Author Topic: 4558 vs TL072  (Read 13663 times)

LJ King

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4558 vs TL072
« on: July 31, 2007, 03:03:13 PM »

Ok, I'm an op-amp novice, so be gentle.

The Mike Matthews Dirt Road Special's preamplifier is built around the 4558. Two pretty simple non-inverting stages with two feedback paths each - one being a resistor only and the other being "frequency selective" for implementation of the tone and bite control.

I'm thinking I want to replace the 4558 with a TL072. For no other real reason than I have an amp that uses TL072 and it sounds pretty good, and as I understand it, the 4558 is considered a "low quality" device for audio.

I have done some homework. The pin-outs for the 8-DIP package are the same. The critical supply voltage and common mode signals and a whole bunch of other things I don't have a clue about are the same if not better with the TL072.

I can't see any reason why I couldn't just swap a TL072 for a 4558.

Anyone see anything I can't?



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Re: 4558 vs TL072
« Reply #1 on: July 31, 2007, 03:13:23 PM »
TL072: JFET input
4558: BJT input

It should be ok to replace BJT input opamps with FET inputs opamps but the opposite (FET->BJT) may cause some impedance mismatch problems. Some opamps also contain internal compensation capacitor, while some others don't. Replacing an opamp that has compensation with an opamp that does not have it may cause instability. (In this case both have it). Some opamps behave differently with varying rail decoupling configurations - some opamps are very sensitive to it and may oscillate with poor configuration while others do not. Anyway, I see no reason why you can't at least try the new opamp.
« Last Edit: July 31, 2007, 03:20:37 PM by teemuk »

LJ King

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Re: 4558 vs TL072
« Reply #2 on: July 31, 2007, 08:20:05 PM »

Cool... I'll use a socket. Thanks!

Gary M

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Re: 4558 vs TL072
« Reply #3 on: August 02, 2007, 12:36:28 PM »
A socket is a always great addition. Other types with the same pin out for experimenting include the 1458 and LF353.



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