Best Op amps to use in Phase Linear Series 2 preamps and amps?
- Thread starter bscote
- Start date
For the power amp
If you are using a stock pl control board the only easy upgrade, if it is not already done , is a lf351. This also requires changing the power dropping resistors to 7.5 k 5 watt or larger. These dropping resistors may be wire wound or film. It’s the only place to even thing of using wire wound resistors in a Phase Linear . Beyond that you need supply caps on the op amp to prevent oscillations . The lf351 is all you need . The best solution is buy a new control G board from Joe and install it . It has opa134 op amps.
for preamp use what is in place. Upgrading needs special adapters and can have troublesome results
If you are using a stock pl control board the only easy upgrade, if it is not already done , is a lf351. This also requires changing the power dropping resistors to 7.5 k 5 watt or larger. These dropping resistors may be wire wound or film. It’s the only place to even thing of using wire wound resistors in a Phase Linear . Beyond that you need supply caps on the op amp to prevent oscillations . The lf351 is all you need . The best solution is buy a new control G board from Joe and install it . It has opa134 op amps.
for preamp use what is in place. Upgrading needs special adapters and can have troublesome results
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Any changes to the opamps should be met with an oscilloscope and low distortion oscillator, or better yet, a distortion analyzer to check stability. At a minimum decoupling caps on the power supplies (at the chip) should be installed. That's not an easy task. Consider installing sockets to make replacement easier. The alternative is to install them, pull up a chair and decide for yourself.
White Oak Audio. Joe is "Gepetto" here on the forum.
https://www.whiteoakaudio.com/
https://www.whiteoakaudio.com/
Joe is also a BSEE and an OPAMP engineer. He spec'd the Texas Instruments, (formerly Burr-Brown Division) "SoundPlus" OPA134 OPAMP for a single channel, the OPA2134 for 2 channel, and the OPA4134 for Quad use in all our Phase Linear gear upgrades. The pinout for the OPA134 is the same as LF356N, LM351, and many other single channel OPAMPs. The pinout for OPA2134 is the same as TL072, MC1458, and most other Dual OPAMPs. Unfortunately, the pinout of the OPA4134 is not the same as the Quad OPAMPs used in the Phase Linear Preamplifiers which used Raytheon 4136 and 4739 Quad OPAMPs. To use the superior OPA Series OPAMPs in the Phase Linear Preamplifiers, you need the BrownDog adapters as George mentioned. Just google BrownDog Adapters. I can hear the difference...
Here from TI:
The OPA2134 series are ultra-low distortion, low-noise operational amplifiers fully specified for audio applications. A true FET input stage is incorporated to provide superior sound quality and speed for exceptional audio performance. This, in combination with high output drive capability and excellent DC performance, allows for use in a wide variety of demanding applications. In addition, the OPA134 has a wide output swing, to within 1 V of the rails, allowing increased headroom and making it ideal for use in any audio circuit.
The OPA2134 SoundPlus™ audio operational amplifiers are easy to use and free from phase-inversion and the overload problems often found in common FET-input operational amplifiers. They can be operated from u00b12.5-V to u00b118-V power supplies. Input cascode circuitry provides excellent common-mode rejection and maintains low input bias current over its wide input voltage range, minimizing distortion. OPA2134 series operational amplifiers are unity-gain stable and provide excellent dynamic behavior over a wide range of load conditions, including high load capacitance. The dual and quad versions feature completely independent circuitry for lowest crosstalk and freedom from interaction, even when overdriven or overloaded.
Here from TI:
The OPA2134 series are ultra-low distortion, low-noise operational amplifiers fully specified for audio applications. A true FET input stage is incorporated to provide superior sound quality and speed for exceptional audio performance. This, in combination with high output drive capability and excellent DC performance, allows for use in a wide variety of demanding applications. In addition, the OPA134 has a wide output swing, to within 1 V of the rails, allowing increased headroom and making it ideal for use in any audio circuit.
The OPA2134 SoundPlus™ audio operational amplifiers are easy to use and free from phase-inversion and the overload problems often found in common FET-input operational amplifiers. They can be operated from u00b12.5-V to u00b118-V power supplies. Input cascode circuitry provides excellent common-mode rejection and maintains low input bias current over its wide input voltage range, minimizing distortion. OPA2134 series operational amplifiers are unity-gain stable and provide excellent dynamic behavior over a wide range of load conditions, including high load capacitance. The dual and quad versions feature completely independent circuitry for lowest crosstalk and freedom from interaction, even when overdriven or overloaded.
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I finally found time to run the tests. From the limited testing I've done, Perry was correct in stating the BrownDogs offer no advantages. Ran THD and THD+N with a 50 pass average with three configurations installed. Original opamps, bare BrownDogs with OPA2134UA, and same BrownDogs with WIMA 0.1uF MKP film caps. Only changes I made were unplugging the preamp, removing the top cover, rolling the opamps, reinstall cover, plug in the power cord. Nothing else was changed on the preamp or test equipment.
The original opamps are the clear winner of these limited tests. Each screen shot is labeled.
Putting the originals back into my main system preamp to see if I can hear any difference.
Going to do some more reading about other tests I can run.
The original opamps are the clear winner of these limited tests. Each screen shot is labeled.
Putting the originals back into my main system preamp to see if I can hear any difference.
Going to do some more reading about other tests I can run.
Attachments
Will do Mark. Probably get to it later tonight or tomorrow morning. Will post results.
Now listening to the main system with original opamps in preamp. Really can't tell any difference. My hearings not the best and those differences in the numbers are very small, especially at those low levels.
Listening to a classic country album. Ferlin Husky...Green, Green, Grass of Home.
Now listening to the main system with original opamps in preamp. Really can't tell any difference. My hearings not the best and those differences in the numbers are very small, especially at those low levels.
Listening to a classic country album. Ferlin Husky...Green, Green, Grass of Home.
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Was doing some THD & N on the amp I fixed 2 days a go. Unweighted from 80K to 10- hz. A brutal test. Started out at .402% at 80 and was still .290% at 10 hz. Having tested a few off these I knew that wasn't right. Did the AP self test, ok there. Weighted IEC, 30 to 30K was still high. .275% to .256% at 10. Put it on the horns to see if IO could hear the problem. By the time I had it hooked up had lost the right channel. After poking around i noticed everytime I bumped a wire it changed. The Normal/ Direct coupling switch was trash. Lots of mechanical slack and the traces were shot. Bypassed the switch and the figures were right where they should have been. IEC A Weighted, 30K-.05% to 10 hz-.043%..... Unweighted from, 80K to 10 hz was .20 to .26..........acceptable.
Oner has to bear in mind that every connection, solder joint and fastener has an effect....and I guess our jobs as assembly and techies is to minimize those effects to whatever degree possible. The design and Joe's relentless pursuit of better deserves it...
Oner has to bear in mind that every connection, solder joint and fastener has an effect....and I guess our jobs as assembly and techies is to minimize those effects to whatever degree possible. The design and Joe's relentless pursuit of better deserves it...
