Author Topic: Stax DA50 mono amplifiers  (Read 1032 times)

Offline brenden

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Stax DA50 mono amplifiers
« on: March 11, 2018, 12:26:48 AM »
Stax da  50  mono blocs   now paired  with the Stax CAX  Pro .
   These are the small brother to to my
Stax DA100  full class A amps .
   The DA50 is   50 watts per channel 
   
 Modding has begun and already showing signs of greatness .
   
« Last Edit: March 11, 2018, 12:30:24 AM by brenden »

Offline brenden

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Re: Stax DA50 mono amplifiers
« Reply #1 on: March 11, 2018, 12:57:56 AM »
Side view  showing heatsinks . Stax used a liquid sodium cooling system for heatsinks .
     Some of the mylar caps have been replaced with  very rare  Rubycon stlx  film and foil non inductive  caps .
   These are fantastic sounding caps  with extremely low esr and  made by rubycon  as  a high end partner for  their expensive    black gate capacitors  .
 

Offline brenden

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Re: Stax DA50 mono amplifiers
« Reply #2 on: March 11, 2018, 01:08:09 AM »
This is the circuit board  with th excellent   2sk 240 dual fet in can .
   The larger brown  1uf  bypass  caps are gone . They really ruin the sound .  They have been replaced with  .01 uf auricaps . After that simple replacement it is a different amp altogether. Everything improved from bass mids and treble . Much better timbre and detail .
« Last Edit: March 11, 2018, 01:29:40 AM by brenden »

Offline brenden

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Re: Stax DA50 mono amplifiers
« Reply #3 on: March 11, 2018, 02:33:48 AM »
Front .
« Last Edit: March 11, 2018, 02:39:18 AM by brenden »

Offline stevenvalve

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Re: Stax DA50 mono amplifiers
« Reply #4 on: March 12, 2018, 02:12:47 AM »
Nice toy to work on. It will be interesting to see the necessary modifications of a transistor amp.

Offline brenden

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Re: Stax DA50 mono amplifiers
« Reply #5 on: March 12, 2018, 09:47:50 AM »
Probably easier than a cd  player Steve  .  Best to start with a better mouse trap . Begin with amps that  have good power supplies   .  I prefer fet inputs with bipolar  outputs .
   The Staxes have quality  in all the main areas  ,its just a matter of replacing the cheap  mylar caps with  top quality caps .  I am beginning with caps from my parts box  to get a baseline for improvements then may try some jupiters etc . So far results have been very encouraging.  The areas for further improvement  i see, seem to align with the key areas that Jupiters and Duelunds  are good at .  I may need some technical advice  with  input filtering    at some stage but for now  keeping the design mostly stock apart from  reducing the bypass caps from 1uf to a quality .01uf ..
   I have modded the DA100s and these are almost  the same  but only 50w  so lessons learned  form the DA100 willl be used on these .
   

Offline brenden

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Re: Stax DA50 mono amplifiers
« Reply #6 on: March 26, 2018, 10:13:23 PM »
Work is progressing on the DA50 monos .
   2 electrolytics  in the super shunt regulators replaced with Elna Silmic 2 alpha  super golds . All the small blue caps  0.1uf  replaced with 0.01 uf  Auricaps . The .01 size  is so much more  natural  its not funny . I have proven  this many times  over. Curiously the big brother , Stax DA100  used all .01 uf caps  and apart from the output  transistors  the circuit  is identical  to  the  DA50.
     So how is it sounding ?       Stunning. !
           
        .

Offline brenden

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Re: Stax DA50 mono amplifiers
« Reply #7 on: March 31, 2018, 02:05:12 PM »
More parts going in .
    Hitachi  Copper foil polystyrenes  and   Elna Silmic 2   Super Gold  capacitors
     Nothing but the best 😊
  The two Silmics here are replacing the decoupling caps in the discrete  super shunt regulators  , which  were  10 uf .  It seems to be fairly  common industry  practise is to use these lower values after regulators   , but after many  experiments over the years , I have found that a minimum of 25uf  to 100uf  is needed to develop deeper bass and control of the deeper  bass . Bypassinfg with a .01uf  Auricap is essential  for the highs and mids  . The Elnas and Auricaps  blend perfectly .
     
        So , deeper and more controlled bass is exactly what i got as well as every other parameter improved also .
    The copper foil polystyrenes replace the stendard aluminium foil polystyrenes  . 
     
« Last Edit: March 31, 2018, 02:23:30 PM by brenden »

Offline stevenvalve

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Re: Stax DA50 mono amplifiers
« Reply #8 on: March 31, 2018, 08:22:41 PM »
I have tried the Silmics 2s and they are nice but in general i prefer not to use any electrolytic capacitors, but we have to fit caps in constricted space so we use them. Auricaps are good and great value for money and obviously work well as a bypass cap. 
« Last Edit: April 01, 2018, 06:36:14 PM by stevenvalve »

Offline brenden

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Re: Stax DA50 mono amplifiers
« Reply #9 on: April 01, 2018, 09:18:35 AM »
My opinion of electrolytics has changed over the years . The silmic 2 alpha super gold are a step up  from the basic silmic 2  . By themselves they cant achieve the standards that  you and i desire ,but when combined with a top class film  bypass cap of the correct value  my experience indicates that  they can easily compete with a top quality film cap .
    A top electrolytic is very good for bass and lower mids but doesnt have the beauty in the upper ranges . When combined with the auricap  .01  the result is seamless .top quality sound from   top to bottom .
     There  is no doubt there are  other excellent film caps apart from auricaps that could work great . The Jupiter is another one that works really good .
  If you use a second rate electrolytic with an average film cap you wiĺl get a   second rate result  .
            Maybe one day soon i can demonstrate what can be done with a solid state amp  whith the right treatment .
        So far  the Staxes are  allowing the beauty of my 94 mk2  to shine  .
      The sound is refined ,  dynamic  , and with a beauty  rarely heard in commercial equipment .   Gone is the bloat ,and  smearing  that i heard before the mods .
   None  of this comes cheap mind you .