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Thread: Fully Discrete 400 / 700 Driver Circuit (Full Comp Only)

  1. #1
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    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 robust. The latest power supply caps pack more Farads, so updating to more capacitance is easy in the space allotted. I've wanted to use a 400 or 700 chassis with a new driver circuit for awhile now. No output relay protection is included (yet). I'll work on that last.

    A few sample boards are being completed to test and debug the circuit. Once the bugs are worked out, I will begin the final PCB layout. I'm going to offer bare PCB's for sale, but have no intention of offering "stuffed" PCB's. This is only a hobby for me and not my main source of income.

    The design is based on currently available transistors that should be easy to source for the near future. Due to the design, a wide variety of transistors can be used with slight variance in performance.

    With the exception of using a 400 or 700 power supply and chassis, the "new amp" will not be a Phase Linear.

    Click image for larger version. 

Name:	Phase Linear 400-700 PLX_New Driver Board_Initial Design_v1.1_071417.jpg 
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Name:	Phase Linear 700 PLX_New Driver Design_Output Section_v1.1_071417.jpg 
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  2. #2
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    Halfbiass...Electron Herder and Backass Woof
    Will it still have the Phase Linear "sound"??
    taking something that's already good, and making it better...........and for the knowing smiles that cross their faces.......Nando-2011...

    "Silence cannot be Misquoted"--Lazarus Short-2012 "

    " I Just Collect Smiles Craig......Cheap Smiles!-----Fishoz-2017

    "anything can be done, it's finding the easiest way that's hard"-----Bobbysdad--2014

    " Synth percussion is deadly to children, house pets and shitty power supplies"---Stephen Evans 2014

    " You have not reached the point of diminishing returns, you've just ran out of money

    " The Pioneer U-24, unfortunately, is just too expensive and rare to find. That's why I have one."--Nando-2014

  3. #3
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    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 distortion will be low, but we all know that that doesn't really mean anything when it comes to personal preference and listening. We all hear in a different manner.

    In my opinion, a few items that define the "Phase Linear" sound are;
    1. Class B output biasing
    2. Triple output stage configuration
    3. High voltage (compared to other amps in the early 70's) unregulated power supply
    4. And finally, to some extent, the front-end driver circuitry


    The Phase Linear output stage (either quasi or full comp) is the easiest part of the amp to modify for best performance. If configured properly, the quasi-comp can offer good performance (as we Phase Linear lovers all know), but a full comp output stage is so easy to implement today there is no reason to not make the conversion. My ears appear to be extremely sensitive to crossover distortion, so I prefer Class A amps or Class B amps that are properly designed and biased.

    If you build the circuit and it is too "sterile", I suppose you could always bias (true Class B) the output stage similar to a standard Phase Linear 400 or 700. It's all part of the fun.

  4. #4
    Forum Veteran Northwinds's Avatar
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    I am pretty sure Joe addressed all those issues with the White Oak line of componentry, are you offering something better??? It would have to be damn good to even touch a FC WOPL
    "I really can't begin to describe what happens at that frequency when you hit that SPL, but it's serious. We saw a mouse stagger out of a crack in the concrete floor and die"
    Quote Originally Posted by laatsch55 View Post
    Yweblwrs...
    Quote Originally Posted by skynyrd77
    The only toilet I have seen that didnt swirl was in a trailor
    Quote Originally Posted by TheWOPLwhiffer View Post
    now I need a Dim Bulb Tester to test my Dim Bulb Tester
    An audiophile is someone who's stereo is worth more than his car

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    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 the end, when the PCB is available and you want to try it, great. If not, I'll still be tinkering with different designs and offering them to DIYer's.

  6. #6
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    Do you treat feedback differently in this design??
    taking something that's already good, and making it better...........and for the knowing smiles that cross their faces.......Nando-2011...

    "Silence cannot be Misquoted"--Lazarus Short-2012 "

    " I Just Collect Smiles Craig......Cheap Smiles!-----Fishoz-2017

    "anything can be done, it's finding the easiest way that's hard"-----Bobbysdad--2014

    " Synth percussion is deadly to children, house pets and shitty power supplies"---Stephen Evans 2014

    " You have not reached the point of diminishing returns, you've just ran out of money

    " The Pioneer U-24, unfortunately, is just too expensive and rare to find. That's why I have one."--Nando-2014

  7. #7
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    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, minimal global feedback is needed. I prefer to keep a design a simple as possible and not use esoteric type designs. I also like the amp to be easily serviced, if needed.

    In the design I posted, the input stage is degenerated to improve linearity and slew rate. The VAS stage is isolated from the input stage via an emitter follower which also increases linearity. The feedback capacitor (Cdom) across the emitter follower/VAS is the only cap needed for stability (usually). The triple OPS lightly loads the VAS, which also increases linearity. In the end, you only need a moderate amount of global feedback to reduce distortion.

    Audio amp design used to be a considered a "black art", but with people willing to share knowledge such as Self, Slone and Cordell (and others) amp design has been broken down to a systematic approach. If you follow their design methodology, it is very easy to design a reliable, stable excellent sounding amplifier. A lot of design derivations are possible with great performance. It just depends on the individual and how the amp will be used.

    Don't get me wrong, low noise and distortion is not everything. I still design and build (low power) Class A tube amps! If it amplifies, I will more than likely be intrigued by it.

  8. #8
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    Halfbiass...Electron Herder and Backass Woof
    Have you played with a good mosfet, high powered design?
    taking something that's already good, and making it better...........and for the knowing smiles that cross their faces.......Nando-2011...

    "Silence cannot be Misquoted"--Lazarus Short-2012 "

    " I Just Collect Smiles Craig......Cheap Smiles!-----Fishoz-2017

    "anything can be done, it's finding the easiest way that's hard"-----Bobbysdad--2014

    " Synth percussion is deadly to children, house pets and shitty power supplies"---Stephen Evans 2014

    " You have not reached the point of diminishing returns, you've just ran out of money

    " The Pioneer U-24, unfortunately, is just too expensive and rare to find. That's why I have one."--Nando-2014

  9. #9
    Forum Veteran Northwinds's Avatar
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    Quote Originally Posted by THD+N View Post
    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 the end, when the PCB is available and you want to try it, great. If not, I'll still be tinkering with different designs and offering them to DIYer's.
    I would give it a whirl, is it a drop in replacement or is a major overhaul needed with an already made WOPL (out of curiosity)
    "I really can't begin to describe what happens at that frequency when you hit that SPL, but it's serious. We saw a mouse stagger out of a crack in the concrete floor and die"
    Quote Originally Posted by laatsch55 View Post
    Yweblwrs...
    Quote Originally Posted by skynyrd77
    The only toilet I have seen that didnt swirl was in a trailor
    Quote Originally Posted by TheWOPLwhiffer View Post
    now I need a Dim Bulb Tester to test my Dim Bulb Tester
    An audiophile is someone who's stereo is worth more than his car

  10. #10
    New Around These Parts krellmk's Avatar
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    Are you satisfied with the life you're living

    Leach super amp

    Isn't this design similar to the Leach Super amp and the Low tim amp?

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