tabs touching, no output

Matttcattt · 23rd June 2003, 08:26 PM

has anyone else found that when the tabs of two gainclone chips are conected electrically, one channel has no output? both my gainclones are mouned directly on the heat sink, but they are on seperate heatsinks. today, i tried connecting both heatsinks together with a pice of metal, and one channel stoped working! i immediatly disconnected power, and felt the chips, they were not even warm, so i tried again, with the same result. has anyone else noticed this? i do not know why this would happen, because both tabs are at -v.

Cradle22 · 23rd June 2003, 08:40 PM

Hi!

One thing that comes to my mind is that even if you connect both to the same supply, I bet you still use seperated filter caps for supply voltage.

So both ships are not "really" sharing the same supply, because of their own filters...

I will not check this out, but on my P3A I have one toroid, but apart from that totally seperated power supplies... and I bet that my P3A woult not like it very much if I connected V- from one supply with V- from the other...

They still share mass, though...

But maybe someone else can shed more light on this...

Bye,

Arndt

Matttcattt · 23rd June 2003, 09:00 PM

no, one chips -v pin is connected directly to the other's -v pin.

raindog · 23rd June 2003, 09:38 PM

to what pin is the tab conected (if so?)

Matttcattt · 24th June 2003, 06:32 AM

Quote:

Originally posted by raindog
to what pin is the tab conected (if so?)

pins 3 and 4.

Jennice · 24th June 2003, 07:51 AM

Hi folks,

I haven't built a gainclone, so I'm taking a wild guess about the typical IC amp circuits here...

Am I right in assuming that the inputs are (somewhere along the electrical path) connected at the audio source or pre-amp?

In that case the circuits have at least one common reference level.
Connecting the heat sinks (and thereby taps) you create a second common level (more or less). Since this is not at precicely the same potential, it causes a fault current, which is sensed by one of the sensing circuits on the chip. This triggers it's alarm state. This, in turn, shuts off the output to avoid self-destruction or un-intentended operation.

Try checking for multiple electrical paths for the same signals/potentials...

Jens

zobsky · 24th June 2003, 01:52 PM

on the side, ..... does anyone have 2 chips mounted on the same heatsink? ..i thoght i saw some pictures on the www with this arrangement

because this is what i intend to do, ..scrounged a working transformer from an old reciever and got my 3845 chips yesterday.

tiroth · 24th June 2003, 02:05 PM

Generally the chips will be isolated from the heatsinks at any rate. These amps usually stay cool enough that you can afford the insulator.

carlosfm · 24th June 2003, 02:11 PM

Matttcattt,
You forgot to say what power op-amps are you talking about.
I think you use OPAs, don't you?

I remember reading on one datasheet (don't remember what) that the tabs shouldn't be used do conduct power.
That is to say they should be isolated.
But if you used a single supply (+ and ground) the tabs would be at ground potential and no problems.

Matttcattt · 24th June 2003, 03:39 PM

Quote:

Originally posted by carlosfm
Matttcattt,
You forgot to say what power op-amps are you talking about.
I think you use OPAs, don't you?

I remember reading on one datasheet (don't remember what) that the tabs shouldn't be used do conduct power.
That is to say they should be isolated.
But if you used a single supply (+ and ground) the tabs would be at ground potential and no problems.

oops, forgot

yes, OPA541, free samples

23rd June 2003, 08:26 PM	#1
Matttcattt diyAudio Member Join Date: Feb 2003 Location: Bristol	tabs touching, no output has anyone else found that when the tabs of two gainclone chips are conected electrically, one channel has no output? both my gainclones are mouned directly on the heat sink, but they are on seperate heatsinks. today, i tried connecting both heatsinks together with a pice of metal, and one channel stoped working! i immediatly disconnected power, and felt the chips, they were not even warm, so i tried again, with the same result. has anyone else noticed this? i do not know why this would happen, because both tabs are at -v. __________________ If it aint broke, don't fix it. If it is broke, fix it. If you can't fix it, take it apart and see how it "worked".

23rd June 2003, 08:40 PM	#2
Cradle22 diyAudio Member Join Date: Jan 2003 Location: Dortmund, Germany	Hi! One thing that comes to my mind is that even if you connect both to the same supply, I bet you still use seperated filter caps for supply voltage. So both ships are not "really" sharing the same supply, because of their own filters... I will not check this out, but on my P3A I have one toroid, but apart from that totally seperated power supplies... and I bet that my P3A woult not like it very much if I connected V- from one supply with V- from the other... They still share mass, though... But maybe someone else can shed more light on this... Bye, Arndt __________________ ************************ A Sacrifice For Freedom

23rd June 2003, 09:00 PM	#3
Matttcattt diyAudio Member Join Date: Feb 2003 Location: Bristol	no, one chips -v pin is connected directly to the other's -v pin. __________________ If it aint broke, don't fix it. If it is broke, fix it. If you can't fix it, take it apart and see how it "worked".

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23rd June 2003, 09:38 PM	#4
raindog diyAudio Member Join Date: May 2003 Location: Timisoara	to what pin is the tab conected (if so?)

24th June 2003, 07:51 AM	#6
Jennice diyAudio Member Join Date: Jun 2003 Location: Planet Earth	Hi folks, I haven't built a gainclone, so I'm taking a wild guess about the typical IC amp circuits here... Am I right in assuming that the inputs are (somewhere along the electrical path) connected at the audio source or pre-amp? In that case the circuits have at least one common reference level. Connecting the heat sinks (and thereby taps) you create a second common level (more or less). Since this is not at precicely the same potential, it causes a fault current, which is sensed by one of the sensing circuits on the chip. This triggers it's alarm state. This, in turn, shuts off the output to avoid self-destruction or un-intentended operation. Try checking for multiple electrical paths for the same signals/potentials... Jens

24th June 2003, 01:52 PM	#7
zobsky diyAudio Member Join Date: Mar 2002 Location: Dallas, Tx, USA	on the side, ..... does anyone have 2 chips mounted on the same heatsink? ..i thoght i saw some pictures on the www with this arrangement because this is what i intend to do, ..scrounged a working transformer from an old reciever and got my 3845 chips yesterday.

24th June 2003, 02:05 PM	#8
tiroth diyAudio Member Join Date: Dec 2001 Location: Pittsburgh, PA, USA	Generally the chips will be isolated from the heatsinks at any rate. These amps usually stay cool enough that you can afford the insulator.

24th June 2003, 02:11 PM	#9
carlosfm Banned Join Date: Mar 2003 Location: Lisbon, Portugal	Matttcattt, You forgot to say what power op-amps are you talking about. I think you use OPAs, don't you? I remember reading on one datasheet (don't remember what) that the tabs shouldn't be used do conduct power. That is to say they should be isolated. But if you used a single supply (+ and ground) the tabs would be at ground potential and no problems.

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