From: sleeper75se (sleeper75se_at_yahoo.se)
Date: 2002-01-11 02:28:53
--- In buildcheapeeg_at_yahoogroups.com, "Jim Meissner" <jpmeissner_at_mindspring.com> wrote:
> Dear Andreas:
Hi Jim,
>
> Looks great!
Thanks!
> Additions: I would like to see an option to be able to adjust the
gain. Probably R22, rather than going to ground, have it go to pin
that could be grounded ( normal ) or run to an external resistor or
pot with R22 shorted out.
A pot in the feedback loop would be bad, right? Otherwise that would
make the adjustment linear rather than 1/x-shaped.
I can add pads/test pins at both ends of R22. Instead of mounting the
resistor, one can put in a couple of wires to the pot. Or is it a
trimpot you're really after?
> Additions: I would like to see the output of U3B pin 7 available
externally to be used for biofeedback. Make C6 much smaller to give a
10 KHz bandwidth.
No problems. My brain is too tired right now, so I'll ask rather than
do the math: is 100pF ok?
> Additions: It is good practice to put a 100 nf cap right at the op
amp power pins to ground. ( You already know this) Also you should
put a 10 mf or so tantalum near the 100 nf.
A 10uF tantalum for each IC? Sounds a bit much...?
> And then a 100 mf electrolytic should be on the power bus.
Ok, but isn't it sufficient to have those on another board, common to
the whole analog section?
> Each of these capacitors covers a different part of the frequency
> spectrum. This is the ideal, and many people do none of these and
> sometimes get away with it.
>
> Cautions: Not all capacitors are created equal. I must caution
> you again not to use electrolytic capacitors, especially in the
> signal path or as an integrator.
I can understand why when it comes to integrators (because of the
leakage), so I'll change that too. But what is the main problem with
electrolytics in the signal path? Bipolars are used in speaker
filters as far as I know... I'm just asking because I want to know.
If I change one HP-stage, the other will be changed also.
> Try to stay with monolithic ceramics or tantalums. Please look at
> the LT1167 application note Fig. 10 page 17. Notice that they use
> 0.3 mf for the integrator capacitor. That could be a monolithic.
> If you cannot do it with a monolithic, the next best is a pair of
> back to back tantalums. For your design, a 1 meg resistor and
> a .47 mf monolithic ceramic will give you the same time constant.
Are plastic (such as polypropylene) and plastic/metal film materials
ok? That's what I'm considering for the filter caps (+/-5% precision).
Time to catch some zzz's....
/Andreas
This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:36 BST