Hi all!
I have to change a defective IC: uA747 in a 40 years old equalizer.
There are 12 of it used in the device.
Afaik uA747 is a double uA741 (747: DIL-14)
I think about changing all of them to better ones.
Any suggestions for a pin matching part?
I have to change a defective IC: uA747 in a 40 years old equalizer.
There are 12 of it used in the device.
Afaik uA747 is a double uA741 (747: DIL-14)
I think about changing all of them to better ones.
Any suggestions for a pin matching part?
Those are in an antiquated and obsolete package I'm afraid.
The best option might be to have small adapter boards made that would take a modern dual replacement.
Another thing to beware of is power consumption. Twelve dual '741's' take little, and there are plenty of suitable replacements (apart from the package) but there are also plenty of others that could be to power hungry overall.
The best option might be to have small adapter boards made that would take a modern dual replacement.
Another thing to beware of is power consumption. Twelve dual '741's' take little, and there are plenty of suitable replacements (apart from the package) but there are also plenty of others that could be to power hungry overall.
RS still supply them and TI still make them!
http://uk.rs-online.com/web/cp/0305816,0305816P,1218283/?sra=p&r=t
http://uk.rs-online.com/web/cp/0305816,0305816P,1218283/?sra=p&r=t
Yep. It's still an active part, i.e. TI still makes it.
I would hesitate to swap them out. Many of the older circuits resorted to all sorts of tricks to wring as much out of the old parts as possible. If you apply the same tricks to a newer opamp you could get all sorts of nasty surprises - including instability. Some of the circuit tricks also used the offset adjust pins to gain access to the input stage of the opamp. If your equalizer uses those pins for anything other than offset adjustment, I'd leave the uA747 in there.
Should you decide to swap out the parts, I'd make a small adapter board with an OPA1612 or LME49720 in SOIC-08 that plugged into the 14-pin socket for the uA747.
Tom
I would hesitate to swap them out. Many of the older circuits resorted to all sorts of tricks to wring as much out of the old parts as possible. If you apply the same tricks to a newer opamp you could get all sorts of nasty surprises - including instability. Some of the circuit tricks also used the offset adjust pins to gain access to the input stage of the opamp. If your equalizer uses those pins for anything other than offset adjustment, I'd leave the uA747 in there.
Should you decide to swap out the parts, I'd make a small adapter board with an OPA1612 or LME49720 in SOIC-08 that plugged into the 14-pin socket for the uA747.
Tom
Thanks for the answers.
I know that one can buy the "ua747" still new. I get it here in D for 0.74 € / ea. But it is not exactly the first choice for audio application and since I have to exchange anyway, I looked for replacement, but so far nothing found pin compatible.
I've already thought about an adapter board . However, the OPA1612 is too expensive to exchange 12 pieces (2 channels), which costs me 7.30 € /ea. NE5532 would probably do it as well in this application. There are no "tricks" in the circuit, the offset pins ect. are not used at all.
I will probably continue to use 747, so the equalizer once again runs. To build 12 adapters takes a time first.
I know that one can buy the "ua747" still new. I get it here in D for 0.74 € / ea. But it is not exactly the first choice for audio application and since I have to exchange anyway, I looked for replacement, but so far nothing found pin compatible.
I've already thought about an adapter board . However, the OPA1612 is too expensive to exchange 12 pieces (2 channels), which costs me 7.30 € /ea. NE5532 would probably do it as well in this application. There are no "tricks" in the circuit, the offset pins ect. are not used at all.
I will probably continue to use 747, so the equalizer once again runs. To build 12 adapters takes a time first.
Attachments
To retrofit a line-level equalizer, I might be tempted to use the even-lower-cost LM833 rather than the NE5532. But I'm a heretic.
SOmetimes you can replace older types with more modern "better" ones, but the circuit the IC is in may not allow the newer part to actually display the betterness.
the DC circuit Z is better matched to a fet input
TL072 are fine if you don't need to swing too negative on output - the 270 Ohm series output R is about right for them
the 5x more expensive OPA1642 is arguably among today's best
TL072 are fine if you don't need to swing too negative on output - the 270 Ohm series output R is about right for them
the 5x more expensive OPA1642 is arguably among today's best
And remember to check power consumption of any replacements. The uA747 could be around 4ma, an NE5532 nearer 12ma. Depending how the supply is configured, it may just collapse powering twelve 5532's or similar.
No sign of offset in use, so the TL072 should work with a pin out adaptor and is lower current if anything.
Thanks for the advices.
First, I would test some single different OPs until I decide which type I choose for all.
The power consumption will not be a problem. The power supply is a 30VA transformer and standard +/- 15V voltage regulator (7815/7915). I could change the power supply in case of emergency, it is a separate component.
As far as I know, some (FET-) OP-types do not like, if (neg.-) input and output are connected directly. I would have to consider this in the selection, because preferably I want to make no further changes to the circuit or the PCB. But TL072 does not seem to belong to those.
Perhaps first not an adapter board, but a diy-adapter-socket would be better. Bottom side to fit in the 747-sockets at the equalizer board, top with DIL-8 socket to test various up-to-date ICs.
First, I would test some single different OPs until I decide which type I choose for all.
The power consumption will not be a problem. The power supply is a 30VA transformer and standard +/- 15V voltage regulator (7815/7915). I could change the power supply in case of emergency, it is a separate component.
As far as I know, some (FET-) OP-types do not like, if (neg.-) input and output are connected directly. I would have to consider this in the selection, because preferably I want to make no further changes to the circuit or the PCB. But TL072 does not seem to belong to those.
Perhaps first not an adapter board, but a diy-adapter-socket would be better. Bottom side to fit in the 747-sockets at the equalizer board, top with DIL-8 socket to test various up-to-date ICs.
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The circuit diagram you posted is all classic 'text book' circuitry. The TL072 should be an ideal swap I would have thought.
Jfet opamps have a peculiar 'problem' of phase inversion if the common mode input voltage range is exceeded... that will never happen with your circuit.
Jfet opamps have a peculiar 'problem' of phase inversion if the common mode input voltage range is exceeded... that will never happen with your circuit.
"all classic "textbook"circuits" That I had also thought.
When I buy parts the next time, I will order some of the suggested IC types and test them.
When I buy parts the next time, I will order some of the suggested IC types and test them.
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