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Square Wave on the MG (LFO) Instead of Triangle?

Square Wave on the MG (LFO) Instead of Triangle?

2013-08-22 by chipaudette

Hi All,

I'm looking to mod my Polysix to get other waveforms for the MG (LFO). Right now, as you all know, the MG has a triangle waveform. I'd really like a square wave. I'd also like a ramp, but I think that a square wave ought to be a lot easier.

I looked at the schematic for the MG Oscillator section of KLM-367 but didn't see anything obvious where I could turn the triangle into a square. I'm not a master of understanding how these oscillators work, though, so I'm hoping that others might have some ideas.

My only idea was to insert an op-amp somewhere after Q1. I'd set the opamp with no feedback, so it would simply rail positive or rail negative as the current triangle waveform swings through zero.

I'm really hoping to not have to add an active component because it is so much easier simply to add a switch that shorts something, or adds a cap, or something like that.

Does anyone have any ideas?

Chip

RE: [PolySix] Square Wave on the MG (LFO) Instead of Triangle?

2013-08-22 by backshall1

There's definitely a square wave there already on the LFO. I can't remember
exactly where, but I know I've seen it on the scope. I've got too many other
projects in pieces on the bench right now to pull out a Polysix and open it
up, sorry.

Don B.



_____

From: PolySix@yahoogroups.com [mailto:PolySix@yahoogroups.com] On Behalf Of
chipaudette
Sent: Wednesday, August 21, 2013 9:09 PM
To: PolySix@yahoogroups.com
Subject: [PolySix] Square Wave on the MG (LFO) Instead of Triangle?






Hi All,

I'm looking to mod my Polysix to get other waveforms for the MG (LFO). Right
now, as you all know, the MG has a triangle waveform. I'd really like a
square wave. I'd also like a ramp, but I think that a square wave ought to
be a lot easier.

I looked at the schematic for the MG Oscillator section of KLM-367 but
didn't see anything obvious where I could turn the triangle into a square.
I'm not a master of understanding how these oscillators work, though, so I'm
hoping that others might have some ideas.

My only idea was to insert an op-amp somewhere after Q1. I'd set the opamp
with no feedback, so it would simply rail positive or rail negative as the
current triangle waveform swings through zero.

I'm really hoping to not have to add an active component because it is so
much easier simply to add a switch that shorts something, or adds a cap, or
something like that.

Does anyone have any ideas?

Chip





[Non-text portions of this message have been removed]

Re: Square Wave on the MG (LFO) Instead of Triangle?

2013-08-22 by chipaudette

Taking another look at the schematic (I don't have my oscilloscope right now, so I can't just go measure things to answer my own question), I think that I now see that Pin 7 (ie, the output) of IC16 might be a square wave.

Can anyone confirm (either through analysis or through measurement) that this is true? At Pin 7, does it swing +/- 5V, or +/- 15V, or something else? ...I can't see where the power supply pins for IC16 are defined...

If this is a square wave at this location, I'd need to grab that signal, scale it with a voltage divider to get it the right amplitude for IC21, and then inject it into Pin 3 of IC21. If I want a square wave MG, I'd inject this signal instead of the triangle wave coming down from R26. That doesn't seem too hard to implement. Cool.

The main trick is figuring out where to put a switch for this!

Chip


--- In PolySix@yahoogroups.com, "backshall1" <backshall1@...> wrote:
>
> There's definitely a square wave there already on the LFO. I can't remember
> exactly where, but I know I've seen it on the scope. I've got too many other
> projects in pieces on the bench right now to pull out a Polysix and open it
> up, sorry.
>
> Don B.
>
>

Re: Square Wave on the MG (LFO) Instead of Triangle?

2013-08-23 by chipaudette

I brought home an oscilloscope last night. It is indeed a square wave at Pin 7 of IC16. Great!

In looking at its amplitude, I see that the amplitude of the square wave at the R53-R54 junction is the same as the amplitude of the triangle wave coming out of Q1. So, if I want to use the square wave for my MG (LFO), I even know how to scale it! (come off Pin 7 of IC16 with a 47K/33K voltage divider)

So, now I have to figure out how to do the switching. I need to be able to switch out the triangle wave and switch in the square wave. And, it needs to be done in a way that doesn't mess up the timing of the MG oscillator, which means that I can't disconnect R26 from IC21 without reconnecting it to ground somewhere. Should be straight forward enough, it'll just take some consideration.

Chip

--- In PolySix@yahoogroups.com, "chipaudette" <chipaudette@...> wrote:
>
>
> Taking another look at the schematic (I don't have my oscilloscope right now, so I can't just go measure things to answer my own question), I think that I now see that Pin 7 (ie, the output) of IC16 might be a square wave.
>
> Can anyone confirm (either through analysis or through measurement) that this is true? At Pin 7, does it swing +/- 5V, or +/- 15V, or something else? ...I can't see where the power supply pins for IC16 are defined...
>
> If this is a square wave at this location, I'd need to grab that signal, scale it with a voltage divider to get it the right amplitude for IC21, and then inject it into Pin 3 of IC21. If I want a square wave MG, I'd inject this signal instead of the triangle wave coming down from R26. That doesn't seem too hard to implement. Cool.
>
> The main trick is figuring out where to put a switch for this!
>
> Chip
>
>

Re: Square Wave on the MG (LFO) Instead of Triangle?

2014-05-27 by radek.tymecki@op.pl

Has anyone tried it? Seems quite interesting. Or maybe somebody can guide how to make additional selectable LFO's and how to put it into p6? Good place would be placing a selector in the place of LFO led