[sdiy] Ray Wilson's Single Bus Keyboard

Wed Mar 9 14:19:43 CET 2005

The chip should not get hot and the .0047uF caps will be fine. Lets walk
through the circuit and see if we can get this thing going and find out
what's wrong.

>From what you've described it sounds like you have current or you would not
be getting voltage changes as you press the keys.

For reference though when measuring the current you need to open the
connection between the collector of Q1 and the resistor ladder. The current
has to flow through your meter in order to be measured so open the
connection and put the red lead on the collector side and the black lead on
the terminal of the first resistor in the ladder and then you should see
833uA. The reason I suggest starting on the high range is so if there is a
problem and the current is higher than expected you don't blow the meter's
internal fuse.

Starting from the beginning, With the current adjusted properly you should
be seeing voltage on the resistor ladder starting at 0 volts at the ground
end and then multiples of 83mV as you go up the ladder toward the current
source. So... 83mV on the first resistor beyond ground, 166mV on the next,
249mV on the next, etc. At each octave point you should see a multiple of
1V. If your keyboard  starts at C then you should see 0 volts for the lowest
key 1V for the first octave, 2V at the next, etc.

If all of that is good then your current source is working and R8 is
adjusted properly. If you are not seeing the correct voltage intervals then
adjust R8 until you do.

Now the buffers. IC1 is just buffering the voltage from the buss. As you
close keys the bus assumes the voltage associated with the lowest note. That
is because we are using a constant current source to produce the voltage on
the resistor ladder. With no keys down the bus should be at about -.6V due
to R10 and CR1.

The outputs of IC1-C and IC1-D should reflect the bus voltage as you press 
and release keys.

The output of IC1-A will be at about -0.13 volts with no keys pressed or 
with a key pressed
the bus voltage plus 0.4704 volts.

OK point Z is connected to IC1-D's output so it will be the same voltage as 
that. When you press keys
you should see the output of IC1-D (which is the raw changing bus voltage) 
at pin 2 (as you know
the caps don't have numbered pins but the schematic numbers them so you know 
which side I'm
talking about) at pin 2 of C8 (the side connected to point Z). The cap will 
pass the changes in voltage only and
not the DC levels so you will see little spikes at the non-inverting input 
(pin 12) of IC5-D. This is known
as differentiation. The spikes will be dropped across R37. IC5-D provides a 
gain of 200 (actually 201) to the spikes
and you should see them as much larger spikes on the output of IC5-D (pin 
14). The spikes will be rather dirty
because they are generated from the closure of the key switches. But they 
will go positive when the change in voltage is
positive (you went from a lower note to a higher note) or negative if the 
change in voltage is negative (you went from a
higher note to a lower note). The positive going spikes at the output of 
IC5-D go through CR6 and drop on R38.
The negative going spikes are inverted by IC5-A and then go through CR5 and 
drop on R38. So if you look there you
will see a positive spike every time you hit a key no matter which direction 
you play. Those spike are further amplifed by
IC5-B. So you should see -V to +V spikes on the output of IC5-B every time 
you press a key. The positive going portion
of those spikes are dropped on R46. So you should see ground to +V spikes on 
R46 every time you press a key.

>From my previous email... and see the attached gif.

The ground to +V spikes
> charge C14 via CR4 and effectively stretch the pulse a bit. The rising
> edge of the stretched cleaned up pulse is dropped across R47 via C12. The
> pulse is inverted by IC6-D and the rising edge of the inverted pulse is
> dropped across R48 via C13. IC6-B inverts that pulse which is anded with
> inverted point B (effectively the keydown logic). The upshot of thewhole
> thing is that the negative going pulse at IC6-B pin 4 is slightly delayed
> from the edge of the inverted point B signal. This insures that samples
> (and triggers) are only generated when a key is first pressed, when a note
> is changed with the key down (legato) and NOT when the key is released.
> The last key down's voltage is the last sampled voltage and not the
> no-key-down bus voltage (which is about -0.6V). The point T pulses are fed
> to pin 13 of IC3-A and the current bus voltage is sampled onto C2 which is
> buffered by high impedance buffer IC4-B. The output of IC4-B is fed via
> R18 to the non-inverting input of  IC4-A whose output feeds the keyboard's
> sampled and held control voltage to the world via 100 ohm output
> protection resistors.

The IC6 CD40106 chip should not be getting hot. I suggest that you remove 
the chips and ring out the board layout
something is not connected properly. The chip is not being called on to 
deliver any appreciable current anywhere in the
circuit. Several folks have built this circuit successfully (including me) 
so I know it works.

Hope this helps.

Ray

----- Original Message ----- 
From: "Pat Kammerer" <spivkurl at wearerecords.com>
To: "Ray Wilson" <raywilson at comcast.net>
Sent: Tuesday, March 08, 2005 7:47 PM
Subject: Re: [sdiy] Ray Wilson's Single Bus Keyboard

> Okay I think I'm getting my pulses at IC5-D. But I think I've found that 
> my
> current source is not working properly.  I'm really poor at measuring
> current, but I followed your directions and get zero current.  I don't
> understand this, because I get a changing voltage on the bus.  Another 
> thing
> I noticed is the the inverter is getting pretty damn hot.  I removed the
> lm3900 and the 40106, checked all continuity and traces, replaced Q1,
> replaced the 4066, and checked for power at each supply pin.  Nothing 
> seems
> amiss.  The hot chip worries me.  It could be fried or close, but even
> worse, I can't figure out why it's getting hot.
>
> Your last message was a bit unclear about C8.  Does it cut the magnitude 
> of
> the pulses some how between point Z and the other side of this cap?  I am
> getting an amplified, but somewhat dirty pulse at the output of IC5-D.
>
> Oh, do you think my problems would be caused by using .0047uF caps instead
> of .005uF.  I din't have any and couldn't find them at the places I 
> ordered
> from last time.  Would ceramics be required, because I'm using film.  I 
> know
> usually they are interchangable.
>
> Strange... but the two chips that I'm most worried about. the 3900 and the
> 40106 are the two that I did not buy backups of.  Oh well.
>
> If you have any suggestions as to where to go next it would be 
> appreciated.
>
> Thanks,
> Pat
> ----- Original Message -----
> From: Ray Wilson <raywilson at comcast.net>
> To: Pat Kammerer <spivkurl at wearerecords.com>
> Sent: Monday, March 07, 2005 9:00 PM
> Subject: Re: [sdiy] Ray Wilson's Single Bus Keyboard
>
>
>> If you are seeing voltage changes at the output of IC1-D (point Z) and 
>> not
>> on the other side of C8 I assume you are looking with a scope because you
>> will only see low voltage narrow pulses (50 to 80 mV) dropped across R37.
>> IC5-D provides a gain of 200 to these weak pulses. If you aren't seeing
> them
>> and your are not getting large pulses out of IC5-D you may have an open
>> trace on your PC board (assuming you have one) or point Z is not 
>> connected
>> to C8.
>>
>> If you need more help let me know. The one good thing to know is that the
>> circuit does work so you can get there from here.
>>
>> Ray
>>
>>
>>
>>
>> ----- Original Message -----
>> From: "Pat Kammerer" <spivkurl at wearerecords.com>
>> To: "Ray Wilson" <raywilson at comcast.net>
>> Sent: Monday, March 07, 2005 10:00 AM
>> Subject: Re: [sdiy] Ray Wilson's Single Bus Keyboard
>>
>>
>> > Okay,
>> >
>> > I got a bit of time, but not as much as I would hope to trouble shoot.
>> > Point Z seems to be okay, but I'm not getting voltage changes after C8
>> > which
>> > leads to the differentiator.  So I'm thinking that this is atleast one
>> > problem.  I wouldn't think a film would be bad, but I might try a
>> > replacement.  Maybe I'm misunderstanding it's purpose though. 
>> > Shouldn't
> I
>> > see a voltage after this cap?  I think this is the reason that I'm not
>> > seeing spike like I should after the differentiator.  All spikes are
>> > negative and center around -.12v or so.  Does this ring any bells?
>> >
>> > Thanks,
>> > Pat
>> > ----- Original Message -----
>> > From: Ray Wilson <raywilson at comcast.net>
>> > To: Pat Kammerer <spivkurl at wearerecords.com>; sdiy
>> > <synth-diy at dropmix.xs4all.nl>
>> > Sent: Monday, March 07, 2005 7:03 AM
>> > Subject: Re: [sdiy] Ray Wilson's Single Bus Keyboard
>> >
>> >
>> >> Hi Pat
>> >>
>> >> You should be seeing a change in voltage every time you press a new 
>> >> key
>> >> whether you are playing legato or stacato at point Z in the circuit.
> That
>> >> point is the raw voltage that appears on the keyboard bus as you press
>> > keys.
>> >> When you are playing legato you get changes of 83 mV per half step.
> When
>> > you
>> >> play stacato you will get changes from  about -0.6 volts to the 
>> >> voltage
>> >> of
>> >> whatever key you press. If you are not seeing changes in voltage then
>> > check
>> >> that the constant current source (IC2-A, Q1 and associated components)
> is
>> >> providing 833 uA by putting your DVM set to Amps between the collector
> of
>> > Q1
>> >> and the the keyboard resistor stack. I say AMPs first then decrease 
>> >> the
>> >> range until you are sure that you have the necessary 833 uAs flowing
> into
>> >> the resistor stack. If all o that is good then process to the
>> > differentiator
>> >> (IC5-D and associated components). Every time you hit a key or play
>> >> legato
>> >> you will see a spike at the output of IC5-D. It is differentiating the
>> >> changes in voltage from point Z. They go positive if the change is
>> > positive
>> >> and negative if the change is negative (relative to the last note's
>> >> voltage). The positive and negative spikes are rectified by IC5-A and
>> >> associated components (CR5 and CR6). Op amp IC5-B is used as a
> comparator
>> >> and you should see a ground to V+ going spike at the kathode of CR4
> every
>> >> time you change notes. If you don't then something is not connected
>> >> correctly in the differentiator/rectifier/comparator section. The
> ground
>> > to
>> >> +V spikes charge C14 via CR4 and effectively stretch the pulse a bit.
> The
>> >> rising edge of the stretched cleaned up pulse is dropped across R47 
>> >> via
>> > C12.
>> >> The pulse is inverted by IC6-D and the rising edge of the inverted
> pulse
>> > is
>> >> dropped across R48 via C13. IC6-B inverts that pulse which is anded
> with
>> >> inverted point B (effectively the keydown logic). The upshot of
> thewhole
>> >> thing is that the negative going pulse at IC6-B pin 4 is slightly
> delayed
>> >> from the edge of the inverted point B signal. This insures that 
>> >> samples
>> > (and
>> >> triggers) are only generated when a key is first pressed, when a note
> is
>> >> changed with the key down (legato) and NOT when the key is released.
> The
>> >> last key down's voltage is the last sampled voltage and not the
>> > no-key-down
>> >> bus voltage (which is about -0.6V). The point T pulses are fed to pin
> 13
>> > of
>> >> IC3-A and the current bus voltage is sampled onto C2 which is buffered
> by
>> >> high impedance buffer IC4-B. The output of IC4-B is fed via R18 to the
>> >> non-inverting input of  IC4-A whose output feeds the keyboard's 
>> >> sampled
>> > and
>> >> held control voltage to the world via 100 ohm output protection
>> >> resistors.
>> >> (I know the outputs are probably short proof but hey why not be belt
> and
>> >> suspenders safe). I am going to update the page with this info and I
>> >> replaced the abysmally out of date timing chart (my sincere 
>> >> apologies).
>> >>
>> >> I hope this helps
>> >>
>> >> Ray
>> >>
>> >> ----- Original Message -----
>> >> From: "Pat Kammerer" <spivkurl at wearerecords.com>
>> >> To: "sdiy" <synth-diy at dropmix.xs4all.nl>
>> >> Sent: Monday, March 07, 2005 12:14 AM
>> >> Subject: [sdiy] Ray Wilson's Single Bus Keyboard
>> >>
>> >>
>> >> > Hi everyone!
>> >> >
>> >> > I just finished all of the stuffing and wiring of Ray Wilsons Single
>> >> > Bus
>> >> > Synth Keyboard.  I have a partial problem with it.
>> >> >
>> >> > If anyone has built this circuit, then I'm curious.  What should I
>> > expect
>> >> > as
>> >> > an interaction between the 40106 and the 4066?  Am I right in
> assuming
>> >> > that
>> >> > part of the 40106's job is to cause the switch to close when a key 
>> >> > is
>> >> > pressed. I'm not getting CV output or trigger where I should.  I can
>> > trace
>> >> > the keyboard reaction in the circuit, and I seem to run into a dead
> end
>> >> > somewhere around the 40106 and the 4066.
>> >> >
>> >> > I've never use the 40106 before, so I'm a bit above my head.  If any
>> >> > one
>> >> > can
>> >> > help me understand what's going on in the CMOS part of this circuit,
>> > then
>> >> > I
>> >> > would be grateful for help in troubleshooting.
>> >> >
>> >> > Take care,
>> >> > Pat
>> >> >
>> >>
>> >>
>> >
>>
>>
> 
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