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BCbox's VCA "Click be Gone" Mod
Moderators: altitude, adafruit_support_bill, adafruit, hamburgers, phono

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Re: BCbox's VCA "Click be Gone" Mod

by guest on Thu Aug 12, 2010 3:59 pm

there are a number of places
this could be coming from
and beta differences in transistors might be it
i dont have my x0x currently
but when next i do i will compare betas
with my 303 and see whats up

the main culprit would be q32
although q38 and q31 also have an effect

you can try increasing r134 or c41 to see if it helps
which is actually a 72hz lowpass filter
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Re: BCbox's VCA "Click be Gone" Mod

by Luap on Thu Aug 12, 2010 4:05 pm

Aha.. I was looking at Q37 and Q32 already.. I changed Q37 from a 536 to a 945, zero change. But i'll be trying Q32 shortly and report back. That said, i've not been checking the beta's of them. But I have socketed the ones im changing, so I can test them easily enough later.
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Re: BCbox's VCA "Click be Gone" Mod

by antto on Thu Aug 12, 2010 4:38 pm

guest wrote:...
you can try increasing r134 or c41 to see if it helps
which is actually a 72hz lowpass filter

no clue about the circuit (as i said, i'm not an electrician at all)
but 72Hz would be even smoother than the audio sample i posted so it's not it
btw, it might have something to do with the gate signal release slew, or the accent release slew or something similar..

one clue i'll give you: most (all?) audio samples of x0xb0xes i've ever seen have the same odd attack curve right there.. on the other hand i don't remember if i've seen a 303 sample that has such a nasty attack..
what i think about the x0x is that there's simply no slew, or maybe there is but there is some (nasty?) nonlinearity that makes it look very bad (again, look at the curves in red on my image)
We are here too: irc.freenode.net >>> #x0xb0x
..:: c0nb0x v1.00 ::.. http://forums.adafruit.com/viewtopic.php?f=7&t=29282 (new control app - win/osx)
VCO Tuning: http://forums.adafruit.com/viewtopic.php?f=12&t=24759 (do it the EASY way)

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Re: BCbox's VCA "Click be Gone" Mod

by Luap on Thu Aug 12, 2010 6:25 pm

No luck with Q32, and I tried 3 or 4 different 945's in there. If the 536's are somehow still playing a part, then perhaps it is a cumulative effect, but I don't have enough spares to replace them all.

Clearly we're on the right track with the whole gate deal though. Now I know what to look for on the waveform, I can see what is going on quite clearly. But my electronics knowhow ends about here.. :| So perhaps I have to leave it to you more knowledgeable folk to sniff out. I may try Q31 and Q38 later however, but these are 733's (AP's in my case), where as my thinking was leaning towards the 536's.. Im sure i'll try out any further suggestions from you guys though!?
Last edited by Luap on Thu Aug 12, 2010 7:17 pm, edited 1 time in total.
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Re: BCbox's VCA "Click be Gone" Mod

by phono on Thu Aug 12, 2010 6:55 pm

Altitude wrote:So the million dollar questions are what values and where?


I built a quad slew for my modular which was based on that schematic I posted, 4k7 resistor and 1uf electro cap, if that helps at all
Image
x0x #733 Image SH-101 MC-202 TB-303 TR-606 TR-808 TR-909 MKS-50 Juno-106 A-100 Virus-B E-6400 SX-150 Monotron
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Re: BCbox's VCA "Click be Gone" Mod

by rv0 on Sat Aug 14, 2010 7:52 pm

friend of mine just advised the following:

"try injecting DC instead of the oscillator, then you can see exactly what its doing"

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Re: BCbox's VCA "Click be Gone" Mod

by antto on Sun Aug 15, 2010 2:17 am

true
altho when the oscillator is set at very high freq you can still see the VCA response quite clear
another way is to increase the resonance a lot (think of resonance boost mod here) so that the filter resonance almost is louder than the oscillator, and then push the filter high..
We are here too: irc.freenode.net >>> #x0xb0x
..:: c0nb0x v1.00 ::.. http://forums.adafruit.com/viewtopic.php?f=7&t=29282 (new control app - win/osx)
VCO Tuning: http://forums.adafruit.com/viewtopic.php?f=12&t=24759 (do it the EASY way)

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Re: BCbox's VCA "Click be Gone" Mod

by Kritical Audio on Sun Aug 15, 2010 8:44 am

Would be cool if Altitude could post some dry examples showing the VCA mod? :) However, switching to a BA662A will reduce the clicking a bit.. at least it did for me anyway.
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Re: BCbox's VCA "Click be Gone" Mod

by altitude on Sun Aug 15, 2010 8:51 am

the DC offset click varies for chip to chip and this is also true for the BA662. Out of the last 5 I have have built, some were better some were worse. The mod allows for complete removable of the click associated with the BA6110

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Re: BCbox's VCA "Click be Gone" Mod

by Kritical Audio on Sun Aug 15, 2010 8:58 am

Could you record the mod please? :)
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Re: BCbox's VCA "Click be Gone" Mod

by altitude on Sun Aug 15, 2010 9:47 am

i'm not sure what recording silence would achieve :mrgreen:

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Re: BCbox's VCA "Click be Gone" Mod

by Luap on Sun Aug 15, 2010 10:23 am

Kritical Audio wrote:Would be cool if Altitude could post some dry examples showing the VCA mod? :) However, switching to a BA662A will reduce the clicking a bit.. at least it did for me anyway.


As Altitude said, you won't hear anything, which is kind of the point ;) If your x0x has this problem, you can test for it by holding the waveform switch in a central position while it plays. This will disable the oscillator. If you hear any clicks where the notes would be, there is your DC offset problem. If it is silent, then you have no need for this VCA tweak.

My second x0x had this problem (to a lesser degree than my first x0x), and swapping to a BA662 fixed it. But swapping VCA's is largely luck of the draw. Plus I realised that the particular BA662 I used was one of the special colour dot selected ones, which according to BC's website, is selected for minimal DC offset. So now im not surprised it was fixed 8)

However, as this thread discusses, the VCA is not the only source of clicks either. So the VCA tweak or VCA swaps is not going to work for every x0x.
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Re: BCbox's VCA "Click be Gone" Mod

by antto on Sun Aug 15, 2010 10:37 am

oh wait
you are talking about DC offset in the VCA?
"center the waveform switch.." yeah i also have this bug.. hearing some mains hum filtered by the filter tho it's quiet
but i was thinking we're talking about the clicking of the notes, not DC problems
We are here too: irc.freenode.net >>> #x0xb0x
..:: c0nb0x v1.00 ::.. http://forums.adafruit.com/viewtopic.php?f=7&t=29282 (new control app - win/osx)
VCO Tuning: http://forums.adafruit.com/viewtopic.php?f=12&t=24759 (do it the EASY way)

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Re: BCbox's VCA "Click be Gone" Mod

by Luap on Sun Aug 15, 2010 10:51 am

antto wrote:
but i was thinking we're talking about the clicking of the notes, not DC problems


The thread is discussing both. However, the solution to the DC offset thing is now known, obviously. Because Altitude kindly posted the solution in the first post here.
But the note/gate click issue currently has no proven fix yet..
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Re: BCbox's VCA "Click be Gone" Mod

by antto on Sun Aug 15, 2010 11:50 am

Luap wrote:
antto wrote:
but i was thinking we're talking about the clicking of the notes, not DC problems


The thread is discussing both. However, the solution to the DC offset thing is now known, obviously. Because Altitude kindly posted the solution in the first post here.
But the note/gate click issue currently has no proven fix yet..


i suggested adding a LP filter wherever the Gate signal is (unfortunately i can't tell "where" )
We are here too: irc.freenode.net >>> #x0xb0x
..:: c0nb0x v1.00 ::.. http://forums.adafruit.com/viewtopic.php?f=7&t=29282 (new control app - win/osx)
VCO Tuning: http://forums.adafruit.com/viewtopic.php?f=12&t=24759 (do it the EASY way)

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Please be positive and constructive with your questions and comments.