Good idea!
Thanks, PMA - very nice and simple idea.
Tried it out - didn't hear anything that I couldn't pick up with the amp powered down ...
So at present I'm rather well content with the OPA's - considering finishing the input selector prior to further experimentation though - starting to get annoyed with fiddling plugs every time I want to change source!
Cheers - cdl
Thanks, PMA - very nice and simple idea.
Tried it out - didn't hear anything that I couldn't pick up with the amp powered down ...
So at present I'm rather well content with the OPA's - considering finishing the input selector prior to further experimentation though - starting to get annoyed with fiddling plugs every time I want to change source!
Cheers - cdl
OP vrs OPA
The original manufacturer of the OP27 and OP37 was PMI. They had great opamp. Analog Devices bought PMI. TI who purchased Burr Brown is making a copy of the those devices. I don't know if they share the same mask or if Burr Brown just made an attempt to copy them. Anyway, if your going to use them stick with the Analog Devices parts, for those opamps.
The best parts are the OP37AZ and OP27AZ in that family.
The original manufacturer of the OP27 and OP37 was PMI. They had great opamp. Analog Devices bought PMI. TI who purchased Burr Brown is making a copy of the those devices. I don't know if they share the same mask or if Burr Brown just made an attempt to copy them. Anyway, if your going to use them stick with the Analog Devices parts, for those opamps.
The best parts are the OP37AZ and OP27AZ in that family.
bmcevers said:
Hmm, wonder why noise performance is so important in your eyes. In my experience, it's only important if you want to amplifier MM or MC signals. If you are dealing with high level signals only, and avoid using 100 k pots and super high impedence feedback, noise even with simple TL081 parts is so low it cannot be detected at 10 cm from the speakers. And broadband noise is probably the least offensive reproduction error, provided it is at least 70 dB below the signal.
It's true that you can calculate that the 627 will surpass the 5532 only above a certain impedance, but what is the relevance of this?
Do you have measurements that document the superior common mode disto performance of the 5532 over the 627? True, the 627 has FET inputs, which generally have a higher input capacitance, but the 627 sports Difet isolation and input cascodes, both of which reduce the effective nonlinear input capacitance substantially.
It's worth mentioning that common mode distortion increases with source impedance, or rather with the difference of the impances at both inputs...
All the posts about all these opamps and not one mention of the best sounding one of them all, if utilized right, the ONE the ONLY
OP275 originally made by PMI now done by Analog Devices.
I`ve done extensive ab-ing of all the best of them, and musically the OP275 wins hands down. It is musicaly right, makes all the others sound hifi`ish, it does`nt focus on any particular part like bass slam or treble detail or dynamic impact, it just lets the music wash over you like a very good valve amp seems to do, btw it does do all the above also just does`nt seem to focus on any particular area.
THATS MY 2CENTS WORTH ANYWAY
OP275 originally made by PMI now done by Analog Devices.
I`ve done extensive ab-ing of all the best of them, and musically the OP275 wins hands down. It is musicaly right, makes all the others sound hifi`ish, it does`nt focus on any particular part like bass slam or treble detail or dynamic impact, it just lets the music wash over you like a very good valve amp seems to do, btw it does do all the above also just does`nt seem to focus on any particular area.
THATS MY 2CENTS WORTH ANYWAY
fmak said:cdl said:
Sorry, fmak, I didn't really mean that they sounded the same - just that both played music fine
You are right that the characteristic of the sound is quite different; 627 is impressive, and maybe on the bright side for my setup. Until now, my impression of 825 is that it is softer, and a little bit more leaned back, which is comfy especially for orchestral music.
Will keep posting - cheers, cdl
Power supply I am using is nothing special, I'm afraid. In sequence:
A big encapsulated toroid transformer (which I already had).
Rectifier with 100nF's in parallel with the diodes.
Two smoothing caps in parallel (i.e. 2 from + to gnd, 2 from gnd to -).
Then 7815/7915 regulators.
Smoothing caps.
Inductors (chokes) and more smoothing caps.
At last, right and left power supplies separated by a small resistor for each channel, and individual smoothing caps.
Most smoothing caps are 1000µF (470µF where I thought it would be less critical), most of them bypassed by small 100nF's. Have a couple of 10µF's decoupling the 7X15 regs as well.
Opamps are locally decoupled with 100nF's.
It's not special, or high-tech or anything, but 50Hz hum is not audible at all (not even close to speakers), nor visible using soundcard as scope. In general, the preamp stage seems very quiet.
I will replace 7X15 with LM317/377 sometime.
And definately improve decoupling, probalby with 47µF, 4,7µF and 100nF - hope I get around to that in the weekend.
Cheers, Cdl
P.S. georgehifi, thanks for your contribution. I'll try OP275 as well. The list is getting long, though...
A big encapsulated toroid transformer (which I already had).
Rectifier with 100nF's in parallel with the diodes.
Two smoothing caps in parallel (i.e. 2 from + to gnd, 2 from gnd to -).
Then 7815/7915 regulators.
Smoothing caps.
Inductors (chokes) and more smoothing caps.
At last, right and left power supplies separated by a small resistor for each channel, and individual smoothing caps.
Most smoothing caps are 1000µF (470µF where I thought it would be less critical), most of them bypassed by small 100nF's. Have a couple of 10µF's decoupling the 7X15 regs as well.
Opamps are locally decoupled with 100nF's.
It's not special, or high-tech or anything, but 50Hz hum is not audible at all (not even close to speakers), nor visible using soundcard as scope. In general, the preamp stage seems very quiet.
I will replace 7X15 with LM317/377 sometime.
And definately improve decoupling, probalby with 47µF, 4,7µF and 100nF - hope I get around to that in the weekend.
Cheers, Cdl
P.S. georgehifi, thanks for your contribution. I'll try OP275 as well. The list is getting long, though...
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