I need help to replacing uA709 and lt1114

[Midouu]

hi evry one
What is a good modern day replacement for the uA709 and lt1114 operational amplifier?
thank you

 

[aliarifat794]

Here are some suggestions regarding the replacements of uA709.

UA709MJ Op Amp Replacement - Amplifiers forum - Amplifiers - TI E2E support forums

Other Parts Discussed in Thread: TLV9002 , OPA172 , OPA170 , OPA171 , TLV9062 Need to find a replacement for the UA709M

e2e.ti.com

 

[FvM]

uA709 uses external compensation, suitable replacement depends on application parameters.

 

[crutschow]

Requirements?

 

[Midouu]

uA709 uses external compensation, suitable replacement depends on application parameters.

thank you bro. That means, should I try more than one alternative and then see which one is closest?

 

[betwixt]

As Crutschow stated, it depends on your application. The uA709 is now very old and it needed external components to keep it stable across its (narrow!) bandwidth. Modern op-amps sometimes offer compensation but most do not need it. You might also have to consider the package, most ua709 were made in metal cans with wires, not a package used these days although the pin functions are still valid.

LT1114 is still in production.

Brian.

 

[crutschow]

The 709 has poor characteristics compared to modern, general-purpose op amps, so it makes no sense to try to find something that matches it.
If you are looking for a general-purpose op amp replacement, then tell us the likely applications for the amp.

 

[Midouu]

Well, a passion for old electronics and the goal was to assemble the parts to make a GS4 metal detector. I think the NE5534 circuit can be a suitable alternative

 

[betwixt]

I don't know the schematic but the NE5534 might be a bad choice, it has anti-parallel diodes across its input pins which limit its use except for amplifying small signals.

Brian.

 

[Midouu]

hello here is the dschematic my brother

 

[betwixt]

Strange design - I would expect poor performance.
I can't understand why a uA709 is used when the other op-amps are of much superior design. I suggest removing the compensation components and using a TL071 instead.

Brian.

 

[Midouu]

Brian.

Mr Brian Thank you, important note and good advice. I will see what can be changed

 

[FvM]

Don't know what's required bandwidth of uA709 gain stage, uA709 has about 1 MHz bandwidth at G=450, GBW 450 MHz would be required to achieve 1 MHz. TL071 (GBW 5 MHz) has only 11 kHz bandwidth in this configuration.

 

[betwixt]

To be honest FvM, I doubt it works well at all anyway. It seems to measure change in inductance in the pickup coil by pulsing it with high current via the IRF740 and measuring the resulting voltage across it through the uA709. At first I thought it might be looking for residual resonance in whatever it detected, a bit like TDR but that would require the uA709 to be gated off during the pulse transmission. Given the pulses come from a 555 timer running at about 450Hz, even with the relatively high gate current, I wouldn't expect a wide bandwidth is required. There are better ways of detecting metals and seeing if they are ferrous or not. I think the idea that is can distinguish gold from other non-ferrous metals is hard to believe.

Brian.

 

[FvM]

Must confess that I didn't try to analyze circuit operation in detail, see that we have a kind of a synchronous rectifier following uA709 gain stage, thus harmonics of 500 Hz pulse frequency may play a role as they translate into phase shift. Can be that 11 kHz bandwidth if TL071 is sufficient. I would probably try decompensated OP like LF357 (20 MHz GBW).

 

[Midouu]

Must confess that I didn't try to analyze circuit operation in detail, see that we have a kind of a synchronous rectifier following uA709 gain stage, thus harmonics of 500 Hz pulse frequency may play a role as they translate into phase shift. Can be that 11 kHz bandwidth if TL071 is sufficient. I would probably try decompensated OP like LF357 (20 MHz GBW).

thank you for your response brother....In the sniffer xr 71 (delta pulse 2) device, the LF357 circuit was used. But there is a difference between the two schematics

--- Updated Yesterday at 8:16 PM ---

To be honest FvM, I doubt it works well at all anyway. It seems to measure change in inductance in the pickup coil by pulsing it with high current via the IRF740 and measuring the resulting voltage across it through the uA709. At first I thought it might be looking for residual resonance in whatever it detected, a bit like TDR but that would require the uA709 to be gated off during the pulse transmission. Given the pulses come from a 555 timer running at about 450Hz, even with the relatively high gate current, I wouldn't expect a wide bandwidth is required. There are better ways of detecting metals and seeing if they are ferrous or not. I think the idea that is can distinguish gold from other non-ferrous metals is hard to believe.

Brian.

(( I think the idea that is can distinguish gold from other non-ferrous metals is hard to believe ))
Certainly this is impossible...some devices PI metal detectors distinguish ferrous from other non-ferrous metals or reject iron With some problems like the loss of detection range

--- Updated Yesterday at 8:24 PM ---

Must confess that I didn't try to analyze circuit operation in detail, see that we have a kind of a synchronous rectifier following uA709 gain stage, thus harmonics of 500 Hz pulse frequency may play a role as they translate into phase shift. Can be that 11 kHz bandwidth if TL071 is sufficient. I would probably try decompensated OP like LF357 (20 MHz GBW).

I have used the LF357 circuit in other devices, but the results are very different depending on the manufacturer.....