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I HAVE INSTALLED A NEW OP AMP (AD826AN) IN THE ANALOG SECTION OF MY ARCAM CD72T CD PLAYER TO REPLACE THE STANDARD UNITS (JRC2114D), AND I HAVE OBSERVED THAT THEY RUN VERY, VERY HOT FROM THE START.I HAVE CHANGED TO ANOTHER OP AMP (OPA2604)AND THE SAME OCCURS.
THE VOLTAGE OF THE SUPLY RAILS IS +/-12V.
THE OP AMPS ARE BYPASSED BY EVOX 100pF CERAMIC CAPACITORS.
THE INTERCONNECT CABLE IS VDH THE FIRST ULTIMATE.
THE ANALOG SECTION OF THE CD PLAYER (ACCORDING TO A REVIEW OF WHAT HI*FI MAGAZINE) RUNS IN CLASS A.
WHAT IS HAPPENING?
ARE THE OP AMPS OSCILLATING?
WHAT CAN I DO?I CAN SEND PICTURES OF THE ANALOG SECTION SHOWING HOW IS ALL CONNECTED.
THANKS IN ADVANCE FOR ANY HELP.
THE INTERCONNECT CABLE IS VDH THE FIRST ULTIMATE.
Follow Ups:
If so, you got problems elsewhere such as a solder bridge....
Use google and search for these two part numbers. You will find the manufacturer's datasheets. They will often show how the model in question should be bypassed. That is the case for the first opamp named and it looks like you need something different from just a 100pF cap.For the second opamp model, the datasheet has information on maintaining phase margin, a minor detail which if not attended to can result in oscillations. Since it is mentioned in the datasheet it is likely to be a problem area. The circuit into which you are plugging the thing may not meet these conditions.
General comment (repeating myself, I know): opamps are not plug-n-play. Sometimes you can just pull one out an stick in another, but without some prior information that the substituion is workable it's just a crap shoot.
One more thing. Are you soldering these or are they socketed. If socketed be aware that some opamps, especially high speed ones don't work well with sockets and may oscillate when used with one. If soldeting, be aware that a less than perfect solder joint can trigger oscillation - they are said to behave in a diode-like manner.
We're all human and sometimes frustration that something doesn't work when you assume it should can be a nightmare,if you can't solve it.Is'nt this why we have this Asylum.We're all mad.We read loads get confused then come here,or just come here first.I don't know.I'm going back to my padded room.
all the best langel.mikee55
I was not irritated with the poster but rather with purveyors of dubious advice. I've had a couple of friends who had expensive experiences after following authoritative advice without much comprhension of the consequences. One shorted the fuse on his Magnepans, then about 6 months later a guest stumbled, nudged his TT and bang went the tweeters! The other decided to do some magic mods the PS on an amp by means I think it better not to describe and created a dangerous situation; fortunately only the amp died but the friend coud have.In the case of the above poster, had he not not noticed the heat but just putn the cover back on ther heat from the opamp could damage nearby components. Although they seem mysterious at first, datasheets often contain information that is useful even if one can't follow the whole thing. If they seem to go heavy on a particular topic like bypassing or driving capacative loads, you can bet that those are special concerns for that model. And if you have internet access all you need to do is use Google or some other search engine - unless the component is very old or very obscure it will pop up.
Hi Sam9,no I wasn't havin a go either,I was grumpy,I couldn't solve a earth prob with my amp.I had nearly a volt of dc on my speakers and some hum.Irritating earth picking up stray feilds from my PSU.But I spent weeks trying to eliminate it,on my last tweak I'd accidently moved a gnd wire to one side,didn't disconect it,just moved it out the way.Would you believe it?
We should leave alone,but Tweakalitis gets ahold of us and off comes the lids....
Happy Tweaking all.mikee55
hi langel, have you tried disconnecting one end of your class a biasing components? i'd try that and see if your op amps run alot cooler. if not, i would be looking for solder bridges, bad solder joints etc. do all voltage supply pins check normal with amps installed in circuit board? if everything checks out good,and runs cooler without the biasing, the heat sinking would probably help. i'm no tech. just a few thoughts good luck! alley-kat
The only time I ever saw an opamp get very hot,(we are talking milliwatts normally), was when I put one in backwards by mistake. Make triple sure that the new op amp is oriented correctly in the socket.
If its in backwards,(power would be applied to the wrong pin, maybe a signal input pin instead of pin 7). That would heat things up real fast.
mg16
Just checked the AD datasheet for pin out.
With the notched end of the opamp facing left, pin 1 is to the far left bottom row. If its turned around, pin 8,(+voltage input pin), and pin 4,(-voltage input pin), are swapped. That would be a definite overheating problem.
Are you sure the AD is pin for pin compatible with the original op-amp
mg16
Yes, I am sure the new op amps are pin to pin compatible with the old ones and that they are correctly oriented in the socket. No doubt about this. The problem must be another.
increase the surface area of the chip so the heat can disipate faster. If you wanna cool it get a piece heatsink (larger surface area will fuction more efficiently) and epoxy it onto the IC with a thermaly conducting adhesive, that'll cool it down a little
I'm no expert,but 150pf ceramic caps?shouldn't they be 150nf?and if the output is true class A,things are usualy hot.Take the caps off and try again.I'm not familiar with this op-amp,are you sure its a pin for pin replacement?
Sorry if I can't help,I try to help inmates where I can,I'm not that experienced,but I think your cap values are wrong.But I could be wrong.Did you choose this value?Also scrutinize your handy work.I've been caught by a tiny short whilst soldering.It can happen.
Mikee55.Goodluck.
Yes. The bypass capacitors (which I have not installed; they came already installed in the player) are EVOX MNK 100pF. The datasheet of the OP2604 recommends 1uF tantalum capacitors, but, could be a low value bypass capacitor cause of oscillation?
Are we sorted yet??Have you tried it without by-pass caps?
Goodluck Mikee55
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