[Tinker]

GK-1 Review

*Bias declaration*
Many of you may know that I, the Tinker (obsessive audio tinker, that is) actually had a hand in design of the GK1 remote system. That said, here are a few words on preamps for your delectation:

What kind of preamp do you think I have? Behold! The mechanic's car: a passive preamp built in an old PC router box with components stripped from a Sony bookshelf system that went into the clearing at the end of the path a few years back.
As an exercise I built up a GK1 with Hugh, then Hugh and I (well, mostly Hugh) engaged in some modifications and blind listenings tests, and after several weeks came to the conclusion that the original is still the best. Hugh put it into the Swift case, I handed him the requisite sum of money
and now I am the proud owner of a GK1-Swift. I took it home last night, plugged it in, and put in some music. Suddenly it was 1am.


For reference my system is as follows:
- a modified Phoenix dipole speaker system (basically different baffle dimensions and EQ, home-brew PSU, but otherwise very similar to the orginal)
- 6 channels of AKSA55, v1.8 (I've had them for years) with Nirvana+ upgrade
- Rotel RCD950 CD player
- shoddy A/B comparsion switch
- Mixture of homebrew and Goertz I/Cs and speaker cables


Here are my listening impressions.

Overall:
- The GK1 adds amazing life and smoothness to vocals, particularly male vocals.
- Stereo image becomes very smooth, 'solid,' deep and integrated - like a velvet curtain of sound.
- Sound is very engaging, while at the same time being beautfully laid back. This makes long listening periods easier.
- There is a hint of tube warmth, but it is almost impossible to detect any real colouration of the sound.
- Bass is augmented, probably a contrast caused by the mids and highs being less edgy.
- Acoustic background is very 'black' and calm.
- Feet tend to tap rhythmically and uncontrollably.
- Slight hiss/hum audible with ear right next to tweeter. Can't be heard from about 15cm.


Specifics:

(Some) Test tracks

Lior: 'Old love' and 'Daniel'
- Amazingly intimate vocals, Acoutic guitar has real warmth and vibrancy - sounds like a real guitar!

Peter Gabriel: the 'US' album (SE remaster), particularly 'Love to Be Loved' and 'Washing of the water'
- Vocals sounded integrated and real.
- Image was like a velvet curtain. Beatifully enveloping and all instruments meshing in acoustic space.
- All sorts of microdynamics suddenly appeared. I could hear brushes on drums, breath noise, fingers on instruments etc.
- the acoustic bass drum was huge and resonant (see next entry)

John Mayer: 'My stupid mouth' and 'Neon'
- the Gk1 gives the bass a really solid state tilt, but has tube grace to burn in the mid range. After listing to Johnny I have to get out a screwdriver and adjust the bass contuour on the crossover. It's way too much now that the mids are sitting better.
- Drums sound a little warm and not at all edgy as they are wont to do on CDs.

Ana Caram: 'Summer Samba' and 'Sonhandue'
- Female vocals rich. Wood bass "alive." Chesky recording amazing. It's like the band is in the room with you. Which is no good to me: I live in a small flat.

Pink Floyd: Dark Side of the Moon - whole album (original Japan EMI pressing)
- So smooth you don't need the reefer. Again all sorts of little minutiae become apparent in the background of the original recording.
- The hint of mid range tubeness at high volume settings really makes the 70s-80s electric guitar sounds nice and warm.
- Again, drums sound organic.

Rachmaninov Vespers - Telarc
- See Peter Gabriel minus the drums

Skunkhour - '9 to 5'
- Sounds like the vocalist is right in your face. Very smooth and realistic. Every vocal nuance comes through.
- Percussion elements pinpointed in space all around the soundstage.
- Guitars sound awesome.

I couldn't be more pleased. This little preamp has reinvigorated my desire to listen to music. The preamp adds the convenience of switching between multiple sources and adjusting the volume without getting up, which is nice, but the real joy is the palpable increase in musical engagement. The GK1 certainly adds a little colour to the sound, but not much! It has an almost indefinable magic that just makes everything sound a little more intimate, emotional and real. The listening experience is less fatiguing too.

Well done Hugh, as we say in Oz, the GK1 is an absolute ball-tearer.

In the words of Ferris Bueller, if you have the means, I highly recommend picking one up.

T.

[AKSA]

Thanks Ben,

Time I responded;  I'd thought I'd leave a bit of time for others!

I am overjoyed you love the GK1.  Darl Singh feels the preamp is the best product yet, but I suspect it level pegs with the amps actually.  Certainly the preamp exactly and properly matches the power amps.

A terrific amount of work went into power supplies on the GK1.  The audio electronics is fairly straightforward;  the input stage to the pot is a discrete operational amplifier using a similar circuit to the front end of the AKSA, and the output stage is a carefully tuned self-biased cathode follower.  But the power supplies are a significant part of the sound.

I had always felt that a power supply should be quiet, and stable.  Once you had that, it was apples.  But it turns out that an amplifier is in fact a modulated power supply, so any modulation we perform using the amp should factor in the interaction with the power supply.  This is difficult enough with a semiconductor, but it's vital with a tube.

How many times have you read that the power supply is everything with tubes?  If I had a dollar for each time, .............!!

The big news is that it's true.  The interaction of the tube - in any configuration - with its power supply is pivotal to the sonics.  This is where the GK1 gets tricky.

I have always favoured high impedance power supplies for tubes.  Generate a higher voltage than needed, then use massive dropper resistors and multiple caps to get the noise down to vanishingly low levels.  With signal tubes, running only a few mA, you can thus avoid using inductors, which are expensive and bulky.  And if you use two resistors and three capacitors, you can make a CRCRC filter which uses inexpensive components, drops about 50-70% of the B+ during the filtering process, and delivers sub-millivolt ripple.  This principle is used on the TLP and the GK1.

However, voltage sag at the rails of a tube tends to soften the impact of the sound.  All the leading edges become a little sluggish.  This is romantic and pleasant, but lacks the thwack many of us like, particularly in bass.  I needed a high impedance supply for the GK1 tube, but I wanted thwack as well.  What to do?

After a lot of playing around, Darl and I ended up with a shunt, conjugate supply.   The second triode in the tube was set up in antiphase to the first, so that the total current draw was the same regardless of signal level or frequency.  This sounded terrific, with marvellous impact and slam, didn't sound like a tube at all!

Hmmm.  We wanted it to sound a bit like a tube.......  so I detuned the supply so that the current draw was constant at low frequencies, for tight bass, then progressively reduced with increasing frequency, to add the necessary 'romance'.

And this is the GK1.  AFAIK, there is no circuit like this in audio at present.  Nothing else has conjugate shunt operation of the power supply.  This makes the GK1 unique, and in almost four years there has been nothing in the market to use this principle.

That Ben likes it so much is a great accolade to the work Darl and I did four years ago.  Thank you Ben, you have a lot of recording and playing experience, as well as a huge academic experience.  I really appreciate your comments!

Cheers,

Hugh

[econ]

the pictures of the swift look just stunning. well done guys.

Are there differences between the GK1 and swift ?

Are those transformers behind the valves ?

Magnificent work

[Geoff-AU]

sounds like a great little circuit you've got to power those tubes Hugh!  I hope I get to audition a GK-1 one day, even if it means I have to build it myself  (won't be happening for a while - too many other hobbies vying for my bank balance!)

[kyrill]

hi Hugh

IS this pre amp structurally different than yr preamp from 2004?

And if yes ( i think) can you mod the 2004 version into this version?
 
Kyrill

[AKSA]

Kyrill,

Thanks for the post.....  nice to hear from you, as always.

Schematic is the same, no different, but packaging has been subtly changed over time.

Still the same chrome domes and chromed reflector behind the tubes.  Timber panelling.

Lots of people are hotrodding the GK1/Swift with teflon caps from Sonicraft.  It does make a very marked difference, particularly at C1, as Steve Harrison has published in some detail.

Cheers,

Hugh

[andyr]

For reference my system is as follows:
- a modified Phoenix dipole speaker system (basically different baffle dimensions and EQ, home-brew PSU, but otherwise very similar to the orginal)
- 6 channels of AKSA55, v1.8 (I've had them for years) with Nirvana+ upgrade

I couldn't be more pleased. This little preamp has reinvigorated my desire to listen to music.

T.

Hi obsessive audio Tinkerer!   

Imagine how much more you'd like listening if you had some good speakers!!      

Perhaps you'd like to come round and listen to my AKSA-driven, 3-way active Maggies!!??    And we can play "Dark Side of the Moon" ... although I don't have that Japanese pressing.

Give me a call on oh four one eight, one four oh, three oh six!   

Regards,

Andy

[AKSA]

Andy,

Ben is in UK at present;  back in two weeks!

He likes the VSonics, and is thinking of changing over, if that informs your comments......

Hugh