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


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

    Share

    8xlaxx

    Posts : 9
    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

    Posts : 9
    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 8:55 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

    Posts : 756
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    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.

    peterh

    Posts : 718
    Join date : 2012-12-25
    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

    Posts : 9
    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.

    Pillo69

    Posts : 111
    Join date : 2012-04-11
    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 ?.

    peterh

    Posts : 718
    Join date : 2012-12-25
    Location : gothenburg, sweden

    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).

    Pillo69

    Posts : 111
    Join date : 2012-04-11
    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 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.


    Sponsored content

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

    Post by Sponsored content Today at 1:10 pm


      Current date/time is Tue Jan 17, 2017 1:10 pm