Problem: PIMETA with insane DC Offset (7v)
Apr 3, 2005 at 8:56 AM Thread Starter Post #1 of 15
aeroes

aeroes

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Greetings to all Headfiers!

I recently built a PIMETA according to schematic diagram from Tangent's website. It works perfect with OPA227/OPA2227, OPA627/OPA2227 (<1mv). When I plug-in OPA637 it gives out 7v! Is there a particular way to configure OPA637 in PIMETA? I've assumed the schematic works fine with any OPamp?

Here's my configuration:
not biased
single buffers
Resistors are the same as schematic
No input caps

Some pics:

Pix011.jpg


Pix006.jpg


TIA!
 
Apr 3, 2005 at 9:01 AM Post #2 of 15
just a guess: the opa637 is not unity gain stable and therefore not the proper opamp for groundchannel amplification!
 
Apr 3, 2005 at 9:27 AM Post #4 of 15
Quote:

Originally Posted by steinchen
correct, opa637 is not unity gain stable and needs a gain of 5 at least (better 7 or 8) to work stable. Never use opa637 in ground channel.


Is gain=R4? Correct me if Im wrong. I set R4 to 10k (as I mentioned in the 1st post). Ive never used opa637 in the ground channel, it currently has OPA627 running on it.

7volts still weird though even if I set R4 lower than 7...
 
Apr 3, 2005 at 9:33 AM Post #5 of 15
next guess: opa637 is a single opamp. what you need for the pimeta in the signal channels is a dual opamp or (browndog-)adaptor to use 2*single as dual.
 
Apr 3, 2005 at 9:44 AM Post #6 of 15
Quote:

Originally Posted by BrokenEnglish
next guess: opa637 is a single opamp. what you need for the pimeta in the signal channels is a dual opamp or (browndog-)adaptor to use 2*single as dual.



LOL, OPA637 is a single opamp? I guess that's my fault then! as I only used 1 chip! Too bad I dont have an adapter to test with.

Thanks for the help guys! I'll post later if the adapter solves the problem.
 
Apr 3, 2005 at 9:46 AM Post #7 of 15
third guess: it will solve your problem - just compare the pin-layout in the datasheets of your opa2227(dual) vs. opa627/637(single)...
wink.gif
 
Apr 3, 2005 at 9:57 AM Post #8 of 15
This the adapter I needed right? LINK
 
Apr 3, 2005 at 5:50 PM Post #11 of 15
Also, you mentioned it worked fine with an OPA627 - but this is also a single op-amp, and requires the same adaptor.

Good luck!
 
Apr 4, 2005 at 3:38 PM Post #12 of 15
Quote:

Originally Posted by individual6891
You'll probably need a new OPA637 chip too
rolleyes.gif



Probably not. I've accidentally plugged singles in dual sockets and vice versa several times and haven't killed a chip yet.
 
Apr 4, 2005 at 3:55 PM Post #13 of 15
From what I gather, the chip he is rolling is the ground channel, as the OPA2227 chip is a constant.
The OPA637 will not work as a ground channel chip, as like said, its not unity gain stable.

there is no adapter that enables him to use this chip as a ground channel chip, as its exactly what the ground channel wants (a single ch opamp).
My advice, if you have an adapter, get another 637 chip, and use the 2 chips w/adapter in place of your opa2227, and take a opa627 chip and place it in the socket you're "rolling" your opamps in.
 
Apr 4, 2005 at 4:10 PM Post #14 of 15
Quote:

Originally Posted by Mitch318i
From what I gather, the chip he is rolling is the ground channel, as the OPA2227 chip is a constant.
The OPA637 will not work as a ground channel chip, as like said, its not unity gain stable.


Quote:

Originally Posted by aeroes
Ive never used opa637 in the ground channel, it currently has OPA627 running on it.


this was discussed at the beginning, mitch..
 
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