My experience with the 4BST is that it doesn't get so hot that you can't keep your hand over it. What kind of cables are you running to the speakers? High capacitance cables succh as the "Goertz MI" series can cause the amp to run hot (in my experience).
My 4B-ST runs warm, but not hot to the point it's uncomfortable to keep your hand on the lid -- even when driven hard. Is your amp getting sufficient ventilation? If it's in a cabinet or has less than 3-4 inches on all sides, you may need to provide it more space, or install a small fan (there are some very quiet types made for audio installations).
Four inches above the amp, open all around. Rack is Lovan. I use Audioquest Lapis ICs and Audioquest Sterling speaker cable--terminated for bi-wire at store. I must add that the heat seems concentrated on the right side of the top lid (if you are looking straight at the amp). The cooling fins on the sides of the amp are always warm, but not uncomfortably hot. However, the sound does not suffer at all, in fact at first I attributed the heat to normal amp life. I always turn my amp off after a listening session, so I don't know about the temperature when the amp is not that active. I don't know if there is something wrong with the amp that will crop up in the future. I wanted to bounce all this off everyone here first before I start shipping it back to Bryston.
Argent, I have used Bryston 48's and 7b's for years with low impedence Magneplanars, Thiels, and Apogees and have never experienced any excessive heat problems. I will say that the Brystons run hotter with Apogee Caliper signatures than with the Thiels or Maggies, but never so hot that you can't put your hand directly on them. I would advise getting a calibrated cooking thermometer and measure the heat at several points on the top and sides of the amp...then call Bryston with your temperature measurements and a description of your components, and see if they think it is running too hot.
I'm not familiar with the speakers that you have, but, if they aren't very sensitive or dip into the low ohm range (1-3 ohm) they can make your amp run pretty hot. Especially if you like to listen to your music quite loud. I used to have a pair of Infinity Kappa 8's and they would dip into the 1 ohm range (with sensitivity at about 84-86db)and would make my amp run VERY hot, could even cause the amp to activate it's protection circuitry if we really cranked it up. And this amp had plenty of arse. I now have a pair of Legacy Focus that are sensitive speakers (95-96db and operate @ 4 OHM) and don't have this problem. My amp rarley even gets warm. That Bryston has tons of arse, so either your speakers are the cause, as mine were, or the problem is elsewhere. Maybe someone else has another suggestion. Don't know if this helps. Good luck.
I have the Legacy Convergence, which were rated by Legacy as having the same sensitivity as the Focus. Audio magazine reviewed the Convergence and measured their sensitivity at 92db. Legacy seems to include room gain in their figures. I still love em !! (the speakers). My OCM 500 amplifier runs around 115 degrees with these speakers. At 130 degrees things become to hot to hold your hand on.
You mentioned that the amp seemed hotter on the right side of the top. The 4B-ST is a symmetrical construction, with the heat sink modules each containing a separate channel of amplification, with the twin toroid amps occupying the center of the chassis. The only other factor I can think of that might cause excessive heat on one side (given the symmetrical internal layout) is a badly adjusted DC offset. I think your problem merits a call to Bryston, since excessive heat will decrease the life of the solid state parts and output transistors.
My 4B-ST runs warm on the top and warmer on the sides as there is little space between the heat sinks and the sides of the cabinet. Never too hot to touch but the sides do get verrrry warm...
Argent, have you tried swapping the amps input cables left for right to see whether their are any sources issues? Ie now the left side is hotter than the right. Similiar experiment would be to swap left for right speaker leads (with source correctly connected) to isolate whether there are any "load" issues. This info will probably be useful if you talk with Bryston.
My speakers have a 90 dB efficiency, 8 ohms nominal impedance, recommend 110 watts for amp power. The 4B-ST should kick them around the block no problem. The funny thing about all of this--Bryston is the distributer for PMC monitors in the US and Canada. PMC uses Bryston amplifiers when they test their speakers. I thought I was buying the best possible match for my amp. Oh well, I'll just put a bag of ice on the amp and it'll be fine. Just kidding :) I forsee a call to Bryston in my immediate future. Hopefully the amp will not be out of my life for long. By the way, if you all have never heard of PMC speakers, you should check them out. You might find it interesting to know that PMC (Professional Monitor Company) boasts that about 90% of all CDs made are mastered on systems using PMC monitors. Thanks for all the help.
Alright, just a follow up. I put the amp through the paces tonight for about an hour. It stays cool for about two songs (rock, R&B) at a pretty good volume. Then it begins to warm up pretty steadily, favoring the right side of the amp. After about an hour of playing, moderate to loud volume (classical, single vocalist and small assortment of instruments) I checked out the amp. The left side of the amp is merely warm, both the heat sinks and top of the amp are the same temperature. The right side of the amp is too hot to leave a hand on for long. The heat sinks on the right side are scalding also. The heat is present from the front of the amp to the back of the amp on the right side. I did not record the temperature as I do not have a thermometer to check it with, but I figure it was pretty damn hot if I couldn't leave my hand on it. Now, the interesting thing is that when I stop the music, the right side of the amp slowly returns to the same warm state the left side of the amp is at. I plan on calling Bryston soon.
Mullen, glad to hear you love your Legacy's. My wife and I love ours also. An increadible improvement over the Kappa's. Hoping Argent finds out his problem. I'm starting to upgrade and am considering the same amp he is running. Hey, us Legacy owners are at a minimum around here... keep on enjoying!
Argent, there is something wrong with the amp. It is not your load. It is in need of repair if it gets that hot on one side.
Argent, I had the exact same "problem" with the 4BST as you have: The right side of the amp was damn hot! It was happen a month ago. I called Bryston, they suggest that I should switch the speaker cables. And then I found out that I connected the channel1 with right speaker and channel 2 with left speaker; also with my interconnect as well. But I have used the 4BST like that for almost 2 years with no problem. I thought that maybe the problem now, so I correct the connection: Channel 1 connect to left speak and channel 2 connect to right speak and also changed the interconnect. The funny thing is, after that, the right side become pretty steadily as normal as the left side?! Since then, I don't have the warm problem with the right side of the amp. And I don't have any idea why...?
Nope, my speaker cables and interconnects are hooked up correctly. The only other thing that might be causing this is my pre-amp. For anyone who owns a Conrad-Johnson product, you know that they are not phase inverting. This means that when I send the signal out from the amp to the speakers, the red terminal on the Bryston must correspond to the black terminal on the speaker. But even if I hooked that up wrong, which I did not, I still don't see how that could hurt the amp. Phase inversion really just affects the speaker, I think. Anyone else out there who owns a CJ product want to chime in?
Just got a response from Bryston. They want me to see if I can duplicate the problem after I switch my speakers around. Guess they want to rule out a bad speaker or cable. I'm going to try it again, but I've moved my system to different rooms in my house often enough to have switched the speakers around several times. This heat thing has pretty much been a feature of the amp since I got it. Oh well, I'll keep everyone posted on what happens.
Guys, I had this problem and here is the fix which I got from Bryston. I had the same problem with my 3B getting hottor on one side more than the other. You have is Biasing problem. Here is the procedure to fix it.
The bias procedure for the 3B amplifiers is as follows:
Remove the top panel of the amplifier, and locate the 2 pairs of test points on the PCB. They will be on the left side of the main board for each channel, between the large 5W power resistors.(The newest amplifiers have them at the top left corner of the
board). Using a millivolt meter, measure the Voltage between
each of the pairs of test points. It should read between 10 and 15millivolts on each pair, or a TOTAL of 20-3OmV. (One may be higher than the other, this is not important, only the total). If it is higher, or lower, than 20-3OmV total, the bias may be adjusted by the rotary potentiometer control in the center of the board,(clockwise is to increase the reading). When the reading is within
the correct range, with the amplifier idling and no input connected, temporarily place the top panel on the amp, and leave it for 15-20minutes. Repeat the reading, and adjust if necessary. The bias is properly set when the reading stays within the correct range for 2successive readings. Then re-install the top screws, and the amp is now set. (Note: on older amplifiers, the test points may not be present. The readings may be taken directly across the large 5Wresistors in that case, and only one resistor need be used for the test. In this case, the reading is only the 10-15mV reading of one).
Well, switching speakers or cables around did nothing to diminish the heat problem. The unit is going back to Bryston tomorrow. Hopefully the excessive heat did not damage the internal components.