David's Phase Linear 700B Thread

[Phase Linear Phanatic]

Should I also mention that as soon as power hits the amp, the amps lights turn on and the meter swings 1/4 of the way to the right, then back into its sitting position, then you can hear Don's relays click after that? Is this an indication of something?

 

[laatsch55]

Take any other amp you have, hook it up to the speakers, leave the RCA jacks empty, hum now??

 

[laatsch55]

Should I also mention that as soon as power hits the amp, the amps lights turn on and the meter swings 1/4 of the way to the right, then back into its sitting position, then you can hear Don's relays click after that? Is this an indication of something?

Yes, standard reaction of the meters responding to the chaotic environment present until the front diff amp takes control. NORMAL.....

 

[Phase Linear Phanatic]

Take any other amp you have, hook it up to the speakers, leave the RCA jacks empty, hum now??

One moment while I do this..........................................

 

[Phase Linear Phanatic]

Current situation: I plugged in the spare PL 700B. (the 700 watt R.M.S. version I use as the spare with the white LED's pictured below just now). Put it in place with NO RCA's connected. Turned on the power center with the amp being the only thing plugged in. NO HUM! No meter dancing either. Just a small turn off thump ten seconds later. Unlike the other two B's which don't do that. (That's normal though. This is the oldest B I have with the oldest design and components. And original factory parts. The other two have been later designs and/or white oaked). So no worry about that issue.

But Hmmmmm..........something happended in shipping then????

 

[laatsch55]

Is the normal/direct coupling swith in normal??

 

[Phase Linear Phanatic]

Is the normal/direct coupling swith in normal??

That was a good question asked by Jerry during a PM. He had it in direct/coupled when I received it. So I switched it to normal. And NO. It makes no difference.

What If I had semi-bad fuses?..............................................................

 

[laatsch55]

Did you switch it where you were listening to the hum?? I'm asking to see if there was any perceptible change at all. Without a pre-amp plugged in and on or shorting plugs in the RCA's no matter which amp I had it sounded horrible.

 

[laatsch55]

Ya know it could be as simple as a wire hanging from the volume pots to close to the wires on the bottom of the amp. Yeah it gets that silly. And can be just as hair pulling as anything can be.

 

[Phase Linear Phanatic]

Did you switch it where you were listening to the hum?? I'm asking to see if there was any perceptible change at all. Without a pre-amp plugged in and on or shorting plugs in the RCA's no matter which amp I had it sounded horrible.

See that's the thing. That's not the case here. I can unplug pre-amps, take out RCA's, and unplug all devices, and switch the switch both ways and the hum only exists as long as the amp is on. Take out the amp and put another in its place, with NO pre-amp, NO RCA's and NO other eqt. hooked up, (same scenario) and NO HUM. It's gotta be the amp. Jerry and I discussed the option of sending it back once I got Doug's meter, and he would install the new meter while trying to figure out the issue. He was reasonable on the shipping charges too. But we also discussed talking to you and Joe to see if it could have been ANYTHING but the amp. It's not looking too bright in that department today. Now that we have eliminated a LOT of potentials here. And luckily I have a spare amp just sitting around. That's helped a lot. But I am becoming saddened that I may have to send it back somewhere and get another pair of eyes on it. Internally, a lot has been done here. New 21196's, resistors, DCP board, Caps, rectifier, RCA inputs, driver board, LED board, soon to be new meter, new 0db switch, and on and on. I've gone so far. I just wanna get this thing right.

 

[Phase Linear Phanatic]

Ya know it could be as simple as a wire hanging from the volume pots to close to the wires on the bottom of the amp. Yeah it gets that silly. And can be just as hair pulling as anything can be.

Yeah, that's why I think the next best step is to wait till I get the meter. THEN I will pull the amp back out of the system and open her up. While in there for the meter; I will look around for the wires you are talking about. I will use some canned air just to be sure nothing is in there. And put it back together. At that point, if BOTH meters swing now, and I still get hum, then it's a safe bet I need it re-examined. We shall discuss that next weekend when I get back to this project. For now.......I guess I'll lay low.

 

[Phase Linear Phanatic]

I did not switch the switch while listening to the hum. The PL manual seems to advise against doing that. I turned the amp off before I switched it both ways and back again. Either way, same result. HUM. And I could not tell a difference in more or less hum. Besides..that stack is on one side of the room and the huge speakers 30 ft away on the other. It's not audible to me unless I get 15 feet away. Even if it was, the phase linear fan drowns it out, and on top of that I can't hear it when the volume goes up. As the hum does not increase with the volume. It's just a standard annoying 60HZ hum.

 

[laatsch55]

We understand that, it's also not a cut and dried procedure. It amounts to a process of elimination.

 

[jbeckva]

You have an AC voltmeter, correct? With the RCA's unplugged and with the level controls at minimum, measure AC across the speaker outputs please. Do that with and without the speakers connected.

 

[Phase Linear Phanatic]

You have an AC voltmeter, correct? With the RCA's unplugged and with the level controls at minimum, measure AC across the speaker outputs please. Do that with and without the speakers connected.

YES. Finally! I grabbed it from my parents house a few weeks ago. As many recall, I didn't have it here to do the initial tests pre-white oak. How about that Lee? I'm two for two today!

Okay. I tested ALL three, just to be sure. My results:

-White Oak PL 700B
L channel~ 9.4mv R channel~ 6.2mv /without speakers
L channel~ 7.6mv R channel~ 10.0mv /with speakers

-International PL 700B
L channel~ 38.6mv R channel~ 7.7mv /without speakers
L channel~ 39.3mv R channel~ 6.9mv /with speakers

-PL 700B (700 watt R.M.S.) version
L channel~ 40.4mv R channel~ 52.5mv /without speakers
L channel~ 38.8mv R channel~ 50.0mv /with speakers

I know we are talking mv here, but why so much difference? Even between left and right speaker? I did not take any tests with the phase linear fan plugged in. I can do that too if you like?

 

[laatsch55]

What you are measuring without speakers is DC offset. An artifact of matching the input diff pair. Factory said do something when DC offset got to 75mv. Anything under 15 is excellent. I've had some come in at .002, and.003, but that took some work.

 

[Phase Linear Phanatic]

What you are measuring without speakers is DC offset. An artifact of matching the input diff pair. Factory said do something when DC offset got to 75mv. Anything under 15 is excellent. I've had some come in at .002, and.003, but that took some work.

Then It looks like I am A-okay here? I guess that's what Jerry was wanting to know. If I was pushing some crazy DC out or something? But look at my measurements on the white oak? Hmmmmmm now compared to the FACTORY components in the other two; what does that tell you?

 

[laatsch55]

Well I'm about a dumbf^%$. Try it in DC mode. Jwer was looking to see if the hum was measuable..

 

[jbeckva]

Well I'm about a dumbf^%$. Try it in DC mode. Jwer was looking to see if the hum was measuable..

Gotta ask.. was that AC? THAT is what I was asking for.

Lee it should have been measurable. If it's 60hz, then why was the non WO HIGHER than the WO??

 

[Gepetto]

Are the transformer bolts loose? Common issue after so many years.