[painkiller]

I've been living with a SKA GB300D amp for a while, but it burned and I need a new amp. What bothered me with the SKA was the dull and lifeless sound that made me lose interrest after 5 minutes of listening.  I guess it's a result of under dimensioned input stage unable to drive the output stage properly. The amp really fails when it comes to impulse response.

Now I'm trying to decide if I should go for tubes or if I should try the Lifeforce amp. I want a lightning quick amp, one that can really scare you. How is the LF55 in this regard? I also want an amp that sounds natural. Imaging and detail aren't really as important as the ability to convey the nerve of the music, bringing the listener closer to the live performance.

So what should it be? Transcendent sound OTL or Aspen Lifeforce 55?  Both are receiving rave reviews.

Regards from Norway

[AKSA]

Painkilller,

This is a vexed question.  OTLs are perhaps the ultimate tube amp topology, but they are really compromised by very heavy feedback to reduce the output impedance for driving speakers, and this feedback greatly reduces the open loop sonic signature of tubes.

Thus, OTLs sound very clean, very delicate, but really require highly damped, high efficiency, high impedance speakers such as Fostex or Hammer Dynamics, at least 95dB/watt/metre.  This does put constraints on your speaker choice, of course.

Bruce Rozenblit has tamed most of the criticisms of this topology;  he runs each 509 at around 15W in Class AB, not bad for a 35W tube, and the danger of self-immolation, a problem with all the Futterman designs, has been licked.  But you are still stuck with 15W, no more, and a mighty complex assembly process, without the 'tubey' sound most people actually like tube amps for.

All tube amplifiers require periodic replacement of the tubes.  On most OTLs, there is a need to match the output tubes (I don't know Bruce's approach, he might use individual bias on each tube, that is possible, but as a rule the best sound comes with matched tubes) and this means replacement around every three to five years, depending on use.  That can be expensive......

Unless you are particularly entranced by the topology, and the notion that high impedance tubes can actually be configured to defy physics and actually drive low impedance speakers, I'd think carefully.  OTL is not for everyone, and it certainly does not sound anything like single ended circuits, which are open loop, or close to it, and sound 'tubey'.

And yes, I can strongly recommend my LF55.  And it comes with the modules pre-built!!  Can anyone here with LF55 add to this?  What do you feel about the sound, can we offer some suggestions?

Cheers,

Hugh

[SamL]

Hi painkiller,

Have not tried the SKA GB300D but to what I know it is 300W into 4/8 ohm. How do you manage to burn it?  What speaker are you using? Just wonder if the LF55 will satisfied your taste. Maybe a LF100 will be more suitable if you wanted high SPL and have a hard to drive speaker. Oh yes! I replace my Plinius SA100MkII with AKSA100n. LF is another 2 generation about mine and that tell a lot about the quality.

Just my 2c.

Have fun 

[bluesky]

Hi

I am somewhat surprised as to your listening impressions regarding the Aksa and the SKA.  I have listened to the SKA quite a bit as a friend has one and I have the Aksa. 

I like the Aksa better as I felt the SKA "too" smooth for my liking.  I have to say both are damn fine amps but the Aksa beat the SKA in a number of areas.

One thing that I have found to be true is that I have never come across two audiophiles with the same components or music collection.  I have attended a few of our local audio club meetings and there have been times when other members have gushed over a set up that I thought sounded crap.  Which I believe shows that we all hear a bit differently as well.   

Synergy is everything in audio in my experience and I would humbly suggest that you look at your whole system as it may be that you need to look at your preamp, source, wiring etc to get the mix right.  I would also suggest installing bypass caps on your electros (thanks Ginger) as I have found these provide extra speed in an amp.

Cheers

Bluesky
     

[rabbitz]

Don't forget the AKSA 55 or AKSA 100 family as they do bring you closer to the music and emotion than any other amp I've tried.

I've tried the SKA GB150 as well as I have 2 AKSA 55's as well as a LF55. I didn't like the sound of the SKA and commented on it at diyAudio. I didn't build it so I have no idea if there was a problem. This was confirmed by a friend using a SKA and when he added an AKSA, the SKA was no longer used as he thought it lifeless in comparison and the bass did not have the drive or definition. There are plenty however who love it.... personal taste and I'm sure partnering equipment plays a large part.

The AKSA and LF have both endeared themselves here and I won't part with either. I'll keep one of each as they are both different amps for different applications. I find the AKSA a warmer involving music maker which I find great in an intimate system and the LF really gets into the music and brings it all out... less warmth but more life IMO.

You need to have a listen as with all amps it's down to personal taste.

One thing I find that can make or break a power amp is a good pre, so maybe you need to look at that. I have found all power amps (bar the LM3875) benefit from an active pre or buffer and to find a good one is harder than finding a good power amp. For a tube pre, Hugh's GK-1 is a good bet.

[painkiller]

I never liked the sound of my SKA, and I have talked to others which found it flat and boring. Most people preferred the 8W Hiraga Monster over SKA, for it's dynamic abilities. I drove mine with +/-56VDC for about 200W into 8R. I used it DC coupled with no feedback cap, and with elevated driver current and bias. Tweaked to the teeth. aa Still it was severely deficient in transient response. The MOSFET burn I experienced was caused by a temperature sensor issue I think.

I have not listened to any AKSA amp, but I've been following the evolution of these amps for quite a while. The Soraya seems very interresting, but sadly a bit out of my budget. I think the LifeForce seems like a cost effective solution at the time being.

My speakers are Triangle Altea, which are a fairly easy load. They are supposedly happy with low power tube amps. I do however plan on upgrading to more efficient speakers eventually. Maybe then I can move on to low power zero feedback SET amps if I feel like it.  The total cost of a LF55 and a SET amp will be lower than the cost of OTL monoblocks with a total of 32 output tubes. So I guess I'll try the LF55 and see how it goes.

I'm very aware of the different preferances we all have. I know people who absolutely love the sound of Audio Note cardboard box speakers. I hate them, but I adore the dynamic sound of Avantgarde horns.

I guess there will be more upgrades in the future, but right now I need a power amp that can satisfy me until I can afford new speakers and a good tube pre. I hope it will. I guess we'll find out.

Hugh, you've got mail.

[painkiller]

Thanks for the response by the way! And thanks to Hugh for the insightful reply.