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Thread: Carver C-500 - valid candidate for White Oak Audio upgrade???

  1. #21
    Forum Veteran grapplesaw's Avatar
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    Quote Originally Posted by savaden View Post
    OK, I purchased and installed the output protection relay board and after firing it up I had some hum on the right channel. . So in the process of trying to track down the source, I managed to touch something that bricked it. (DC at output) Well, not really, because I painstakingly went through all of the components and circuits trying to find a bad component, and everything looked fine. Grrr. Then I decided that I needed to figure out how the thing is supposed to work so that I could track the voltages through the driver board. (driver board had to be the culprit) I took a photo of the trace layout, flipped it and overlayed with the component layout photo. I brought those into Visio and added components and traces. You know how much a PITA it is to reverse engineer even a fairly simple circuit? Well this circuit is not all that simple... Anyway I then got a copy of LTSpice and entered the circuit from the service manual (there are two versions in the manual), then compared the actual circuit from the unit to the spice drawing. Not the same. A third version! They are all fairly similar but there are some differences mainly at the signal input and somewhat different resistor values in various places. I wanted to try to get the DC bias analysis from the spice model to figure out why I had DC at the output. I never really got that to work, partly I think because the amp uses a transient at startup to bootstrap the driver into an "on" state. That is what I think, anyway.

    Result. I gave up on the spice model but I learned a lot about the circuit in the process. Carver inverts the signal to the right channel at the input. There is an op-amp at the input to each channel (LF356) and in the manual he drives the left side into the non-inverting input and the right side into the inverting input. On my amp, it is different. He drives both on the non-inverting input. He then added another op amp with unity gain to the right channel to invert the input phase. This turned out to be the problem as that op amp must have gotten fried and was putting out about 2V DC with zero volts input. What I did for now was just to hook the right input directly to the non-inverted input op-amp and bypass the extra op-amp. That seemed to set everything straight.

    My question then is... Why did Carver invert the right channel phase? I mean he makes a big deal of it in the output connectors and in the service manual, but is it really necessary? Is this a trick to even out the power draw in the amp reducing distortion?

    Oh, and I now have driver board layouts and circuit schematics. I still have no idea how the protection circuits are supposed to work, and I don't really understand the signal flow from input to output of the driver board.

    Anyway, the beast works, and I'll probably order an RC4136N quad op-amp if they still make them. It's funny that he had used this extra quad op amp on the right side but only used one section and shorted the other three.

    Sterling
    Sterling I am glad you have it running. The carversite has the manual with schematic drawings if you go ther you can down load them. http://thecarversite.com/manuals/man...e%20manual.pdf

    To to try to answer your question on why the one inverted channel it is done to give the ability to make a bridged mono output from both channels. The two channels are in fact out of phase. The wiring on the stock binding posts reversed the pos and neg of one channel so it would deliver in phase out put. By bridging the two outputs the mono channel is created by using the two hot legs of each channel to the speakers. When in bridged mode the amp sees a load equal to 1/2 the connected speaker load. so if you have 8 ohm speaker the amp sees a 4 ohm load. This also more than doubles the output power and cuts the damaging factor in half. This bridged setup is useful to drive a sub or in a multi amp system.

    inverting the op amp on one channel is done by having the dual op setup on that one channel. Installing a Whiteoak pl14-20 board you loose this ability, how offen does one need to bridge an amp other than Perry and Me that is.

    If if you added Don's protection board as I did then you must check the path of each pos an neg input to the board from the backplane. This should reverse the binding posts from stock on one channel. Check if the binding posts are now out out of phase. With the DCP board in is imparitive that the ground and hot go through the board correctly. If you have done this correctly the binding posts will now be out of phase and this can be easily corrected by revering the positive and negative on one speaker cable. Bob jockeyed the wiring in the original to make it simple to get back in phase at the outputs.

    The last thing is the protection circuit is kind of smoke and mirrors combined with some function. This circuit is a derivative of the Pl32 board used in the d-500 phase linear. It reduces the input signal to the opamp on both channels to a point where the variance dectected is reduced back to normal range though lowering output
    with the added DCP board you have increased the safety margin to the point where I think the on board cuircuit is redundant and can be eliminated if you choose.


    Here are photos of the DCP board setup on a stock c-500 output. The board I built for my c500 is built inverted compaired to the phase 400. The c500 is shown in the top half of the two assembly pictured and the phase 400 in the lower half. This was necessary due to the outputs and inputs location being inverted on the chassis between the c500 compared to the phase 400
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    Last edited by grapplesaw; 04-27-2017 at 11:49 AM.
    try the Lightening Bolt WOPL 1000 for a hair lifting experience today

    Warning !!! Use only when you want to blown the town down

    proud father of the only WOPL Fully Comp dual 500

  2. #22
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    Thanks for the explanation. I did think about that after I posted the question, so I suppose that is the whole reason. (bridging). There are two versions of the driver board schematic in the service manual, an early and later one. Also the board layout for the early version shows hand Xed out components and jumpers. None of those match the component layout of the actual board or "engineering changes". Ha. I did install the output relay board just as you did, and it works fine. I did use a shielded cable to run the AC from the bridge rectifier over to the board. Overkill, perhaps. I also rearranged the output wires and did some other cleanup of wire routing.
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    SV

  3. #23
    Forum Veteran WOPL Sniffer's Avatar
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    Quote Originally Posted by Funky54 View Post
    Great thread. Very encouraging the many WO parts work. One of mine needs some repair.

    I'm at a loss, can somebody tell me what "vertaclly bi-amped" means???
    I had the nations problems figured out one night while on blah blah blah........ huh?

    Big amps
    Kenner Close N Play

  4. #24
    Forum Veteran grapplesaw's Avatar
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    Quote Originally Posted by WOPL Sniffer View Post
    I'm at a loss, can somebody tell me what "vertaclly bi-amped" means???
    That's when you stack two amps with one on top of the other and run the bass with one and the mid/ highs with the other and then try to tell all about it here on the forum using your phone to type without spell check turned on.

    But of coarse you need to have a working phone Perry

    I am sorry for your loss
    Last edited by grapplesaw; 04-28-2017 at 02:17 AM.
    try the Lightening Bolt WOPL 1000 for a hair lifting experience today

    Warning !!! Use only when you want to blown the town down

    proud father of the only WOPL Fully Comp dual 500

  5. #25
    Forum Veteran WOPL Sniffer's Avatar
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    Screw it
    Quote Originally Posted by grapplesaw View Post
    That's when you stack two amps with one on top of the other and run the bass with one and the mid/ highs with the other and then try to tell all about it here on the forum using your phone to type without spell check turned on.

    But of coarse you need to have a working phone Perry

    I am sorry for your loss
    Thats some funny shit there Glen.........
    I thought I was learning some new fancy processes or procedures..... damn, all i need is a brokedick phone? Hell, got that cuvered...
    I had the nations problems figured out one night while on blah blah blah........ huh?

    Big amps
    Kenner Close N Play

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