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    Lost ground on phono stage of PAS 3

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    starwatcher

    Posts : 11
    Join date : 2018-02-26

    Lost ground on phono stage of PAS 3

    Post by starwatcher on Mon Feb 26, 2018 1:32 pm

    Hello.

    I buy a PAS 3 recently and it didn't work properly because of bad contacts, i order new potentiometers a new selector switch and i remplace the RCA connectors in the back and i follow the instructions on the Curcio Audio website.

    The preamp work if i plug a CD player but only on the right channel if i plug a turntable, i see on the schematic #4 connexion on PC-6 is directly grounded via #10 but not #11 on the left channel. If i put #11 and #4 together with #10 both channels worked.

    I didn't think i made any mistake and i check the old selector still attached to the old RCA strips and both channel didn't share the same ground.

    Any advices to solve this problem.

    Best regards.
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    peterh

    Posts : 1070
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Lost ground on phono stage of PAS 3

    Post by peterh on Mon Feb 26, 2018 3:19 pm

    starwatcher wrote:Hello.

    I buy a PAS 3 recently and it didn't work properly because of bad contacts, i order new potentiometers a new selector switch and i remplace the RCA connectors in the back and i follow the instructions on the Curcio Audio website.

    The preamp work if i plug a CD player but only on the right channel if i plug a turntable, i see on the schematic #4 connexion on PC-6 is directly grounded via #10 but not #11 on the left channel. If i put #11 and #4 together with #10 both channels worked.

    I didn't think i made any mistake and i check the old selector still attached to the old RCA strips and both channel didn't share the same ground.

    Any advices to solve this problem.

    Best regards.
    As the "rebuild" has created problems, the best advice is to go back and follow the
    dýnaco pas manual exactly.

    The alternatice is to send the pas to Curcio .


    boeingpilot

    Posts : 20
    Join date : 2015-06-20
    Location : Central PA

    Re: Lost ground on phono stage of PAS 3

    Post by boeingpilot on Mon Feb 26, 2018 10:33 pm

    I did the same thing and almost had the same issue. Go slowly with the Curcio instructions. If I remember correctly, the instructions were a little confusing. I ended up comparing all the circuitry to the PAS manual and figured it out. You'll trace it. Also Joe is very good on answering questions, sonfire him and email.
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    daveshel

    Posts : 155
    Join date : 2011-11-06
    Location : Tucson AZ USA

    Re: Lost ground on phono stage of PAS 3

    Post by daveshel on Tue Feb 27, 2018 3:32 pm

    Make sure the phono grounds are tied to the other input grounds (as in the original). If you're using a ground plane circuit board for the rear panel jacks, the phono grounds may be isolated and need to be jumpered.
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    erhard-audio

    Posts : 48
    Join date : 2017-04-07
    Age : 60
    Location : Tucson, AZ

    Re: Lost ground on phono stage of PAS 3

    Post by erhard-audio on Tue Feb 27, 2018 5:17 pm

    daveshel wrote:Make sure the phono grounds are tied to the other input grounds (as in the original). If you're using a ground plane circuit board for the rear panel jacks, the phono grounds may be isolated and need to be jumpered.

    actually, I recommend to treat/keep the phono stage as a completely separate entity so to say, that is what the phono ground plane on the RCA pcb I sell is separated from the remaining RCA ground plane. This only applies to the phono input wiring. Through trial and error, I found this to be the best way. Also, use of shielded audio/mic style cable is recommended for wiring between the RCA pcb phono in and the phono preamp pcb in, but only for the phono input, the remaining connections from the RCA pcb to the selector switch can be twisted hookup wire.
    Sure, the phono preamp pcb ground and by virtue, the phono preamp in and outputs are of course connected to the main PAS ground as well, but keeping the phono inputs separate as pointed out above does give the best results. And doing it this I have never had, nor heard, of any ground loop issues.

    starwatcher

    Posts : 11
    Join date : 2018-02-26

    Re: Lost ground on phono stage of PAS 3

    Post by starwatcher on Wed Feb 28, 2018 4:03 am

    I found the answer in a sticky post.

    In an original PAS preamp, PC6 eyelet 4 and eyelet 11 have two separate connections to chassis ground,
    when I service these preamps I cut both ground wires out and run a single ground connection to eyelet 10,
    and then connect eyelet 4 and eyelt 11 together with a wire, as shown on the bottom schematic.

    Thanks.

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