The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Dynaco VTA tube amp kits, all Tubes4hifi.com products and all Dynakitparts.com products


    PAS back panel rewire

    Share

    PeterCapo

    Posts : 380
    Join date : 2008-12-05

    PAS back panel rewire

    Post by PeterCapo on Wed Jun 09, 2010 11:29 pm

    Trying to head into the home stretch of my PAS rebuild and am stuck. I have done a fair amount of reading online about hum problems in the PAS, even after some corrective measures have been taken. I am trying to think of some proactive, preemptive measures before I finish the rebuild.

    In particular, I am doing the new wiring for the rear panel I/O. For the L/R pre-out main connections, some have made twisted pairs of wires, with one wire grounded to the I/O ground on one end and to ground on PC5, either eyelet 8 or eyelet 1, on the other end. The signal wire then goes from pre-out main to eyelets 7 and 14 for left and right channel, respectively.

    Here's the thing. Because of the difference in location of ground eyelets 1 and 8 vs. signal eyelets 7 and 14, the signal wire is not shielded through its entire run. For the last leg of the run, the signal wire is unshielded, more so to the right channel than the left.

    I am thinking of making a THREE wire twisted trio, one signal, the second connected to ground at the outputs and at eyelet 8 on PC5, and the third grounded only at one end (at the outputs on the back panel) but wrapped around the signal wire throughout its entire length.

    Would this three-wire twist introduce too much capacitance and roll off the high end vs. a two-wire twist?

    I also have large 1uF caps (K40Y-9) mounted in approximately the same positions the original smaller 1uF electrolytics were mounted (vicinity of the right/left channel bass and treble pots). Should I wrap a ground wire around the caps and their leads, as well? The reason why I am thinking of doing this is because of their proximity, especially the one for the right channel, to the power switch. Many posts online seem to complain of greater hum in the right channel of the PAS than the left.

    What do you think?

    howardnair

    Posts : 21
    Join date : 2010-05-31

    Re: PAS back panel rewire

    Post by howardnair on Wed Jun 16, 2010 7:44 am

    peter--it may be a little late with this reply--if you look in the curcio switch rewire instructions--from I/O BOARD preamp out to pc5 the right channel is a twisted pair of wires with the hot one going to 14 and the ground to 8 and the left channel twisted wires with hot to 7 and ground to 8 instead of the single wire to eyelet 1 from connected grounds on the i/o board--howie

    PeterCapo

    Posts : 380
    Join date : 2008-12-05

    Re: PAS back panel rewire

    Post by PeterCapo on Wed Jun 16, 2010 8:40 pm

    Thanks for writing. I must be getting senile... yes, I intended to say eyelet 8 (not eyelet 1) for the ground connections to PC-5. The twisted pair is only twisted to a certain point when connecting the grounds to eyelet 8. The ground wire veers away from the signal wire, leaving the signal wire to finish its run to eyelets 7 and 14 respectively - especially 14 - unshielded. I am thinking of running the twisted pair with the shield wrapped around the signal wire all the way to eyelets 7 ad 14, with enough extra ground wire to then run it straight back to eyelet 8.

    howardnair

    Posts : 21
    Join date : 2010-05-31

    Re: PAS back panel rewire

    Post by howardnair on Wed Jun 16, 2010 9:43 pm

    hey peter--i am not a expert but having put several pas's together -3 the old way with grnd only to 1 i have never experienced a hum issue--so what you are suggesting should work quite well--if you ping??? GP49- he is more than knowledgable and very helpful so is ray mottram--the only issues that i have had were crosstalk --which there seems to be no cure--i even ran all i/o to switch wires in shielded with shield cut at one end -i also ran shielded wire from tape switch to selector and from i/o out to 14 and 7 on pc5 still crosstalk --i just finished a pas2 with pc boards ,cap board and I/O board from ray mottram--nice everything--he was very helpful--have fun howie

    jerdobi

    Posts : 6
    Join date : 2010-05-30

    PAS 3 connector strip rewiring and hum

    Post by jerdobi on Sun Jun 20, 2010 7:41 pm

    I created me a new output connector strip and had the hum problem after the new selector switch and connector strip. Finally, I solved the constant hum problem after the rewire. You can look at my post on "Fixed Hum : Dynaco PAS 3 using shielded cable to the RCA outputs" for the details. Basically, follow the PAS 3 wiring pictorial exactly, don't ground to eyelet 8, use the resistors to the output jacks per systematics and SHIELD the cables to eyelet 7 and 14.

    howardnair

    Posts : 21
    Join date : 2010-05-31

    Re: PAS back panel rewire

    Post by howardnair on Mon Jun 21, 2010 8:28 am

    peter-as of this am--i have ray mottrams i/o board on my pas2-ray has only 7 rca's instead of 9 -more room on i/o board-the preamp out and the phono have totally separate grounding's from the other 5-i used no resisitors on the i/o board- from my preamp out to pc5 i used the twisted pair scenario with ground to 8--and then from the separate ground rail for the other inputs except phono-i ran 1 wire to chassis-this worked well with this particular scenario using rays board---if you are using a original pas i/o setup or similar then you may want to use jerdobi and gp 49 suggestions-which i have done on other pas's-the shielded wire is a good idea--howie

    PeterCapo

    Posts : 380
    Join date : 2008-12-05

    Re: PAS back panel rewire

    Post by PeterCapo on Mon Jun 21, 2010 10:48 am

    Coincidentally, I also made an I/O PCB similar to jerdobi’s. I will be using twisted wire pairs for shielding and I will be following what I believe to be the original Dynaco grounding scheme as closely as possible. I’m in the home stretch now, but it could still take me several weeks to finish assembly. I hope to report back when I am done. I will be using the PAS as a line stage only, so PC-6 is not connected.

    PeterCapo

    Posts : 380
    Join date : 2008-12-05

    Re: PAS back panel rewire

    Post by PeterCapo on Mon Jun 21, 2010 10:50 am

    Although I will try connecting the grounds on PC-5 to eyelet 8 first.

    Sponsored content

    Re: PAS back panel rewire

    Post by Sponsored content Today at 6:07 am


      Current date/time is Thu Sep 29, 2016 6:07 am