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    PAS 3 Selector switch

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    michael heit

    Posts : 3
    Join date : 2018-04-13

    PAS 3 Selector switch

    Post by michael heit on Tue May 15, 2018 12:42 pm

    HI All
    I am somewhat a newbi and I hope my question does not ruffle any one.
    I own a PAS that I was gifted sometime in the 1980's.
    I have used it everyday ever since with my ST 70. Also from that time.
    My question or really request is that I want to rewire the selector switch so was to transfer the two low level inputs to regular line level and leave the phono as the only low level input.

    My switch works ok so a change is not necessary at this time.
    I know about the questionable RIAA response etc.
    That is all ok with me right now.
    I have some experience with electronics. When I first got the PAS I had to get another choke from Stereo Cost Cutters. I also just switched out the PC-6 phono board as the original just met it's end.
    Any help with how to rewire the switch or directions to others who have done this would be much appreciated.

    btw I have followed Bob Latino and his advice a long time as a lurker. Especially for refreshing my St 70 and adding diodes and cap changes etc.

    sincerely
    michael heit
    Very Happy
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    peterh

    Posts : 985
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: PAS 3 Selector switch

    Post by peterh on Tue May 15, 2018 1:11 pm

    michael heit wrote:HI All
    I am somewhat a newbi and I hope my question does not ruffle any one.
    I own a PAS that I was gifted sometime in the 1980's.
    I have used it everyday ever since with my ST 70. Also from that time.
    My question or really request is that I want to rewire the selector switch so was to transfer the two low level inputs to regular line level and leave the phono as the only low level input.

    My switch works ok so a change is not necessary at this time.
    I know about the questionable RIAA response etc.
    That is all ok with me right now.
    I have some experience with electronics. When I first got the PAS I had to get another choke from  Stereo Cost Cutters. I also just switched out the PC-6 phono board as the original just met it's end.
    Any help with how to rewire the switch or directions to others who have done this would be much appreciated.

    btw I have followed Bob Latino and his advice a long time as a lurker. Especially for refreshing my St 70 and adding diodes and cap changes etc.

    sincerely
    michael heit
    :D  

    You "think" you know about "the questionable riaa" ??
    Read http://www.audioregenesis.com/PAS_Phono.pdf , forget the misconceptions some ( desk pilots ) have.

    About rewiring the low level tape and "special" inputs, yes it's certenly
    possible to rewire, but i think you are on your own here. I have read
    about changing them to additional phone inputs, but not changing them to
    bypass the riaa part.
    avatar
    Bob Latino
    Admin

    Posts : 2673
    Join date : 2008-11-26
    Location : Massachusetts

    Re: PAS 3 Selector switch

    Post by Bob Latino on Tue May 15, 2018 1:14 pm

    michael heit wrote:HI All
    I am somewhat a newbi and I hope my question does not ruffle any one.
    I own a PAS that I was gifted sometime in the 1980's.
    I have used it everyday ever since with my ST 70. Also from that time.
    My question or really request is that I want to rewire the selector switch so was to transfer the two low level inputs to regular line level and leave the phono as the only low level input.

    My switch works ok so a change is not necessary at this time.
    I know about the questionable RIAA response etc.
    That is all ok with me right now.
    I have some experience with electronics. When I first got the PAS I had to get another choke from  Stereo Cost Cutters. I also just switched out the PC-6 phono board as the original just met it's end.
    Any help with how to rewire the switch or directions to others who have done this would be much appreciated.

    btw I have followed Bob Latino and his advice a long time as a lurker. Especially for refreshing my St 70 and adding diodes and cap changes etc.

    sincerely
    michael heit
    Very Happy  

    Hi Michael,

    As peterh has said > I believe you can rewire the "Special" input on a PAS preamp for a "crystal or ceramic cartridge" which would in effect be another high level input. There are instructions on page 12 of the PAS-3 manual on how to do this ? If I am wrong, maybe someone who has done this can comment on the possibility of doing this .. Link to PAS-3 manual below ..

    Dynaco PAS-3 manual

    Bob

    michael heit

    Posts : 3
    Join date : 2018-04-13

    Re: PAS 3 Selector switch

    Post by michael heit on Tue May 15, 2018 1:55 pm

    Hi
    Thanks for getting to my question so quickly.
    The reason I wrote this is because I saw a post in another forum (audiocircle) where a poster in 2008 did a total rebuild and and replating of a pas3.
    In the post he specifically mentioned that he rewired the selector to have only one phono to the PC6 board and that he somehow rerouted the remaining special and tape head to provide line level inputs.
    I reached out to the forum and attempted to pick his brain. I did know that i was several years after the original post.
    Well several members of the forum informed me that the poster had passed away.

    I was very sorry. I must have seemed totally insensitive.
    No other posters took up the issue their.
    My only hope would be here.
    I will keep on trying
    I will take a look at page 12 thanks Bob.
    btw Has anyone ever put a diode in a PAS and have they also replaced those big green caps the selenium wafers sit on.
    finally: I have soldered and changed parts for years but I am like a trained monkey who can solder without cold joints. I wish I knew how the amp works and how it all flows. (cant get my head around negative feedback and testing for negative voltage in the bias circuit ). Anyway Has anyone ever taught the theory and practical aspects of the Dyna amps, like an "intro to ST70" night school class.

    Sincerely
    michael heit
    avatar
    Peter W.

    Posts : 831
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: PAS 3 Selector switch

    Post by Peter W. on Tue May 15, 2018 2:46 pm

    A few things:

    a) Bob is correct, each input may be wired for a number of purposes. Careful reading of Page 12, and some understanding of the relevant circuitry is necessary to get it right, however. But, I have done this. My present example has one (1) Phono input, and the rest are line-level, with the the tape-monitor switch still useful as I do run audio tape, both reel and cassette.

    b) I have entirely replaced both the B+ and bias power-supplies on my unit, and included a separate fuse - not present in the OEM. Here is a link to another unit with the same board - that also eliminates the 12X4 thereby reducing load on the transformer.

    http://usr.audioasylum.com/images/y2011/09/51512/2011_0905preamp0002.JPG    

    c) The RIAA Curves and NAB curves for the PAS3 are just fine. Within the claimed deviation, or a little bit better. Not worse.

    d) If you have the X-version (where the tone controls null at center) do not be tempted to remove the controls. There is no need. Repeat, there is no need. To that end, even in the non-X versions, the tone controls can be very nearly nulled out such that leaving them in place is OK. Note that that same group that feels that this is a poor RIAA performer is the same ones that tend to yank the tone controls.

    e) Some of the earlier of these devices will mismatch to some solid-state amps. There is a mod for this that should be done in any case (if necessary - most are already this way). in any case - from Dynaco:  

    1. Obtain two 100,000 ohm, 1/2-watt 10% tolerance resistors.
    2. Unsolder and discard the two 510,000 ohm (green-brown-yellow)
    resistors connected to the audio-output sockets on the back panel of
    the preamplifier and replace them with the 100,000 ohm resistors.
    Solder all connections.
    3. Snip out and discard the two 62,000 ohm (blue-red-orange) resistors
    on the PC-5 circuit board adjacent to eyelets 8 & 18. This completes
    the modification. Side-bar: Use 5% resistors. They are cheap.

    Above all, enjoy it!

    michael heit

    Posts : 3
    Join date : 2018-04-13

    Re: PAS 3 Selector switch

    Post by michael heit on Tue May 15, 2018 4:55 pm

    thanks Peter
    I have no desire to take out the tone knobs. Every room is different and all need a little tweeking to sound good. Also I just like to play with bass and treble.
    I also think the RIAA is fine. All those claiming otherwise must likely had older units with dried up caps.
    finally is there a link to your wiring of the selector switch.
    You have exactly what I am hoping to do.
    One phone and all the rest line level.
    I dont mind using the existing switch. (it is still working fine)

    again thanks
    michael

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