AMZ dual buffer

[BJM]

Hi all,

I,m building the AMZ dual buffer, schematic here: http://www.muzique.com/tech/op-amp.htm.

So far no problems but a question someone maybe could answer? On the page it says the voltages on pin 3 and 5 are 4,2 V and 4,5 V. I already built the power supply and I get Vr (4,5 V as it should be) with the two 10K resistors (R11 and R12). But then the 4,5 V goes through the 1M resistor and I'm measuring 2,2 V at pins 3 and 5 (without the IC in the socket, as it says on the page). Is that OK or am I missing something here?

Cheers,

Bert

[antonis]

What is your multimeter's impedance..??

[BJM]

Thanks for the quick reply. Not sure I understand it though, I'm measuring voltage (20 V=) on the meter. The rest appears to be OK, I measure 9V before the two 10K resistors, 4,5K after that, just before the 1M and 2,2 after the 1M resistor. The 1M resistor seems to halve the voltage?

Cheers,

Bert

[ashcat_lt]

Yeah, the impedance between the two probes of the meter is in parallel with the opamp input and that total is the bottom of a voltage divider with about 1.05M on top.  The opamp input is HUGE, so probably doesn't impact things much, so if it's dividing the voltage in half, your meter is probably around 1M itself.  If you listened to it while probing, it would probably go all misbiased and weird, but when the probes aren't there, it works fine, so...

[PRR]

> the 4,5 V goes through the 1M resistor and I'm measuring 2,2 V

Then your meter is about a 1Meg impedance also. (2,2 is about half of 4,5.)

Got another meter? Measure the DC on the output of that stage. Betcha 4,5V. Now put the first meter on the 1Meg point. Now the output is 2,2V.

So when you aren't poking at it, it is 4,5V.

[BJM]

Thanks for the replies! You guys are great