Splicer... (new mini-project)

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amdagan
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Post by amdagan » Wed Nov 20, 2013 12:25 pm

Nice idea this!
Wondering what would happen if you apply a CV directly to pins 3 and 5 of U1 ?

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Post by ashleym » Wed Nov 20, 2013 12:27 pm

Would there be any mileage in putting in some germanium diodes to mess the sound up a bit?

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J3RK
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Post by J3RK » Wed Nov 20, 2013 12:32 pm

The inverted output is really a lot less useful than a CV input, so I'll repurpose the last op amp for an input buffer for the CV signal. I can redraw this tonight after I wrap up a project for someone, and get the board changes in as well. (euro header, CV addition, etc.)

:party:

As to Germanium diodes... I'm not sure. I've never used them for anything personally. There's no reason you couldn't pop them in there, and see what happens.

Thanks again :bugbrand: !
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BugBrand
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Post by BugBrand » Wed Nov 20, 2013 12:43 pm

Germaniums wouldn't alter anything - you have pairs of diodes, rather than just a single, to overcome the inherent voltage drop of the diodes. (think I phrase that right).

CV to the non-inverting inputs? There could be something, but.. hard to say what - probably a dead end, to be honest. (ie. you'd have to add a fair bit - simple approaches are not good, frankly (having checked with sim))

The circuit is beautifully simple.

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Post by ashleym » Wed Nov 20, 2013 12:56 pm

....that means I will just have to get two boards and test against each other :party: :party:

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J3RK
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Post by J3RK » Wed Nov 20, 2013 1:04 pm

I'm thinking the CV input as is with a buffer would work, but if we want to sum in a manual control, that may need to be inverted as well. Which isn't a big problem, but it would flip which way it's modulated. At least that's the way I'd think to do it. (or could invert/reinvert the CV) Perhaps just a buffered CV input would be enough.

My FadeX crossfader circuit does a good job of doing VC and manually faded waveforms, and gives you control over the range of the fade/pan as well, so maybe I'll just stick to the CV input on the Splicer to keep it small and simple.

I'm sure there are still some Plan B splicers out and about too, if that manual control is really needed. It would be cool though, and I'm a consummate feature-creeper... :mrgreen: If nothing else, I could put this in a third schematic on the first page of the thread.
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CJ Miller
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Post by CJ Miller » Wed Nov 20, 2013 1:06 pm

Neat! I love simple, useful modules like this. Hope I can get my $ problems sorted out to buy a few boards.

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Kakihara
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Post by Kakihara » Wed Nov 20, 2013 2:20 pm

I would be down for 2 of those... Anyone will be in for euro faceplats making?

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BugBrand
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Post by BugBrand » Wed Nov 20, 2013 2:23 pm

ashleym wrote:....that means I will just have to get two boards and test against each other :party: :party:
Get two boards, of course - but, really, don't bother using up germaniums.

I was already convinced that changing to different diodes wouldn't do anything but then thought perhaps you could just change one in each pair - that'd surely do something? Well, real-life may beg to differ, but the simulations suggest if doesn't make the slightest bit of difference.

J3rk: dunno whether you even really need the buffer, to be honest. You could, if you wanted to use the 'standard' 100k input impedance, change all the 10ks to 100k (and the ones on the out summer can be the same too - basically, all identical) [oh, and put the R8 inside the loop]

You could buffer the CV input (but then, why not buffer the other inputs too?!) and then just have a manual control joining the opamp nodes in the same way as I added the CV input - just simple summing.

But, yeah, what to do with the extra opamp.. For audio, the output invert would be of minor use, but could be useful for CV work? Or put it down as an inverter, but 'un-committed'?

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Dave Kendall
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Post by Dave Kendall » Wed Nov 20, 2013 2:38 pm

Hi.

Nice!
A tiny request - would it be possible to add extra pads for R5, R6, R7, R9 and R10 in parallel? That way pairs of 100K resistors could be used for each, instead of 49.9Ks, which are more expensive/harder to find. 100ks are used everywhere, and you can never have too many of them. They're like beer and munchies - stock up on them, so you never run out! :)
R7 and R9 might be tricky to get the pads in, but the others look relatively easy to add. Just a thought.....

cheers,
Dave

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Post by J3RK » Wed Nov 20, 2013 2:51 pm

Dave Kendall wrote:Hi.

Nice!
A tiny request - would it be possible to add extra pads for R5, R6, R7, R9 and R10 in parallel? That way pairs of 100K resistors could be used for each, instead of 49.9Ks, which are more expensive/harder to find. 100ks are used everywhere, and you can never have too many of them. They're like beer and munchies - stock up on them, so you never run out! :)
R7 and R9 might be tricky to get the pads in, but the others look relatively easy to add. Just a thought.....

cheers,
Dave
You can actually just replace all of those with 47K or 100K or anything in that range. The ratios are what is important. You don't want to go too small though, so I'd stay in the 47K-100K range.
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Post by J3RK » Wed Nov 20, 2013 2:54 pm

BugBrand wrote:J3rk: dunno whether you even really need the buffer, to be honest. You could, if you wanted to use the 'standard' 100k input impedance, change all the 10ks to 100k (and the ones on the out summer can be the same too - basically, all identical) [oh, and put the R8 inside the loop]
Putting R8 inside the loop would increase DC accuracy, but for audio use, doesn't that create some errors? I seem to remember some graph-plots from Dave Jones a while back that showed some interesting characteristics of doing that. I do this for my DC mixers, but not for AC devices.

Hmm, best to have a pair of these perhaps. One using a Linear Technology op amp and output resistor in the loop, and the other using an Analog Devices or Burr Brown and the resistor outside. :party:
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Kent
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Post by Kent » Wed Nov 20, 2013 2:56 pm

I regret having sold my Plan B Wavesplicer. I'd like one of these for sure.

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Post by J3RK » Wed Nov 20, 2013 2:58 pm

It looks like there's some interest, so I'll incorporate some of these changes and ideas, adjust the layout, and see about getting some made.
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J3RK
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Post by J3RK » Wed Nov 20, 2013 4:14 pm

Here are the threads I was talking about:

viewtopic.php?t=81108&start=10&postdays ... r+feedback

viewtopic.php?t=64576&start=0&postdays= ... r+feedback

Maybe the jumper/switch to optimize for either wouldn't be a bad idea. :despair:
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Post by J3RK » Thu Nov 21, 2013 12:20 am

This one seems to work fairly well. I didn't really like how the pot behaved when summing it in via summing amp. It could be fixed with more parts, but I think just a CV will be more than sufficient for this. Basically it would fade it all the way to -500mV to 5V or 500mV to -5V on the other end. Interesting, but I'd like things to stay centered around DC0V for this. (and I'd like to keep it small) I also left in the inverting amp for the output. It could be useful for CV use.

I'm thinking about whether or not to add a switch or jumpers for the output resistors to move them in or out of the feedback patch. Some pads on the board would be simple enough to either switch or jumper. That way, one could build it with DC accurate op amps, and move them in the loop. Or build with audio, and move them out. I think this is how I will handle it. Just a couple of SIL headers.

Anyway, here is the updated schematic:

Image
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J3RK
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Post by J3RK » Thu Nov 21, 2013 2:10 am

New PCB layout is done. I will post it when I get a minute or two.

:cloud:
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vurma
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Post by vurma » Thu Nov 21, 2013 2:54 am

Well this whole thing escalated quickly. ^^
J3RK wrote:
I'm thinking about whether or not to add a switch or jumpers for the output resistors to move them in or out of the feedback patch. Some pads on the board would be simple enough to either switch or jumper. That way, one could build it with DC accurate op amps, and move them in the loop. Or build with audio, and move them out. I think this is how I will handle it. Just a couple of SIL headers.
Sound like a good idea. Adaptability is always preferable. So is feedback.
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Post by BugBrand » Thu Nov 21, 2013 4:29 am

You know, I don't think it is worth bothering with jumper etc (not even sure why I brought up the resistor placement ha! But good digging on those 2 old threads - great info)

Last night I ordered a little test-board just to use up 1.5 sqr-inch spare for a proto board order. (haha - just realised I forgot to add the CV in to the final sum stage - idiot!!)
I put on a Mod depth dial and an Initial control - the initial control is to generate a -5 to +5 V offset. I actually used the spare opamp to generate a negative -10V ref (+10V from lm4040) and then sum the Initial via 200k resistors (ie. double the others)

Worth pointing out to people that this is kind of set for symmetrical waves, all of the same amplitude. Of course, waves often aren't precise bang-on 10V p-to-p (what's a few millivolts between friends?) so it is quite possible that in the real-world some small tweaks will be needed.

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Post by KNYST » Thu Nov 21, 2013 5:52 am

voltage control :guinness:
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transistor logic
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Post by transistor logic » Fri Nov 22, 2013 12:45 am

i love simple little projects like that. they help me getting back in diy .

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lightworks
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Post by lightworks » Fri Nov 22, 2013 6:21 am

Hi!
Cool project!
Some time ago i did something similar for my own use, but with some simple LM13700 VCAs on each input. Might be a nice addition to your project also :tu:
My ideia was to control the amplitude of each side of the wave with a joystick for FM stuff.


here is how it turned out:
Image

All the best,
Ruben

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J3RK
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Post by J3RK » Fri Nov 22, 2013 11:38 am

Nice! Yeah, I was thinking about adding VCAs before the inputs. I'll have to play around with that a bit. :tu:
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J3RK
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Post by J3RK » Fri Nov 22, 2013 6:49 pm

I'm ordering prototypes for the basic boards tonight. As long as everything checks out, and I don't see what could really go wrong with this little guy, I'll be placing an order for Synthcube. These should be available in 3ish weeks. I would think.

As far as the excellent idea for VCAs by lightworks above...

My Mike Sims VCA board is the same 1"x3" size as the Splicer board. So two of those can be stacked right behind one of these for the same functionality. It's not as elegant as a single board, but I'm thinking some people won't want the VCAs, while others will. Myself included. I know some people can never have too many VCAs, but I think I've got something like 10 of them in my current system, so two more... I probably don't need right now. hehehe

I'll post more as soon as I get the protos back next week. I'll post a little audio from them as well.
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iL
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Post by iL » Mon Nov 25, 2013 9:52 am

great project. i tryed to get one of those plan b splicers but with no success. like the idea of this thing. so i am in for some boards too!

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