MOTM

Started on Todd's OMS-410 kit last night (got mine a few days ago), and ran into a few snags, mostly due to my own rushing. Thought I'd detail them here to help out anyone else, and hopefully get clarification on a few questions of my own...

First off, does anyone know if the LM13700 is the same as the 13600? My kit came with a 13600, but the schematic and PCB call for a 13700.

Second, be careful about where you put your 33pF ceramic caps. The user's guide only mentions C8, C10, C11. But for the supplied panel, they need to go into C8, C12, and C15.

There's a few notes about the user's guide... READ IT ALL FIRST. I didn't, and I did a little extra work. (Pay particular attention to page 9, third to last paragraph-- it details what you DON'T need to do for the supplied panel.)

a) The resistors section calls for two different values for R45 and R46. Which one you use depends on which panel layout you want. The one supplied by Todd calls for those two resistors to be 47K, just to be perfectly clear.

b) The caps section omits caps C12 and C15, which are 33pF ceramics.
c) The IC section omits the LM13700 at U7.

I'm a little confused as to whether we're supposed to short the LK for the supplied panel. I'm assuming no, but I don't fully understand where VCA leads to on the schematic. And finally, maybe I'm blind, but on the schematic, where's CV3 and LFO Level? :)

--PBr

On Thu, 25 Apr 2002, Brousseau, Paul E (Paul) wrote:

> First off, does anyone know if the LM13700 is the same as the 13600?  
> My kit came with a 13600, but the schematic and PCB call for a 13700.

  If the 13600/700 buffers aren't being used, it doesn't matter.  I do 
not have the OMS-410 schem in front of me at the moment, but I seem to 
recall the buffers being left unconnected and FET opamp followers used 
instead.

Crow
/**/

Firstly I am unsure whether you have got my User Guide or one that Todd
has written. I know Todd was going to re-write some of mine to make it
more applicable to the front panel supplied.

>First off, does anyone know if the LM13700 is the same as the 13600?

No difference in this application. I use op-amp 'buffer' stages instead
of the differing output darlingtons in the 13600 and 13700.

>Second, be careful about where you put your 33pF ceramic caps.  The
user's guide only mentions C8, C10, C11.  But for the supplied panel,
they need to go into C8, C12, and C15.

Only C12 and C15 are needed. I don't think you are using the invertor
circuit at all.

>The one supplied by Todd calls for those two resistors to be 47K, just
to be perfectly clear.

Yes, this is true.

> The caps section omits caps C12 and C15, which are 33pF ceramics.

Sorry, my fault on this one. It was updated in the next issue User Guide
for the newest board layout, although that doesn't help you with issue
one boards. My apologies.

>I'm a little confused as to whether we're supposed to short the LK for
the supplied panel.

LK is fitted if you are only controlling the VCAs with one CV. I think
you are in Todd's panel design. If this is so, then fit LK but do not
fit Q2 and the components around it.

>And finally, maybe I'm blind, but on the schematic, where's CV3 and LFO
Level?

The third CV input goes to IN3 on the PCB. 'LFO level', I call it 'LFO
mod' on the standard OMS-410 front panel, is labelled on the board as
CV1. I didn't call it 'LFO mod' on the board because the board can be
used for other uses.

If some of you are wondering why there are so many unused sections on
the board, well, we took a vote on all the features we wanted to see on
a sidecar to the MOTM-410. What you see in the OMS product is all the
features everyone on the Oakley-Synths list wanted except for one.
Separate CV control of the LFOs pitch... this would have meant track
cuts on the MOTM which wasn't part of the deal.

BTW: Has anyone actaully used all the features on the 2U OMS-410 panel?

Hope this helps,

Tony

I don't see any comments on the user's guide to indicate that it's been rewritten.  The panel is the 2nd in the users' guide (3 knobs, 6 jacks), just to be clear.  Thanks for the conf. on the caps and ICs!  R15-17, TL071 (U1), and 3rd 33pF cap (C8) were supplied for the inverter, so I popped them in there.  Suppose it doesn't matter since the in and out pads won't be connected?  (Again, should have read more closely before starting...)

So I've already gone and soldered in Q2, D4, and R30-32.  I won't have anything attached to CV2; should I remove this when I LK up LFO 1 and 2?  I'm guessing it won't effect the circuit, but I'm not sure...

(No need to appologize for the oops in the user's guide, BTW.  I'm more than happy that I got the sucker and am actually enjoying this debugging process.  Call it in-house skills training.  ;)

Thanks!!  :)

--PBr

-----Original Message-----
From: Tony Allgood [mailto:oakley@...]
Sent: Thursday, April 25, 2002 12:31 PM
To: MOTM List
Subject: Re: [motm] OMS-410 kit questions...


Firstly I am unsure whether you have got my User Guide or one that Todd
has written. I know Todd was going to re-write some of mine to make it
more applicable to the front panel supplied.

>Second, be careful about where you put your 33pF ceramic caps.  The
user's guide only mentions C8, C10, C11.  But for the supplied panel,
they need to go into C8, C12, and C15.

Only C12 and C15 are needed. I don't think you are using the invertor
circuit at all.

>I'm a little confused as to whether we're supposed to short the LK for
the supplied panel.

LK is fitted if you are only controlling the VCAs with one CV. I think
you are in Todd's panel design. If this is so, then fit LK but do not
fit Q2 and the components around it.

Nice MOTM pics:

http://www.stucki.com/krhen/downloads/jdiaz/jd11.jpg
http://www.stucki.com/krhen/downloads/jdiaz/jd12.jpg
http://www.stucki.com/krhen/downloads/jdiaz/jd17.jpg
http://www.stucki.com/krhen/downloads/Frankensynth/03100093.jpg
http://www.stucki.com/krhen/downloads/Frankensynth/03100115.jpg
http://www.stucki.com/krhen/downloads/Frankensynth/03100128.jpg

This is OT, but interesting IMO:

http://www.stucki.com/krhen/downloads/AndromedaRACK.jpg

--Shemp

>R15-17, TL071 (U1), and 3rd 33pF cap (C8) were supplied for the
inverter, so I popped them in there.  Suppose it doesn't matter since
the in and out pads won't be connected?

Yes, this won't matter. That part of the circuit will be quite happy
just sitting there. If your TL071 is in a socket you could remove it to
save the excess 3mA it will draw.

>So I've already gone and soldered in Q2, D4, and R30-32.

If LK is fitted then Q2 must be removed. You can leave the other bits in
place but Q2 should be snipped out.

If everyone has my User Guide with these kits, then do not fit any parts
listed in the parts list that have been marked with an '*'. Even if Todd
has supplied them. The '*' marks optional parts and these are only
fitted if you are building the full 2U panel.

Hope this helps,

Tony