Doepfer

Hi Monroe,

Sorry to be the bearer of bad news, but soldering resistors to the inputs whilst reducing load current will only act as a further potential divider causing an even worse situation because it adds to the output resistance of the SH101.  The only way forward is to have an active buffer (e.g. A185-1 or Dieter may be able to suggest other alternatives). Most Doepfer modules have a low output resistance, normally 1k or lower which as you can see is significantly lower than the SH101. 

I must still stress that I don't actually know what the input resistance of the MFB EGs is and that neither has a fault. My gut feel is that the MFBs should be higher than the 10k that I suggested in my example. It would be useful if all manufacturers produce a spec sheet stating input and output resistances and voltage levels etc. It would help in determining compatability between different manufacturer's modules. I'll ping off a question to MFB to find out.

Cheers
Tony



--- In Doepfer_a100@yahoogroups.com, Monroe Eskew <monroe.eskew@...> wrote:
>
> Ah, sorry, I didn't really read the details.  Sounds like he should be able
> to fix it by soldering high value resistors to the inputs of the MFB EG... I
> think.
> 
> On Sun, Nov 15, 2009 at 3:49 PM, Synthomaniac <tony.steventon@...>wrote:
> 
> >
> >
> > Hi Guys
> >
> > There seems to be some confusion about what's going on with loading, volts,
> > current etc. The good news is that Ohm's Law isn't about to be disproved
> > anytime soon. Volts and current are linked in Ohm's law by resistance, in
> > this case the output resistance of the SH101 - this is about 22k and it
> > connects to +15V in the SH101 gate out circuit.
> >
> > The MFB EG acts as a load and two in parallel act as a greater load, i.e.
> > more current will flow. If for argument's sake the MFB has an input
> > resistance of 10k then two EGs in parallel would then give a load of 5k.
> > I'll ignore the A140 since that that has a very high input resistance (mine
> > are around 5M to 7M).
> >
> > The arithmetic for this example is that 15V is loaded by 22k out plus a 5k
> > load = 27k. This acts as a potential divider thus 15/27 x 5 = 2.8V. Not very
> > big! So the more current out the more the voltage drop across the output
> > resistance and hence a smaller gate voltage. So yes it needs a buffer to
> > isolate the SH101 output's high output resistance; I use an A185-1. If you
> > just had A140s then these have such a high resistance that it shouldn't make
> > any difference.
> >
> > Hope that helps clear up the mystery.
> > I'd be inteested if anyone can tell me what the MFB EG input resistance
> > actually is.
> >
> > Cheers
> > Tony
> >
> >
> > --- In Doepfer_a100@yahoogroups.com <Doepfer_a100%40yahoogroups.com>,
> > Monroe Eskew <monroe.eskew@> wrote:
> > >
> > > Pardon if this is a dumb question, but are you sure you're measuring
> > voltage
> > > and not power? Is Ohm's law really that blatantly false? I've noticed
> > VCOs
> > > don't respond to voltage only; they are influenced by the amperage as
> > well.
> > >
> > > On Sun, Nov 15, 2009 at 2:43 PM, Computer Controlled <acidted@>wrote:
> >
> > >
> > > >
> > > >
> > > > That's why there are Buffered Multiples, passive ones drop the voltage
> > > > levels. So they need to be buffered to keep them at original levels.
> > > >
> > > > I just didn't think that the level would drop by so much!
> > > >
> > > >
> > > > Monroe Eskew wrote:
> > > > > It's strange because in theory the voltage should not drop since
> > these
> > > > are
> > > > > parallel circuits-- only the current should change.
> > > > >
> > > > > On Sun, Nov 15, 2009 at 2:16 PM, Computer Controlled <acidted@
> > ...<acidted%40gmail.com>
> >
> > > > >wrote:
> > > > >
> > > > >
> > > > >> I've noticed recently that the A-180 Multiple really cuts the
> > voltage
> > > > >> signal down quite substantially. I just got an MFB Dual ADSR and
> > noticed
> > > > >> that when i mult the Gate Output of my SH-101 by 3x, it drops the
> > gate
> > > > >> voltage down to where the MFB won't trigger anymore. Basically, i
> > had it
> > > > >> set up where the gate out went into the A-180, then the first 2 outs
> > > > >> went to the two Gate Ins on the MFB and the 3rd out went to my A-140
> > EG.
> > > > >> If i pulled the cable out that went to the A-140, the MFB would
> > fire,
> > > > >> but not with it inserted. However, it works if i use my 303, which
> > has a
> > > > >> hotter Gate signal. I checked the gate out voltages coming of the
> > 101
> > > > >> direct, then at each output of the A-180. I got the following:
> > > > >>
> > > > >> Direct Out from 101: 11.56v
> > > > >> Into the A-180 w/no other cables inserted: same as above
> > > > >> with 2 cables inserted: 7v
> > > > >> with 3 cables inserted: 5.5v
> > > > >>
> > > > >> This is quite a bit of voltage drop if you ask me. Is there anyway
> > to
> > > > >> mod the A-180 so it doesn't eat up all my voltages?
> > > > >>
> > > > >> -Larry
> > > > >>
> > > > >>
> > > > >>
> > > > >
> > > > >
> > > > > [Non-text portions of this message have been removed]
> > > > >
> > > > >
> > > > >
> > > > > ------------------------------------
> > > > >
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> > > > >
> > > > >
> > > > >
> > > >
> > > >
> > >
> > >
> > > [Non-text portions of this message have been removed]
> > >
> >
> >  
> >
> 
> 
> [Non-text portions of this message have been removed]
>