Precision Adder

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Haralds:Werk
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Precision Adder

Post by Haralds:Werk » Thu Sep 10, 2020 9:12 am

This is a useful and often needed utility module. The input voltages are precisely added to the outputs.The inputs 1, 3 and 5 are normalized. It can be used in different ways: As three independent adders, as buffered multiple, adding a modulation source simultaneously to all three outputs, adding two, three or four voltages precisely and a few more, depending on your patch. The accuracy depends on the used operational amplifier. For pitch CV I recommend precision OpAmps like the LT1014.

Specs and features
• 3 independent precision adders
• Input 1, 3 and five normalized
• Buffered multiple
• Additional common modulation inputs
• Runs on +/-12V and +/-15V
• Power consumption below 10mA each rail

The documentation and the Gerber files for download can be found in my website.

Precision_Adder_EB_090_schematic.png
Precision_Adder_EF_090_schematic.png

All inputs are buffered with high impedance inputs. They are followed by precision adders where the two inputs and the two additional modulation inputs are added together. The last stage buffers the output and corrects the phase. Inputs 1, 3 and 5 are normalized. The accuracy depends on the used operational amplifier and the matching of the resistors. For pitch CV I recommend precision OpAmps like the LT1014. Match all 10k resistors to 0,1% or better.

Precision_Adder_front.JPG
Precision_Adder_side.JPG
Precision_Adder_PCB.JPG
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Re: Precision Adder

Post by Grom » Fri Sep 11, 2020 2:22 am

wow, just what I was looking for in utillity, looks brilliant mate.

I'm learning EASYEDA. Mind If I try to replicate it in smd format?

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Re: Precision Adder

Post by whyfarer » Fri Sep 11, 2020 5:25 pm

awesome! thanks for sharing. how precise have you found it to be in practice? really, I want to know if you've found it good enough to add v/oct without the need for a quantizer after the summing.

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Re: Precision Adder

Post by Hutenberger » Sat Sep 12, 2020 3:17 am

Thanks for sharing this! Have need for such a module but not gotten one yet.
Do you have experience if it will keep its precision with other opamps like e. g. TL074 too? Or is the type of OpAmp critical?
I would guess, that precision comes mainly from using buffered inputs and selecting matched resistors.
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Re: Precision Adder

Post by cygmu » Sat Sep 12, 2020 4:04 am

Hutenberger wrote:
Sat Sep 12, 2020 3:17 am
Thanks for sharing this! Have need for such a module but not gotten one yet.
Do you have experience if it will keep its precision with other opamps like e. g. TL074 too? Or is the type of OpAmp critical?
I would guess, that precision comes mainly from using buffered inputs and selecting matched resistors.
Things like the offset voltage and noise of the op amps are important. A TL07x has 3mV or so offset voltage, which will introduce an error in the summing. That's why Harald chose LT1013/4 which have much better specs there -- 50 uV offset.

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Re: Precision Adder

Post by Rex Coil 7 » Sat Sep 12, 2020 4:47 am

That could be a very nice addition to these two ... make a nice ensemble (perhaps).

Come out of the 1v/oct source (kybd, sequencer) and into the Precision Adder ....
Harold Precision Adder - 01.JPG
Then out of the Precision Adder (with modulation signals ~added~ to the 1v/oct signal) into the VPME.DE T-43 Interval Adder ....
VPME-DE - T-43 precision adder - 01.jpg


Out of the T43 interval adder and into this ....
AJH Synth - V Scale variable buffer - 01.jpg



Out of the V-Scale and distributed to all of the 1v/oct destinations.


NOICE !!!!!!!!!!


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Re: Precision Adder

Post by KSS » Sat Sep 12, 2020 4:55 am

@Hutenberger
As a designer, you choose your place to spend money. Either by using a less expensive op amp and then needing to add trims and time and PCB space to deal with its inherent weaknesses, or by getting a higher quality op amp in the first place.

There are reasons to choose one or the other in a given situation. In this case, Harald apparently determined the 1014 is good enough -at a low enough difference in cost- to go ahead and go that direction.

Replacing it with an 074-072 will be a definite and significant downgrade without adding trims and their 'glue' components to the circuit.
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Re: Precision Adder

Post by KSS » Sat Sep 12, 2020 4:59 am

@Rex Coil 7
Thanks for showing that V-scale. Hadn't seen it before. First buff mult that makes sense!
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Re: Precision Adder

Post by Haralds:Werk » Sun Sep 13, 2020 5:18 am

Grom wrote:
Fri Sep 11, 2020 2:22 am
wow, just what I was looking for in utillity, looks brilliant mate.

I'm learning EASYEDA. Mind If I try to replicate it in smd format?
Feel free to do so. This is what this forum should be fore. DIY.
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Re: Precision Adder

Post by Haralds:Werk » Sun Sep 13, 2020 5:21 am

whyfarer wrote:
Fri Sep 11, 2020 5:25 pm
awesome! thanks for sharing. how precise have you found it to be in practice? really, I want to know if you've found it good enough to add v/oct without the need for a quantizer after the summing.
Adding 1V to 1V. Good enough?
IMG_5152.JPG
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Re: Precision Adder

Post by Haralds:Werk » Sun Sep 13, 2020 5:29 am

Hutenberger wrote:
Sat Sep 12, 2020 3:17 am
Thanks for sharing this! Have need for such a module but not gotten one yet.
Do you have experience if it will keep its precision with other opamps like e. g. TL074 too? Or is the type of OpAmp critical?
I would guess, that precision comes mainly from using buffered inputs and selecting matched resistors.
As others said above you need precision OpAmps if you do it this way. And I selected my resistors to 0,01%.
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Re: Precision Adder

Post by KSS » Sun Sep 13, 2020 6:37 am

Gotta add that selecting cheap resistors to tight tolerance is a fools errand. Start with decent resistors. 50ppm 1% metal film are only a few cents.

With cheap resistors. You'll get a set of -intitially- matched resistors all right. But what they'll do under aging, self-heating and ambient temp changes is another thing entirely.

By cheap I mean those with uncertain source, like you might find at Tayda -though I've heard they've much improved their offered R's- or those from a generic importer-exporter listing on Amazon or aliexpress.
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col
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Re: Precision Adder

Post by col » Sun Sep 13, 2020 7:34 am

can't you do most of this by transposing one octave on a sequencer? Beatstep Pro etc can do this easy.

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Re: Precision Adder

Post by whyfarer » Sun Sep 13, 2020 10:45 am

Haralds:Werk wrote:
Sun Sep 13, 2020 5:21 am
whyfarer wrote:
Fri Sep 11, 2020 5:25 pm
awesome! thanks for sharing. how precise have you found it to be in practice? really, I want to know if you've found it good enough to add v/oct without the need for a quantizer after the summing.
Adding 1V to 1V. Good enough?

IMG_5152.JPG
Quite! :yay:

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Re: Precision Adder

Post by whyfarer » Sun Sep 13, 2020 10:54 am

col wrote:
Sun Sep 13, 2020 7:34 am
can't you do most of this by transposing one octave on a sequencer? Beatstep Pro etc can do this easy.
I'm looking to do much more than octave transposing. Many sequencers might can do some of the things the precision adder can do, but within the modular CV is king and that can usually let you do more if you set up an interesting patch. Here's two examples. The first is an extension of what you describe, the later is something I don't think many sequencers can do:
  • you can use the multiple inputs of the precision adder to add an offset (not necessarily an octave) to multiple v/oct signals. now you can transpose within the modular which means you can transpose pragmatically or generatively/randomly
  • take one v/oct sequence as your main sequence. Line up a few others (including an empty input) in a sequential switch and rotate through adding different secondary sequences to the primary. set it up so that some random some source is triggering the seq.switch and, voila, you have a melodic song structure on the modular ABA, ABCABC, ABACABA, ... Or set it up so that you have something random triggering the switch and now you have a somewhat generative melody that can wander away from the original line and return.
edit: if you haven't seem them, take a look at the tutorial video that goes along with Steevio's "Primes" video. he describes how he uses adders to change up melodies and rhythms (precision adder is not needed for rhythms. for that matter, you could always add cv and then quantize, avoiding the need for the precision adder, but this may require many quantizers and if the adder is imprecise enough quantization may not fix the imperfection)

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Re: Precision Adder

Post by ZTX500 » Sun Sep 13, 2020 11:12 am

Looks like a very handy module. I'm interested by the choice of LT1014 here... When building something similar I used OPA4197, which as far as I can tell is is cheaper, has a lower offset voltage, and has a bias current a factor of 2000 less than the LT1014 at modular case temperatures - so I didn't need the input buffers. Am I missing an advantage of the LT1014?

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Re: Precision Adder

Post by Haralds:Werk » Sun Sep 13, 2020 11:32 am

ZTX500 wrote:
Sun Sep 13, 2020 11:12 am
Looks like a very handy module. I'm interested by the choice of LT1014 here... When building something similar I used OPA4197, which as far as I can tell is is cheaper, has a lower offset voltage, and has a bias current a factor of 2000 less than the LT1014 at modular case temperatures - so I didn't need the input buffers. Am I missing an advantage of the LT1014?
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Re: Precision Adder

Post by col » Sun Sep 13, 2020 7:59 pm

whyfarer wrote:
Sun Sep 13, 2020 10:54 am
col wrote:
Sun Sep 13, 2020 7:34 am
can't you do most of this by transposing one octave on a sequencer? Beatstep Pro etc can do this easy.
I'm looking to do much more than octave transposing. Many sequencers might can do some of the things the precision adder can do, but within the modular CV is king and that can usually let you do more if you set up an interesting patch. Here's two examples. The first is an extension of what you describe, the later is something I don't think many sequencers can do:
  • you can use the multiple inputs of the precision adder to add an offset (not necessarily an octave) to multiple v/oct signals. now you can transpose within the modular which means you can transpose pragmatically or generatively/randomly
  • take one v/oct sequence as your main sequence. Line up a few others (including an empty input) in a sequential switch and rotate through adding different secondary sequences to the primary. set it up so that some random some source is triggering the seq.switch and, voila, you have a melodic song structure on the modular ABA, ABCABC, ABACABA, ... Or set it up so that you have something random triggering the switch and now you have a somewhat generative melody that can wander away from the original line and return.
edit: if you haven't seem them, take a look at the tutorial video that goes along with Steevio's "Primes" video. he describes how he uses adders to change up melodies and rhythms (precision adder is not needed for rhythms. for that matter, you could always add cv and then quantize, avoiding the need for the precision adder, but this may require many quantizers and if the adder is imprecise enough quantization may not fix the imperfection)
Interesting, I saw the Steevio vids back when they were released. At the time I purchased a Doepfer A-185-2 and a A-151 with the intention of using them in a generative patch, combined with a couple of Ornaments and Crime modules for the quantization but I never achieved results I was happy with, maybe I gave up too early, not sure.

@Haralds:Werk just looking at your website, thats an impressive body of work! :tu:

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