The recent Polar Toneohm I acquired uses five op amps, 4 x MC1458CP and 1 x MC1458JG. I've found data for the former, but nothing can be found for the latter. I'm just curious as to the difference of JG version to the other for CP's.
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A quick Google suggests the -JG package is ceramic (so extended temperature range) whilst the -CP version is plastic. One site suggested the CMRR is better on the -JG device.
Can you find an original Motorola data sheet for the device? That'll probably tell you.
There's a data sheet here, very strange a 0 to 70 device in a ceramic package rather than plastic.
A later revision of the data sheet here drops the MC1458JG and only has the MC1558JG a -55 to +125 version of the same chip which makes a lot more sense.
I guess that there was a shortage of CP devices and the more expensive JG device was used. It would be interesting to see what the manual says.
Nice bit of kit, I'm envious.
Jim
Sorry didn't see Cathovisor's reply until I posted.
Thanks guys, I did search Google, but for some reason my Google ninja skills evaded me. Brilliant Jim, that's just what I needed. This op amp world is all new to me.
I guess that there was a shortage of CP devices and the more expensive JG device was used. It would be interesting to see what the manual says.
If only I had one.
I am also curious as to why three of the op amps are socketed, whilst the other two are not.
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I am also curious as to why three of the op amps are socketed, whilst the other two are not.
As you've said it has Kelvin probes, I'm wondering if the unsocketed devices are tied in with those in order to remove any vagaries caused by contact resistance in sockets? Pure speculation of course.
That's interesting, in the absence of any service data I was thinking of trying to scan the PCB on both sides and trying to map all the component relations. Then the clever folk such as yourself and Jim will most likely understand the circuit.
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Here we go, scanned print and component sides, reversed horizontal of print then superimposed it as a new layer onto component side.
The Kelvin pairs are red and green and both pair route into U1, the MC1458JG ceramic op amp.
The originals
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The Kelvin pairs are red and green and both pair route into U1, the MC1458JG ceramic op amp.
Ah - the one with the apparently greater CMRR (Common Mode Rejection Ratio). That sort of makes sense. I am still trying to find a Kelvin adaptor for my Wayne Kerr 4221 Autobalance Bridge.
