[justpassinthru]

I am considering replacing my venerable Hafler DH-220 with an Odyssey Stratos.  (Also considered the Halo A23 but for now am focused on the Odyssey) Speakers are VMPS Super Tower/R's.  Pre-amp is either an PS Audio 4.5 or an Onkyo P-304, depending which I decide to use.  Currently feeding the Hafler with the PS Audio.  My question is two fold.  I know that reviews talk much about the clarity and openess of the Stratos, but I am wondering if with the aforemention equipement,  it might produce a too stringent or bright output?  Remeber that the Hafler's MosFet's produce a more warm tube like sound (although some would disagree and say that the MosFet's "mask" the sound).  Secondly what is the type of devices and topology used in the Stratos, both for the input, driver and output stages?
Thanks for your time and advice.

[kujocku]

Hello, I owned and used a Hafler 220 for 17 years, one of the best audio purchases I ever made. Wanting to upgrade after all those years I purchased a used Dual Mono Stratos about three months ago, the difference was significant in my opinion. While the hafler was kinda tubey and I enjoyed it for years, it seemed a little harsh at higher volumes. The Stratos came across as natural and neutrel, better highs without being bright or harsh. The sound stage also improved. Bass was full, tight and rich without being bloated. If you decide to buy a Stratos keep one thing in mind: IT NEEDS A PROPER BREAK IN, HUNDREDS OF HOURS, DON'T JUDGE IT UNTIL THEN! IT CAN SOUND HARSH FOR A LITTLE WHILE. MY DUAL MONO TOOK THREE WEEKS TO REACH ITS FULL POTENTIAL EVEN THOUGH I BOUGHT IT USED!  I am satisfied with my purchase and I have also found even greater fidelity by also getting the Tempest preamp and groneberg IC's and speaker cable. The bottom line is this, if I had to do it over again, I would still buy the odyssey equipment.  You also might ask Klaus about the match between your preamps and the stratos. I hope this helps, Kujocku

[KarlDL]

You are considering what I did 10 months ago.  Would I go back to my Hafler?  No.  And my Hafler has been through major upgrades.

My DH-220 served me well for 22 years and continues to provide enjoyment in its upgraded form in a secondary system, or in the mains if the Stratos is at Indy for upgrades or on my bench for exploration.  

The Hafler can't touch the Stratos on low-end punch and authority.  Midrange and higher is a less-clear comparison, but I've come to prefer the overall impact of my Stratos, upgraded to Stereo Extreme form and likely to morph into Mono Extreme configuration later this Fall.

My DH-220 has been through what I call the HiPer mod: dual-mono power supplies using a new toroidal power transformer from Musical Concepts, IXYS FRED rectifier bridges, substantial (2.4X) storage capacitance increase per channel, and Musical Concepts driver boards.  IMHO, it is a "dead heat" with the Stratos Stereo Extreme for midrange and high-end clarity, with perhaps a (very) slight nod to the HiPer Hafler.  But, despite these substantial power supply improvements, the Stratos (even in its prior "plus" configuration) simply clobbers the HiPer Hafler on low-end transients and pipe organ pedals.  And it sucks less juice at idle.

The Stratos circuit topology is nothing special; a well-refined implementation of classic BJT complimentary-symmetry architecture, with symmetrical NPN and PNP differential-input pairs.  But Herr Gemein and associates have been tweaking this design for many years, so the synergy of components is more refined than in most products, including the venerable DH-220 and the more recent Musical Concepts upgrade thereto.

Ultimately, your decision should be based on listening.  Klaus's trial offer starts you down that road, with minimal risk.

[justpassinthru]

Karl,
Thanks much for the information.  I did speak with Klaus last week and at that time decided that the Stratos was definitely the amp I would choose.  I was ready to order thet Plus version, with Silver Faceplate, when I came across a 9/10 on Audiogon.  With the warranty transfer it was a no-brainer.  The money I saved in all likelihood will be used to take it to the next lever once I have had a change to listen for a while.  The Hafler has served me well for the past 20 years.  It has not failed now, but must compete with younger, faster, more nimble rivals.   With age comes respect for past accomplishments, yet the future belongs to the young!