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Old 6th March 2007, 07:08 AM   #1
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Default Dynaco Pas 2

Hello all,
I'm an extreme nubie when it comes to circuitry, but I am trying to make some upgrades to my already extremely modified Dyna Pas 2. The modifications were done by someone else so I canít take credit for that. However, I want to upgrade the RCA jacks and add an IEC power cord. I was wondering if any people that are familiar with this preamp could recommend some ways to reground/isolate the RCA jacks to provide better separation and imaging. Also, what should be connected to the ground prong of the IEC jack? I just donít know enough to know what would give the best results. Any details would be greatly appreciated.

Jarrett
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Old 6th March 2007, 10:59 AM   #2
1108 is offline 1108  United States
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Default Dynaco PAS

Jarrett,
Take a look at http://www.curcioaudio.com/dynadr_3.htm. You'll find everything you need for the PAS. There's a great fourm too.
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Old 6th March 2007, 11:11 AM   #3
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bad link. try this one: http://www.audioasylum.com/forums/dynaco/bbs.html
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Old 6th March 2007, 11:38 AM   #4
SY is offline SY  United States
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Actually, your question is more mechanical. The power line ground ("safety ground") needs to be securely attached to the chassis. The RCA jacks on the back, as you recognize, need to be isolated from the chassis and attached to signal ground.

Unfortunately, the way Dynaco did the back panel, you're pretty much forced to strip and remove it, then drill or mill out the holes for new isolated RCA jacks. The original Dyna ones are simply awful and ought to be crushed and burned.
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Old 6th March 2007, 11:41 PM   #5
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Quote:
Originally posted by SY
Actually, your question is more mechanical. The power line ground ("safety ground") needs to be securely attached to the chassis. The RCA jacks on the back, as you recognize, need to be isolated from the chassis and attached to signal ground.

Unfortunately, the way Dynaco did the back panel, you're pretty much forced to strip and remove it, then drill or mill out the holes for new isolated RCA jacks. The original Dyna ones are simply awful and ought to be crushed and burned.

An alternative is AVA's method. Buy a nibbling tool and cut away the portion of the back panel that holds those nasty OEM jacks. You close the rectangular opening created with a piece of FR4 substrate PCB material. The new jacks are mounted on the PCB material.

BTW, AVA does not isolate the jacks (except the phono I/P). They use the PCB laminate as a ground plane. I have experience with 2 AVA rebuilt Dyna chassis and find their method to work well.


Edit: fixed typos
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Old 7th March 2007, 01:50 AM   #6
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Eli... I would love to install new jacks and this sounds like I could do it. Do you have any more info, pics, web sites, directions. I also install a grd. lug for the turntable grd (something else that bothered me on the PAS preamps)... Hey, ANOTHER project!!
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Old 7th March 2007, 03:04 AM   #7
ArtG is offline ArtG  United States
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About a year ago, I replaced the jacks in my PAS using the techniques that Eli described. Rather than use a nibbler to enlarge the opening, I simply settled for fewer inputs. I have no need for a "tape head" input as well as a "second phono" or "microphone" input, and I doubt that today, many others do either. If the low level phono compensation components were moved from the center section of the selector switch to the board, as they are in at least some of the PAS mods, these other low level options are no longer available anyway. If you can live without all these jacks, the task will be simplified, as you will have more space and fewer wires to deal with. Now is also a good time to rewire the input wiring, which is probably a rats nest, causing crosstalk and possible other problems. Also, plan on replacing the carbon 510K (or whatever value you're using) load resistors and 10ohm ground isolation resistors with new ones. These resistors are mounted on the rear jack panel, and aren't worth the effort to save and reuse them.
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Old 7th March 2007, 04:22 AM   #8
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Thanks for the replies. I am not worried about preserving all of the inputs. I'm actually only going to save Aux 1&2 and Phono 1 so space isn't an issue. I guess what I'm still wondering is if there is a better place on the board to ground the inputs and outs (seperately) as not to have them all wired together at the jacks. Can the resistors be eliminated somehow? I'd like to clean it all up a bit.
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Old 7th March 2007, 02:13 PM   #9
ArtG is offline ArtG  United States
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You cannot delete the output loading resistors without dramatically altering the sound. In fact, these should be tailored to the input Z of your power amplifier.

You can try deleting the 10 ohm resistors, but, a friendly warning. Your posts state that you want to: 1/ add an AC ground, 2/ add a turntable ground, 3/ change the Dyna grounding scheme (which has it's drawbacks, but works pretty well). All this can lead to nasty "hum headaches", unless you know exactly what you are doing, to begin with. I think you should carefully consider your objectives before you start cutting!
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Old 7th March 2007, 06:13 PM   #10
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Ok, so I don't know what i'm doing, but my objectives are simple. (a)Eliminate Crosstalk. Crosstalk is a major problem because one of my inputs is being used for my cable box. The problem is that it is always on. I like to watch the news and listen to music, and I don't want to have to unplug the TV audio when i listen to music. It seems that imaging and stereo seperations is being effected by the crosstalk. I am new to this Pas, and it might just be an inherent problem, but the Pas's reputation lead me to believe otherwise.
(b) Upgrade the RCA jacks, my interconnectcs are not allowed to touch such nasty jacks.
(c) Allow for the use of a higher quality power cord (for quality's sake, not grounding issues) Could this cause problems?

So, crosstalk is my biggest problem. I know that a better wiring job will solve some of those problems, but i was just petitioning for advice on better isolation. I guess the 10 ohm resistors are getting replaced. While im at it I think I'll replace the .1uf's with some Auri's. But as far as further isolation of the in's/out's, I guess since i don't know much, I'll just leave them grounded the way they are.
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