PLAN B analog blog

Hello Peter,

I've just acquired a M15 v.2 where the fine freq pot doesn't do 
anything at all, the guy who sold me assured me it was working, so it 
must be the traveling that changed something... do you have any 
possible diagnostic of what it could be, what I should check, and what 
I coukld do to fix it?

thanks as usual :)

g.

Sounds like this is a used one, yes?

OK, unfortunately you have to open it up.  Not hard, just have to be
careful.   Remove the knobs (make sure you don't dent your faceplate
if you use a flat-blade screwdriver to lift them off).  The you have toremove the nuts for the pots and the output jack nuts and the 1v/oct,FM in, morph VC row.  do NOT remove the nuts on the fine fune, sync,VC PWM, PWM not and Wave B switch.

The carefully separate the faceplate form the back and you'l see it
open up like a book, with wires going from the main board to the
faceplate mounted components. The wires are long enough so the
faceplate will pay facedown next to the electronics.

First thing to do is check if the wires and soldered jumper is intact
on the fine tune pot.  looking at the back of the pot with the leads
on bottom, there should be a piece of buswire shorting the far left
lead to the center lead.  Then there should be two wires coming off
the pot as follows:

The one coming from the far righthand lead should go to pad FF1 on the
main board.

The second wire, which can come from either the center or far left
lead of the pot should go to a pad labeled FF2 on the main board. 
It's right next to FF1.

If the wires are all on in place, just look down them, inspect them to
see it there are any kinks or cuts in the wire, or places where the
insulation has ripped and exposed the wire strands.  If you see any of
this, replace that wire.

Last thing to check, but really - don't get your hopes up:  R11 may be
missing ( I would kiss your butt in Macy's window if it were).  I use
these to calibrate the tracking when they ship.  If it was missing,
I'd know about it. Anyway, R11 is the 680K (blue/grey/yellow bands)
right next to the FF1 and FF2 pads on the main board.

If all those are intact then you need to check the pot.  Basically I'd
just replace it.  It's a 100K linear Alpha type.  Not sure where you
get then in your neigborhood, but you can get them in the US from
Mouser (they only hace log in that config, but it'll work) or
Futurlec, who will have the pot you need but it may take longer to get it.

Then just slap that pot in place where the old one was.

Feel free to post any results you find here.  Sorry you're havng this
problem.

- P










--- In PLAN_B_analog_blog@yahoogroups.com, "gabu_004" <gabu_004@...>
wrote:

>
> Hello Peter,
> 
> I've just acquired a M15 v.2 where the fine freq pot doesn't do 
> anything at all, the guy who sold me assured me it was working, so it 
> must be the traveling that changed something... do you have any 
> possible diagnostic of what it could be, what I should check, and what 
> I coukld do to fix it?
> 
> thanks as usual :)
> 
> g.
>

Hello,

Thanks for explanations :D

So first inspection is done and yeah! Don't worry Peter, we won't have to go to Macy's ;P

I'll head @Addison tomorrow morning to get a potentiometre and see if it works!

I'll post updates right once I've checked! :)

g.

--- In PLAN_B_analog_blog@yahoogroups.com, "(i think you can figure that out)" 
<peter@...> wrote:
>
> Sounds like this is a used one, yes?
> 
> OK, unfortunately you have to open it up.  Not hard, just have to be
> careful.   Remove the knobs (make sure you don't dent your faceplate
> if you use a flat-blade screwdriver to lift them off).  The you have toremove the nuts for 
the pots and the output jack nuts and the 1v/oct,FM in, morph VC row.  do NOT remove 
the nuts on the fine fune, sync,VC PWM, PWM not and Wave B switch.

> 
> The carefully separate the faceplate form the back and you'l see it
> open up like a book, with wires going from the main board to the
> faceplate mounted components. The wires are long enough so the
> faceplate will pay facedown next to the electronics.
> 
> First thing to do is check if the wires and soldered jumper is intact
> on the fine tune pot.  looking at the back of the pot with the leads
> on bottom, there should be a piece of buswire shorting the far left
> lead to the center lead.  Then there should be two wires coming off
> the pot as follows:
> 
> The one coming from the far righthand lead should go to pad FF1 on the
> main board.
> 
> The second wire, which can come from either the center or far left
> lead of the pot should go to a pad labeled FF2 on the main board.
> It's right next to FF1.
> 
> If the wires are all on in place, just look down them, inspect them to
> see it there are any kinks or cuts in the wire, or places where the
> insulation has ripped and exposed the wire strands.  If you see any of
> this, replace that wire.
> 
> Last thing to check, but really - don't get your hopes up:  R11 may be
> missing ( I would kiss your butt in Macy's window if it were).  I use
> these to calibrate the tracking when they ship.  If it was missing,
> I'd know about it. Anyway, R11 is the 680K (blue/grey/yellow bands)
> right next to the FF1 and FF2 pads on the main board.
> 
> If all those are intact then you need to check the pot.  Basically I'd
> just replace it.  It's a 100K linear Alpha type.  Not sure where you
> get then in your neigborhood, but you can get them in the US from
> Mouser (they only hace log in that config, but it'll work) or
> Futurlec, who will have the pot you need but it may take longer to get it.
> 
> Then just slap that pot in place where the old one was.
> 
> Feel free to post any results you find here.  Sorry you're havng this
> problem.
> 
> - P
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> --- In PLAN_B_analog_blog@yahoogroups.com, "gabu_004" <gabu_004@>
> wrote:
> >
> > Hello Peter,
> >
> > I've just acquired a M15 v.2 where the fine freq pot doesn't do
> > anything at all, the guy who sold me assured me it was working, so it
> > must be the traveling that changed something... do you have any
> > possible diagnostic of what it could be, what I should check, and what
> > I coukld do to fix it?
> >
> > thanks as usual :)
> >
> > g.
> >
>

The short answer is not much.


Going into a little more detail, outside of a second change to the
sine wave circuit (which was put there for easier initial set up (us)
and really doesn't effect the end user and the 15A port, the
differences are slight:

We've added an output buffer to the PWM circuit (which was handled
another way in the older versions) and a bypass cap or two.  Nothing
serious.

The new (flat) VCO also has a pathway for the (I promise) soon to be
released 15A expander.  It's another connector.  Look on this blog for
what the 15A does.  Btw - I've found the missing link which was making
the +/- octave switch behave so poorly...so this should be coming out
with the rest of the ELF's.

Most the bigger changes had already happened by the time we flattened
the unit out, namely:  the AC offset triangle output (the first
release was offset all above ground), the harmonically improved sine
wave, the use of an SMT tempco resistor, the substitution of our
analog switch - initially used only because I really thought I'd only
be making 25 of these for that semi-custom , very limited order on the
Doepfer list and I happened to have 150 of these really expensive 18
pin SPDT analog switches. So once those ran out, I replaced it with a
more affordable SPST switch which was better suited for the application. 

The additional trimmer now found on the current rev VCOs was added
stop us from having to hand-select the fixed resistor which would
yield the best overall sine shape.  When the Model 15 first came out
we used an over-speced (read:  unnecessarily expensive) FET in the
sine shaper. We found that a less expensive part offered no sonic
degradation once set up correctly, but required a bit more tuning as
the lesser expensive model had a wider gain range.  So we added a
resistor which set the amplitude where it need be.  The net effect
instead of a $3 part we could use a $.20 part with the same exact
results.  Further, we also added a new function which reduced the
amount of total harmonic distortion, so make that a $2.80 cent gain
with superior results. This did require I hand tune each sine shaper
by selecting the proper fixed resistor value to compensate for the new
FET's part to part gain variance (FETs in general are very
loosy-goosy).  About 100 VCOs after I became completely sick of doing
this I then added a trim pot to adjust this easier. Even though we
lost $.60 of our initial $2.80 gain, it was money well spent as I was
REALLY tired of going through this exercise.

That's probably more info than you wanted, but that's the full story.

Hope this helps...


- P







--- In PLAN_B_analog_blog@yahoogroups.com, Anthony Rolando
<goldenechos@...> wrote:
>
> 
> Aside from the redesigned form factor and improved sine waveform,
what are the differences between revision 1 and 2 Model 15 oscillators?
> 
> Tony
> 
> 
> 
> 
> _________________________________________________________________
> Need to know the score, the latest news, or you need your
Hotmail®-get your "fix".
> http://www.msnmobilefix.com/Default.aspx
>

Aside from the redesigned form factor and improved sine waveform, what are the differences between revision 1 and 2 Model 15 oscillators?

Tony




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