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Roy Mottram
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    Removing PAS-3X Tone Control.

    Tiziano73
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    • Post n°1

    Removing PAS-3X Tone Control. Empty Removing PAS-3X Tone Control.

    Post by Tiziano73 Sun Feb 03, 2013 1:05 pm

    Hi to everybody.

    I did try to make Curcio Audio PAS-3X Tone Control removal but something seems to not be ok.
    Joe Curcio say to begin with the Left Channel and connect a jumper from terminal 4 to terminal 6 on the foil
    side of PC-5, then connect another wire jumper from terminal 6 to terminal 7 of PC-5. De-solder the wire connected to terminal 3. You will find that it is connected to
    the center lug of the Left Treble Control and once desoldered from PC-5 terminal 3, you may cut it at the connection to the Left Treble control.
    Next we will make the same changes to the Right Channel.

    Now if you follow this modifications on the PAS schematics:

    https://i.servimg.com/u/f10/17/84/41/68/scherm13.jpg

    The red line is that Curcio say. As you can see the DC component go to the output with a 47K resistor. It's all right?!?!
    What do you think about?
    Regards.

    Tiziano
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    Roy Mottram
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    • Post n°2

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    Post by Roy Mottram Tue Feb 05, 2013 10:16 pm

    you are correct, the cathode voltage is going thru the 47K to the output. It's probably got a couple volts on it.
    Here is the way I would do it - cut each of the wires on the tone controls, and remove them.
    Then jumper eyelet 6 to 7, and 13 to 14. You're done. And BTW, you don't need those 510K resistors across the output jacks!
    This schematic is also easier to read . . .

    Removing PAS-3X Tone Control. PAS-PC5-sch
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    • Post n°3

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    Post by Guest Wed Feb 06, 2013 2:51 pm

    .


    Last edited by PeterCapo on Wed Dec 02, 2020 3:54 pm; edited 1 time in total
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    • Post n°4

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    Post by Roy Mottram Wed Feb 06, 2013 4:50 pm

    you've still got C4 (and C12) blocking the DC from the output, and this value should be fine for most people, but it could be made larger if you need freq response below 20Hz. Of course on any 30-50 year old PAS3 I'd be replacing ALL of the capacitors!!
    C5 needs to remain in the circuit for loop feedback.
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    • Post n°5

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    Post by Guest Wed Feb 06, 2013 5:19 pm

    .


    Last edited by PeterCapo on Wed Dec 02, 2020 3:54 pm; edited 1 time in total
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    • Post n°6

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    Post by Roy Mottram Wed Feb 06, 2013 8:29 pm

    I realize that schematic is drawn the same as the one in the PAS-3X manual, but as far as I know
    (someone who actually has a PAS-3X correct me please) the circuit actually works as I've redrawn it.
    So C5 is in circuit as is part of the loop feedback.
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    • Post n°7

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    Post by Tiziano73 Thu Feb 07, 2013 3:13 am

    Probably I think to understand what Peter want say. I modified tubes4hifi schematics with original Dynaco Pot control.
    With that PAS pot (the original ones) in center position, C5 and C12 are short circuit and C7 and C14 too is paralleled with the 1uF cap.

    https://i.servimg.com/u/f10/17/84/41/68/pas-pc11.jpg

    So the output coupling cap for each channel is Cout= https://i.servimg.com/u/f10/17/84/41/68/formul10.png

    Isn't it?

    Tiziano


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    • Post n°8

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    Post by Guest Thu Feb 07, 2013 12:55 pm

    .


    Last edited by PeterCapo on Wed Dec 02, 2020 3:54 pm; edited 3 times in total
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    • Post n°9

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    Post by Roy Mottram Thu Feb 07, 2013 1:25 pm

    those plots are pretty ugly, with the original circuits the PAS3 MUST see a 100K load.
    I guess that's why some people MUST have tone controls, to try to fix a bad circuit and incompatible amplifier load.
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    • Post n°10

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    Post by Guest Thu Feb 07, 2013 2:07 pm

    .


    Last edited by PeterCapo on Wed Dec 02, 2020 3:54 pm; edited 2 times in total
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    • Post n°11

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    Post by Tiziano73 Fri Feb 08, 2013 4:24 am

    Whith all yours considerations I believe that the fastest and less invasive way ro retain original Hafler project without the tone controls (minimalist approach) is:

    1) disconnect the center lug and Short circuit the two external lugs of Bass Control then connect one of them to terminal 6.
    2) disconnect the center lug of Treble Control.
    3) Make the same modification to the other channel.

    In this way the Ctot that the 47K resistor can see between it self and the amplifier output is C7+1uF and there is no direct connection for DC component with the output stage. I want remember that stock MKIII and ST-70 are direct coupled to the input (there isn't a capacitor on tube imput grid).

    https://i.servimg.com/u/f10/17/84/41/68/pas-pc12.jpg

    Tiziano
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    • Post n°12

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    Post by peterh Fri Feb 08, 2013 5:28 am

    Tiziano73 wrote:Whith all yours considerations I believe that the fastest and less invasive way ro retain original Hafler project without the tone controls (minimalist approach) is:

    1) disconnect the center lug and Short circuit the two external lugs of Bass Control then connect one of them to terminal 6.
    2) disconnect the center lug of Treble Control.
    3) Make the same modification to the other channel.

    In this way the Ctot that the 47K resistor can see between it self and the amplifier output is C7+1uF and there is no direct connection for DC component with the output stage. I want remember that stock MKIII and ST-70 are direct coupled to the input (there isn't a capacitor on tube imput grid).

    https://i.servimg.com/u/f10/17/84/41/68/pas-pc12.jpg

    Tiziano
    Thanks for the re-drawn cirquit, much clearer now.

    I wonder however, would'nt this be equivalent with
    a pas3x with tone ccontrols centered ? Or do i misread
    the schematic ?

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    • Post n°13

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    Post by Tiziano73 Fri Feb 08, 2013 9:52 am

    I believe that is the way to exlude tone control by the cirtcuit.
    PAS manual say that in flat position tone control are trasparent.

    In this way the joint in circuit is not the crawling contact of the pot but a solder connection.

    Isn't it?

    Tiziano
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    • Post n°14

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    Post by GP49 Fri Feb 08, 2013 11:31 am

    tubes4hifi wrote:those plots are pretty ugly, with the original circuits the PAS3 MUST see a 100K load.
    I guess that's why some people MUST have tone controls, to try to fix a bad circuit and incompatible amplifier load.


    No, a lot of people must have tone controls because not all recordings are perfect. A lot of them sound better with tonal corrections.

    I do not listen only to audiophile records.
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    • Post n°15

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    Post by Guest Fri Feb 08, 2013 5:05 pm

    .


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    • Post n°16

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    Post by Pillo69 Fri Feb 08, 2013 7:22 pm

    GP49 wrote:
    tubes4hifi wrote:those plots are pretty ugly, with the original circuits the PAS3 MUST see a 100K load.
    I guess that's why some people MUST have tone controls, to try to fix a bad circuit and incompatible amplifier load.


    No, a lot of people must have tone controls because not all recordings are perfect. A lot of them sound better with tonal corrections.

    I do not listen only to audiophile records.

    +10
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    • Post n°17

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    Post by Tiziano73 Sat Feb 09, 2013 5:20 am

    Peter, i believe your schematic is the correct solution to the post:

    Removing PAS-3X Tone Control.

    It has been a pleasure.

    Tiziano

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    • Post n°18

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    Post by tonebells Tue Jul 23, 2013 8:39 pm

    tubes4hifi wrote:you are correct, the cathode voltage is going thru the 47K to the output.  It's probably got a couple volts on it.
    Here is the way I would do it - cut each of the wires on the tone controls, and remove them.
    Then jumper eyelet 6 to 7, and 13 to 14.   You're done.  And BTW, you don't need those 510K resistors across the output jacks!
    This schematic is also easier to read . . .

    Removing PAS-3X Tone Control. PAS-PC5-sch

    I did the bypass as above and had to much bass. I add the jumpers from 4 to 6 and 11 to 13 and it flattened right out.
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    • Post n°19

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    Post by tonebells Wed Jul 24, 2013 9:12 pm

    Here is what I ended up with.
    PAS-PC5sch
    I put the 510K resistors back as well.
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