Yet another failed attempt to better the 55N+

ginger · « **on:** 13 Dec 2004, 02:51 am »

On the weekend just past I completed a pair of Menno Vandervenne 100W Monoblocks. These are TUBE amps, 12AU7 preamp/phase splitter/driver with a matched quad of Svetlana EL34s in Ultralinear Mode. And of course the bloody expensive Toroidal Output transformers.

Frequency response is an incredible 12Hz to 140kHz (at 10W output). So how did they sound - artificial is the word. Output Impedance of 17 Ohms means huge speaker colouration as the power output follows the impedance curve of the speakers - YUK.

It was a relief to disconnect them and hook up the 55N+ in their place.

Oh well - back to the drawing board (and the feedback theory books).
Actually I'll rewire the outputs to triode mode first to get the output impedance down by a factor of 4 and then have another think!!!!.

The fact is that the 55N+ has shifted the goal posts so far into the audio excellence direction that I'm having serious trouble getting a tube amp to approach it. Not for want of trying or for want of best quality components.

Cheers,
Ginger

AKSA · « **Reply #1 on:** 13 Dec 2004, 09:44 am »

Ginger,

I can't help thinking that the choice of tube has something to do with it. If you use 6SN7/6SN7/KT88, I believe you'll make a better amp. But operating points and cap choices are really important.

It's nice to know the 55N+ is still your favorite, and thanks for the plaudits, but I have to say that I've heard SE amps which have some qualities which are even better. Of course, they lack the slam, and many are rolled off top and bottom, but the midrange is magical. The optimum would be the slam of the AKSA N+ with the luscious mids of the SET; this is something I work on all the time. I'm getting closer, but I suspect I might get rather old and maybe die before I approach audio utopia...... Ah, yes, that's what I'll call it, The Utopia!!

Cheers,

Hugh

WerTicus · « **Reply #2 on:** 13 Dec 2004, 10:57 am »

its okay hugh maybe when you die you will be rewarded with that which you seek... or maybe you just rot in the ground, im not really qualified to know which

kyrill · « **Reply #3 on:** 15 Dec 2004, 09:58 pm »

Quote from: WerTicus

its okay hugh maybe when you die you will be rewarded with that which you seek... or maybe you just rot in the ground, im not really qualified to know which

Both WerTicus. Both will happen. While your body rot or burns, your mind enjoys out time. Only sex seems to be an illusion

ginger · « **Reply #4 on:** 15 Dec 2004, 10:55 pm »

Hugh,
The KT88 Amp with Ultralinear Connection + Cathode Feedback (Menno's SuperTriode arrangement) is still on the go - prototype half built.

These Monoblocks were intended to answer a couple of question -
1) How big a damping factor is really required?
2) How much bandwidth is really required?

Being a reactionary old coot I take the view that what every one knows is probably WRONG and was determined to find out for myself.

I could'nt really assess the bandwidth because the dampung factor was clearly inadequate. For my nomiinally 6 Ohm VAF DC-Xs the damping factor was around 0.46 (note the Zo was actually 13 Ohm not 17 Ohm as stated above).

I have now converted the amps to Triode Mode - The new Zo is 5 Ohm giving me a damping factor of 1.2 . I'm finding that this is enough for lovely sound.

I've got a new theory forming on damping factor - every valve amp I have tuned the feedback level by purely listening I have ended up with damping factors around 1. The largest is 1.4 - possibly its just what suits my speakers.

I've spent the last 3 days swapping back and forth between these monoblocks and the 55N+ and currently don't have a firm preference.

The Monoblocks in Triode Mode have a more natural high mid and top end. They also have a humungous image (but slightly unfocussed).

The 55N+ has tighter bottom end and smaller but more focussed image.

Overall I'm very happy with these monoblocks now.

Cheers
Ginger

Grumpy_Git · « **Reply #5 on:** 16 Dec 2004, 10:54 am »

Ginger,

I just have one comment regarding your attempts to improve on the AKSA 55N+.

Why take the easy route

, surely if you really wanted to beat the 55 at its own game you would go the whole hog and be trying to do it with sand rather than the magic Glass?

Nick

ginger · « **Reply #6 on:** 16 Dec 2004, 11:37 pm »

When tilting at windmills its best to take them on one at a time.

Cheers,
Ginger

AKSA · « **Reply #7 on:** 16 Dec 2004, 11:40 pm »

Now, Nick,

That's not fair!! If only you knew - Ginger has put in almost as much sandpit time as me trying to improve on the AKSA 55W N+!

Besides, you need balance in your life. Perhaps it is no coincidence that sand is the basic ingredient of glass???

Cheers,

Hugh

ginger · « **Reply #8 on:** 22 Dec 2004, 01:24 am »

I have now run the monoblocks in Triode Mode for the last 2 weeks.
They took some time to run in - maybe the Blackgate FKs I used for the cathode bypass on the wimpy phase splitter/driver.

I now definitely prefer these to the 55N+ - Sorry Hugh. - Its the high mids and top end - more tingly tops and better imaging BUT less bottom end and slam.

Merry Xmas and Happy new year to all.
Cheers,
Ginger

kyrill · « **Reply #9 on:** 23 Dec 2004, 08:51 pm »

Quote from: ginger

..

I now definitely prefer these to the 55N+ - Sorry Hugh. - Its the high mids and top end - more tingly tops and better imaging BUT less bottom end and slam.

Merry Xmas and Happy new year to all.
Cheers,
Ginger

Hi Ginger,

Hearing the differences also with CD ?
are the audio opamps in the output of the dac capable of bringing sound worth the tubes? or are you hearing the DAKSA kind of DAC?

Kyrill