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    Restoring Heavily Modded PAS 2 so it can be used

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    thinker1920

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    Restoring Heavily Modded PAS 2 so it can be used

    Post by thinker1920 on Thu Apr 04, 2013 8:59 pm

    Hi Everybody,

    I got this PAS 2 from a friend and it was really altered and it's not working right. The one channel is just hum with nothing of the source, and the other channel is the source but it fades in and out. I'm thinking that the only way to fix it is to take everything off the boards and start fresh. I was looking at board layouts and the original manual but, there's a bunch of stuff I would like to remove from the original circuit, the loudness, filter, and tone controls. I did see Pyre posted a layout that eliminated a lot of stuff and was wondering if that's the way I should go.

    I'm going to try adding pics to show you what shape it's in.








    hawaii.ken

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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by hawaii.ken on Thu Apr 04, 2013 9:30 pm

    affraid The word frankenstein comes to mind!

    GP49

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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by GP49 on Fri Apr 05, 2013 2:47 am

    A bare chassis is what you REALLY need to start over from!

    Bob Latino
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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by Bob Latino on Fri Apr 05, 2013 7:45 am

    Seeing as how it was rewired together, I don't wonder that this PAS preamp is not working correctly. I agree with both Ken and GP49 ... The best thing that you can do is remove everything and start over ... IMHO the place to start is to check out the Tubes4hifi link for the Dynaco PAS preamp mods at the link below ...

    Dynaco PAS preamp parts and mods

    Bob

    tubes4hifi
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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by tubes4hifi on Fri Apr 05, 2013 2:16 pm

    I agree with GP49 and Bob, rip out EVERYTHING and start fresh! See my post on PAS3 rebuild. Do it right and do it much better than original!

    DarthBubba

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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by DarthBubba on Fri Apr 05, 2013 4:34 pm

    thinker1920 wrote:Hi Everybody,

    I got this PAS 2 from a friend and it was really altered and it's not working right.

    He was not your friend. No

    I see a hodge-podge of ideas that make sense individually, strung together with little understanding of how a working system is not just a bunch of parts that happen to be connected together electrically.

    Carefully unsolder or snip apart the components for possible re-use, strip the chassis to just the metal, RCA jacks on the back, volume control, and MAYBE the selector switch, and then follow Master Latino's advice and get some properly designed circuit cards from knowledgeable sources.

    Then beautiful music will fill your ears and warm your heart. Invite your friend over for music and wine to show him how skillfully executed, well-designed equipment can truly sound. cheers If your friend says anything starting with, "Now what you need to do is..." give him more wine until he falls asleep, then load him in a wheel barrow and take him to his home. Handcuff him to the doorknob so he can't wander off into traffic. drunken Be the better friend. king

    thinker1920

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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by thinker1920 on Fri Apr 05, 2013 11:05 pm

    I stripped down the line stage board and using Pyre's diagram re-stuffed it.



    I'm spending as little as possible, the parts were $28 and I was able to use some of the extra resistors to start on the phono board. I'm saving my pennies to build a really nice preamp based on the Marantz 7. I just want something for the meantime and I love a project.

    thinker1920

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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by thinker1920 on Sat Apr 06, 2013 3:48 am

    I've been going over the phono stage and I don't know which output goes to the line stage. The schematic is hard to read, I want to say it's eyelet 2 & 8 but that's just a stab in the dark.

    DarthBubba

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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by DarthBubba on Sun Apr 07, 2013 12:57 am

    thinker1920 wrote:I've been going over the phono stage and I don't know which output goes to the line stage. The schematic is hard to read, I want to say it's eyelet 2 & 8 but that's just a stab in the dark.

    Eyelets 1 (Right channel) and 7 (Left channel) are the phono board outputs.

    thinker1920

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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by thinker1920 on Sun Apr 07, 2013 1:47 am

    Thank You!!! Very Happy

    thinker1920

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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by thinker1920 on Sun Apr 07, 2013 6:11 pm

    Does anyone know what the voltage is at eyelet 16 on PC 5 and what it is on PC 6?

    tubes4hifi
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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by tubes4hifi on Sun Apr 07, 2013 6:37 pm

    refer back to the sticky note on the PAS3 board layout and schematics. PC5-16 goes to 330v and PC-16 goes to 210v.

    thinker1920

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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by thinker1920 on Sun Apr 07, 2013 7:42 pm

    Thank you Smile

    thinker1920

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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by thinker1920 on Sun Apr 07, 2013 9:13 pm

    I was going over the circuit and I don't understand the purpose of the circled area, could this be removed? I know there was some kind of "special feature" that involved a mic and was wondering if that is what this part was meant for?



    DarthBubba

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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by DarthBubba on Sun Apr 07, 2013 9:34 pm

    thinker1920 wrote:I was going over the circuit and I don't understand the purpose of the circled area, could this be removed? I know there was some kind of "special feature" that involved a mic and was wondering if that is what this part was meant for?



    That's the RIAA phono network. Removing that ends your preamp's phono/vinyl record playback career. It also is involved with tape playback via the components on the switch wafer "SSB" & "SSC." There also are RIAA component changes that need to be addressed to bring the PAS RIAA de-emphasis curve into alignment with the real world. This is findable at Curcio's web site www.curcioaudio.com as "Dynaco PAS 2, 3 & 3X Phono Board RIAA EQ Modification". It's a downloadable pdf.


    thinker1920

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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by thinker1920 on Sun Apr 07, 2013 9:44 pm

    Thanks, bookmarked that....... I'm trying to reuse the Russian pio's I have and I have two rated at 250v and two at 500v should I use the 500v or save them and use the 250v ones?

    DarthBubba

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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by DarthBubba on Mon Apr 08, 2013 12:08 am

    thinker1920 wrote:Thanks, bookmarked that....... I'm trying to reuse the Russian pio's I have and I have two rated at 250v and two at 500v should I use the 500v or save them and use the 250v ones?

    What's the capacitance value for each voltage range? .1uF? .22uF?

    thinker1920

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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by thinker1920 on Mon Apr 08, 2013 2:40 am

    .1 uF.... also wanted to ask about the differences between the diagram in the sticky on this forum and the pdf you recommended, which one should I follow? the pdf says to bypass two of the .1 uF caps and the sticky still has them in place, the pdf says 2.0 meg resistor, the sticky a 2.2 meg. Sorry to be a pain, and thank you for your help.

    DarthBubba

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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by DarthBubba on Mon Apr 08, 2013 4:27 pm

    thinker1920 wrote:.1 uF.... also wanted to ask about the differences between the diagram in the sticky on this forum and the pdf you recommended, which one should I follow? the pdf says to bypass two of the .1 uF caps and the sticky still has them in place, the pdf says 2.0 meg resistor, the sticky a 2.2 meg. Sorry to be a pain, and thank you for your help.

    Oh, and it gets much worse my friend!

    Depending on whom you read, some of the modders say to replace the plain-wire-bypassed cap with a bigger cap!

    My take is: the fewer parts in the signal path, the better. So, measure the voltage at eyelet 3 (R-Ch) and eyelet 9 (L-Ch). If there's no DC voltage there on your DVM's most sensitive level (and DO start at it's highest voltage range then step down, please affraid ) I'd say just jumper it out. If there IS voltage DC voltage there, keep the cap. The answer about what to do with your spare Russian PIOs also is answered - put the 500v one between each eyelet and the tube that "feeds" it; the other between eyelets 3 & 5 (R-Ch) and between eyelets 7 & 9 (L-Ch). BTW, if you have the Black Cat capacitors that came with the board originally - you may want to save you Russian PIOs for something else. The Black Cat branded caps are PIO also, just American made.

    2.2meg vs 2meg is inconsequential. Use the quietest ones, or the two that match the best.

    I also differ with the usual RIAA mod instructions at this step: Replace the 68pF cap with the 750pF cap you removed from the selector switch. 750pF is closer to the correct value than 820pF. The math says so. So does E.E. Professor Stanley Lipschitz, AES member who presented the corrected RIAA network at the AES convention in 1976, or so. People use 820 because 750pF isn't a standard value.

    thinker1920

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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by thinker1920 on Tue Apr 09, 2013 2:50 am

    put it all back together and the heaters aren't turning on Razz everything seems to be connected properly and I used my meter to make sure the connections are good. What's the voltage going to them suppose to be?

    thinker1920

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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by thinker1920 on Tue Apr 09, 2013 5:01 am

    my heater transformer that came with it has to be wired in parallel not series, I did a little tweaking and it worked. problem now is the power supply is out of wack, instead of 330 for PC 5 and 210 for PC 6 I have 317 and 316 Razz I hooked up headphone to the output and ran my computer into it and it sounds great but, I know I have to fix the voltages Razz The only thing I can think of is that the transformer I have puts out 350 volts AC a leg and I think the original only did 330 volts a leg Sad I might have to cave and buy a board Razz

    thinker1920

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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by thinker1920 on Tue Apr 09, 2013 5:28 am

    current pics








    Sorry they're side ways photobucket's being stupid Razz

    DarthBubba

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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by DarthBubba on Tue Apr 09, 2013 12:18 pm

    thinker1920 wrote:my heater transformer that came with it has to be wired in parallel not series, I did a little tweaking and it worked. problem now is the power supply is out of wack, instead of 330 for PC 5 and 210 for PC 6 I have 317 and 316 Razz I hooked up headphone to the output and ran my computer into it and it sounds great but, I know I have to fix the voltages Razz The only thing I can think of is that the transformer I have puts out 350 volts AC a leg and I think the original only did 330 volts a leg Sad I might have to cave and buy a board Razz

    Look carefully at the power supply schematic. The voltage dividing network branches to supply the two boards at one point and resistor values change. Did you follow them carefully?

    thinker1920

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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by thinker1920 on Tue Apr 09, 2013 12:59 pm

    I just looked at the resistors again think I got 10 ohms instead of 10 K ohms Embarassed I feel stupid Razz

    thinker1920

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    Re: Restoring Heavily Modded PAS 2 so it can be used

    Post by thinker1920 on Tue Apr 09, 2013 1:05 pm

    I'm still surprised that PC 5 is suppose to be fed 330 volts seems high.

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