Originally Posted by AllsWell
Ok so I finally received my "Burr Brown OPA637AP with Class A Biasing Mod" for my Matrix M Stage which I'm VERY pleased with.
The soundstage on my DT990 (600ohm) has received more depth, there is more of a viscerality to the music, more of a "grandeur" . everything is just more "powered up" and better lol. I am pleased, except for one thing.
The new Burr Brown Opamp I purchased from Tams Audio generates (or adds to) a bit more heat on my Matrix Amp. It's much warmer now than it was before at stock configuration.
Has anyone noticed this / experienced this ?
Is this a normal thing (nothing to worry about ?) It's not HOT to the touch , just warmer than before.
Anyways, I think it was well worth the extra 50 bux for the upgrade IMHO.
I assume you are talking about the Class A biased OPA637 Op Amp running hotter than the stock Op Amp?
Yes the Class A biased OP Amp will run hotter than the stock one and hotter than a standard OPA627 or OPA637.
The Matrix M Stage itself always runs very hot regardless of which Op Amp you use.
But the OPA637 in any format is not recommended for use in the M.
Try using a standard OPA627, personally I don't hear a huge difference between the two versions (Class A and non Class A) myself, in fact, I think the stock OPA627 is a touch clearer.
Originally Posted by nullpo
The OPA637AP isn't well suited for this circuit and coupled with the class A biasing I'm sure it runs quite hot.
He's using the OPA637 which is NOT unity gain stable (i.e. 0 dB gain stable), but you are correct, it will oscillate in this circuit at 0 or 10 dB of gain.
OP should run the M Stage at 20 dB or 18 dB of gain to avoid oscillation with the OPA637 (bad, very bad!).
The output stage of the M Stage uses two output transistors per channel.
One is used for amplifying the positive half of the signal, the other is used for the negative half of the signal.
In Class A, both transistors are ON all the time for all of the signal. Class A runs hot.
In Class A/B the positive transistor is ON only for the positive half of the signal and negative transistor is only ON for the negative half of the signal. Class A/B runs much cooler.
In Class D the output transistors are switching ON and OFF at a speed much, much higher that the audio signal, think 500 kHz or 100 kHz. It's a bit like recreating a signal from ONEs and ZEROs in a DAC.
Maybe I'll add something to the Glossary Of Terms.
Edited by Chris J - 1/28/12 at 11:48pm