The GM 2O power amplifier uses an OTL (output transformerless) and OCL (output capacitorless) configurafion. The benefits of this type of circuit are very widely recognised and may be summarised as providing unrivalled transparency, speed and dynamics. OTL / OCL designs avoid the need to couple the loudspeaker load by means of an output transformer. In the GM 2O therefore the output stages are directly coupled to their respective loads. The circuit in each of the two power stages is based on a bridge in which the 6C33C tubes represent two of the four sides. The GM 2O uses a fully differential and balanced configuration (i.e. symmetrical) and is DC coupled between each of its stages with great benefits in terms of immunity to noise, including noise from AC mains.
Summary: Have been listening to various amps in the past, both solid state & tubes. Although most of them sound impressive, I feel it always either lacking soul, or sometimes too 'hard' sounding. Got the GM20 by accident and never regretted it.
As the previous reviewer said, the sound stage projected by this amp is huge, very 3 dimensional. Have matched it with various speakers, Quad ESL 57, various LS3/5A (especially the 15 ohm), Sonus Faber Concertino (original) etc. sounds so darn good. And with the ESL 57, the sound is to die for! The GM 20 as you probably know by now, loves sensitive speakers with high impedance (8 ohm and above). Match it such speakers, sounds like heaven! Mid range lovely, very detail and in the right company, boy can it rock! If anybody tell you that tube amps can't rock, they have never heard of the GM20 yet.
Try this amp, match it with speakers the kind that I mentioned above, regardless of your music genre, I sure you'll love it.
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Summary: The Graaf GM20 is out of production forever now but remains one of the very best amplifiers around.
Having said that, there are some serious issues with it. The amplifier does not have auto bias and because of that it needs to be serviced at least once a year. If you are not comfortable to set the bias current and offset yourself, you need to visit a dealer. This is, however, essential, not only for the sound quality but also to keep the tubes in perfect condition. If you do not do this, you will inevitably destroy your tubes.
Another 'thing' with this amplifier is the need to find suitable accompanying speakers. The best sounding ones have a high impedance (> 6 ohm) and a high sensitivity. Some folks try to circumvent this by transforming the GM20 in a mono version. But then you will need two amps and twice the amount of tubes (why then not go for the GM100?). There is no real need to do this because there are some good speakers around.
The last issue with this amp is that it runs hot. With four beefy 6C33's, the GM20 is not something you want to expose your small children to.
Why then is it worth all this trouble? Simple, because the sound of the GM20 is very, very seductive. It has a lovely tube (triode) sound but at the same time it is very open, fast and controlled (OTL characteristics). Some people think the amp lacks bass response but I do not agree. This OTL does not come with the down side of (old-school) transformers and is in fact very competent in the lower regions. But, as said, it is sensitive for the choice in speakers.
I own one for 7 years now and I have never considered buying another amplifier.
New ones will be hard to find as Graaf does not produce them anymore. I think this is a shame and I am sure that Graaf also think of it in this way. I guess that the service requirements made Graaf change it's minds at the end. The GM20 is not just a plastic box that will let you enjoy music for many years without any care whatsoever.
But boy, if you take good care of it you will have a winner.
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Summary: I have listened to a number of amps, this amp releases a huge soundstage with extremely realistic vocals, strings, bass strings. The feeling is soothing and elegant. This is a wonderful sounding amp , very quiet, reveals all musical details, female voice is spectacular with this amp, I am using it with:
Sonus Faber Guarneri speakers (best)
Graaf 13.5B preamp
Cyrus dad3q cd player
Cyrus fm7 tuner
Monster sigma retro gold cabling
Strengths: Soundstage very high and wide.
Quiet and clear, beautiful midrange
Weaknesses: Needs at least 30 to 45 minutes before warming up. Maybe a little more bass, but not bad for only 20 watts.
Similar Products Used: YBA 1, audio research vsi55, unison s2, copland 505, shanling stp80, unison unico i (Graaf is much better than all of these, also looks much nicer to)
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