"unconnected" IC Pins 1/8 showing voltage!>? Ro

[analog kid]

I am hoping that anyone can tell me what could cause IC pins that are unconnected to anything(pins 1+8 in this case) , to NOT read Zero vlts.  but rather to show small vltgst?(as high as .4vlt) I recently built another ROSS compressor clone, this time off the Tonepad layout, a first for me, and though it is functioning normally when volume and sustain are turned on... I noticed that if I turned the Volume pot OFF I could hear very faint Gating coming through the amp when striking the strings!! This really through me for a loop because as I said it was functioning normally otherwise, as soon as the volume hits "1" and the effect signal come on , the gating disappears. OR at least is so faint that it's inaudible.  '
So while taking vltgs, and all relevant Pin vltgs and trannie pin vltgs were spot on with my others, I noticed that the two UNCONNECTED pins were showing very small voltage readings! TO ME that seemed to be a good explaination for the gating with the volume off> BUT I can't remedy it!!!
- I have tried several different CA3080's , and of course checked the pins of the IC socket for anti-continuity, as well as looking for relevant traces possibly shorting... everything looks fine, It's really MindBoggling!!
 Anyone ever heard of this or have an explanation for it??!
I"M DESPERATE  :?

[R.G.]

I am hoping that anyone can tell me what could cause IC pins that are unconnected to anything(pins 1+8 in this case) , to NOT read Zero vlts. but rather to show small vltgst?(as high as .4vlt)

While the pins may not be used in a particular circuit, they may be internally connected to things and not supposed to be used. A "no connection" note on a datasheet may mean that the pin is truly not internally connected, or it may mean "We use this pin for special testing at manufacture, so don't connect anything to it or strange things will happen."

I noticed that if I turned the Volume pot OFF I could hear very faint Gating coming through the amp when striking the strings!!

I suspect that the circuit is providing its internal gating signal and that the very low frequency thump is getting through as a DC shift on the bias level.  If the pedal is otherwise working, ignore it.

[analog kid]

"If the pedal is otherwise working Ignore it"
REALLY!?
Firstly I am building this particular pedal for a friend who does alot of shows with area musicians as well as with me and I kind of wanted it to be as properly working compressor as possible. At least the same as my others I've built.  So i'd at least like to KNOW exactly WHY this gating comes through and why voltage is showing up on those unconnected pins!?
( I don't completely understand your explanation of why you believe it may be there in this crkt and not in the others I have when using the same exact Op amp)
Secondly though when the effect is "in use" (vol.:sustain Ups) it does seem to be just as clean compression as the others Ive built that don't have this "gating" or Pin 1/8 vltgs, It still makes me worry that that gating could be there in the form of a slight distorted sig. mixed with the compressed signal. OR  it may be dissapearing altogether as soon as the Pot hits 1 ? but as I said IF there's something there other than when the VOLUME is OFF,  it can't be heard by the "naked" ear if it is SO I guess what you don't Hear won't hurt you? I'd just feel most comfortable if I could either make that gating with the volume off , and the phantom vltgs , go away  OR at least actually KNOW why it's happening~
Thanks for the explanation R.G.~~!
NOTE: I should probably mention that the "gating" IS controlled by the sustain pot . Meaning that though it's faint gating and the amp's volume needes cranked to extreme to hear it.. that it does get loudest with Sustain turned up full and completely Gone with Sustain full CCW.  
 Important??

[R.G.]

You know, I'm sorry I stepped on your toes.

I suppose you could have said something like - "No, I really do need to find out be cause this unit is special and it just worries me a lot, so could you help me dig in and find out what's causing it?" but I guess my reply was a bit too prosaic.

As I said, sorry I stepped on your toes, and gosh, I sure hope you get that figured out some day. Seems to be beyond me.

[analog kid]

No , I think you must've took my meaning wrong on that one R.G.  :oops:
I definitely wasn't disregarding your explanation one bit, and I don't know what you meant by stepping on my toes but you surely were not! You helped me understand what "Unconnected" Pins of an IC means a bit if anything. I kind of thought that the thing was that they would still be "internally" connected whether the physical pins were hooked to anything or not, thereby being forced into small "voltages" maybe by improper bias or wrong vltgs at OTHER pins??  
All I was saying about it  being for someone else instead of me was I was hesitant to let it go w/o remedying the gating IF I COULD , If it was mine I wouldn't care so long as it worked..Definitely not that it was Special to me and i wasn't Listening to your advice and explanations. Quite the Opposite!! IF you really thought it to NOT be a "problem" I would just ignore it  and let it be used that way, (not being for me though) THAT I'd rather at least KNOW exactly what would cause that gating and /or the Unconnected Pin voltages IN THIS PARTICULAR UNIT.
I was just trying to give you a little more perspective into when it was gating and what effected it doing so.
As I said , sorry I gave the impression that your advice was not well taken and appreciated.  Matter of fact I always get a little happier everytime I see your ID Posting on a thread I started because I KNOW that I am about to LEARN SOMETHING and get some SOLID ANSWERS to my problem!
No offense was meant by my response

[JHS]

In a typical single OPAmp pin 1 and 8 are for offset and/or frequency compensation, some circuits as voltmeters will need a proper offset setting, some ICs like LM308 need external frequency compensation.

Look in the IC's data sheet. If the IC has internal frequency compensation, ignore it. If external freq. compensation is recommended do it (in most cases only a small pF-cap must be added between pin 1 and 8).

JHS

[R.G.]

The CA3080 is not a standard opamp. It is an operational transconductance amplifier (OTA). Pins 1 and 8 are not used for compensation in any of the datasheets I've ever seen. And I have looked.

[analog kid]

I've looked this sheet over and can't find any "frequency compensation" in the application schematics or features , all I can find is "storage and phase compensation", this seems to be between pins 4 and 6.  So I am assuming that this means it has INTERNAL compensation , but I will give a link to a Spec sheet of the Intersil CA3040 I found:
http://www.futurlec.com/Linear/CA3080E.shtml
I was wondering though, this is the first time I've heard mention of this compensation in an IC,  so would it hurt anything to try putting a small pf cap across 1/8 just for kicks to see if the gating goes away OR is it totally uneccessary?

[Paul Perry (Frostwave)]

Analog Kid, you say you built "another" Ross, if you still have the first one & it doesn't behave weird, I would open it up beside the 2nd one, run identical (split cable) sigs to both, and start comparing voltages & probing everywhere.
I have used this technique to repair stuff that I don't understand AT ALL!
But I will say this, compressors are a bitch, because behavior depends so much on signal input level, and also style of signal.
Some 3080s have much more offset than others as well, that's why many circuits have a trimpot across the inputs & the wiper to ground, to null the output.

[analog kid]

thanks , yes I have done that. Voltages (*except for 1/8 on the new one) are almost identical, IC and 5 transistors.  That was what It finally came down to for me. I thought I'd switch back and forth between a perfect behaving compressor using the exact same battery and IC chip and probe/meter each one looking for differences. I can't find anything that explains why I"m getting the gating. Audio probe gives the same amount and type of signal on each one throughout the crkt. (I didnt do the split cable thing though)
I am starting to think R.G. has the right idea as far as just ignoring it if there is no sign of the gating when the volume pot is turned up. (?)