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old-school patch preset... relays or logic???
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celebutante



Joined: Jun 29, 2007
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PostPosted: Fri Sep 07, 2007 3:26 pm    Post subject: old-school patch preset... relays or logic??? Reply with quote  Mark this post and the followings unread

Hi y'all. I've new to the forum but I've been lurking for a while. I've got a .com modular system and I've built a couple of CGS PCB modules.

My next project is going to be a 2 osc self-contained monosynth, to be optimized for live bass. I intend to use mostly prefab PCB's, though Yusynth's Mini filter is looking like a good reason to jump into DIY PCB etching world!

Here's my question... I thought it would be neat to have some preset envelopes for the filter and amp for live, and figure three presets would cover it. I figured I could have a 4-pos rotary switch (3 presets+"manual"), and use relays along with trim pots for the presets, like the old Yamaha CS-60/80. Futurelec sells some neat PC mount 4PDT relays, but they're $4.50 each and I'd need at least six of them (I could use a normal DPDT relay for attack on both envelopes, since it'd be zero for all the presets).

So I got to thinking about it, and I realized that CS-80's, Polymoogs, etc, probably didn't have a zillion relays to change the routings of pots...I'm pretty dumb about this stuff, but I'm guessing there was some kind of 4000-series logic that switched all the routings? So... could I do it that way, would be cheaper and/or easier? (and/or, that's logic right :>P)

And if so, I could probably "preset" more parameters, though I don't want to make this thing too much of a mess.

Anyone got any info on this?

thanks in advance,

Mitchell Sigman
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EdisonRex
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PostPosted: Fri Sep 07, 2007 3:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

There is a little leap of faith into using DACs. Remember that all the pots are doing is providing voltages.

80s synthesizers had analog functions controlled by digital controls. A lot of it was ADC from the pot's voltage reading to some memory location, and DAC back to recall it. Actually, the pots were far from the control, while they still existed. By the mid 80s you might recall that most synthesizers had dispensed with knobs altogether.

It's not hard to implement, overall, but it does increase the parts count significantly. Unless you aren't building analog in the first place. Anyway, my two penneth.

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celebutante



Joined: Jun 29, 2007
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PostPosted: Fri Sep 07, 2007 3:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

To clarify, I understand how 80's polysynths work, in the sense that pots really were just acting as digital encoders, and implementing that is way over my head.

All I was asking was if I could use some kind of very basic logic instead of magnetic relays to switch routings to alternate sets of trim pots, not to replace the pots, per se.

thanks,

mitchell
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EdisonRex
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PostPosted: Fri Sep 07, 2007 3:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

Keith Emerson had had some basic preset stuff done around 1974 or so, using relays and a lot of patch cords. It was only signal routing though. It's impossible to really preset the pot positions without some sophistication.

You could probably do a lot of the control patching with 4016/4066 analog switches. Again, think of a large switching matrix with the ability to A/B or mask with a counter (for say 10 or 16 presets). but again, you're looking at a fairly substantial subsystem or module.

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Peake



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PostPosted: Fri Sep 07, 2007 4:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

IIRC, Will used variable resistors in the Emerson Moog 911 envelopes (source would be Mark Vail's "Vintage Synthesizers" book).

I've recently seen a variable or VC resistor online, but I don't remember where. If you merely want a preset, variable decay, this and a four-position logic chip should set you up. Or, you could merely switch between trimpots set to the values you like (or just use resistors of the values you've found you like).

If I'm totally off it, please let me know Wink
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celebutante



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PostPosted: Fri Sep 07, 2007 4:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

Peake wrote:
IIRC, Will used variable resistors in the Emerson Moog 911 envelopes (source would be Mark Vail's "Vintage Synthesizers" book).

I've recently seen a variable or VC resistor online, but I don't remember where. If you merely want a preset, variable decay, this and a four-position logic chip should set you up. Or, you could merely switch between trimpots set to the values you like (or just use resistors of the values you've found you like).

If I'm totally off it, please let me know Wink


I think we're on the right track. I'm guessing the idea behind VC resistors was to avoid having zillions of trimpots, but if I do my 3 presets, I'd have 18 trimpots, which isn't too horrible (decay, sus, rel for filt+amp env), and you can get 'em for like 15 cents a piece.

I guess my dumb question is this... I just looked at the datasheets for 4016 chips... is there any functinonal difference between this and a magnetic relay? (besides it costing about 1/10th as much!)

The only difference (besides the voltages) was that from the specs, it seemed there was a bit of resistance (about 400 ohms) when the ciruit paths were in "on" state, as opposed to a magnetic relay which outta have zero ohms res like a normal switch. But in my case that probably wouldn't matter anyway because I could adjust the trims to compensate, and 400 ohms is very little anyway... right?

Am I missing something huge here?

btw, thanks for everyone responding so quick!

Mitchell
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EdisonRex
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PostPosted: Fri Sep 07, 2007 5:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

4016 rocks for low current stuff. You have to be REALLY CAREFUL not to overdrive it. Adding a transistor to the output stage is typical.

But you're on the right thought track, by my reckoning.

Wink

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frijitz



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PostPosted: Fri Sep 07, 2007 6:05 pm    Post subject: Re: old-school patch preset... relays or logic??? Reply with quote  Mark this post and the followings unread

celebutante wrote:
Anyone got any info on this?

Yes. Instead of relays you want to use analolog switching chips. The DG211 is a good choice. Very easy to set up.

Ian
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Randaleem



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PostPosted: Fri Sep 07, 2007 7:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

celebutante wrote:
All I was asking was if I could use some kind of very basic logic instead of magnetic relays to switch routings to alternate sets of trim pots, not to replace the pots, per se. thanks, mitchell


Hi Mitchell,

Funny you should ask... Yes, you can.

I've attached a pic of the Dave Simmons designed SDSV hi hat module which inspired me to create the presets module also shown attached as a prelim frac format. I first became aware of the SDSV presets as a result of research into the SDS3 clone PCB I'm working on. I was surprised by the SDSV preset simplicity and eminently usable functionality. It has 4 sets of 6 presets, where the module I've designed has 4 sets of 5. In place of that extra preset I've added some things that i hope will make up for its loss Laughing

One really cool thing is that I've found some trimpots which have removable shafts allowing a regular sized knob to be fitted as needed! So in the prelim frac pic you see the black circle representing a knob on the Scale trimpot, and a couple of grey circles in the trimpot field representing possible positions of "temporary knobs" to be used for setting up and even during a performance. And you always have the 5 permanent knobs of preset A available for live use.

I've added a VC input and scaling to allow the selection of presets to be made under voltage control. Scaling allows the switchpoint spacing to be set to fit a given incoming CV source.

I'm pretty excited about this module for which I'll be offering a PCB set at under 20 bucks later this month after the present PCB orders are shipped. (I'll probably offer a mini parts kits so the cool fullsize knob able trimpots (which can be hard to get in small qtys.) may be gotten and used. (regular screwdriver trimpots like those of the SDSV will also fit the trimpot field PCB.)

Adding CV switching for the presets gives many more options for use compared to the pushbutton only method of the SDSV. The blend/step switch makes use of a pot quantizer I've developed from work done by John Simonton. I'm considering a deluxe version of this module that would implement the Scott Stites idea of setting different max voltages for the pots. This is something Scott added to the EM Klee sequencer, and I think it is an idea that has wide applications where pots are needing to be set quickly and precisely. IOW, Scott's idea seems a very nice and worthwhile addition to any CV pot that will be setting "musical" or "scaled" CV's.

The SDSV circuit uses a 4013 and 4556, with a 4011 driving 4016's to do the actual switching. The DG series Ian mentioned are a better choice when you want to allow for bipolar signal switching. I can send you the SDSV circuit this module is based upon (or it can be found at the major Simmons drum websites) And of course I'd be pleased to have you get one or more of the PCB's I'll soon be offering if that makes sense for you. (I'll be doing Dotcom and MOTM panel FPD's as well. )

I think this can be a pretty useful module. (I've set it up to be chained. So if you need to change say 20 CV's at once, instead of 5, you'd just get 4 and use the jumpers onboard to select the master panel(s) for PB and CV input. With appropriate CV input and pot settings, it can behave as a milton style sequencer, fancy EG, Arb wave gen, etc.

Kind regards,

Randal


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celebutante



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PostPosted: Sat Sep 08, 2007 3:12 am    Post subject: Reply with quote  Mark this post and the followings unread

Frijitz... I looked up the datasheets on the DG211/DG212 and this does seem like a good way to go, specifically the DG212 which is nominally open.

So for my 3 preset+front panel knobs, this means I could use one DG212 for each control (total of 8 for 2 ADSR's). Since each DG212 is a quad switch, each chip would switch one of its four switches on depending on the position of the 4 pos preset selector.

I might be inclined to still use a small DPDT relay for the attack knobs, because the datasheet says there's 40 ohms of resistance when on, and I'm afraid this might mush up my attack times (I never checked out how ADSR pots work, but I'm guessing that 0 ohms= fastest attack time? If zero ohms is the slowest time, i.e. knob turned full clockwise, then disregard this paragraph.... I'll figure it out when I build it!).

Randaleem...

I assume your preset module is just for your Simmons clone? Or does it output voltages only?

mitchell
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Randaleem



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PostPosted: Sat Sep 08, 2007 4:30 am    Post subject: Reply with quote  Mark this post and the followings unread

celebutante wrote:
Randaleem...
I assume your preset module is just for your Simmons clone? Or does it output voltages only? mitchell


No, it's not for the Simmons SDS3 clone at all. Though it could be used that way I suppose. Funny, until you just mentioned it; I never even thought of using it with the SDS3 circuitry Shocked . I've always seen it as just a generally capable CV source. Other than being inspired by the SDSV (which I discovered only through the SDS3 project); there is no correlation between the module described and my SDS3 clone.

The SDP707 PCB/module is a chainable and scalable preset and live CV source, which is also capable of other uses due to the CV input.

Kind regards,

Randal
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Dave Kendall



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PostPosted: Sat Sep 08, 2007 4:51 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi.

Have you seen the digisound patcher module?
The downloadable pdf on this page could be used. I guess it could be modified to use 4052s for 4 patches with each IC routed to 2 destinations. 3 of these chips would cover ADSR, FRQ, and RES settings.The section using the 4011 looks to be mostly a switch de-bouncer, the 7445 could be replaced by a CMOS 4511, (with some changes to the LED circuitry), and the BC184s look like they're just level switching trannies, which would probably be redundant if using a 4511 off±15V.
The main limitation is that it's configured for positive voltages only, which shouldn't be a problem for ADSR and VCF settings.
It's also configured for an increment type of switch - pressing the button advances through the patches.

hope this helps.
cheers,

Dave

Last edited by Dave Kendall on Sat Sep 08, 2007 7:41 am; edited 1 time in total
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frijitz



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PostPosted: Sat Sep 08, 2007 6:14 am    Post subject: Reply with quote  Mark this post and the followings unread

celebutante wrote:
I might be inclined to still use a small DPDT relay for the attack knobs, because the datasheet says there's 40 ohms of resistance when on, and I'm afraid this might mush up my attack times (I never checked out how ADSR pots work, but I'm guessing that 0 ohms= fastest attack time? If zero ohms is the slowest time, i.e. knob turned full clockwise, then disregard this paragraph.... I'll figure it out when I build it!).


I think you would still be OK. A typical time constant might be something like 1 microFarad times 100 Ohms which is 0.1 milliseconds. (Anything below about 10 ms will give you clicks.)

There are two problems with using relays: (1) they eat up a lot of power (2) they are not reliable. Everybody I know who has worked with relays has had trouble with them failing.

If you are only switching positive voltages, then CMOS logic will work, as the other guys mentioned. But the on resistance will be quite a bit higher. If the on resistance is an issue you can use a more expensive analog switch with a lower resistance, or you can connect several switches in parallel.

Sounds like an interesting project -- please keep us posted as it goes along.

Ian
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revtor



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PostPosted: Sat Sep 08, 2007 11:54 am    Post subject: Reply with quote  Mark this post and the followings unread

along similar lines, ken stone offers PCB's for an old Serge design, a 4 step programmer.. basically a 4 step sequencer with 4 lines of CV out. expandable.

I think a set of 5 or 6 interlocking pushbuttons (light up Smile connected to the DG or 4000 series switcher IC's to switch a few sets of trimpots in and out would probably be the simplest way to go to give you control over the set of your parameters... there are alot of these CMOS switches, you can search for the ones with the lowest on resistance. amke a little panel on you synth , a door so you can get in there and change settings as on the CS80...

One thing I might think about is how the circuits will act when you push the switch .. make before break? break before make? perhaps the switching time will be short enough where it wont have any effet, especially if its just for controlling your EG's..

good idea, definitely a useful thing to have for live use!!

~Steve

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celebutante



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PostPosted: Sat Sep 08, 2007 12:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

Frijitz...

Reliability issues with relays did cross my mind (since I plan to use it live), and I hadn't even thought about power consumption. Honestly, until a couple of days ago, I didn't have a clue about 4000 logic or what they did, but I've been reading up on wiki and datasheets like mad, so now I do! Gotta love learning new things that your girlfriend will think is really useless Smile

As for the on resistance, I was referring only to the CMOS logic, not the relay. But I think can get away with it... I have the datasheet for a Vishay DG211/212 here (not what I want to use, but for ref), and on resistance is 50 ohms... I think I'd be ok with that, right?


Dave...

The Digisound switcher is really close to what I need. It seems like a fair amount of circuitry (the entire second board) is dedicated to making the 8 patches selectable with buttons and an LED display, which is silly for me. I plan to just use a 4-pos rotary switch, and I imagine you could wire it up to provide, "logic" switching (i.e. each position sends the voltage to the pins in different combos... you guys should all be jealous, because I just invented the modern computer. I'm going to be rich!).

Just reading the data on the Digisound switcher really clarified things; it was a huge help. You are right, I don't really need 8>1... a 4052 dual 4-ch multiplexer would be best, because I'd only need four of them to control two ADSR's.


Revtor...

I took a look at Ken Stone's switcher, which I'm sure would work, but it seems like it'd be overkill for what I'm trying to do, especially since the ability to voltage control/randomly switch stages isn't necessary here. And it looks like a pretty delicate build, which scares me for synth that might get smacked around a bit.

Again, thanks to everyone for inspiration! Right now I'm just collecting parts... I gotta get crackin' and build this sucker!

Mitchell
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frijitz



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PostPosted: Sat Sep 08, 2007 7:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

celebutante wrote:
Reliability issues with relays did cross my mind (since I plan to use it live), and I hadn't even thought about power consumption. Honestly, until a couple of days ago, I didn't have a clue about 4000 logic or what they did, but I've been reading up on wiki and datasheets like mad, so now I do! Gotta love learning new things that your girlfriend will think is really useless Smile
Great -- sounds like you are a quick study. Very Happy
Quote:
As for the on resistance, I was referring only to the CMOS logic, not the relay. But I think can get away with it... I have the datasheet for a Vishay DG211/212 here (not what I want to use, but for ref), and on resistance is 50 ohms... I think I'd be ok with that, right?
Yes, I'm pretty sure. BTW you can get free samples from Maxim, so you could try out the DG's or any of their other choices at no cost.

Ian
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