[sdiy] rectification/min/max question

[Dave Manley]

You may not have noticed, but as you change the gain setting, the output 
goes from inverted, to off, to non-inverted (there are different names 
for this, bipolar amplitude control, attenuverter, etc).  This can be 
easily changed if you don't like it.

Depending on your needs, it may work better if you put the offset 
circuit in front of the gain circuit.  That way you can null out the 
offset and then change the gain without having to always tweak both.

You may also want to reduce the offset range by putting resistors on 
either side of the pot to the supply rails.  Say you have a 50K pot, put 
a 50K resistor from the positive rail to one end of the pot, and another 
from the negative rail to the other end of the pot.  This will reduce 
the range by a third and give finer control around 0 volts.

-Dave

Derek Holzer wrote:
> Hi Dave, Ian, the list...
> 
> thank you Ian for the references on op-amps. The Wikipedia article and 
> the op-amp applications sheet were ones that I came across in my 
> research as well. I looked through the Wikipedia page for a couple 
> hours, but I'm not much of an engineer when it comes to math, so I ended 
> up beating my head against the wall for a while. Still, a good learning 
> experience...
> 
> Then I went to the breadboard and tried out the circuit that Dave 
> suggested, which works quite well. I'm listening to it modulate an LPF 
> right now. I did simplify it a bit, removing the second op-amp pair 
> which was providing reference voltage and just putting +/- 12V to the 
> two ends of the Offset pot. Quite a simple circuit and does what I need 
> it to!
> 
> thx + best,
> d.
> 
> Dave Manley wrote:
>> Take a look at this, it has adjustable gain and offset:
>>
>> http://www.oldcrows.net/~patchell/synthmodulesII/200-1018.pdf
>>
>> The circuit could be simplified, as there is a voltage reference for 
>> the offset pot you probably don't need.
> 
>> Ian Fritz wrote:
>>> Some references on general op amp summers
>>>
>>> http://en.wikibooks.org/wiki/Circuit_Idea/Simple_Op-amp_Summer_Design
>>> http://www.edn.com/index.asp?layout=ednPDF&file_name=/archives/1998/030298/05df_05.pdf 
>>>
>>> http://www.phy-astr.gsu.edu/nelson/AN-31.pdf
> 
>