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Infinite Melody Question

Infinite Melody Question

2003-12-15 by vtl5c3

I was testing out my Infinite Melody module this evening. The Mix
output works well... like a Psycho LFO on steroids.

The other three outputs have really low levels, even with the
output pots turned all the way up. Has anyone else encountered
this? When I first tested the module, I'd forgotten to put in the
jumpers that provide -15V to the opamps for those stages.
Could that have fried them?

Thanks,

Romeo

Re: Infinite Melody Question

2003-12-15 by sasami@hotkey.net.au

It is possible you have the "optional" 200k resistors at the MSB position of
the D/A ladders too. Check the diagram - it's the greyed out resistor.

Ken
Show quoted textHide quoted text
>I was testing out my Infinite Melody module this evening. The Mix
>output works well... like a Psycho LFO on steroids.
>
>The other three outputs have really low levels, even with the
>output pots turned all the way up. Has anyone else encountered
>this? When I first tested the module, I'd forgotten to put in the
>jumpers that provide -15V to the opamps for those stages.
>Could that have fried them?
>
>Thanks,
>
>Romeo
>
>
>
>See the following URLS for the CGS Modular Synth home page:
>Main: http://www.cgs.synth.net/
>Secondary: http://otherunicorn.0catch.com/synth/
>To unsubscribe from this group, send an email to:
>cgs_synth-unsubscribe@yahoogroups.com
>
>
>
>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
_______________________________________________________________________
Ken Stone sasami@...
Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>

Re: Infinite Melody Question

2003-12-15 by vtl5c3

I think I do... but which ones are they on the PCB? Is it the six
that connect to ground? It seems like the DA sections on the
PCB don't quite match what's on the schematic.
Show quoted textHide quoted text
--- In cgs_synth@yahoogroups.com, sasami@h... wrote:
> It is possible you have the "optional" 200k resistors at the MSB
position of
> the D/A ladders too. Check the diagram - it's the greyed out
resistor.
>
> Ken
>
> >I was testing out my Infinite Melody module this evening. The
Mix
> >output works well... like a Psycho LFO on steroids.
> >
> >The other three outputs have really low levels, even with the
> >output pots turned all the way up. Has anyone else
encountered
> >this? When I first tested the module, I'd forgotten to put in the
> >jumpers that provide -15V to the opamps for those stages.
> >Could that have fried them?
> >
> >Thanks,
> >
> >Romeo
> >
> >
> >
> >See the following URLS for the CGS Modular Synth home
page:
> >Main: http://www.cgs.synth.net/
> >Secondary: http://otherunicorn.0catch.com/synth/
> >To unsubscribe from this group, send an email to:
> >cgs_synth-unsubscribe@yahoogroups.com
> >
> >
> >
> >Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
> >
> >
> >
>
__________________________________________________
_____________________
> Ken Stone sasami@h...
> Modular Synth PCBs for sale
<http://www.blaze.net.au/~sasami/synth/>
> Australian Miniature Horses & Ponies
<http://www.blaze.net.au/~sasami/>

Re: Infinite Melody Question

2003-12-15 by sasami@hotkey.net.au

>I think I do... but which ones are they on the PCB? Is it the six
>that connect to ground? It seems like the DA sections on the
>PCB don't quite match what's on the schematic.

The three at the bottom of the long row, near the B5D pad. Note THREE, not six.

Ken

_______________________________________________________________________
Ken Stone sasami@...
Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>

Re: Infinite Melody Question

2003-12-15 by Richard Brewster

Interesting. I have a couple of observations. First, there is a 100K
resistor *not shown* on the schematic which goes between the junction of
these optional 200K resistors and the 100K from the B5 node and pin 2 on
the TL072s. (Without the optional resistor, this makes the input to pin
2 total up to 200K.) If the circuit was really like the schematic, the
200K optional resistors wouldn't do anything. I do have those optional
resistors and yes, the output levels are not really high, but I have not
found this to be a problem. The range seems about right. I can see
that installing these resistors decreases the range. How much is it
actually? About 50%?

Second observation. There is another optional 200K resistor on the B0
node. This is not shown on the schematic either. I installed those,
too. I wanted to get the most accurate scale. I'm not really sure if
I've accomplished that.

Ken, can you explain the purpose of both of these optional 200K
resistors in this R-2R ladder? Why would we want to include or omit them?

Thanks,

Richard Brewster

sasami@... wrote:
Show quoted textHide quoted text
>>I think I do... but which ones are they on the PCB? Is it the six
>>that connect to ground? It seems like the DA sections on the
>>PCB don't quite match what's on the schematic.
>>
>>
>
>The three at the bottom of the long row, near the B5D pad. Note THREE, not six.
>
>Ken
>
>_______________________________________________________________________
>Ken Stone sasami@...
>Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
>Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>
>
>
>
>

Re: Infinite Melody Question

2003-12-15 by sasami@hotkey.net.au

I can see
>that installing these resistors decreases the range. How much is it
>actually? About 50%?

Yes.

>Second observation. There is another optional 200K resistor on the B0
>node. This is not shown on the schematic either. I installed those,
>too. I wanted to get the most accurate scale. I'm not really sure if
>I've accomplished that.

Hmm. I'll have to recheck the diagram.

>Ken, can you explain the purpose of both of these optional 200K
>resistors in this R-2R ladder? Why would we want to include or omit them?

The optional resistors are the wired as an extra 7th bit, pernanently wired
to "0". Basically I do this where I wish to prevent a D/A output exceeding
the common mode range of an op-amp. Not really relevant in the Infinite
Melody circuit.

Cheers,

Ken
_______________________________________________________________________
Ken Stone sasami@...
Modular Synth PCBs for sale <http://www.blaze.net.au/~sasami/synth/>
Australian Miniature Horses & Ponies <http://www.blaze.net.au/~sasami/>

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