Opinions on Graaf Amps

Well, many good things already said. Graaf OTL amps are excellent even the GM 20, built to very high standards (Ferrari black and/or red paint, no ordinary tube sockets to mention just some). The only "drawback" if any, is if you have speakers of moderate sensitivity. Get one and... perhaps change your speakers!
Cheers!

I have had my Graaf GM20 for about 3 years now. It was an upgrade (very substantial) from a Sonic Frontiers SFS80. I find the Graaf sound to be immediate, engaging, muiscal, fast, fluid - very typical of OTL and somewhat similar to midrange Atmas - only much better looking. Is the sound colored - probably, but what matters most to me in the amp is its ability to deliver music through my speakers. I focus more on purity issues upstream of the amp, which is why I use a passive Placette preamp also great and a good improvement over my previous passive ReferenceLine). The system drives extra-ordinarily inefficient Alon IVs with an input impedance around 3 ohms.

The challenge is that Tube amps in general and OTLs in particular need to drive speakers with relatively high input impedance, say 8 ohms or more. The Graaf manual specifically wants to see 8 or better. The dealer who sold me the Graaf (and also sold me the Alons years earlier) did not alert me to this issue. So, I listened in some ignorance for about a year and half, always with that nagging feeling of why my system did not sound as good as I thought/knew it should. Finally, an Audiogon TT seller alerted me to an autotransformer as a solution to this impedance problem. The autotransformer is a speaker fix and basically increases the input impedance of the speaker to match the needs (through a simple trial and listen type approach) of the amp. The autotransformer called a Zero, with a link from the Atma-sphere webpage, dramatically improved the sound coming out of the Alons and I suddenly had a system I am more than pleased with. The mids and bass became alive and bloomed. Wonderful.

Be aware though, that some early GM-20s had some build problems and I was one of the few unlucky ones to get a crappy build. After three trips to the repair shop - all warrantied - the unit runs flawlessly now (I was out the amp for something like 6 months over the first 2 years of onwership due to repairs for capaciters, tube socket, and one other item I cannot remember). Ahh, patience. When the opportunity presents itself, I will likely buy a second GM-20. Oh, the amp runs hot enough to fry an egg on top, but I use a stove for that.

I have had the GM20 for about 3 years now, and it has been back for repairs about 4 times. Each time the problem is the same, i.e. one chanel starts to hum and one of the capacitors needs to be changed.

My speakers are JM Lab Utopias.

Has anyone had this experience, and if so, is there a fix? Or do I just have a crappy unit?

None of the above letters seems to indicate any problems, so I'm wondering if there is something wrong with my set that needs to be fixed, apart from changing capacitors every year.

I'm very happy with the sound, but I also dont want to have to struggle with repairs every few months.

ANY help would be appreciated.

Just read your graaf post and I posted just before you about a year ago. My post also cited problems - take a look. My graaf also required replacement of the large capacitors (one or two as I recall), a power tube socket, a resistor, and one other thing I can not recall. However, after I purchased some Zeros - autotransformers - that stepped up the speaker input impedance - all problems went away and the sound improved dramatically. With the zeros in place, the amp had no problems for well over a year of steady use. Before I sold the amp, I had the tubes replaced and the unit fully checked out by an authorized Graaf service facility and was perfect.

My speakers are the Alon IVs with an impedance range from 8 to 3 ohms! I looked up your speakers and it looks like their impedance is 4 ohms. The amp specs say that it wants to push against no less than 8 ohms. So, I suspect that your amp may be working too hard - I recommend the autotransferms by Paul Speltz (you can search direct and there is a link on the atmasphere web page (they make OTLs also). As I understand it, OTLs are very sensitive to speaker impedance, and while tube amps (unlike ss amps) are also sensitive to speaker impedance, the lack of an output transformer makes the OTL design more vulnerable. My dealer (Stereo Unlimited in Walnut Creek, CA) knowingly and ignorantly sold me the $5K amp to drive my Alons (which they also sold me) - I do not do business with them any more.

Wonderful amplifier.

I have had the listening experence in Montreal hifi show this year. The combination of GM200 plus Bosendorfer loudspeaker VC7, and GM20 plus Bosendorfer VC2 are marvelous. Very good playback on piano and vocal. They actually hired live jazz group with female vocalist and a real Bosendorfer grand piano to do A/B comparison live!

More info can be found from link below:

http://www.enjoythemusic.com/montreal2004/rickbecker/page5.htm