Gibsonian's Cherry Pl 700 Ser I, soon to be a PLWO-1000

Old School

I have the old style, the one that pops you in the forehead when you lean in and press the button just as the solder begins to liquify. This one is better and I think they sell replacement tips. When my tip is used up, I will be buying one of these.

Mark
 
Got the solder sucker fixed. Had some solder chunks under the intake reed valve. Populating a Rev "C" board tonight.
 
Made a little progress...
 

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At least I'm not "Accross the Water"..... Where's my solder gun....
 
Lee, I have been checking bias on the Rev C boards the old fashioned way, across R38 and R39. Have you used the Bias test points on the Rev C board? I wonder where the other probe goes because the prints only show the connection on the board as it runs off to 10L and 10R. These are the striped wires that come off the board to the transistor totem pole. The other side of the bias resistors can be found on the 3-terminal strip or eventually at the outputs. I just wonder what your preference is, to be consistent and stuff.

Mark
 
mlucitt said:
Lee, I have been checking bias on the Rev C boards the old fashioned way, across R38 and R39. Have you used the Bias test points on the Rev C board? I wonder where the other probe goes because the prints only show the connection on the board as it runs off to 10L and 10R. These are the striped wires that come off the board to the transistor totem pole. The other side of the bias resistors can be found on the 3-terminal strip or eventually at the outputs. I just wonder what your preference is, to be consistent and stuff.

Mark
Click to expand...

I use a gator clip and connect the other probe directly on the outputs on the back. (that right?) I think it is...
 
Setting the Bias on the PL14_20 Board
Initial setting of the amplifier bias is a very simple procedure with the White Oak Audio PL14_20 board assembly. The bias is not all that critical and will drift around somewhat as the amp warms up. Do not be concerned that the setting is rock solid. It is a feedback control system using Q6 as a thermal sensor in the board circuit. As the amp warms up it is natural to have some movement in the bias voltage setting by design. The final bias setting you are working to achieve is between 0.300V and 0.400V. Most Phase Linear users find a setting near 0.350 – 0.380V close to ideal.

  1. Ensure the amp is powered off.
  2. All measurements will be taken with NO inputs connected to any source and NO outputs connected to any speakers.
  3. Open the top cover to expose the top edge of the PL14_20 PCB. Be careful not to drop any hardware down into the amplifier enclosure.
  4. Turn both bias pots located on the top edge of the board assembly fully counter-clockwise (minimum bias setting). These pots are labeled Left Bias Adjust and Right Bias Adjust.
  5. Attach your DVM positive test clip to the left channel bias setting test point. It is located in the upper left corner of the PL14_20 PCB and is marked Bias - L.

  6. Attach your DVM negative test clip to the LEFT channel WHITE speaker output binding post.
Left_Channel_Bias_Adjustment.jpg

  1. Power up the amp and allow it to warm up and stabilize for approximately 5 minutes
  2. Adjust the Left Bias Adjust pot to achieve a bias setting between 0.300 and 0.400V. Most Phase Linear users find a setting near 0.350 – 0.380V close to ideal.
  3. Carefully move and attach your DVM positive test clip to the right channel bias setting test point. It is located in the upper center of the PL14_20 PCB and is marked Bias - R. This test point is located just to the right of the upper mounting nut holding the board into the chassis.

  4. Attach your DVM negative test clip to the RIGHT channel RED speaker output binding post.
Right_Channel_Bias_Adjustment.jpg

  1. Adjust the Right Bias Adjust pot to achieve a bias setting between 0.300 and 0.400V. Most Phase Linear users find a setting near 0.350 – 0.380V close to ideal.
  2. Power down the amp.
  3. Remove test leads from the DVM.
  4. Reinstall the amplifier top cover. Be careful not to drop any hardware down into the amplifier enclosure.
Bias setting complete.
 
Joe, Thanks for the detailed explanation, just what I was looking for. You might have posted it before, but the cold weather has frozen my brain. I would ask, what about shorting the inputs? The guys over at Hafler say to short the inputs to prevent any spurious signals on the front end. I wonder because I do have a pair of RCA shorting plugs.

Thanks,
Mark
 
That will do no harm Mark, nor will it really do any good :-) The bias circuit is quite independent of input signal, it floats at the virtual ground established/controlled by the front end op amp.
 
The procedure is now in the PLWO Hints and Archive section on the forum.
 
Hi Mark
Did I forget to tell you guys about the magic coil? I thought that I did. :-)

Really it is the vestige of the old ground wire that connects to pin 5 of the original board after I rewire the grounds to the White Oak prescription.

I try to leave "go back to original" hooks in place for experimentation purposes.
 
Mark, it depends, if the output is handy i'll use the new hooks, if not i'll do the each side of R39 thing. No difference in readings.
 
BTW-- Ed had to call me about the bypass cap discussion. The factory bypass caps on the backwall were pro-active anti-oscillation caps, not to clean up the signal.That might be where we are getting some of that enhanced crossover notch.
 
Cathy now sports a new Rev "C" board. The AP is warming up....
 

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Test time is sooooo coooool.
 

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