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


    Original Dynaco PAS circuit driving a low input impedance solid state power amp

    Share
    avatar
    PeterCapo

    Posts : 635
    Join date : 2008-12-05

    Original Dynaco PAS circuit driving a low input impedance solid state power amp

    Post by PeterCapo on Tue Aug 21, 2018 1:08 pm

    Not supposed to be able to do this, right?  Well, it took me a while getting around to it, but here's my solid state Parasound Halo A21 power amp with an input impedance of 33KΩ being driven very nicely by my c. 1961 dynakit PAS-2. It sounds wonderful.

    No problem with audible low frequency roll-off; there's plenty of bass.  This is easily accomplished by bypassing the tone controls.  Retaining the tone controls could make things trickier. But, even if you keep the tone controls, with an appropriate resistor adjustment inside the PAS it is still viable with a broader range of power amps than some may realize.

    When I acquired this PAS, its originality was already compromised. I did a complete tear-down and then built it back up with remaining original parts that I thought were still good and using new parts where needed/wanted. The tone controls are completely bypassed along with all the other bells and whistles on the front panel. It is otherwise the original Dynaco circuit topology - no added output buffer.

    I've got the tubes4hifi cap board in there, though I did kind of go overboard with the B+ capacitance. It's a work in progress, so one of these days I might get around to fiddling with it again. But, for now, it is very enjoyable.  The space and imaging are knocking my socks off, and it desterilizes the A21.  Other goodies include a well detailed, clean presentation with really good separation of instruments and voices.  It is also non-fatiguing with a measure of tube euphony folded-in.

    - Peter




    Last edited by PeterCapo on Thu Sep 06, 2018 10:02 am; edited 3 times in total (Reason for editing : correction to wording and grammar.)
    avatar
    WLT

    Posts : 54
    Join date : 2013-07-13
    Location : Rochester NY

    Re: Original Dynaco PAS circuit driving a low input impedance solid state power amp

    Post by WLT on Wed Aug 22, 2018 8:03 pm

    Very nice work. The attention to detail is wonderful. And it looks very stock from the outside. I always liked PIO caps with carbon comp or carbon film resisters. This should sound great.
    avatar
    PeterCapo

    Posts : 635
    Join date : 2008-12-05

    Re: Original Dynaco PAS circuit driving a low input impedance solid state power amp

    Post by PeterCapo on Fri Aug 24, 2018 10:38 pm

    Thank you for your kind words.  

    At the same time, I don't want to give the wrong impression.  I'm not saying it's a "world beater," and I don't know if there might be some other issue with it driving a low impedance load that isn't immediately obvious.  But, it is undeniably enjoyable to listen to, much better than some might expect.

    Update... I usually listen at low to moderate volume levels, where this arrangement is working well.  I did try turning it up loud and am thinking it sounded strained.  I want to experiment some more with it.  I don't usually listen at very loud levels, and I am thinking the culprit is actually my speakers.  We'll see what shakes out after a while.

    Gary Smith

    Posts : 1
    Join date : 2017-08-10

    Re: Original Dynaco PAS circuit driving a low input impedance solid state power amp

    Post by Gary Smith on Thu Sep 13, 2018 12:45 am

    Very nice work there sir! Congrats on the successful completion Smile

    I am a little saddened by the tone control 'delete' however.... I have a PAS 2 myself, I did a complete cap replacement along with the selenium rectifier changeout and NOTHING MORE... I love the character of the LOUDNESS as well and run it with tone controls at 12pm., which is defeated just beyond that 12 O'Clock position of the 'GO' knob...

    This drives a pair of Mark 3's with new coupling and powersupply quad cap changeout along with the DC rectifier upgrade and nothing more...

    ALL were built at the Dynaco factory by the same tech back on November 8th, 1965 as dated by ink stamp on the chassis. They are nearly consecutively numbered as well..

    They drive an ALL ORIGINAL pair of Klipschorns from 1967 (just new caps on the xover)... It all makes a HUGE yet warm sound! The speakers are 18'5 feet center to center, so there is plenty of breathing room. The seating area is 17' back... Room is tuned with AST sound treatment panels...

    May you enjoy your new amplifier for many years to come !

    .....Gary


    Sponsored content

    Re: Original Dynaco PAS circuit driving a low input impedance solid state power amp

    Post by Sponsored content


      Current date/time is Sat Dec 15, 2018 6:24 am