Kevin's Hafler p-500

[kevin]

Good Morning Mark. Just sitting here at work this morn with nutton to do and thought Id ask about the tank. Not in any hurry what so ever but just wondering if you had a chance to look at it. By the way I am so happy with the PL.... Man.... after living with it for a while it is so clean and strong. I have never seen it even start to get hot. Thanks man.... Yell when you can !!!

 

[laatsch55]

Jeez, if it's not getting hot, you are not PUSHING it!!

 

[kevin]

Well..... I got one hell of a fan on the back of it. It gets real warm. Ive been pretty easy on it, trying not to drive it hard for over 30 min at a time. Id feel REAL BAD if I tore it up. Without a boubt its the best ive ever had... Let me ask this.... IF it overheats will it shut off till it cools then come back on ? I know ive done the haflers that way in the past.

 

[laatsch55]

Yep, and Mark has done a worse case test on this, was runnin g his 700 at +2-3db and left the fan off. The theremodisc's did their job.

 

[kevin]

Ok.. Thats good to know.

 

[speakerman1]

I have owned a lot of DH series components. How does the professional compare with them?

Larry

 

[ksrigg]

I think the P series has variable gain and lights indicating clipping. Beyond that, I'm not sure. Mark would be the expert here..

 

[kevin]

Yea... What Sutton said.

 

[mlucitt]

The P series amps have a servo board that allows bridging and indicators for "Signal" "Clipping" and a pair of volume controls. The other Hafler amps I am familiar with: DH-200, DH-220, DH-500 are just amps and have no volume controls or fancy lights. The "amp" part of the P-500 is the same as the DH-500. Nice and solid, but not as crisp as the Phase Linear equivalent amps, in my opinion. The P series is good for professional sound reinforcement (stage amps).

 

[mlucitt]

Back to the beginning of this thread. The PL amps will shut down when they get hot. It is a gentle shutdown, they pull the 120 AC and the DC collapses quickly because the amp is driving pretty hard.

The potential problem is when the thermo-switch(es) cool off sufficiently the amp will turn back on. If you do not reduce the input or lower the volume control, watch out. There is a real potential for blown speakers because the input has been banging into the front end of the amp. When the drivers and power output transistors get that surge of DC, the amp will be straight out and the speakers are at rest with no signal when all of a sudden - bang!

I'm just sayin'

 

[mlucitt]

Lee,
The Hafler has me cornered. One channel (left) is just fine. The other channel (Right) is severely distorted and only shows a bit of positive going waveform. I have attached a shot of the o'scope view. I tried to put the input signal right on the main board inputs to bypass the volume pots and some of the "signal present"/"clipping" circuitry, no change. The main board has good power at the B+ and the B- terminals and the feedback fuse is good.

The reason I am questioning this is because the Hafler MOSFETs are pretty robust and have diode protection. I have never seen blown outputs.

I would be open to suggestions before I change out the outputs. They are very expensive. Can I pull the outputs and look for a clean signal going to the MOSFETs from the predrivers? Funny how the resistors from the drivers to the MOSFETs on the N-channel are 470 Ohms and the resistors on the P-channel are 220 Ohms.

The view below shows the input signal on the bottom (1X about .5 volt) and the output in the middle (10X about 10 volts).

 

[laatsch55]

Should be able to scope the predrivers without pulling the outputs. I have a book here, let me research this a little.

 

[Gepetto]

Do you have Schems Mark?

 

[mlucitt]

Yes, I have the schematic in front of me. I could not break out the schematic from the PDF document, it is on page 20.

 

[Gepetto]

Do you have an amplified, composite signal on either side of R33 on the board labeled RIGHT CHANNEL on page 21 of the schematic. You should have a clean, class AB output signal driving the gates of the MOSFETs present at this point.

BTW, what an awful schematic.

 

[laatsch55]

What's the DC component of that output signal Mark??

 

[laatsch55]

Joe, on that schematic are PC21 R & L DC protects?? Actually they look more like current limiters.


Also, a lot of familiar numbers in the front end.

 

[Gepetto]

No they are some form of LED indication, suspect they are clip indicators or something of that sort. Not really familiar with this amp.

 

[Gepetto]

Upper right corner section of main schematic is DC protect Lee.

 

[laatsch55]

The IC107's, finally read the circuit descriptions. Jeez.