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    Volume Control on PAS 2,...at 1 o'clock it starts getting loud

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    8xlaxx

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    Join date : 2016-12-10

    Re: Volume Control on PAS 2,...at 1 o'clock it starts getting loud

    Post by 8xlaxx on Thu Dec 15, 2016 8:48 pm

    Thank you for walking me through all this.  

    Again, I am not wanting to do any mods to this little PAS 2 if I can help it.  I just want it to perform as a stock unit would/should,... less the volume control 'issue' which to me, seems like it came this way given the posts I have read.

    Once all the wiring is marked and the said resistors and capacitor legs are desoldered from the stock volume pot, can I re-attach them to the new pot copying the previous stock wiring or should all the resistors and caps be re-soldered to the new PCB board?  I did purchase the 250K pot off of eBay from seller 'lasercollection'.

    Also, is the attenuator already built in to the new volume controller or is this something separate that needs to be purchased and wired into the unit?

    There seems to be a separate section on the board that has 250K printed on it which I am confused about. Again, thank you for the assistance. 

    Finally, GP49,...thank you for the lead on the 250K pot.  Please check your Inbox, PM sent.

    8xlaxx

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    Re: Volume Control on PAS 2,...at 1 o'clock it starts getting loud

    Post by 8xlaxx on Thu Dec 15, 2016 8:55 pm

    FWIW and confirmed,... tubesnirvana does not have the 250K with loudness tap,....ONLY the 100K with loudness tap.

    Just posting for those that are searching and have similar needs.

    GP49

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    Re: Volume Control on PAS 2,...at 1 o'clock it starts getting loud

    Post by GP49 on Fri Dec 16, 2016 12:42 am

    The EBay seller "lasercollection" which is the seller where I got my attenuator, no longer has the 250K with loudness tap and board.  The item number, now expired, was 201655037416.

    But I'd watch his listings, as he only puts a certain number up for sale, sells through them (I checked yesterday, he still had one), and then usually restocks and relists with a new item number.  This may be to conform with EBay rules which restrict "permanent" listings of items.

    8xlaxx, you have a PM.
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    peterh

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    Location : gothenburg, sweden

    Re: Volume Control on PAS 2,...at 1 o'clock it starts getting loud

    Post by peterh on Sat Dec 17, 2016 4:35 am

    For an in-depth discussion of the influsnce of the volume pot, se george rennenkamps
    excellent analysis at http://www.audioregenesis.com/

    8xlaxx

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    Join date : 2016-12-10

    Re: Volume Control on PAS 2,...at 1 o'clock it starts getting loud

    Post by 8xlaxx on Sat Dec 17, 2016 10:31 am

    A common modification involves replacing the 250K volume potentiometer with a modern, higher quality one, at 100K. How will
    this affect the phono response? Well, assuming the blend switch has not been bypassed (deleting the 47K series resistor), and
    the balance pot. remains unchanged, then the phono stage would see a load of about 135K. That would be approximately the
    same as applying a load of 330K at the tape out jacks of the stock circuit. You'd probably be down about half of a dB at 30Hz, and
    perhaps 1dB at 20Hz. Would you hear that? Probably not, as long as you don't connect anything to the tape out jacks.


    I noted this part especially.  Thank you for the post.
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    Pillo69

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    Location : Granada (España)

    Re: Volume Control on PAS 2,...at 1 o'clock it starts getting loud

    Post by Pillo69 on Mon Dec 19, 2016 4:32 pm

    The modification of the volume potentiometer influences the design of the Phono pre-stage ?.
    With a phono stage with Cathode Follower has the same response to a 100k potentiometer ?.
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    peterh

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    Re: Volume Control on PAS 2,...at 1 o'clock it starts getting loud

    Post by peterh on Mon Dec 19, 2016 6:25 pm

    Pillo69 wrote:The modification of the volume potentiometer influences the design of the Phono pre-stage ?.
    With a phono stage with Cathode Follower has the same response to a 100k potentiometer ?.

    Yes on both accounts.
    The phono stage is loaded by the volume pot and some more things. Changing a 250k
    pot to a 100k pot will load the phono much more. It's still within working range but
    it cannot stand much load from something plugged into "tape out" any more.
    This is what rennenkamp documented in the linked document above.

    A phonostage with a buffer( cathode follower or other type of buffer) won't be
    affected so much. But the PAS lacks buffers both at the phono stage and at the output stage. ( that would have been 2 more tubes and double the B+ power).
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    Pillo69

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    Re: Volume Control on PAS 2,...at 1 o'clock it starts getting loud

    Post by Pillo69 on Mon Dec 19, 2016 8:24 pm

    Thank you Peterh.

    I have the PAS power supply in separate chassis, with 3 amps for signal valve filaments and 1.5 amps for rectifying valve (EZ81).
    The power of B+ in transformers of 50 mA.

    Now I'm doing a Phono preamp with two ECC88 per channel (cathode follower). That's why my previous question.


    8xlaxx

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    Join date : 2016-12-10

    Re: Volume Control on PAS 2,...at 1 o'clock it starts getting loud

    Post by 8xlaxx on Wed Jan 18, 2017 11:25 pm

    Reviving this thread,...

    Finally received the 250k pot from Hong Kong.  Seems to be a nice part and the board has ALPS stamped on it, probably a copy or variant of some sort.

    Anyway, I lengthened the wires to accommodate the new attentuator.  I have been reading through this thread here:

    http://dynacotubeaudio.forumotion.com/t2931-user-report-dact-type-21-stepped-attenuator-250k-for-tube-amp?highlight=DACT

    Question(s):
    The diameter of the hole in the chassis and faceplate is indeed larger than the diameter of the attentuator shaft.  It does work but the shaft will need to be lined up fairly precisely.  I want to avoid the possibility of attentuator shifting.  In the linked thread, it was suggested to use a lock washer to prevent slippage of the attenuator while in service.  

    1) Where should the lockwasher be inserted?  I am thinking that it would possibly need to be installed directly against the faceplate (under the stock volume knob) but I might be wrong.  It would be nice to find a matching nut to secure the attenuator to the chassis then use another for the faceplate but unfortunately it only came with one nut and a single flat washer (as pictured in the linked thread).  

    This seems to be a special type of nut and not readily available at the local hardware store.  

    2) Does anyone have a practical suggestion for the proper fit of this attenuator?

    Thank you for the assistance.

    8xlaxx

    Posts : 18
    Join date : 2016-12-10

    Re: Volume Control on PAS 2,...at 1 o'clock it starts getting loud

    Post by 8xlaxx on Wed Jan 18, 2017 11:29 pm

    Forgot something,...

    I did clean the Tone Controls with Deoxit, a few squirts. Worked the controls then shot some compressed air to clean out the excess. Does the same cleaning need to be done to the Balance Control?

    Thank you again for your responses!

    8xlaxx

    Posts : 18
    Join date : 2016-12-10

    Re: Volume Control on PAS 2,...at 1 o'clock it starts getting loud

    Post by 8xlaxx on Thu Jan 19, 2017 10:19 pm

    Weird things are starting to happen with my PAS 2 now.  

    I wired up the new attentuator and installed it.  The fit was OK after inserting a starwasher.  There are no shorts to the chassis.  No buzzing sounds or ground issues but something just isn't right.  It's probably worse.

    1) When I increase the gain it's still fairly low again then it get super loud at position 1-2 o'clock.  Same symptom as I had before with the original attentuator that was in there prior.  

    2) It is also playing through ONLY 1 channel only,....UNTIL.... I increase the volume to the 1pm position and BAM! both channels kick in and the house starts to shake!

    I checked my amp, disconnected and swapped the wires from the one side to the other and it plays on both channels through it.

    Anyplace to start to remedy this?  The old attenuator is pretty shot now because I cut the soldering posts on it so I would not confuse the wiring.  Proabably a bad idea now seeing that there was probably nothing wrong with it!

    GP49

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    Re: Volume Control on PAS 2,...at 1 o'clock it starts getting loud

    Post by GP49 on Fri Jan 20, 2017 12:49 am

    We can't tell, if there a wiring error.  Assuming there isn't...disconnect the loudness tap so the attenuator acts as a simole potentiometer, and let us know what happens.

    This is NOT the same as switching the Loudness OFF on the front panel switch.

    8xlaxx

    Posts : 18
    Join date : 2016-12-10

    Re: Volume Control on PAS 2,...at 1 o'clock it starts getting loud

    Post by 8xlaxx on Fri Jan 20, 2017 1:39 am

    I went ahead and disconnected the Loudness Tap/Switch and re-wired the attenuator with the leftover resistors.  Wow! what a tight fit that was.  I also had to run an additional wire to PCB-5 from the attenuator per link below:

    http://www.curcioaudio.com/PAS%20VC%20Replacement.pdf

    Preliminary testing shows that the unit is tracking fine now in both channels with a smooth, stepped gain increase!  I couldn't increase the gain to the 1 o'clock position as the family is sleeping.  Will do some more follow-up testing tomorrow but it seems to be OK.  I guess the Loudness Tap might have been the issue here?  I'm kicking myself for pulling out the stock attenuator,...Crying or Very sad

    GP49, you got PM.

    GP49

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    Re: Volume Control on PAS 2,...at 1 o'clock it starts getting loud

    Post by GP49 on Fri Jan 20, 2017 2:48 am

    You HAVE gained, as the replacement attenuator is of better quality than the original Dynaco control EVER was. Good job!

    8xlaxx

    Posts : 18
    Join date : 2016-12-10

    Re: Volume Control on PAS 2,...at 1 o'clock it starts getting loud

    Post by 8xlaxx on Fri Jan 20, 2017 8:40 pm

    I might have spoken too soon on this,....Mad

    I tested & turned the attenuator pot up to the 1 o'clock position.  Still doing the same thing,...gain kicks in and is ultra loud.  Wiring is correct, I checked it 5 times.  I defeated the loudness switch.  With this attenuator the gain increases dramatically between positions 11 and 12 (clicks).  If I go to the 13th click it starts to distort the audio badly.  


    8xlaxx

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    Join date : 2016-12-10

    Re: Volume Control on PAS 2,...at 1 o'clock it starts getting loud

    Post by 8xlaxx on Fri Jan 27, 2017 11:39 am

    Another update (for those waiting with baited breath). Laughing  

    Took the eBay 250k pot out.  Secured an ALPS 100k attenuator w/o loudness taps, you know the one with the black box & 2 screws/green bottom.  Very smooth unit.  I haven't listened through the phono stage but am thinking I need to do the RIAA EQ mod given the resistance differences (?).  

    If anyone here has performed the RIAA EQ mod to their PAS2, could you please advise on proper capacitor matching, suggested brands, AND parts numbers if you used a vendor (ie. Digi-key,...no affiliation.)

    Thank you.

    Will start a new thread here:

    http://dynacotubeaudio.forumotion.com/t3284-riaa-eq-mod-pas-2#29415
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    peterh

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    Re: Volume Control on PAS 2,...at 1 o'clock it starts getting loud

    Post by peterh on Fri Jan 27, 2017 5:43 pm

    8xlaxx wrote:Another update (for those waiting with baited breath). :lol:  

    Took the eBay 250k pot out.  Secured an ALPS 100k attenuator w/o loudness taps, you know the one with the black box & 2 screws/green bottom.  Very smooth unit.  I haven't listened through the phono stage but am thinking I need to do the RIAA EQ mod given the resistance differences (?).  

    If anyone here has performed the RIAA EQ mod to their PAS2, could you please advise on proper capacitor matching, suggested brands, AND parts numbers if you used a vendor (ie. Digi-key,...no affiliation.)

    Thank you.

    Will start a new thread here:

    http://dynacotubeaudio.forumotion.com/t3284-riaa-eq-mod-pas-2#29415

    the volume pot ougth to be 250k if anything is connected to the "tape out" port,
    if not the RIAA will be suffering.

    Se http://www.audioregenesis.com/documents/PAS_Phono.pdf for a discussion
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    PeterCapo

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    Re: Volume Control on PAS 2,...at 1 o'clock it starts getting loud

    Post by PeterCapo on Fri Jan 27, 2017 6:06 pm

    8xlaxx, you definitely want to read that AudioRegenesis article about the PAS phono section before committing to making any changes.

    8xlaxx

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    Join date : 2016-12-10

    Re: Volume Control on PAS 2,...at 1 o'clock it starts getting loud

    Post by 8xlaxx on Fri Jan 27, 2017 11:01 pm

    peter(s)-

    Thank you both for the advice and link to the audioregenesis article. I read the article. The author (in so many words) states that the RIAA mod is a bunch of horse hockey. From the conclusions, it is my understanding that a 100k pot is OK with the exception of the Tape Out, where low end frequencies will be compromised.

    Will hold off on any other mods and just enjoy the little pre-amp. I need to play some vinyl when I get a chance.

    Again, thank you for all of the assistance and recommendations.

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    PeterCapo

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    Re: Volume Control on PAS 2,...at 1 o'clock it starts getting loud

    Post by PeterCapo on Sat Jan 28, 2017 12:08 am

    Pete and repete.
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    Peter W.

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    Re: Volume Control on PAS 2,...at 1 o'clock it starts getting loud

    Post by Peter W. on Mon Feb 13, 2017 12:11 pm

    http://www.surplusshed.com/pages/item/r3568.html

    Just came about this in my travels - Center-tapped and all.

    "Between" the existing 220K and the sometimes suggested 100K, and certainly cheap enough.

    I have ordered a couple for my own use - along with a couple of center-null miniature meters (good in vintage tuners). Shipping was a flat $6, and as i am a PA resident I also paid sales-tax.

    Note that they have some tone-controls as well.

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