2A3 - which amp?

[Clive]

I've run various non-Bottlehead 300B amps over the years.  I have a real itch to build a 2A3.  My speakers are around 100db efficient 100Hz upwards, they are dipoles with active solidstate amplification for the bass 100Hz downwards.  The system has good detail and soundstage, it is quite a revealing system.

My choice is between Paramount monoblocks as a 2A3 or Stereomour set up as a poweramp.  The Paramounts are direct coupled as 2A3s I believe.  I'm trying to get a handle on the difference in SQ between these two amps as it would relate to my system.  Any thoughts?

[Grainger49]

Clive,

I'm not getting what "SQ" means from the context of your post.  I probably need more coffee.

I am familiar with the sound of the Paramounts as 45/2A3/300B amps.  The improved iron along with the direct coupled circuit makes the Paramount a better, cleaner, more detailed and open sounding amplifier.  On the other hand you can do some serious upgrades to the Stereomour for the $950 difference in price.  That would include some fine MQ iron if you like. 

I have Paramours (monoblock versions of the Stereomour) with all upgraded caps, bypasses, and MQ iron.  So I am basing my opinion of the Stereomour on my amps' upgrade path.

With 100dBW speakers you could even optimize the Stereomour for 45 outputs (different primary impedance for the OPT, 3000 vs. 5000).  Listening to Paully's Paramours as stock 300Bs, then stock 2A3s and eventually with MQ all nickel OPT and BPC-16 45 output tubes, I thought that the lower power with high sensitivity speakers made a big difference in ultimate detail.  The 45s were the clear winners.

So, stock Paramount iron and one less capacitor in the signal path are the biggest sonic benefits I see for the Paramounts.  Lower cost and larger budget for upgrades seems to be the greater benefits for the Stereomour.  The thing is that Bottlehead is now designing their own iron for the Stereomour.  This is a great improvement over the iron I got many years ago.  So the only improvement you can make to the iron is MQ iron.

Sorry if I rambled, things kept popping into my brain.

[Clive]

Thanks for the reply, a lot for me to consider there!

SQ = Sound Quality. 

[Grainger49]

   .  .  .    SQ = Sound Quality.

D'oh! !   (https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi244.photobucket.com%2Falbums%2Fgg7%2FGrainger49%2FSlapHead.gif&hash=fcbf69d3b645fcd6b78239b0b0dfb85e5a677484)

[Clive]

No problem    Stereomour does seem to make more sense in my situation.  I've 3 pairs of 45s anyway and a pair of Cunningham 2A3.  I did have a 45 amp previously based on the Gordon Rankin Bugle, it had much that liked but in the end my 300Bs had more "grunt" to propel the sound.

[Jim R.]

Just FYI, the stereomour has no Magnequest iron upgrade available, except maybe a plate choke they make might fit.

The paramount will be quieter (though this is not a problem with the stereomour either, be more detailed and articulate, better dynamics and better transparency.  They're both fine amps.

-- Jim

[Grainger49]

Jim, there are good MQ iron choices for 2A3 and 45 tubes that will work well in the Stereomour.  In addition those can be had with nickel pin and all nickel.  There is not a custom Bottlehead Stereomour upgrade set at the moment.

I went with non-Bottlehead upgrade iron form my Paramours.

[Jim R.]

Grainger, of course, but there are no drop-in equivalents -- first because of the operating point being set for a 4k primary, the EXOs don't have the power handling capacity for 2a3s, and the TFA's are a crap shoot at this point if they'll fit.  In any case, some circuit modifications and probably some chassis modifications would be needed, which is not something a lot of people will want to do.

[Paul Birkeland]

Everything about the Paramounts is an improvement over the Steremour, except a few pieces of shared hardware.

[Paul Joppa]

The situation with transformers is complicated, and it appears I should clarify a bit.

First, Paramour/Stereomour is the most confusing. The 2A3 version has always been designed around a 4K nominal primary impedance; our earliest upgrade (not Magnequest) was also a 4K transformer. When we asked Mike at Magnequest for an upgrade package, the best available was the TFA-2004Jr, and the BH-5 is a custom version of that design (a few construction and material changes were made to trade lesser cosmetics for better sonics). That is a 3K transformer, which is an acceptable compromise but produces a low damping factor with the 45. For the Stereomour, we changed to an in-house transformer design (I designed it) which has a 4K impedance, and works well with both 2A3 and 45. At this point, I have no recommended upgrade for either the transformer or the plate choke, for either the 45 or the 2A3.

The Paramount has a 3K transformer and is designed for 2A3s or 300Bs; the BH-5 from Magnequest is an ideal upgrade.

Paramount has less 120-Hz hum, due to its DC heaters; the driver stage is shunt regulated, the coupling in 2A3 mode is direct (no capacitor), and the plate choke is larger than the Stereomour's, giving better deep bass. It can be used with 45s, with some re-design, but it is not optimized for that application.