[sdiy-interim] Trivial OTA summing quiz!

[JH.]

> (B) alone dont work because it overloads! :-)

B alone _will_ work if you make R5 small (and omit R6, or make it equally 
small).

But a small R5 may be uncomfortable for your CV input, which leads to D.

> However your additional sugestion do work (D) but is it the most adequate? 
> :-)

Depends of what you need. If you can afford a low impedance for CV, B + my 
suggestions will be (a tad) less noisy than D.
In most applications, the OTA noise will probably be dominating, so D is 
fine.
I'm sure there are are 20 other elegant solutions, but you only gave a 
choice between 3 or 4. :)

JH.

--- "JH." <jhaible at debitel.net> skrev:

> B looks good, except you don't need R6.
> To attenuate the output, decrease both resistors labelled with R5 by the
> same amount.
> If, for some reason, you don't want to decrease R5, but need extra
> attenuation for the OTAs, R6 alone won't help. But you can connect an
> additional resistor from the left side of R6 to GND, and get attenuation 
> by
> the current divider R6 and the extra resistor are forming.Make sure that 
> the
> GND for this extra resistor and the GND on pin3 of the LF353 go to the 
> same
> geometric point of your layout.
>
> JH.
>
> ----- Original Message ----- 
> From: "Paul Perry" <pfperry at melbpc.org.au>
> To: <synth-diy at vermine.org>
> Sent: Thursday, March 29, 2007 1:32 AM
> Subject: Re: [sdiy-interim] Trivial OTA summing quiz!
>
>
> My money is on C, but I'm not an EE....
>
> best, paul perry Melbourne Australia
> ----- Original Message ----- 
> From: "karl dalen" <dalenkarl at yahoo.se>
> To: <synth-diy at vermine.org>
> Sent: Thursday, March 29, 2007 9:23 AM
> Subject: [sdiy-interim] Trivial OTA summing quiz!
>
>
> http://img63.imageshack.us/img63/4215/otasumdh2.jpg
>
> If one sum's lets say 5 OTA's into one op amp but need to
> dampen the amplitude into the summing OP amp wich method
> is the most adequate to use.
>
> I'm not able to reduce gain before OTA or after OP amp!
> CV are always larger in span then total OTA currents summed.
>
> Never mind the values!
>
> KD
>
>
>
>
>
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