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HELP advise PLEASE - Focal Sopra 2 Speakers - I want a tube amp but " Min 2.6ohm @ 104Hz "

HELP PLEASE advise bought a pair of Focal Sopra 2 Speakers that I absolutely love.

I want to use an integrated tube amp with them but the measurements worry me even though many Sopra owners say they happily use tubes with these speakers.  


HERE IS THE ISSUE:

  From HiFi News September 2015, lists Minimum impedance is around 2.6 ohms at 104Hz. Combined
with high impedance phase angles at low frequencies this results in a minimum EPDR (equivalent peak dissipation
resistance) of 1.1ohm at 85Hz – challenging to the partnering amplifier.

Can I used an integrated tube amp and hope for success? 


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From HiFi News September 2015, minimum impedance is around 2.6 ohms at 104Hz. So the amplifier should be capable of approximately doubling its 8 ohm output power into at least 4 ohms and preferably again into 2 ohms.
Min 2.6ohm @ 104Hz. Focal claims 91dB sensitivity for the Sopra No 2 but our measured pink noise figure of 88.2dB falls almost 3dB short of this. Low impedance is a factor in achieving this figure: Focal specifies a minimum impedance of 3.1ohm (which would indicate a 4ohm nominal rating rather than the specified 8ohm) but we measured a dip to 2.6ohm at 104Hz. Combined with high impedance phase angles at low frequencies this
results in a minimum EPDR (equivalent peak dissipation resistance) of 1.1ohm at 85Hz – challenging to the partnering amplifier. The forward frequency response [Graph 1, below], measured on the tweeter axis, is essentially flat in trend with just a mild presence band dip.




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14 responses Add your response
erik_squires
16,121 posts
 
You can use a tube amp. What will happen is you will hear a depression in the output where the impedance is lowest.

Will you like that? Depends. You may find this adds a bit of loudness.

But for most listeners, the Focal dip usually pushes them to SS amps with lots of current. If you like tube sounds consider a tube pre instead.
tablejockey
3,916 posts
 
Overthinking it.

Just a matter of which tube amp you like. Demo as many as possible. The Sopra's sound great thru a decent tube amp. You'll just get multiple responses  why "x" is better than "y"
audiokinesis
2,740 posts
 
Erik is correct.  I design speakers to be tube-amp-friendly so I am familiar with the issue he brings up. 

You might look into Paul Speltz's "Zero" Autoformer, which is made for exactly this situation.  The Zero Autoformer can effectively and elegantly raise the impedance of the load your tube amp sees. 

Duke 


fsmithjack's avatar
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fsmithjack OP
712 posts
 
Good stuff - I thought I might be overthinking it. 
Also, I didn’t know the dip could make a tube amp sound louder. Glad I asked. Appreciate the info. I read these measurement can be tough on an amp but didn’t know what that meant in real world use.
Do you guys think a reasonably priced used integrated tube amp like Like a VAC 160i or Octave Audio V110SE or even a value one like Ayon Spirit III will work ok? These are all in my used price range of around $4kish. 
I don’t want to tube Pre end SS amp for no other reason then cost of 2 boxes and another IC’s and PC’s is more then I have to spend. Just downsized my speakers and love the Sopra’s so hoping I get lucky with a $4k ish used Integrated amp. These are all around that rough $4k range. 
mofojo
2,301 posts
 
+1 tube preamp. 
ohlala
1,236 posts
 
The VAC has assorted output taps, so that is nice in your situation. I would experiment with a SS amp as another data point/ reference if practical.  
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fsmithjack OP
712 posts
 
Been thinking about SS and tube preamp. I wasn’t but a few of you guys mentioned the idea and it has started to stick with me. I want the Linear power and control from SS but now need that tubes sound. The hybrid integrated I’m now borrowing is so good it’s tough. Wish I could afford it but I can’t. What do you think of GamuT D-200 MKIII and a Alnic L4000 combo. The transformer coupled output on the Alnic provide nice lower output impedance and Gamut is a little tuby on its own so was thinking good match for Focal Sopra 2? Think this would be better then a hybrid like a Mac 352?
joecasey
484 posts
 
Checkout Convergent Audio Technology (CAT) or ARC for tubes driving a tough load.

VAC has 2 ohm tap ... found one VAC 200IQ had trouble driving Wilson Sabrina so probably need 2 running in Mono.

audiotroy's avatar
audiotroy
3,805 posts
 
You can get the flavor ot tubes with an Hybrid  which then has a high current sold state output stage

We have the suberb unison research unico 150 a fantastic italian made tube Hybrid with 180 watts on top you Will have no problens driving your speakers

Dave and troy
Audio intellect Nj
Unison research dealers
jwalsh31
20 posts
 
I would look at the Mac 2301 Mono's.  Would match well with the Sopra's
verdantaudio's avatar
verdantaudio
1,500 posts
 
I have listened to these exact speakers driven by MC275s bridged mono with a C22 preamp.  If anything, the bass might have been a little flabby but the overall presentation was just incredible.  I am not sure about Mc's hybrids and how they will work with it.  

In the end, no tube amp is going to give you the control over bass that SS is going to give you.  There are certainly some SS brands that can sound more tubish though.  

I know the Sopras and they like warmish, SS amplification.  Obviously they pair well with Naim and that is Naim's signature sound profile.  You can't go wrong with a Naim product paired with them.  

Pass is not inexpensive but it will do a lovely job.  I would take a look at their integrated amps as they will provide the sound profile you are looking for.  

If you are looking for a hybrid, I would encourage you to look at AVM.  Warmish sound profile with an ECC83 input stage and a MOSFET output stage in the flagship Ovation A 8.3.  It is $15,995 and has a ton of features, Bluetooth, DAC, Headphone, Amp, etc... that you may not need. 

At a more modest price of $6495, the Evolution A 5.2 is a hybrid Class D with the same tube input stage.  This is modular and you can add a DAC and phono stage cards.  I have customers driving Martin Logans and Magico A3s with this integrated.  It is very revealing and is a strong value given Class D.  Check out Gary Beard's review in Positive Feedback.  

I am an AVM dealer, I have no relationship with McIntosh, Naim, or Pass.  
mijostyn's avatar
mijostyn
8,570 posts
 
If you listen primarily to rock and or jazz a tube amp here is just a bad idea. If you want some tubiness use a tube preamp with a SS amp. Those frequencies at risk are the ones that provide the punch to the the music. The Focals cry out for a 100 watt/ch class A amp. There are amps in this category that are great at mimicking tube amps such as any Pass amp and the big Parasounds. 
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fsmithjack OP
712 posts
 
Thank you for the excellent responses. I downsized my system cost wise (Magico S5 MKII to Focal Sopra 2) and Soulution amp to now wanting tubes in the chain. I should have provided a price range which is around $6k. I am buying used for the reason listed above. I was thinking GamuT / Alnic because they fit roughly in my price range and SS amp wise have the power and have a Pass like tubish sound and the Alnic because it has great Output impedance to match with SS amps. Has anyone heard the Mac 352? It also fits the price range? Any other recommendations? I agree a tube integrated might not match well. Some folks says Octave Audio Integrated amps do well with low impedance dips like the Focal present but I’ve never heard them? 
fsmithjack's avatar
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fsmithjack OP
712 posts
 
What do you think or know about LAMM 1.2 mono’s. Do they have enough tubeness in them. I know they have one 6922 in them. I’m strongly considering them. 
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