This there is continuation of a series of post I have about the Yamaha B-2 in the MiniMe thread:

http://www.GoodSoundClub.com/TreeItem.aspx?PostID=11029

I got today the papers for my B-2 amp.  A quick look at the circuitry and reading the manual did help to solve a few problems with sound that I initially had.  It is an interesting amp and it is fully DC coupled. It does has some distinctive sound not so typical for SS amps. There are some things that I like in this amp and some that I like less. To get the best from this amp it would need to do some minor modifications but I do not decided to go to this route at this point as I do not know year it I would like to keep this amp.

Anyhow, I post the documentation for the amp as I find it is interesting.

Yamaha B-2 User Manual:

http://www.goodsoundclub.com/PDF/YamahaB2_Manual.PDF

Yamaha B-2 Service Manual:

http://www.goodsoundclub.com/PDF/YamahaB2_Service.PDF

Yamaha B-2 Report:

http://www.goodsoundclub.com/PDF/YamahaB2_Report.PDF

Yamaha B-2 Circuitry:

http://www.goodsoundclub.com/PDF/YamahaB2_Circuit.PDF

Yamaha B-2 reportedly was a top-flying amp in end of 70s, during it very brief production period. It has in a way cult reputation, so I’ve bitten it.

I was forced to very mildly and temporary modify it, just running the signal directly the entry of the first stage and was a able to listen it.  The amp is fully DC coupled with no signal cap in path. The output stage is made around the high-biased V-FET transistors.  They are very rare, very expensive and since they have high bias they reportedly make the output stage to operate alike a tube in A1 class.

I do not know how accurate it is but the B-2 does not sound like a regular SS amp, in fact it does not sound as any other SS amp I heard. It is different. It is softer but at same time dynamic and elegant. I do not have a speaker that I might use as some kind of reference and I drive with B-2 my MiniMe. Sine I addressed the meager problems I generally like what I hear. The interesting question would be it this 30 years-old amp consumer is compatible with the contemporary high-end amps. I do not know how to answer this question. I generally do not like the contemporary powerful high-end amps. I might say that I do not like in Yamaha B-2.

There are two major aspects that I feel would disqualify B-from being the “great amp”, at least those that I recognized so far with my MiniMe. First is the imaging. The B-2 has very primitive imaging, I have no idea why. If I keep the amp I might look as the crosstalk and rejections but as is (my amps is virtually new) it has very bad imaging, not bad but there VERY bad. Second is bass. The Yamaha B-2 has different bass then it shall be, there is no more hyena bass that I reported before and what I have is the good Yamaha B-2’s bass. It is deep and extended but it is wrong bass. There is something very abnormal in it. I did not look deeper into it and frankly I do not care as if I keep the amp then I will high-pass my MiniMe me with passive radiators. Still, great amps, if B-2 is willing to be, shall have different bass.

Last few days listening MiniMe with B-2 my patients was running out. With all more or less OK sound my B-2 had wondering eye about imaging. The amp has a minor fluctuation of gain between the channels and this fluctuation can be addressed by …kicking the map. I was keep hitting the amp with all my stupid force and it become to develop some odd noises – obviously it needed some service.

I kind of felt that I have finished with soldering in my live and I very intentionally do not even keep solder in my home. Couple weeks ago one audio-devil brought solders to me and I felt that I might invest some time to fix up my Yamaha B-2. So, I did. It took 2.5 hour and I re-wired the B-2 with direct paths to input out, replace most of the parts that I felt need/might to be replaced and recalibrated the amp. As the result it become superbly imaging stable, with no noises of any kind and with quite nice sound. The only things that I did not do was to un-mount those V-FET transistor and to put between then and the heat sinks the contemporary much better performing thermo compound, probably I will do it in sometimes feature. Still, I do not get as lot of power from it now, so it might stay as is for now.

I was listening the amp after the face lift and I kind of begin to like it in a new way. In addition it is a very powerful beast – something that did not experience for a while.  What would be interesting sometime is to take my B-2 in a room with more or less capable conceptual speakers that need a lot of power, driven by let say Boulder 2050 , or Halcro MC-70, or Spectral DMA-360,  or Lamm M1.1,  or MBL 9007,  or Mark Levinson 33, or Krell MRA, or Edge NL,  or Gamut S-300,  or Burmester 909, or Jeff Rowland 9T, or Bryston SST or Pass X.5 and to see how that stinky 30 years old 140W V-FET consumer amp will push up against the “industry” leaders. In face if I have the Lamm M1.1 then I would be more then enough to say what is going on. Unfortunately my MiniMe is not the “investigative” speaker but for a sake of general education and I would like to hear Yamaha B-2 on something more conventional.

Anyhow, if you are near New England, have a good acoustic system that you drive with 100-150W of power, has no problem with ego and have an interest how an old V-FET will sound then my B-2 now in a condition to show off what those amps were able to do. It would be interesting to see if we have any progress in powerful SS amplification.  I think we do and I think that Lamm M1.1 in Class A would be more interesting then my B-2 ….but I am so long off from the powerful SS amps that it might be fun to play it again as the “quest star”.

There are some information about that new Japanese amps in the threads below:

http://www.audiocircle.com/index.php?topic=65312.0

http://www.diyaudio.com/forums/solid-state/37247-any-info-manual-about-yamaha-b-2-a.html

It looks as it is some kind of custom production (though I think it is lie) but they went for Yamaha B1 version where plus and minus made on the same polarity transistor. The B2 use commentary pairs, so they are different all together.

I would like to pass some comments about my Yamaha B-2 experience. I cannot comment confidently about sound.  I do not want to drive with it the Macondo line-arrays, so I use it with MiniMe. The MiniMe has very good Focal Utopia TN51 tweeter (I love it a lot) but everything else is not what it need to be. The B-2 is very cool designed amp, small and sexy. The whole mixing-switching board shall be trashed and bypassed. This leaves a lot of space inside right next to the front panel. Those 4 regulators in the front panel need to be trashed and instead then placed multi-turns for adjustment of bias and DC. In the real word it would be very cool to set bias with a respect to the given specific load of the B-2, measuring the lower distortions and at maximum power.

I based my B-2 at 68mA and I will let it to be as it for a while. After all that 30 year the amp does very nice with .000 if DC at output. I t would be more fun if I have better speakers for the B-2

Paul S wrote:

my own recent experiments have shown that dialing in voltage and current is just as Big a Deal with SS as it is with tubes.  Those who merely accept the "factory settings" are (potentially) missing out.

It it not as Big Deal with SS as it is with tubes – it has different effect and sonic impact. From a different perspective the B-2 use transistors that have very high voltage on bias, it might make all things different. BTW, there are no “factory settings” as many amps allow you to select idling current. The Lamm M1.1 has on the back a speaker impedance switch. What do you think that switch changes? Of course the output stage current! Many amps has the same feature on one way or another any person who use SS and understand how to get power from SS to a given load do set an optimum current for the given load of their speaker.

Paul S wrote:

BTW, the B2 was idesigned from the start as a "cult" amp, with the whole "clean-sheet" design and Bushido/nutso attention to detail that truly set it apart.  Plus, it was Really Expensive!  Talk about your wet dream: this and the Esprit were the stuff of Cult Nerd Fantasies, Back in the Day.

I do not know. It looks like a regular amp to me. I do not buy into and not willing to propel the myths. If you say that it was Really Expensive then it was a reasonable to the price amp. It is was Cult Nerd Fantasies amp then it was not good fantasies as there are few things that need to be done differently.

The greatest thing that happened to my Yamaha B2 amp was the fact that I got rid of my MiniMe ported bass section. The MiniMe is truly nice now and I operate in the highly desirable not annoying status. That all made me to pay more attention to what Yamaha B2 does. 

It had to say what Yamaha B2 does – it sounds in the way how it sounds as I have absolutely no problem with it sound.  It has no annoying SS character and it sound very soft and lash, though the fact the I own the tweeter that B2 driver might have a lot of to do with this fact. I put in the B2’s input a 24 step-attenuator with 250K impedance to fight the huge B2’s gain. All together it turned out to be a nice amp. It has a great protection circuit that does work VERY well and it’s outputs are perfectly shortable – I do not like when they are not.

I did play with Yamaha B2’s bias. The service manual insists 40mA. Still I asked me what would be the right bias for my specific load. My fist sentiment was to get max power to my specific speaker. The amp has much more power then I even need for my room. They I decided to go not for power but for LF character at high volume.  Experimenting with bias I feel that the amp sound more polite with much higher bias. I do not know why – I presume that the amp is running at higher power before it switched to class B – I did not measure it. Still, juts purely by listening I end up with 120mA bias – 3 times higher than it was designed for.

Now my B2 runs quite hot, that is not end of the world for winter. I decided to not risk the B2’s unique V-FET transistors and put the forced cooling in the game. I put atop of B2 two of my favorite Antec 200mm "Big Boy" fans. I am huge fun of the Big Boy fan. It is large 7.8 inch, thin, DC, low spin that at low voltage is absolutely silent with very food air flow. Even at higher spin it has very pleasant LF harmonics. So, I put two of them above each transistor heat sink and powered from a high resolution thermosensor . After the calibration of the thermosensor it begins to work very well. The amp starts and run for 10 munutes with no fans spinning. Then the fans very slowly to pick up rotation and at 65 degree Celsius the funs run at ~200RPM with no sound of any kind. The temperature is stabilized with surprising stability. I took 8R power resistor and drove the amp for a half hour at fill power. The fun spins faster but still far from it max 800RPM speed. Very cool.

It is ridicules how pleasant the Yamaha B2 sound when it operates in class A and how much worse it sounds when it switches to class AB. I did not measure the power but with default 40mA it switches to class B very soon. With my current cooling techniques I can run the amp at 120mA where it plays in class A up to the volumes (or a bit less) where I typically listen.  I would like to keep the amp further without switching into class AB but it does not dissipate heat good enough with my cooling. What would be very good is to have a pure class A biased amp on the V-FETs.

I will probably try a different cooling, trying to bias the B2 at 150mA. A bit dangers as it looks like B2 has no thermo-protection. Also one of B2 channels is switching to class AB at 8dB sooner than the second channel driven with the same current. It needed to be adjusted but I do not have too much knowledge about SS. So, I guess I need to find a local technical who would calibrate both of channels to enter class AB at the same time. It shall be very simple to do. Probably to throw in there a thermo-relay would be a good idea, if I intend to drive it too hot. Perhaps I would need to put in there a switch that would drop bias to 50mA, switching it to summer mode….

It is not too hard to do myself but I would like not to. It would be cool to have a local guy around Boston who is accustom with SS amp and who would be motivated to work on my Yamaha B2.

Hm, this is interesting. I have fixed one of my B2 power amps. It works very nice but the most important is that it looks like I have found a local technician who actually can do the job.

When I got a problem with my second bough B2 I called to Stereo Surgeons at East Hartford, Connecticut . Kenneth Bernacky is very experienced and very responsible in his work person and I felt very comfort able to send both of my B2 to him. Unfortunately Ken also have highly paranoiac attitude and I asked myself of I want to be exposed to it. I did not want to hear lectures from him hot to live and how bad people around him – I wan fast fixing of my amps. So I was looking other avenues.

A few years back after the event with that retard repair-mad in Waltham who almost killed my R&S tuner I had a very pleasant conversation with a guy from QAudio in Cambridge. I never cared too much about QAudio but it was old QAudio. It looks like QAudio store was bought a guy name Dariusz. He care the same low-hi product line but his is the guy who does reappears himself. It looks like he is in town for a while and before owning QAudio he made rehears for other Boston shops that just collected jobs for him.

Like anybody else in this field he has his own attitude and he begun to explain me that that amp is garbage and need to be thrown to trash. I was taken back as I was not prepared to this move. When I go to doctor I do not anticipate that he would tell me that I need to die.  Also, Dariusz did not strike me as the person with whom I might argue about Sound. However, his attitude toward to repair itself was in my estimation just what the doctor ordered. When I begun to explain to him what was wrong with the amp and what I did with it he with smile informed me that he does not care and I shall pretty much shut up and let the people who know what they do to do their job. With all honesty it was exactly what I was looking for in a technician. I instantly stopped to worry and in a few days I got my B2 in perfectly operational order, wonderfully repaired and serviced, the price was reasonable and the whole thing was great.

Dariusz, swiped it at full power and the amp got perfect symmetrical clip at 153W – what else to expect! If he fix my second B2 and have some extra time in his hand I might commission him to finally assemble the Zarathustra II. I am very enthusiastic as he is looks like know what he does and he is young enough do not behave like a jerk.

EchoWars wrote:

Was cruising the web, looking for a pic of the back of a B-2 (for various reasons) and saw a pic of Romy and had to check it out. Hope he is well and healthy. Mark Twain once said "When a man loves cats, I am his friend and comrade, without further introduction." I second that notion. You get anything odd happening with the B-2's (provided you still have them, as I can see how old these posts are), by all means, drop me a line. I'd be happy to help if I can.