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Mooly · 1st Dec 2021, 8:54 pm

The OPA2604 was always was of my favourite devices but I don't think it was around when the Quad was produced. Apart from its higher power consumption the OPA2604 should be OK replacing the TL072. In fact the OPA2604 was always one of my favourite devices and it is a shame it was dropped in DIP8 form.

The TLE2072 is a later variation on the original TL072 and is a valid swap (again these were not around when the Quad was first produced).

The only real limitation of the original TL0xx series is a limited drive ability although the Quad comes nowhere near that point with its circuitry. They were and still are capable of excellent results.

That OPA381 is a true mystery. Please read the data sheet yourself to see how unsuitable it really is. The maximum supply voltage is just 5.5v, it should not even survive running on the rails the Quad uses. Truly bizarre that someone should fit that.

There are lots of misguided attempts and ideas to 'improve' equipment and while some have a genuine basis to improve certain aspects, many more do not. Correctly used electrolytics have no detrimental effect in passing audio signals.

1st Dec 2021, 8:54 pm	#39
Mooly Octode Join Date: May 2011 Location: Lancashire, UK. Posts: 1,351	Re: Quad 34 preamp volume knob clicks The OPA2604 was always was of my favourite devices but I don't think it was around when the Quad was produced. Apart from its higher power consumption the OPA2604 should be OK replacing the TL072. In fact the OPA2604 was always one of my favourite devices and it is a shame it was dropped in DIP8 form. The TLE2072 is a later variation on the original TL072 and is a valid swap (again these were not around when the Quad was first produced). The only real limitation of the original TL0xx series is a limited drive ability although the Quad comes nowhere near that point with its circuitry. They were and still are capable of excellent results. That OPA381 is a true mystery. Please read the data sheet yourself to see how unsuitable it really is. The maximum supply voltage is just 5.5v, it should not even survive running on the rails the Quad uses. Truly bizarre that someone should fit that. There are lots of misguided attempts and ideas to 'improve' equipment and while some have a genuine basis to improve certain aspects, many more do not. Correctly used electrolytics have no detrimental effect in passing audio signals.