I have a couple Yamaha B-2 VFET amps. Uses 2SK76/2SJ26
pairs. The extensive input and speaker switching circuits
have been getting really noisy and intermittent lately and
does not sound tubelike at all lately.(very solid state sounding).
I'm thinking about doing away with the rear connections including
the cheap speaker connectors and removing all switches/relays
from sig path. I'm even thinking about taking both amps
apart if pairs match close enough and paralleling them with
a new drive stage (want to safely drive my Carver ribbons),
maybe even running lower voltage for pure Class A.
Any thoughts about a Zen, balanced Zen or other simpler
input and drive stage?
pairs. The extensive input and speaker switching circuits
have been getting really noisy and intermittent lately and
does not sound tubelike at all lately.(very solid state sounding).
I'm thinking about doing away with the rear connections including
the cheap speaker connectors and removing all switches/relays
from sig path. I'm even thinking about taking both amps
apart if pairs match close enough and paralleling them with
a new drive stage (want to safely drive my Carver ribbons),
maybe even running lower voltage for pure Class A.
Any thoughts about a Zen, balanced Zen or other simpler
input and drive stage?
Hi coloradosound,
Just a thought. Those amps are worth more as Yamaha's than Frankenamps. The outputs are unobtainium on top of all that.
To play, use fresh, available transistors and a proven design. If something blows up, okay. Fix it. Not possible with the Yamaha outputs.
In short, fix the Yamaha's, build new amps if you want to.
-Chris
Just a thought. Those amps are worth more as Yamaha's than Frankenamps. The outputs are unobtainium on top of all that.
To play, use fresh, available transistors and a proven design. If something blows up, okay. Fix it. Not possible with the Yamaha outputs.
No speaker disconnect protection? It's a brave new world I guess. I wouldn't consider doing that.
In short, fix the Yamaha's, build new amps if you want to.
-Chris
Good point on the protection circuit, Chris. Just some thoughts
I had without the schematics in front of me. The switching
circuit for the speaker select is really noise though and I'll
only be using one set of speakers, but still don't think these
would be suitable for driving the Carver ribbons with the
4 ohm rating. Something like 4 stages of bipolars driving
the VFETs also (I think the old "heavy global feedback cures
all distortion" hilosophy was used.
I had without the schematics in front of me. The switching
circuit for the speaker select is really noise though and I'll
only be using one set of speakers, but still don't think these
would be suitable for driving the Carver ribbons with the
4 ohm rating. Something like 4 stages of bipolars driving
the VFETs also (I think the old "heavy global feedback cures
all distortion" hilosophy was used.
As someone who uses B-2 amps to drive my main system I, too, would hate to see these 'reworked' with the new Deoxit (CDA or something like that - supposed to be carbon wiper friendly). You can do a good job of cleaning all the switches and contact points. Or simply by-pass the controls you don't want. You can also replace the speaker terminals without butchering the back. The back is hinged, so can be tipped open about 30 degrees to help access. Also, you can pull the covers off the relays and clean the contacts, as well.
I've done a recap on mine. If you want the parts listing of the caps changed you can PM me. Now that I say that, Its been so long since I've been over here I don't even know if that is possible. If not, reply here and I'll post the list. Also replaced the the bias trim-pots with 10-turn Bourns.
I've done a recap on mine. If you want the parts listing of the caps changed you can PM me. Now that I say that, Its been so long since I've been over here I don't even know if that is possible. If not, reply here and I'll post the list. Also replaced the the bias trim-pots with 10-turn Bourns.
Hi gpdavis2,
Man, I wish people would stop sticking 10 turn pots in amplifiers. I can understand since Yamaha has too much range with most of their adjustments. All a 10 turn pot is , is a pot were the wiper is geared down. The contacts are not rated for DC current in a bias circuit. I would put anything but a standard 270 ° trimmer in one.
-Chris
Man, I wish people would stop sticking 10 turn pots in amplifiers. I can understand since Yamaha has too much range with most of their adjustments. All a 10 turn pot is , is a pot were the wiper is geared down. The contacts are not rated for DC current in a bias circuit. I would put anything but a standard 270 ° trimmer in one.
-Chris
I see nothing here that states that these 10-turn posts are not rated for DC service. And, in many years of use I've not had one fail (other than a few that started out bad and I did not realize it until they were in the circuit).
http://www.bourns.com/components.aspx?cmsphid=7631383|7163299|895905
http://www.bourns.com/components.aspx?cmsphid=7631383|7163299|895905
Hi gpdavis2,
Bad link.
Anyway, I've seen various 10 turn pots fail. There is nothing that is poor quality about a 270 ° pot. I just have a problem thinking that 10 turn pots are better just because they cost more.
Never use a lower wattage part to replace a higher wattage part. Most 10 turn units are rated to a lower power than the part they replaced. I am talking in a general sense here.
-Chris
Bad link.
Anyway, I've seen various 10 turn pots fail. There is nothing that is poor quality about a 270 ° pot. I just have a problem thinking that 10 turn pots are better just because they cost more.
Never use a lower wattage part to replace a higher wattage part. Most 10 turn units are rated to a lower power than the part they replaced. I am talking in a general sense here.
-Chris
I've got three of them and the most recent worked fine
for a few weeks, but has now developed a random loud pop
in one channel!!, which triggers the protection circuit to cut
off both channels for about 5 seconds, then palys fine again
for about 10-15 minutes till the next POP!!!!
Any ideas on where?, what? the fault is?
for a few weeks, but has now developed a random loud pop
in one channel!!, which triggers the protection circuit to cut
off both channels for about 5 seconds, then palys fine again
for about 10-15 minutes till the next POP!!!!
Any ideas on where?, what? the fault is?
No idea what the problem could be, other than I would turn off and leave off until I figured out what to do to fix. As mentioned earlier, the VFETs are not available and you simply cannot buy new ones if you blow the ones you have. 
On the upside, EchoWars, a regular contributor to this website, is probably the most knowledgeable tech in NA on VFET gear. Yamaha or Sony. He is in a suburb of KC, so is only a short trip across I-70 from you. If it were me and I wanted to keep the amp, I'd send it to EW. He has gone through about six of them for folks I know of in the past year (including two for me). Well worth the effort. And, should you decide not to keep, they sell in the $700+ range once EW has worked his magic on them (recapped, etc.).
If you decide you don't want to bother with repairs, I know two people who would like to purchase a non-working B-2 with good VFETs to repair ones they have with blown outputs. If interested, I'll pass along their contact info.
On the upside, EchoWars, a regular contributor to this website, is probably the most knowledgeable tech in NA on VFET gear. Yamaha or Sony. He is in a suburb of KC, so is only a short trip across I-70 from you. If it were me and I wanted to keep the amp, I'd send it to EW. He has gone through about six of them for folks I know of in the past year (including two for me). Well worth the effort. And, should you decide not to keep, they sell in the $700+ range once EW has worked his magic on them (recapped, etc.).
If you decide you don't want to bother with repairs, I know two people who would like to purchase a non-working B-2 with good VFETs to repair ones they have with blown outputs. If interested, I'll pass along their contact info.
That might be the one to start experimenting with.
The Zen v5 looks like something as a good starting
point if the N and P pairs can be swapped in their
sockets to the heatsinks. By giving it voltage gain
by the common source topology I think I can eliminate
at least one of the prior gain stages. Don't know what
type of biasing circuit to use. I think some type of class A
driver/bias circuit should work. I have tons of transformers
of all kinds of voltage ratings, all with fairly high current
ratings that I could build something to run on a lower
voltage to keep dissipation reasonable.
The Zen v5 looks like something as a good starting
point if the N and P pairs can be swapped in their
sockets to the heatsinks. By giving it voltage gain
by the common source topology I think I can eliminate
at least one of the prior gain stages. Don't know what
type of biasing circuit to use. I think some type of class A
driver/bias circuit should work. I have tons of transformers
of all kinds of voltage ratings, all with fairly high current
ratings that I could build something to run on a lower
voltage to keep dissipation reasonable.
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