of these components are busted without desoldering them? I'll start looking for shorts, anyway.

Thanks again! Could anyone record a sample demonstrating the lowest normal decay? Just out of curiosity.

[antto]

here: https://www.box.com/s/b10394c92835a3ab517f
this is a simple pattern of 4 "normal" and 4 "accented" notes running at 80BPM
decay knob is set to maximum all of the time

[r.odent]

I have now measured R138 and it is close to 68 KOhm over its terminals, and the traces from the pot and to R152 are fine. Shorting it out shortens the minimum decay time to nothing, as suspected, but now I'm at a loss as to how to find the source of the problem.

I'd rather not desolder anything, but I guess looking at the pot ought to be the next step. I really only have a very basic idea of electronics, so any help with how to take this further is appreciated.

[r.odent]

The rightmost two pins of VR6 (looking from the top of the main board) seem to be joined -- are they supposed to be? If not, can I just cut the rightmost pin as it doesn't seem to be connected anywhere else?