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  1. Replies
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    I have long suspected that the bias circuit on...

    I have long suspected that the bias circuit on the 400 / 500 / 700 was too sensitive. A small change to the bias circuit confirmed this. See revised schematic for changes.

    Adding RNew (27 Ohms)...
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    Audio Control used the 4136 extensively in their...

    Audio Control used the 4136 extensively in their early car audio products in the mid 80's and after. Their products were not what I would call "inexpensive", but they did develop a cult following...
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    Let's do it. How do I pay.

    Let's do it. How do I pay.
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    There is a free basic box program called Win ISD....

    There is a free basic box program called Win ISD. It works good for box alignments. Check it out.

    http://www.linearteam.dk/default.aspx?pageid=winisd
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    WTB - PL 400 Parts

    What is the going rate for a 400 power transformer and one Dixon meter?
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    The sound improvement will probably not be as...

    The sound improvement will probably not be as incredible as you might think. Certainly not worth $5. If 100 people answered your question, you would get 100 different answers.

    My advice is to not...
  7. Thread: PL D500

    by THD+N
    Replies
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    603

    More re-drawn D500 schematics. I'm working on the...

    More re-drawn D500 schematics. I'm working on the rest of the LED meter(s) and control section next. I can't believe PL (attempted to) squeeze the entire schematic on one lousy page and made the...
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    This is a full comp amp, so it uses MJ15024 and...

    This is a full comp amp, so it uses MJ15024 and MJ15025's. A quasi comp would use all MJ15024's. I have a lot of these MJ150xx types and I don't run my amps hard so they are fine for me. The MJ21xxx...
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    In stock configuration this may be a true...

    In stock configuration this may be a true statement. It depends on your listening habits. When I first acquired my pair of 1974 La Scala's, I was listening to a pair of Heresy's (1977). The La...
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    Images showing how to reconfigure pre-driver and...

    Images showing how to reconfigure pre-driver and driver resistors and head sinks used on VAS transistor.

    300323003330034
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    400 / 700 Modifications (Full Comp Only)

    I have been experimenting with some easy modifications on the PL36 driver board. My main interest has been to modify the pre-driver and driver circuit to reduce crossover distortion that, in my...
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    With a 48dB/octave slope, you can cross over a...

    With a 48dB/octave slope, you can cross over a speaker right up or down, to its limits, without damage. Al K. knows his stuff.

    Although nowadays with access to good laptop based hardware and...
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    The C-500 is a nice amp (I have 2 of them). Build...

    The C-500 is a nice amp (I have 2 of them). Build quality of the C-500 is just as good as the PL gear. It is very similar to a PL 400. The C-500 puts out a little more power than the 400 and has 8...
  14. My intention is to make the new PCB the same...

    My intention is to make the new PCB the same dimensions as the original PL36 board with connections at the bottom. The only modification will be to the 150 Ohm pre-driver and 10 Ohm driver resistors....
  15. The Leach DB design used stacked output...

    The Leach DB design used stacked output transistors to increase power output. The "stacking" (a variation of cascoding) also allowed the use of transistors with a lower voltage rating.

    However,...
  16. Each stage (input stage, VAS stage and output...

    Each stage (input stage, VAS stage and output stage) is optimized / linearized with local feedback (degeneration), then global feedback is used. Since each stage is operating in a very linear manner,...
  17. Joe's design and my design are totally different....

    Joe's design and my design are totally different. Joe's design is similar to the original PL circuit. Mine is not.

    My design offering is not meant to be a "competition", it's an alternative. In...
  18. Probable not. It may be better. It may not be....

    Probable not. It may be better. It may not be. From a technical standpoint the design will address distortion mechanisms that have been identified and documented (Cordell, Self and Slone). Noise and...
  19. Thread: PL D500

    by THD+N
    Replies
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    603

    Here are some parts of the D500 schematic that I...

    Here are some parts of the D500 schematic that I re-drew awhile back. The original is too small to easily follow. I'm slowly working on (re-drawing) the rest of the circuitry.

    296212962229623
  20. Fully Discrete 400 / 700 Driver Circuit (Full Comp Only)

    I have finally had a chance to design a new driver circuit for the 400 and 700. The 400 and 700 make excellent project amps because of the way the chassis is laid out and the power transformers are...
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    I have access to about 100 of the 3439 as well as...

    I have access to about 100 of the 3439 as well as the 3440/5415/16. NOS, not clones or junk. About $1.00USD a piece.
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    Here is the schematic of the famed 80's Class A...

    Here is the schematic of the famed 80's Class A amp. I drew the schematic in Orcad, next I'll start on the PCB layout.
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    I did the layout and a Chinese associate got one...

    I did the layout and a Chinese associate got one of his vendors to make the boards in Asia.
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    75317530

    75317530
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    Series II 400 / 700 PL36 PCB

    If anybody needs a PL36 driver board for a PL Series II 400 / 700 I have a few extra that I can let go for cheap. I needed a driver board for a 700II that I was restoring and I had some made. These...
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