TL071 vs. TL072

[MartyMart]

Thanks Vsat, I watchd the voltages for some time and it never went
above 25.5v at pin 7 so +/- 12.7
There must be an answer, I'll try another PSU and a TL072 tomorrow

Marty.

[puretube]

markr04 measures:

7&4: error (DMM shows -1, which usually means error I think)
4&3: -1.1v
V- & GND in: -1.5v and falling. Measuring between these two points causes the opamp to go quiet.

in the other thread (of the 3 currently running...):
http://diystompboxes.com/sboxforum/viewtopic.php?t=35100

[Vsat]

Hmmm...
for pins 7,4: "-1" might be the DMM being overloaded (indicating wrong range setting, my DMM says "OL" in this case) or indicates the op amp is passing WAY more current than it should be - destructive latchup perhaps. Are you sure that the op amp was not damaged on the first try and you are repeating the experiment with a bad op amp?  Might be worth trying the circuit with a smaller supply voltage (say a 9V transformer) just to establish whether the op amp is happy, without any danger of excessive voltages. The op amp should work as a simple variable gain amplifier with gain of about 450 max.  An oscilloscope would be useful to check if any HF oscillation is occurring.
Mike



Quote:
7&4: error (DMM shows -1, which usually means error I think)
4&3: -1.1v
V- & GND in: -1.5v and falling. Measuring between these two points causes the opamp to go quiet.

[Paul Marossy]

Just to give this some closure, the actual problem was that the builder didn't connect the power supply ground to ground. That caused the opamp to freak out and misbehave the way it was. But, I did learn some things that I didn't know before. Thanks for all the help!  

[puretube]

well, we still have to wait for MartyMart`s result here:
http://diystompboxes.com/sboxforum/viewtopic.php?t=35105...

(while markr04`s problem is solved:
http://diystompboxes.com/sboxforum/viewtopic.php?t=35100&start=15).

btw: the PS problem in that other recent thread about the S.T. was a 12V DC wallwart being used instead of an AC...

(actually also an obvious question, one normally wouldn`t dare to ask about...  :wink: )

[MartyMart]

http://diystompboxes.com/sboxforum/viewtopic.php?p=246248&highlight=#246248

I asked about "linking" the two "board grounds" ......... yesterday !!
My fault - we had three versions of the same thread going, which does get confusing   :shock:

I'll give it a go asap and report back, did someone say that the TL071
may be "damaged" by this ?

Cheers,
Marty.

[puretube]

missed that thread (woulda been the 4th...)  :oops:

let`s keep the problem in Your thread:
SHAKA almost...

[Paul Marossy]

I'll give it a go asap and report back, did someone say that the TL071 may be "damaged" by this ?

Yes, it's in my TL071 vs. TL072 thread.

Unfortunately, I'm going to be out of town for the next three days, so I probably won't be able to keep up on this during that time. I'll try to find a computer somewhere and check in if I can. I hope everyone gets it straightened out!