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SEQ V4 Line driver break out CV


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Hi Midiboxers,

Line driver breakout CV /gates finished:happy:
i used AOUT and a tweeked DOUTx4 and of course the line driver receiver!

DOUTx4 is stuffed with regular 220 ohm resistors for leds indicators and UDN2981 for gate booster.
UDN 2981 are directly linked at the outputs of 74hc595 (before the 220ohm resistors) .
the gates assigned to CV have two UDN 2981 (input in parallel)  one is powered by 5V (eurorack 5V gates) and go to minijacks and the second is powered by 12V and go to 1/4jacks (oldschool 12V modular gates)
same for the extra drum triggers gates:  8 are in 12V and the last 8 are in 5V...

need 1k resistor at each outputs of UDN for ground short protection !!!!

3 PSU inside: 
12V  for 12V gates, 5V one for the 5V gates /line driver receiver/DOUT/AOUT and bipolar 12V for AOUT.
the 5V line from the seq is cut on the receiver.

i could have used the same 12V from bipolar but a dedicated 12v make sense cause wanted the AOUT "stability"

as usual i've got a  bug :angelnot:
the CV 1 and 2 have the same problem:  at calibration voltage are divided by 2... don't know why...not the ICs , no shorts, ( problem on the 2 first channel!) all other 6 channel working properly.

the calibration "max" voltage is 4V on this two channel
is it possible to be a log error?
i build AOUT because i've got max525 in stock... 

is someone use this config and could confirm that line driver work with AOUT?

Edited by tashikoma
config protection change
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Hi Thorsten
Yes V/oct is properly selected i tried also with other modes.
the bug only affect the voltage range of channel 1 and 2 all others are goods
approximately (calibration can't really be done):

middle =2.5v

max =4.05v

1v= 0.26V



8V= 3.2V

Approximately same range value for channel 1 and 2

changed the max and tl074, same.

resistors are in good place ...trimmers are from the same batch...

less than 10cm core to line driver transmitter, less than 10cm receiver to AOUT


Next test will be AOUT directly connected to the core. and voltage test of real high note.

but it's not really a problem i could use this two channel for filters , 6 goods CV are available , it's perfect for my config! :grin:
now everybody is using AOUT NG...:decayed:


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  • 3 weeks later...

Wow, I was just looking for a way to boost the trigger outs (for my drum modules) as I am building the CV breakout unit for my Sequencer V4.  Several of my drum modules need about  5 volts to fire them off.

The UDN2981 looks like the perfect way to do this.  Since I am not using any of the triggers for LEDs, can I just replace the 220R resistors with the UDN2981 chip?  (and add power and ground connections of course)

Are the 220R resistors even necessary if I'm triggering drum modules (or EGs, or advancing step sequencers, etc) ?

Drew (thanks for sharing the UDN chip idea Tashikoma!)

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Hi Drew, (with pleasure! this is not my idea, it comes from somewhere in the forum ! don't remember)


can I just replace the 220R resistors with the UDN2981 chip?  (and add power and ground connections of course)

YES DOUT pins to UDN pins are connected without 220R resistors.
if you have just 5v trigger drum module you could drive it directly from DOUT without the 220R and without UDN!

UDN is a deluxe solution and protect 74hc595 outputs.

a trig signal is little draw but with UDN outputs are stronger : you could drive a solenoid! (but not the big ones!)

Have a good end of year!


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  • 2 weeks later...


Latigid on raised a bad point: UDN have no protections on outputs!
not good if output is shorted to ground (as this happens every time you plug into a socket).
1k resistors after each UDN outputs do the job!

Edited by tashikoma
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I can think of one way to build this into a regular DOUT module; solder the UDN chip in standing up on one row, then wire through hole 1k resistors standing up on the other row. Connect in the middle, avoiding shorts of course. Comme toujours!

But this looks to be a very good solution for level shifting multiple gates/clocks. CMOS chips like the 4504 and 7407 are an order of magnitude faster, but I don't think it's too relevant in our case. Plus these are hex chips with annoying pinouts and unnecessary /OE pins etc. Good job Nico!

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thanks Andy but i just use infos of the forum! (when i success to find them)

great idea your building tip
be carrefull of the package:  UDN have extra millimeter in front and rear so i use extra sockets on half sockets to fit them!
 you need one pin space between each UDN it can't be equal to doutx4 or not in the same line.....

exemple in simple form cause i can't explain in english:
for four UDN (a - is one UDN):

---- not good
- - - - good
-_-_ good


Edited by tashikoma
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Okay, the datasheet gives 23.37mm long, is that what you have? So did you stagger the UDNs in the vertical dimension by spacing with extra sockets? Another way might be to put one chip on the top of the PCB, one on the bottom. You have to ensure the inputs and outputs are the correct way around and the power connections will also be mirrored.

Also just to mention; Nico did a few tests with fault testing the UDNs like shorting to ground, bipolar (i.e. negative voltage) CV signals and connecting two UDN outputs together. Everything seems to be okay with the 1k resistors in place. It feels like this could be a more robust solution than using CMOS.

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  • 1 year later...

I am happy that I found this, for I am building the CV/Gate breakout for my +-15 V Modular atm.

I already finished the DOUTx4 with bridges and hope the gate/trigger-voltage is sufficient.

The idea to add leds with the 220ohm is interresting too.

Has someone some schematics on adding the UDN2981 if I have to boost my gates/triggers, please?

Where do I have to add the 15V? Or is this too much and I should regulate it to 10V (I think this is the standard voltage on +-15V - yusynth modules generate mostly 10V gates)


Confused ***

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