Opinions on Graaf Amps

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.

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.