[sdiy] discrete ota trimming

[James Patchell]

You buy direct from THAT....now...they don't like to sell in small 
quantities (to them small is anything less that 500 pieces)..., but, they 
are nice folks.  They will sell in smaller quantities, but I think they 
might draw the line at one tube (not sure about that)...also, you can get 
free samples.

They are pretty nice transistors...nice low noise...

At 06:49 AM 10/9/2004 -0700, Metrophage wrote:
>I have been wondering about these HFA3096 units! About two years ago,
>just prior to a SDIY hiatus, I bought some CA3096 chips for use in
>TomG's update of the ARP Axxe VCO. Word on the street being that the
>PNPs are way suckier than the NPNs, I have been wondering about other
>PNP/NPN arrays as well. I don't have a datasheet handy for the CA3096,
>and I don't understand many of the specs involved. Sounds from your
>comments as if the HFA unit has better PNPs.
>
>Probably a very basic question, but what are "Ic" and "hFe"? Sounds
>backward, but I started playing with op amps - I am new to transistors!
>
>As for THAT, I have heard some good things about their arrays. Is there
>any distributor which vends THAT arrays, or does one buy them from THAT
>directly?
>
>CJ
>
>--- Ryan Williams <destrukto at cox.net> wrote:
>
> > thanks, I don't mind a trimmer on each OTA but I may try it that way
> > also.  Incase someone was interested, I measured some HFA3096s I got
> > today and the NPNs were within 1mV and the PNPs were about 3mV. I
> > tried
> > that on 2 different HFA3096 with Ic of 60uA and 260uA on each. maybe
> > I
> > got lucky with these but that seems to be up with the specs for the
> > HFA3046's NPN pair.
> >
> > hfe for these PNPs is only 60, but I'll try it anyway. I was thinking
> > of
> > also trying some THAT340 for this. the PNP hfe on those are also only
> > 75
> > although both the NPNs and PNPs are typically matched to .5mV
> > according
> > to the datasheet.
> >
> > -ryan
> >
> > Tony Clark wrote:
> > >    Hi Ryan,
> > >
> > >    Very good circuit, but if you don't want to deal with trimming,
> > you can
> > > use what's referred to as an "improved Wilson current mirror"
> > (basically 2
> > > PNP mirrors (Q3-Q4 in above image) stacked vertically but
> > horizontally
> > > reversed).
> > >
> > >    BTW, does anyone know what hFe range works best for the PNP
> > current
> > > mirror pairs?  I've read somewhere that it should be as high as
> > possible,
> > > like > 450.  Obviously any matched set works, but I'm just curious
> > what
> > > everyone's opinions are on the subject.
> > >
> > >    Cheers,
> > >
> > >    Tony
> >
> >
>
>
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         -Jim
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