LM13600

[harrybissell at prodigy.net]

Aha....

The LM13700 has NPN darlington with QZ (beta 266) feeding QY (beta 50) : Product = 13300

The LM13600 has NPN darlington with QX1 (beta 200) feeding QY (beta 140) : Product = 28000

So the maximum gain of the LM13600 is about twice that of the 13700.
I presume the LM13600 current mirror will reduce the gain of the buffer as the Gm bias goes up.

Very Cool, yes ???

:^) Harry Bissell


 ---- On Oct 28 Haible Juergen <Juergen.Haible at nbgm.siemens.de> wrote: 
> Good idea !
> 
> JH.
> 
> > -----Original Message-----
> > From:	harrybissell at prodigy.net [SMTP:harrybissell at prodigy.net]
> > Sent:	Thursday, October 28, 1999 4:31 PM
> > To:	Haible Juergen
> > Subject:	RE: LM13600
> > 
> > I'll decypher the spice models (not easy with the program I'm using... it
> > draws a rat's nest.) Maybe there will be some values we can look at.
> > :^) Harry
> > 
> > 
> >  ---- On Oct 28 Haible Juergen <Juergen.Haible at nbgm.siemens.de> wrote: 
> > > 	>The LM13600 has lower buffer (darlington) bias current at low Gm,
> > > and
> > > 	>higher current at higher Gm... at the possible expense of feeding
> > > some
> > > 	>"thump" into the darlington as the Gm bias is varied (like VCA or
> > > VCF with
> > > 	>fast attack...)
> > > 	>The LM13700 has fixed bias for the buffer, alas... at too high of a
> > > value
> > > 	>to be really effective witlow Gm inputs...
> > > 
> > > Do you mean they do load the first transistor of the darlington with a
> > fixed
> > > current sink ? There is nothing like that shown in the data sheet, but
> > it
> > > *does* make sense, and might be the "missing link" to explain why the
> > > 13700 is bad for VCF's that use the buffers.
> > > 
> > > 	>Tom G has a VCO which doesn't work with the LM13700... but says the
> > > LM13700
> > > 	>is OK for the MS-20 VCF design...
> > > 
> > > And I say the 13700's I've tried do *not* work in the (unchanged) Korg
> > MS-20
> > > VCF design.
> > > I have tried, and the 13600's are good, but 13700's no good. The filter
> > > still works, granted,
> > > but you get excessive thumping with the 13700.
> > > 
> > > I never really understood *why* this is so, however. A, while finite,
> > > constantly high Z
> > > buffer ('700) should cause less trouble than a variable Z buffer ('600),
> > > given that
> > > the max Z of the '600 is not higher than the constant Z of the '700.
> > > But Harry's suggestion could be an explanation. Then the constant Z of
> > the
> > > 700
> > > might be lower than the maximum Z of the 600.
> > > 
> > > JH.
> > > 
> > 
> >