OP27. How good is it?

[mudihan]

I was reading a review of Burson's HDAM by TNT.

http://www.tnt-audio.com/accessories/hdams_e.html

OP27 seemed to do OK in the test. I am fairly familiar with OPA627/37s and I like them a lot. But in the test, OP27 got higher praises. I am wondering if anyone knows how good OP27s sound.

[eLarson]

The OP27, if memory serves, it is related to the OP37, with one being decompensated and the other not.

Dejan Veselinovic mentions that the OP27 is used in the highly regarded Burmester gear.

[jacco vermeulen]

Originally posted by eLarson
the OP27 is used in the highly regarded Burmester gear.

the PMI OP27 opamp WAS used by Burmester in his 1980 models.

Dieter Burmester is supposed to have been the first to produce high end pre-amplifiers based on circuitry with the "new" generation opamps. Stuff like the modular 808, the line amplifier 838, and the model 877.
The top notch quality of the foil capacitors used by Burmester in his 80s gear was responsible for half of the good sound quality.
Burmester used pretty expensive and very accurate Siemens styroflex capacitors for the RIAA section of his pre-amps.
(the Burmester model numbers are derived from the year and month of introduction, 808 is 1980 August. Dieter is fond of Ferrari. )
Elektor cloned the Burmester circuits halfway the 80s and came up with The Preamp, based on....OP27.
The Elektor Pre sounded much better with Burr Brown OP27s instead of PMI versions.
Stepping up from OP27 to OPA627/637 a few years later was again a big improvement for pre-amp circuitry. LT1028 was often used for CD-player applications untill the OPA's arrived.

I'm surprised the TNT article does not make a distinction between BB OP27s and PMI Ops.

[mudihan]

The interesting thing is that what TNT mentioned was OP27, the AD version, not OPA27, the BB (or now TI) version. The Analog version has much better specs, comparing to the BB version. I wonder if it sounds better too.

[mudihan]

Originally posted by jacco vermeulen


the PMI OP27 opamp WAS used by Burmester in his 1980 models.

Dieter Burmester is supposed to have been the first to produce high end pre-amplifiers based on circuitry with the "new" generation opamps. Stuff like the modular 808, the line amplifier 838, and the model 877.
The top notch quality of the foil capacitors used by Burmester in his 80s gear was responsible for half of the good sound quality.
Burmester used pretty expensive and very accurate Siemens styroflex capacitors for the RIAA section of his pre-amps.
(the Burmester model numbers are derived from the year and month of introduction, 808 is 1980 August. Dieter is fond of Ferrari. )
Elektor cloned the Burmester circuits halfway the 80s and came up with The Preamp, based on....OP27.
The Elektor Pre sounded much better with Burr Brown OP27s instead of PMI versions.
Stepping up from OP27 to OPA627/637 a few years later was again a big improvement for pre-amp circuitry. LT1028 was often used for CD-player applications untill the OPA's arrived.

I'm surprised the TNT article does not make a distinction between BB OP27s and PMI Ops.

And what is more interesting is that TNT preferred OP27 over OPA627.

[eLarson]

Coming back to your original question of "How good is it?", the answer is "Good enough for some people to form a preference."

That doesn't answer whether you (or me) would like it, though. If you got some, you might as well try it.

[jrdmedford]

I recently upgraded a peice of DJ gear that included an MC
phono stage. The phono stage schematic is right out of
Horowitz and Hill as well as the RJM VSPS out on the net.

I tried a number of op-amps with the phono stage: The Analog
OP-270 (Dual OP27's in an 8 pin PDIP), the Burr Brown OPA2134 and original BA4558 that came with the unit.

The OP-270 outshined all of them... It was more detailed than
my 6922 tube based phono preamp. It was also warmer and more vivid than the OPA2134.

Good stuff. Try it out.

-- Jim

[jacco vermeulen]

Originally posted by mudihan
what TNT mentioned was OP27, the AD version, not OPA27, the BB

Burr Brown made an OP27 in the late 1980s, at the time when PMI made them.
BB developed the OPA627/637 and came out with the improved version, the OPA27/37. IIRC, in that order. Analog Devices took over PMI, then came the OP27/37 with AD printing.

I've used the BB OP27 and 37 from like 1987 for pre's, input stages of power amps, and headphone amp circuits.
The 134/2134 are cheap, but imo not better than the OP27/37.
Funny that there is so much attention for the OPA627/637 and OPA134/2134, but so little for the OP(A)27/37.

[capslock]

The OP(A)27 is optimized for low offset voltage and low noise at medium-low source impedance. While better than say the OP07, some of the optimizations are not those that you would want for audio, such as:

- lowish input stage current
- optimization for high LF open loop gain rather than open loop linearity
- very low open loop rolloff point
- NPN transistors for essentially all gain devices
- noise cancellation circuitry in the input stage (which will only work with symmetrical impedance)

While the OP27 sounds good enough for many preamp applications, even an LF356 would be a better choice at 1/5 its cost.

[Jennice]

Hi all,

This op-amp talk got me interested.
It seems there's some sort of system in the numbering.
Does anyone have an oppinion on the Analog Devs. OP275?
It liiks like a versatile little fella' with nice specs.
Is there a single-amp version of it, and if so, can anyone tell the name?

Jennice