Happily presents to you the :

Odyssey Gm70 Tube amplifier.

 


Introduction:


Here at Aquablue we have always gone the extra mile and since its our passion it doesn't really take that much of an effort , its inherently in our DNA to want to surpass ourselves. The latest series is the Odyssey line , which symbolizes the meaning that's it's a journey , where the destination is not the focus , but the journey.
The journey of this amp is a culmination of 24 years of dedication and passion.
We have had over the years the Enterprise , the Captain 845 , the AAA 845 and
The Outerlimit , which still stands as a design from another world.
As you notice all these amplifiers are SE and use the 845 output tube , we tried many other output tubes , we considered them all . Our quest for the best is our reason of existence.
But so far the 845 has stood the test of time. Until now.
Sometimes it also takes a bit of luck , as the latest batch of Shuguang 845 tubes was a catastrophe , all tubes gassy , and we where still prototyping this latest amplifier we decided to try the GM70.
The Gm70 is Russians equivalent of the 845 but a bit better in every department.
It's a very close cousin , but a very interesting one . Until you build it in a decent circuit you wont be able to judge it when its that close.
We also considered the bigger tubes like GM100 , WE212 , WE241 , 833A or TB1000 , all these tubes are bigger but have worse specification then the 845/GM70 so already on paper you can clearly see they wont have the qualities one seeks in musical enlightment where having power is certainly not the most important criteria.
True High End is a big sound , with all details and all subtleties revealed in a non obtrusive way.
The differences are subtle between the 845 and the GM70, and all are enjoyable , but again we had the itch for something special. We know people like to roll different brands of tubes , with the 845 the supply of NOS has dried up, so you are stuck with current production. Shuguang 845 , 845B , 845C and recently 845WE , or Psvane ( build in shuguang factory ) with their 845T and many variations. Then we have the German Elrog and also TJ Fullmusic. Giving you many choices.
The GM70 has been produced in the 1960/70's and 80's and there are only 2 versions , Carbon plate and Copper plates. So not much tube rolling possibilities but at least its NOS which IMHO is better then current production anyway.

Datasheet 845 , Part 2 datasheet 845

Datasheet GM70


And to our eyes when we mean special , it means something out of the ordinary , more then even the other amplifiers we have been making.


So what makes this amplifier special ?


Its in many ways innovative , the power supply is critical as music is modulated power . The Odyssey innovates .
It's the first commercial tube amplifier with a SMPS power supply that is fully designed for tube amplifiers, our first was the AAA-845 which was only sold as a kit. All an amplifier does is essentially nothing else then modulate the power supply to the music signal , you can imagine how perfect the power supply must be.
We have all types of customers , but the SE scene is home to the most audiophile demanding people. Todays systems have to be bullit proof , dead silent , and have to have that magic harmonic sound that only SE DHT is capable of delivering.
Customers have different speakers , but all demand rightfully so that an amplifier must be dead quiet .Hum kills your signal to noise ratio and smears the sound.
So we set the goals that we do need power , as you can always hear very clearly that a more powerful amp has more balls , better control even when playing at low volumes.


The Circuit :

The circuit computer drawing

The circuit handdrawn with details

Datasheet of EL300 , Datasheet of 6SL7 part 1 , part 2


Full class A biasing of all tubes. What is special is that over the years we learned that to drive low µ tubes like 845/GM70 means you have to have a rock solid driver stage because the grid will swing positive at some point and being the nature that tubes are high impedance it means the driver will fail miserably when this happens.
The Japanese have also much experience , they tried ( and we did too ) different configurations , and careful listening is still preferred to measurements. Srpp , µ follower , DRD , and current sources , emitter followers , cathode followers , paralleling of tubes for Gm doubling , use of power Triodes and mixing up of Penthodes / Triodes . All these circuits and there variants have been tried and none are 100% satisfactory.
Over the last couple of years we have noticed that certain topologies are more musical and measure richer when it comes to spaced out harmonic content hence our use of the name Natural Harmonic Enhancement Circuit . The NHEC is devoid of feedback , has zero ground impedance connection .
We developed our own DDD ( DeDicated Drive ) circuit . This uses a long tail fase splitter and a current source for optimum balance .This also has the added advantage that we could have a direct balanced input if needed. And it is direct coupled to drive a mini PP amplifier which is necessary to drive the output tube. This topology gives the right harmonic distortion .
Harmonic distortion is something very critical, please let me explain:
The best transistor amplifiers have like almost zero distortion like 0.00003% and yet anyone who is sensitive to emotion in music agrees that tube amplifiers are better. Tube amplifiers have notoriously high distortion , its in the area of 0.75%! But compared to their silicon counterparts its mostly even harmonics and those are pleasant to the ear. However to much even and the sound is too warm too tubey , too much odd harmonics and the sound is hard ! So you need a perfect balance of the harmonic content. SE by nature is mostly even , the mini PP stage is mostly odd , the mix of both is perfect.


The power supply :


This is the heart of the amplifier , an amplifier can only be as good as its power supply. So even if it doesn't sound sexy its the most important aspect of any amplifier. Its also the reason why very low power amplifiers seem to sound best. Because as soon as you need high powers you are either going to end up with a huge amplifier weighing 50 to 100Kg if you mean serious business or its just not going to sound right !
We have pioneered SMPS ( Swith Mode Power Supply ) for tube amplifiers , we are currently using our 5th generation circuit and are finally very happy with the results.
The advantages are tremendous , because of the high frequencies , the transformers can be reduced in size , the filtering gets easier and the whole power supply can be optimized at a fraction of the weight of a classic power supply . The added benefit is that its also more stable and has less diode switching currents . Those switching currents have to be avoided as they contaminate all other power supply's because they travel through the magnetic core and are later almost insuppressible . less hum , better noise ratio and lower impedance and better regulation while having timer circuits easier build in.
This novelty is also superb for safety in the event of tube failure.
Panasonic extreme low ESR capacitors in power supply
The wiring can also be altered if there is a preference but we think its perfect as is .
The SMPS now is efficient , light weight , extremely quiet , safe and above all as perfect a power supply as you could build ! You could not do better with a linear power supply because the power factor here is very close to perfect. Only a linear choke input filtered power supply could rival this . This means you don't need any expensive power conditioner or line filters or power cleaners or special power cables.
Our own custom SMPS power supply has ultra low output impedance and is fully regulated and stabilized . In any SE amplifier design the importance of the power supply is often under estimated. But here its over powered , over filtered and over protected .
All power transformers are handwound, in our own workshop , impregnated and baked.
Components & tubes :

We have chosen for NOS tubes, the search means they have to be plentily available. The input tube is the venerable 6SL7 which is still a very common tube, available in various NOS brands , military versions , so lots of tube rolling fun here . The driver tube is the EL300 , which bears quite a resemblance to the 300B / 2A3 family when triode connected which it is . Its powerful enough to drive the GM70 which if compared to the 845 had like double the filament power , can handle 125Watts plate compared to 100Watts for some 845. The µ is slightly higher at 6.7 compared to 5 . We know many people run the GM70 very conservatory and at very low voltages ! This always surprises us as we know you need to run a tube at the highest possible voltage ! If you want the best sonic result.
There is no coupling capacitor
All iron in the audio section is Lundahl , the output transformer is the LL1688 and the interstage is the LL1692A .
The simplicity of the circuit guarantees the proven KIS principle ( Keep it simple )


Options and upgrades :


Its possible to upgrade
What we propose is the following .


Silver interstage transformers by Lundahl with AM cores cost 5000€


Silver output transformers cost 9500€


Next year in 2020 we will also offer the same amplifier with 845 . So the tube rollers can have the ultimate fun .

Listening impression TTM 2019 :


To my own very surprise this amplifier sounded and played flawlessly .We compared with the WE or Altec 300B amps with Japanese 300B tubes and it was pretty clear they where no match . On the Altec A5 set with Altec 1005B horns and JBL tweeters there was absolutely no hum , it was so quiet one would wander if the amp was connected or not ! Or just switched off ! This means excellent signal to noise ratio , great soundstage , depth and width and a clarity , all these essential qualities are all in the superlative department.
Even changing cables was not subtle , differences where easily heard.
We also tried the amplifier on JBL Paragon , mind you an original Paragon from 1962 with original filters ! And yes it sounded great , unbelievably vintage sound like it was new. Again 3D rendering was extremely good , presence and bass surpassing the Altec combo . This amplifier made the speakers perform better then they should.
This was very clear to all participants as they all told me they didn't know that these speakers could sound so good.
We also ran it briefly on the WE13A horn of Mr Sasamoto San, and again dead quiet and musical as expected. What an experience.


In short statements :


Full Class A
Build for horn speakers less then 1mV hum
All NOS tubes for True emotive experience
DDD driver topology
NHEC Natural Harmonic Enhancement Circuit
Extreme protection on powercircuits
Fully regulated power supply
Wooden chassis for organic sound
Big current meters for monitoring of the output tubes
Limited Special Edition
Rated power per channel 39Watts RMS
Rigid low impedance Power supply
Quiet ventilator for heat protection
Blue Leds for contrast and indication of working SMPS
Stereo integrated line level
Totally committed to absolute musicality ( direct cd input )

How to use :


Unpack , inspect for damage
Plug in tubes ( they come numbered )
Always look for either the center pin , or a big fat pin that serves as a postionment

Left channel = L ( Same for Right channel where R will be marked )
6SL7 L
EL300 L1 and L2 ( being 1 most left tube )
Plug the anode caps on , each tube has its own
GM70 locate the big pin and insert carefully
Plug in RCA cable
Connect speaker cable
Plug in power supply cable = std IEC , the amplifier works either on 230VAC or 110VAC . this is factory set
The main fuse is 3.15A , max 4A for safety slow blow .
In front you have the volume control , if you have no pre amp you can play direct .
For phono you will need a pre amp .
The mA meters in the front meter the output tube , there is a little screw right on top so you can adjust bias ( target is 80 to 90mA Absolute max = 100mA )
The amplifier needs to be properly aired , meaning the fan on the back has to be able to have clean cool air , and the tubes heat can radiate safely in the room = enough space on top and sides .

Powering up :


When you power up , the SMPS takes its time to slowly power up , first the filaments , you will see the orange glow of the GM70 Thoriated Tungsten filaments after 2/3 seconds , then after approx. 40 seconds later the blue leds come on signaling that the High Voltage is up and running ( they are lethal ) .
If the blue leds stay dark , switch of and on again ( wait 5 seconds ) . If they wont reset , it means you have a tube failure somewhere. ( EL300 or GM70 ) or other problem.
DO NOT INVESTIGATE FURTHER , DO NOT OPEN , DO NOT TOUCH ANY INSIDE PARTS WHEN AMP IS PLUGGED IN

Pricing :

18000€ VAT incl

Warranty 10 years on parts except tubes and capacitors of power supply ( they are long life )
Warranty covers failure of power supply , and tube failure related damage but not the tubes themselves .
Warranty is just on the amplifier itself .

 

Some construction pictures :

 

 



 

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