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CV Quantizer PCB Layouts
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Sine



Joined: Sep 10, 2007
Posts: 111
Location: Netherlands

PostPosted: Wed Feb 25, 2009 3:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

The staircase generator for this thing is still on my breadboard, I got the DAC at farnell some time ago ( they sell it now for 15,80 euro, not cheap, but certainly not the end of the world )

This thing is VERY tricky with grounding, you really need to keep the analog and digital circuit as separate as possible, I had a terrible bleedthroug from the clock signal ( and yes, the osc as drawn above will not oscillate )
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fonik



Joined: Jun 07, 2006
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PostPosted: Wed Feb 25, 2009 11:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sine wrote:
This thing is VERY tricky with grounding, you really need to keep the analog and digital circuit as separate as possible, I had a terrible bleedthroug from the clock signal ( and yes, the osc as drawn above will not oscillate )

i kept the digital from analog GND right from the start, so no issues on my side. i replaced the oscillator by a very simple one, which is working quite fine.
today i am going to order some cheap DACs. i am curious.

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fonik



Joined: Jun 07, 2006
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PostPosted: Thu Feb 26, 2009 7:07 am    Post subject: Reply with quote  Mark this post and the followings unread

i am optimistic about using a 4024 and a DAC 0800 or DAC 08EP. the 4024 should be perfect to control the 7bits. the AD7245 has a settle time of 30ns, while the DAC 0800/DAC 08EP show up with 100ns/70ns. these DACs are rather cheap: a DAC for a buck. Very Happy
we would clock the DAC with a frequency of about 30kHz, which would result in a period duration of approx. 0.033ms = 33us = 33000ns, am i right?
so these DACs should be more than sufficient speedwise!? or am i thinking wrong about it?

scott used the AD7245s reference voltage to center the staircase roughly around GND, and an additional trimmer for fine adjustment. we could use just a trimmer, i think? or wouldn't it be better to use a 5V zener diode for rough offset, and then a trimmer just for fine adjustment?

i could think of a switch to select bipolar (-5V to +5V) and unipolar (0V- 10V) operation.

i ordered the parts today and will start breadboarding as soon as possible.

any comments appreciated.

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fonik



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PostPosted: Thu Feb 26, 2009 7:35 am    Post subject: Reply with quote  Mark this post and the followings unread

one more question to all, who are interested in this project: the DAC 0800 needs an external reference voltage of 10V in our case. would a voltage regulator be sufficient, or would you prefer a precision voltage reference (REF102), which would be a little bit more expensive (approx. 4$)?
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Sine



Joined: Sep 10, 2007
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PostPosted: Fri Feb 27, 2009 11:28 am    Post subject: Reply with quote  Mark this post and the followings unread

I would go for both, the pads of a 78(L)10 underneath the dil8 socket for the REF, or something in that direction.
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fonik



Joined: Jun 07, 2006
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PostPosted: Fri Feb 27, 2009 1:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sine wrote:
I would go for both, the pads of a 78(L)10 underneath the dil8 socket for the REF, or something in that direction.

yep. a good idea. OTOH most of us would use this for controling VCOs so the most stable voltage reference would be just good enough, i think.


i did not breadboard the s/h yet, since i think there will be no problem with that. yesterday i replaced the 4516s with a 4024 and the next days i will replace the DAC... i hope it all works out as i lined it out in my head. Very Happy

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fonik



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PostPosted: Sat Feb 28, 2009 9:59 am    Post subject:
Subject description: SUCCESS
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today i received the parts and could not wait to breadboard it. and i get a nice upgoing ramp now. Very Happy

a schmitt trigger oscillator clocks a 4024 with approx 32kHz, the 4024 drives 7 of the 8 bits of the DAC0800. the DAC0800 is in bipolar operation, so with the 8th bit allways high it outputs a 128 step ramp from 0.4 to 9.6V, which should be fine enough for us!? the ramp will get centered and trimmed to half steps anyway.

i hopefully get the rest o the circuit breadboarded next week. we are on a good way, i think.

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Sebo



Joined: Apr 27, 2007
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PostPosted: Sat Feb 28, 2009 2:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi:
For the 10V reference voltage for the DAC I recommend you to use a circuit
around a TL431, is cheap and more precise than a 7810.
I built a Marc Bareille's MCV-628 and a Quantix-8 and both calls for the rare
REF01.
Marc suggest me to replace it by the circuit he used in this project:
http://m.bareille.free.fr/mcv32/mcv32.html wich uses the TL431,
and worked great in both cases.

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fonik



Joined: Jun 07, 2006
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PostPosted: Sat Feb 28, 2009 5:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sebo wrote:
Hi:
For the 10V reference voltage for the DAC I recommend you to use a circuit
around a TL431, is cheap and more precise than a 7810.
I built a Marc Bareille's MCV-628 and a Quantix-8 and both calls for the rare
REF01.
Marc suggest me to replace it by the circuit he used in this project:
http://m.bareille.free.fr/mcv32/mcv32.html wich uses the TL431,
and worked great in both cases.

thanks for the heads up, sebo. i intended to use a REF102, which isn't rare at all. however, the TL431 much cheaper! OTOH it requires more boards space and additional. it is 10 times less stable than the REF102 (30ppm instead of 2.5ppm), but i don't think that matters much, since we have to trim the ramp anyways, and then are resistors and OpAmps part of the game, which have about 20ppm!?

more suggestions?

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Sebo



Joined: Apr 27, 2007
Posts: 538
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PostPosted: Sat Feb 28, 2009 7:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi fonik:
About temp stability you're right, but I think it isn't a big difference.
About board space, I used a little piece of stripboard of the same dimentions
of a REF01 (DIP8), to fit the TL431 (TO92), two resistor, a trim, and a cap.
I did it that way because I had to replace the REF01 in two already made
PCBs.
So the space it took is the same (I mounted the resistor vertically).
But if REF102 is easy to find and not too expensive, is a good option, and
anybody that can't find it, could do what I did.

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Tim Stinchcombe



Joined: Dec 07, 2008
Posts: 26
Location: Cheltenham, Glos, UK

PostPosted: Sun Mar 01, 2009 7:40 am    Post subject: Reply with quote  Mark this post and the followings unread

I was just cruising around the forum when this caught my eye:
Sine wrote:
and yes, the osc as drawn above will not oscillate
It looks to me as though that oscillator was originally intended for use with TTL parts - the charge/discharge path for the capacitor is particularly ill-defined, but it just might be OK with TTL, or a TTL-compatible family part for which U1B can source/sink the necessary current. For a straight CMOS part, with virtually no input current, I'd say the chances of getting it to oscillate are small to non-existent.

From looking at similar circuits in the likes of 'The CMOS Cookbook', it might be possible to get it going with a feedback resistor around the second gate, U1B, to the C31/R1 node (but I wouldn't swear to it!)

Tim

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fonik



Joined: Jun 07, 2006
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PostPosted: Mon Mar 02, 2009 7:02 am    Post subject: Reply with quote  Mark this post and the followings unread

hello to all who are interested. here is the schematic i am currently laying out the PCB from (the s/h has not been breadboarded yet). i think it will easily fit on a 3x4in board.
again, any comments or suggestions, especially concerning the voltage reference, are appreciated.

[EDIT 6 MAR 09: schematic updated. circuit tested and working - but there will be improvements i am currently working on)


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Last edited by fonik on Fri Mar 06, 2009 1:43 am; edited 1 time in total
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fonik



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PostPosted: Mon Mar 02, 2009 3:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

less success today. i did not get the sH to work properly.

- the comparator works fine.
- inverting of the comparators output works.
- the pulse conditioner works somehow. i am not quite sure. i cant get hand on the pulse with the scope. i can see an continuous line at GND and some small dots at 15V, however when i try to change the X-axis division on the scope the dots fade...
- the output of the LF398 is always low, near the negative rail. the logics reference voltage is set properly.
pin 6 for the hold capacitor shows a ramp between approx. -12 and -14V!?

i tried to clock the LF398 with the original clock signal for the DAC; didn't work either.

i am puzzled for now. will have to give it a rest!?

did someone get it to work according scotts schematic?

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Sine



Joined: Sep 10, 2007
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PostPosted: Tue Mar 03, 2009 5:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

I think i have a piece of this still on a breadboard, and IIRC it worked, but very jittery.

I'll see if I can get it to work and post the results here.
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fonik



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PostPosted: Wed Mar 04, 2009 12:31 am    Post subject:
Subject description: SUCCESS
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i got it working yesterday. Very Happy

i took a look at chris list's schematic and found he didn't connect the offset input of the LF398 s&h amplifier at all. i disconnected it from GND and it worked.

it actually works quite fine. i recognize some "pops", though. i hope i can post some samples this week.
i still have an email from harry bissell about using latches to improve performance. i will review it carefully but i fear i don't understand what he means. to be honest, i even don't know what latches are Shocked . i could tell from the dictionary that latches are switches!? what is meant here in our context? logical gates?

@scott,
in case you are following this thread: you placed a 10M resistor in the feedbackpath of the comparators. what is this for?

[edit: spelling; and i will update the schematic soon]

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fonik



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PostPosted: Wed Mar 04, 2009 5:32 am    Post subject: Reply with quote  Mark this post and the followings unread

would a d-flipflop be the right thing? or should i ise the 4516 instead of the 4024 again? or both?
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fonik



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PostPosted: Fri Mar 06, 2009 1:48 am    Post subject: Reply with quote  Mark this post and the followings unread

answering this by myself Very Happy
i will try to put latches (D-flipflops) between the comparators output and the LF398s inputs. the latches are clocked by the counters clock. i was told this would give the DACs output 1/2 clock cycle of time to settle.
if this is not sufficient i will replace the 4024 by two 4516s again. i hope this is not necessary, though. the staircase looks really nice on the scope.

BTW: schematic above updated. circuit tested and working - but there will be the improvements i am currently working on...

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Luka



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PostPosted: Fri Mar 06, 2009 2:34 am    Post subject: Reply with quote  Mark this post and the followings unread

matthias will this be much different to the mfos quantizer?
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fonik



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PostPosted: Fri Mar 06, 2009 3:03 am    Post subject: Reply with quote  Mark this post and the followings unread

Luka wrote:
matthias will this be much different to the mfos quantizer?

the principle is slightly different. the incoming CV gets compared to a stepped ramp, just like the MFOS quantizer does. but then the stepped voltage is sampled and held, not stored in a latch.
furthermore my version/adaption of this ARP style/chris list/scott stites quantizer will provide two channels, and will operate uni- OR bi-polar: you could process 0V-10V or -5V-+5V CVs. i am not quite sure if i am able to implement whole step or whatever operation.
at least this is the plan Laughing

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fonik



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PostPosted: Sat Mar 07, 2009 11:53 am    Post subject: Reply with quote  Mark this post and the followings unread

i implemented the d-flipflop today, as once mentioned to me by harry bissell:
the comparators output is fed into the d-flipflop. the flipflop is clocked by the origin clock.
it improved the performance a lot. i don't think it is necessary to replace the 4024 by 4516s (since the staircase is fine anyways). i will have to listen to the output of the current status carefully for a longer time and under different circumstances before i make a final decision, though.
the i will have to try a better capacitor for the hold function (styro?)...

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Sebo



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PostPosted: Sat Mar 07, 2009 2:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

Those are great news!!!
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fonik



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PostPosted: Mon Mar 09, 2009 2:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

for now i made three sound samples. the quantizer is currently set up with the d-flipflop latch, a DAC0800, a CA4024 counter, and a 15nF poly cap from WIMA for the hold function. IT IS NOT CAREFULLY CALIBRATED with the trimmers yet. i hope i will have the time to do complement recordings with the 4516s this week so you can judge by yourself...

each sample is about 500kb

sequencer as source, MFOS 12db filter comes in later:
http://www.modular.fonik.de/sound/quant_01.mp3

LFO, 1 step (half note)
http://www.modular.fonik.de/sound/quant_02.mp3

LFO, 3 steps (1 1/2 note)
http://www.modular.fonik.de/sound/quant_03.mp3

[EDIT: minor grammar changes - i try to do the best i can Wink ]

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Last edited by fonik on Mon Mar 09, 2009 4:26 pm; edited 1 time in total
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zthee



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PostPosted: Mon Mar 09, 2009 2:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the mp3s! I'm really really looking forward to this!
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zthee



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PostPosted: Tue Mar 10, 2009 8:06 am    Post subject: Reply with quote  Mark this post and the followings unread

Would it be possible to drop adress lines or having 2 trimmers to flip the scaling, say between major and minor? Or something like that?
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fonik



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PostPosted: Tue Mar 10, 2009 8:34 am    Post subject: Reply with quote  Mark this post and the followings unread

zthee wrote:
Would it be possible to drop adress lines or having 2 trimmers to flip the scaling, say between major and minor? Or something like that?

no. it would be possible to eliminate steps. so you could have hole notes only and such. but as you can see, this would not be very musical (an western scale has half note steps and hole nte steps).

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