I breadboarded the instrumentation amplifier, from the AAC e-book Vol 111 chapter 8, using three LT1007 op-amps, 1k resistors and with no gain resistor for a gain of 1. With 49mV at V1 and V2, Vout is around 780mV. Any ideas as to what is wrong. Many thanks.

 

Please post a schematic, it is much better than words.

 

I guess you're talking about this page:
http://www.allaboutcircuits.com/vol_3/chpt_8/10.html

...and this schematic?

1k is far too low of a resistance to use. Try starting with 10k to 100k.

Note that the LT1007's are not rail-to-rail I/O opamps. You'll need to use a dual-rail supply.

Here is a very helpful and informative application note on Instrumentation Amplifiers from Intersil: http://www.intersil.com/data/an/an1298.pdf

 

The cavalry turns up! Thanks Sgt. you are a gentleman.

 

I breadboarded the instrumentation amplifier, from the AAC e-book Vol 111 chapter 8, using three LT1007 op-amps, 1k resistors and with no gain resistor for a gain of 1. With 49mV at V1 and V2, Vout is around 780mV. Any ideas as to what is wrong. Many thanks.

I am not sure what you mean when you say no gain resistors. Please clarity.

hgmjr

 

I am not sure what you mean when you say no gain resistors. Please clarity.

hgmjr

I assume that means Rgain=∞. That would make the gain=1.