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    Ground connections for PAS-2 selector switch and input/output connectors

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    maninmac771

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    Join date : 2011-03-07

    Ground connections for PAS-2 selector switch and input/output connectors

    Post by maninmac771 on Sun Jan 08, 2012 3:08 am

    Finally decided to go ahead with the replacement of my PAS-2's 3-wafer selector switch and the antiquated input/output connectors board. While familiarising myself with the wire connections for these two components before starting the actual replacement job, I need to seek help from you guys before proceeding:

    1. I'm going to replace the existing aged input/output connectors board with a DIY board stuffed with 18 (i.e. 9 pairs, same as the existing board) female RCA connector jacks. Since each RCA jack has its own +ve and -ve(Gnd)terminals, do I have to connect all the ground terminals of each channel with bare (or insulated) wires the way similar to those on the old board?

    2. There used to have connection from the selector switch to the L & R ground terminals next to socket #1 of the input/output connectors board - from lug #3 of wafers A & C of selector switch. When this old switch is replaced by a new 2-pole 6-position switch, where should these ground connections go? Or are they no long required for the new switch?

    Thanks.


    tubes4hifi
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    Re: Ground connections for PAS-2 selector switch and input/output connectors

    Post by tubes4hifi on Sun Jan 08, 2012 3:48 am

    1 - all the ground terminals should be tied together, easiest to do with 22 or 24g solid wire, then connect to circuit board ground.
    2 - probably not needed, as long as the grounds are connected as #1
    the way I wire up a PAS3 is to use tightly twisted pairs, with signal and ground connected on the RCA jacks, no connection needed on the selector end, the twisted pair gives SOME extra shielding, certainly better than the way it was done originally. All ground connections are to the common ground buss on the RCA connectors

    maninmac771

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    Join date : 2011-03-07

    Re: Ground connections for PAS-2 selector switch and input/output connectors

    Post by maninmac771 on Sun Jan 22, 2012 3:21 am

    Thanks tubes4hifi for the info. I've been away for a while and haven't got started with the replacement/connection. But before doing, I realise I have to seek further help as follows:

    1) I've done a I/O board with 7 pairs of RCA connectors (same configuration as that shown in your thread above) and it doesn't have the embedded common ground buss. Therefore, I guess I have to link all the grounds of the RCA connectors with solid wire and connect to the circuit board ground. I have some left over of 18awg and 20awg wires. Can I use them in place of 22/24awg? Where is the circuit board ground? Is it the eyelet #1 or #8 of circuit board PC-5?

    2) On the original I/O connector board, there are 2 510K-ohm resistors connected to the Audio Ouput connectors and 2 10-ohm resistors connected to the Tape-In/Tape-Out connectors, as shown in the picture below



    These resistors do not apperar in the up-graded I/O connector in your thread. Are they no longer needed after up-grading the I/O board and the selector switch? Or is there other modification to the circuit board that results in discarding these resistors?

    Thanks in anticipation of your help.

    tubes4hifi
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    Re: Ground connections for PAS-2 selector switch and input/output connectors

    Post by tubes4hifi on Sun Jan 22, 2012 2:53 pm

    you can use 18g or 20g wire, you'll just need more heat, and I'd not recommend 18g solid wire, or you'll need alot of heat AND alot of solder.
    I use 20g solid wire for ground busses only, 22g or 24g stranded wire for everything else. Stranded wire gives a MUCH better solder connection. Note that the phono ground is NOT tied to chassis ground, only to the ground on the phono circuit.
    The 10 ohm resistors on the original are tied to ground, some people prefer that slight isolation between circuit ground and chassis ground.
    The 510K resistors are basically circuit pulldowns, they weren't included on the original design PCBs by Dyna but are already on all the preamp circuits that I sell as upgrades. So reinstall them if you still have original Dyna boards.

    maninmac771

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    Join date : 2011-03-07

    Re: Ground connections for PAS-2 selector switch and input/output connectors

    Post by maninmac771 on Mon Jan 23, 2012 9:38 pm

    Thanks tubes4hifi. Would like to make sure about the followings:

    1) the tied grounds of the RCA connectors, except that for Phono, are to be connected, NOT to the circuit board PC-5 ground at either eyelet #1 or #8, but to the chassis ground which as far as I know is either one of the ground lugs of the quad cap or the lug by the 12X7's mounting socket;

    2) the left & right phono grounds are to be connected to eyelets #11 and #4 respectively on phono board PC-6; and

    3) the 10-ohm resistors can be discarded when a new I/O connector board and selector switch without the Tape-In/Tape-Out are used.

    Thanks again.

    tubes4hifi
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    Re: Ground connections for PAS-2 selector switch and input/output connectors

    Post by tubes4hifi on Mon Jan 23, 2012 10:36 pm

    maninmac
    yes, yes, and yes! easy!

    maninmac771

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    Join date : 2011-03-07

    Re: Ground connections for PAS-2 selector switch and input/output connectors

    Post by maninmac771 on Tue Jan 24, 2012 2:50 am

    Thanks. Much appreciated.

    KelleyMc

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    Join date : 2012-03-09

    Do you really connect all RCA grounds?

    Post by KelleyMc on Fri Mar 09, 2012 6:41 pm

    I also have a new input/output board that is unlike the original, that is, each RCA jack has a hot terminal and a ground. Is it really necessary to connect the grounds of all 18 of the RCA jacks with 20 gauge wire? Also, if the grounds are all connected, is there then just one wire connecting them to the chassis ground? This seems awkward, that's why I'm trying to clarify.

    tubes4hifi
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    Re: Ground connections for PAS-2 selector switch and input/output connectors

    Post by tubes4hifi on Fri Mar 09, 2012 6:54 pm

    take a piece of 20 or 22g solid copper wire and connect all the RCA grounds together, then ONE ground wire to power supply ground.
    see attached photo of a different preamp, but same concept. The PHONO input should be isolated, and it's ground only connected to the phono board ground.


    KelleyMc

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    Join date : 2012-03-09

    Re: Ground connections for PAS-2 selector switch and input/output connectors

    Post by KelleyMc on Fri Mar 09, 2012 7:21 pm

    Thanks a lot! This is very helpful. One other small detail: Do I still need to connect the black wires in the twisted red/black and green/black pairs to the I/O board? If I don't need to connect them, are they even needed at all>

    KelleyMc

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    Join date : 2012-03-09

    Re: Ground connections for PAS-2 selector switch and input/output connectors

    Post by KelleyMc on Sat Mar 10, 2012 4:12 pm

    So, just to be absolutely clear:

    You recommend connecting each "hot" RCA input to a each single switch terminal using two wires (red and black) instead of just one (red). The black wires are not connected to the ground busses on the RCA inputs as in other wiring schemes because the ground is taken care of by the solid copper wire and single wire to power supply ground. The solid copper wire is not connected directly to the power supply ground, but rather is connected via an insulated wire.


    maninmac771

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    Join date : 2011-03-07

    Re: Ground connections for PAS-2 selector switch and input/output connectors

    Post by maninmac771 on Sat Mar 10, 2012 8:55 pm

    Pic below shows what I've done to replace the aged RCA I/O connectors board. Due to the space between L/R connectors, I've used separate solid wires for the ground terminals of each channel. The two wires are joined together and then connected by an insulated wire which is connected to the ground terminal under the chasis beside the tube socket of 12X7. The grounds of L/R channel of the Phono input are connected to the phono board. Everything works fine except I still hear some hum with my ears close to the speakers. Guess I'll have to live with it for now until I can find out how to totally eliminate this.


    maninmac771

    Posts : 30
    Join date : 2011-03-07

    Re: Ground connections for PAS-2 selector switch and input/output connectors

    Post by maninmac771 on Sat Mar 10, 2012 9:06 pm

    Pic below shows completed connection of I/O connectors with the 2-pole 6-position selector switch and the phono board. I used red/green twisted pair of insulated wires (red for R channel and green for L channel). Hope this can give a rough idea.


    KelleyMc

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    Join date : 2012-03-09

    Re: Ground connections for PAS-2 selector switch and input/output connectors

    Post by KelleyMc on Sun Mar 11, 2012 1:01 pm

    So, based on your photos, it seems I need to connect only one wire from each input to each switch terminal. Also, I notice that the two connections from the PC6 board to the switch are composed of a twisted pair, but the black wires are only connected to the PC6 board, not to a switch terminal. I assume the black wires in this case are serving as insulating grounds.

    Another small detail. You have only seven pairs of RCA I/O jacks on your unit, while I have nine. Since I won't be using two of these pairs - FM-MPX and Spare - should I not connect the ground busses of these two pairs to the ground busses of the other pairs with the solid copper wire? (It might not matter, I just want to make sure I'm grounding this thing in the best way).

    maninmac771

    Posts : 30
    Join date : 2011-03-07

    Re: Ground connections for PAS-2 selector switch and input/output connectors

    Post by maninmac771 on Mon Mar 12, 2012 4:03 pm

    Connect the wires of the L & R channels of each inputs to the respective terminals of the selector switch. Check out this link for more info on the connection www.tubes4hifi.com/selector.htm. As for the black wires of the connections from PC6 board being only wrapped around the red wires and not connected to the switch, I don't know if they serve as insulating ground. I've done it by referring th the "Selector Switch Replacement Installaltion & Wiring Manual" (sections E3, 11 & 12) in the following link www.dynaco-doctor.com/PAS%20SSW%20SUPPLIMENT.pdf.

    As for the ground connection of the unused RCA I/O jacks, I don't know if there'll be any difference if they are connnected to the common ground buss or not, because I'm not that knowledgeable about electronics. However, to play safe, I'd incline not to connect.

    KelleyMc

    Posts : 5
    Join date : 2012-03-09

    Re: Ground connections for PAS-2 selector switch and input/output connectors

    Post by KelleyMc on Mon Mar 12, 2012 5:19 pm

    Thanks! Much appreciated. I actually have the two docs you reference, but it helps to just have someone confirm that Dynaco Doctor instructions are still valid even though the ground is handled differently (copper wire across busses to chassis).

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