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Knobs not acting quite right!!
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Please be positive and constructive with your questions and comments.

Knobs not acting quite right!!

by clickerbuzz on Sat Nov 24, 2007 3:43 pm

Hi guys,

I got my x0x kit a while ago and have been gradually building it over the past few months. I didn't have any gear to do the testing so went ahead and put everything together hoping all would be ok.
Well, now I've finished I'm having a little problem:-
Everything about the synth seems to work ok except for my filter cutoff, env mod and accent knobs.

The filter cutoff doesn't seem to have the range that it should. More low than high.

When I turn up the Env mod it has the effect of turning down the filter cutoff. Although it does produce the expected filter envelope modulation.

The Accent knob is having no effect whatsoever. I have put accents on all notes and I can hear no difference.

I'm hoping this will be something minor as opposed to me having to dimantle a large portion of the pcb. :cry:

Any help would be greatly appreciated.
clickerbuzz
 
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by phono on Sat Nov 24, 2007 4:07 pm

make sure you put the right knobs in the right places
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by clickerbuzz on Sat Nov 24, 2007 4:33 pm

Filter cutoff(VR3) and Env mod(VR5) are 50K D
Accent(VR7) is a 50K B

Would getting these mixed up have this effect?
I thought the only difference between these is one is linear the other logarithmic!
clickerbuzz
 
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by guest on Sat Nov 24, 2007 5:07 pm

it sounds like a bunch of independent problems
so lets look at one at a time

do accented notes have a shorter decay time
turn env mod full up
and turn decay full up
and then make half of the notes accented
you should hear the filter sweep speed up
on the accented notes

if not
then check r141 to see if the microcontroller
is outputting a 5v accent signal
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by Sokkan on Sat Nov 24, 2007 5:13 pm

For the filter cutoff: Have you tuned the filter as per the manual? There is a trimmer inside(TM3?) that needs to be adjusted. If you lack the equipment to do it properly do it by ear. I have mine at approximately "a quarter to full" if that makes sense. A to low setting will not open it up properly, a to high setting will make your box lack in the low "bowow-y" end. You can not extend the range of the cutoff knob, only move the available range up and down.

For the accent knob: make sure you have soldered the legs of the pot properly to the board and look for bad solder joints on the pot.

For env mod: sounds weird... is the pot soldered in properly?

In any case it all just sounds like some intermittent connections for the affected pots, nothing serious I would guess.
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by clickerbuzz on Sat Nov 24, 2007 5:55 pm

Thanks for the advice guys.

guest wrote:do accented notes have a shorter decay time
turn env mod full up
and turn decay full up
and then make half of the notes accented
you should hear the filter sweep speed up
on the accented notes


Just tried this.
The accented notes do have a faster filter sweep.

Sokkan:-
I tried adjusting TM3. It did bring the highest point up. But it seems as though when I turn VR3 down the sound disappears too quickly. Maybe I'm just not used to the way the filter operates?!
I have good flow through on all the pot leads, so I would have to guess they are soldered properly.
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by guest on Sat Nov 24, 2007 10:02 pm

there are two parts to accented notes
the first is a faster filter sweep
and the second is louder notes

check to see that d27 is in correctly
make a line of all accented notes
and measure the voltage across c36
when this line is running

this voltage should be at 0v with the accent knob full off
and be around 3v with the accent knob full on
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by clickerbuzz on Sun Nov 25, 2007 5:31 am

OK,

D27 looks ok. Good joints and correct orientation.

I borrowed a multimeter from work. I have it set to 20DCV.
I have set up a sequence with all accents.
Measurements across C36 are:-
With accent knob full off - 0.00
With accent knob full on - 0.10 (tends to fluctuate between 0.07 and 0.11)
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by clickerbuzz on Mon Dec 03, 2007 3:58 pm

Well, I've looked around to see if I've fitted any incorrect parts but I can't see anything obvious wrong.

Does anyone have any more advice with regard to this problem?

I really am stuck, I just want it working!! :cry:
clickerbuzz
 
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by guest on Tue Dec 04, 2007 1:10 am

unfortunately my x0x isnt working at the moment
i think ive taken it apart too many times
so i cant go probing around for voltages
to see what things should be

maybe ill have time with the upcoming break
guest
 
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by booster on Tue Dec 04, 2007 12:16 pm

In the meantime, maybe it would be worth touching up some of the solder joints?

Wouldn't hurt.
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by clickerbuzz on Wed Jan 16, 2008 8:34 am

guest wrote:unfortunately my x0x isnt working at the moment
i think ive taken it apart too many times
so i cant go probing around for voltages
to see what things should be

maybe ill have time with the upcoming break


Apologies for bumping this topic back up!

Any chance to have a look at this yet Guest?

My poor x0x is still in pieces!

:cry:
clickerbuzz
 
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by guest on Thu Jan 24, 2008 10:50 am

if you have a pair of headphones
you dont particularly care about
you can test for the envelope signal with them
it wont destroy the headphones
but you will be putting 12v across them for a short period of time
so it wont be the greatest thing for them
unfortunately its one of the few ways to sense
the short envelope spike

connect the sleeve of the headphones to ground
connect the tip to pin2 of ic12
put the x0x in keyboard mode
press a note key
you should hear nothing
turn on accents
press a note key
you should hear a click

if you hear a click
keep following the signal and see where it ends
turn the accent pot full up
and check the middle pin

if you dont hear a click
check to see that pin13 of ic12
goes from 12v to 0v when the accents are turned off
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by clickerbuzz on Wed May 28, 2008 11:08 am

clickerbuzz wrote:Well, I've looked around to see if I've fitted any incorrect parts but I can't see anything obvious wrong.:cry:


Well, after a long time I think I found the issue, turns out I had fitted Q40 round the wrong way. I guess I didn't look hard enough last time!!

Desoldered and rotated it and I am now part of the x0xb0x elite!! :P
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Re: Knobs not acting quite right!!

by exagonal on Mon May 26, 2014 2:08 am

Well! Very good. I have a problem like this but lightly different...when turn down the cutoff knob, the output sound goes down...the filter seems to affect the sound in correct way, but the filter affect the volume too !! Any suggestions ??
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Please be positive and constructive with your questions and comments.