Cory's Phase Linear 300 Ser II

[laatsch55]

Coming frm a fabricator of your caliber that is high praise indeed!! Thanks Dennis. The outputs were obsoleted 25 years ago. They are also the outputs for one of the biggest, bad ass receivers ever made, the mighty Pioneer SX 1980--270 WPC RMS into 8. Conservative watts tpoo. I suspect at least 360 before it clips. Have never had one on the bench. These outputs were run at the behest of Pioneer during the time Pioneer owned Phase.
I have run into a snag. On bringing it up on the DBT, the relay starts chattering at about 60 volts. If this amp did not have unobtanium outputs I would just throw 120 full on at it as I believe I've reached the point where the coil will actuate but upon doing so drops the voltage enough to drop it out with the DBT doing as it should--limiting current. I have bypassed the relay coil and things are fine. So I guess I should nut up and give er the groceries.

 

[laatsch55]

That's exactly what it was. Contributing to the problem was a very high bias setting which draws a lot of current. Throwing the switch now, I hear the realy click, and 4 seconds later the DC protect relay clicks. all is well, the AP is chomping at the bit . IT IS TIME>

Ye Olde Test Shoppe.............

 

[laatsch55]

Some preliminary numbers....

 

[laatsch55]

So......swapped out the LDF-351's with some Burr-Brown OPA134PA's. the numbers look a whole lot better........

 

[laatsch55]

Until you drive both channels then this happens.... The clean wave is with one channel driven, the weird one when both are driven. Doesn't matter which channel you are monitoring, both exhibit the same behaviour.

 

[laatsch55]

Swapped back to the LF-351's, everything is fine. One more thing to try from an Ed recommendation. Hang on folks, HE'S GOIN IN!!

 

[Skratch]

What do you think caused thst sine wave ?

 

[Gepetto]

Instability
The GBW of the 134 is different from the original LF351. The op amp is part of a global feedback path in this amp, similar to the PL36.

 

[laatsch55]

That what Ed was saying too. So a unity gain would be a necessary feature??

 

[laatsch55]

AND, why exhibit that behavior only when both channels were driven??

 

[laatsch55]

If and when a 300 Ser II oscillates Ed says the service bulletin dated 11-81, states, remove the .0027uf /150volt power supply de-coupling cap and install a 120pf ceramic cap accross the base and collector pads of both positive and negative output drivers. In this case the 2SC2336, and 2SA1006. Just completed that. Now back on the AP it goes.

 

[jbeckva]

Fingers crossed....

 

[laatsch55]

Yep, works like a charm. With the Burr-Browns in VERY stable. Distortion specs are better.

 

[laatsch55]

Until halfway through a frequency response test. had to take em back out. LM-351's back in. Now on the horns.

 

[laatsch55]

It won't push the horns to Mach 8, bass response is not as good as the White Oaked PL's. But , what bass is there is well controlled, not mushy, crisp.

The frequency response graph says it all.

 

[laatsch55]

OK, not gonna break lightbulbs with it, but a good sounding amp, with enough ooomph to annoy the neighbors.

 

[Gepetto]

What happened this time with the B-B 134's Lee? Did they go unstable again?

 

[laatsch55]

Yes Joe, as soon as they warmed up. The first test with those in was running a freq response, halfway through they went bonkers.

 

[Gepetto]

I'd be interested in the oscillation frequency if you have a closeup photo of it Lee...

 

[laatsch55]

Joe it would oscillate at all frequencies. The sinewave looked like it was severly out of focus until the crossover point, then it skinnied up and behaved itself, then fat again as it went to negative.