Bryston B4 NRB fix.

[laatsch55]

During testing of aforementioned Bryston something gave out at 75KHZ while outputting 250 watts. I replaced the 8 amp supply fuse and brought it up on a variac and DBT. The bulb pulsed while the protect relay cycled. A definate high current draw someplace. Took out the left side outputs and did not find any shorted. In circuit tested the TO-220 drivers and no short there. The modular desiogn of the Bryston allows the side of the unit with the heatsinks to be detached in one piece with the driver board unplugging from the power supply board on removal.

 

[laatsch55]

Pretty darn handy.

 

[laatsch55]

Powersupply is pretty rough.

 

[laatsch55]

Chassis almost stripped.

 

[ksrigg]

Power supply looks like it got pretty HOT. Have you found the problem yet? Over the years, I've found Bryston to be pretty user friendly. You might be able to call their service people and get a little advice. I know you probably don't need it, but I'll bet they'de love to help you. One of my amps has visited Canada twice. They never charged a dime. In fact, when I asked about the large rubber feet for the unit, they sent them to me FREE. The only thing was... I did have to buy a Bryston BOX. That's the only way they will accept an item for service. Has to be in THEIR box..I know you don't need it, but


Good luck.

 

[laatsch55]

Sutton, there are times I'll gobble up all the luck available!!! I have not found the problem yet. Just got through checking the obvious stuff. We are now stalled out till I get a service manual.

 

[laatsch55]

With just the AC control board and the transformers on line the 1085 relay clicks to let the secondary voltage up. I was getting some flaky readings on 1 BR. They are soldered to the power supply board so there could be other influences. I'll desolder and check those.

 

[Gepetto]

Looks like the center bridge rectifier has done a number on the PCB laminate Lee. Very discolored and the solder pads for it look heavily oxidized.

 

[laatsch55]

Yes Joe, a new board at least to do it right.

 

[laatsch55]

I installed the power supply board and hooked up to the transformer secondaries, DID NOT hook up the speaker outs or driver boards. Protect relay clicked on after 70-80 volts anfd we now have +/- 85 volts DC on the rails.

 

[laatsch55]

2 green LED indicators mean GOOD things. It is now idling. I believe I interpreted the pulsing DBT as a bad thing and overreacted. I was just jacking off the soft start feature. Without the DBT it ramps up just fine. Oh well, I'll know better next time.

 

[Gepetto]

Good to hear it was just a fuse Lee...

 

[laatsch55]

Me to Joe, Kinda. Was looking forward to seeing what makes a Bryston tick. I've seen enough to know I can fix em. Ya outta see the Freq response and THD & N numbers. I'll post here in a bit.

 

[laatsch55]

Any guess on which pot adjusts bias?

 

[laatsch55]

A little testing...... Look at that THD & N number at 80K

 

[speakerman1]

Do these numbers make it sound better? I look at all THD numbers when buying. After a certain number I pay it no mind. I am serious about the question.

Larry

 

[laatsch55]

Funny you shpould ask that question Larrt. Just l;ast night I ran the Bryston for an entire CD then swapped it out with the restored Spec 2. I like how the Spec 2 sounds over the Bryston by large margin. Some will say I like the Spec because that's what I'm used to, well yes and no. I like the Spec because it's very neutral, very very clean and the bass is way more real sounding than the Bryston. I'm trying to figure out how to describe the Bryuston--Clinical, less soundstage, not as musical?? I know all very subjective descriptions, then there is the power levels. The Bryston flat runs out of gas at 284 watts into 8. The Spec at 348 watts. For what the Brystons cost, I couldn't justify that as long as there were Spec 2 's and PL700's available. The Bryston is not a bad amp by any means, impressive specs and build quality, and with a 20 year warranty that is fully transferable, a lot of people have bought these and swear by them. Just don't count me as one of them.
Distortion, to the average human ear becapomes inaudible around .4% ---AVERAGE--- mind you some more some less so when it gets to .04, or .008 does it really matter??

 

[laatsch55]

What impressed me was the .015 at 80,000 hz. That's hard to do. Says a lot about their componenty selection and that they take the time to match certain components between the +/- rails on each channel and also match components between channels, resiostors , caps and trannys.

 

[speakerman1]

Thanks
Larry

 

[laatsch55]

Well---your welcome. I guess I expected more answer than that DUDE!!