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Bryston tiny transformers in amp.!
- Thread starter tlxaudio
- Start date
gslikker
Super Member
yeah I have seen some high end guy showing off his USA made stuff. He did put the transformers in series. Later on his amp went up in smoke and he did not understand why.
Read: depending on the amount of power used, the power supplies modulate each other.
Although, not cranking up the amp, one may never notice, but it is no good practice.
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I'm doing the same conversion. The original transformers seem to be made by Harris (at least they have a logo that looks like Harris on them), and they have the number 510486 on them. Definitely single primaries. The line fuses are 3A which does equate to 360VA, but I'm guessing these are just over large for the inrush current? The dimensions are identical to Toroidy's 100VA standard transformer. Connected to 120V/50Hz via a step down transformer, they show 59V at the secondaries with the amp on, but no load/signal.
I think I'm going to get the Toroidys, in 58V CT, or 2x28V. Only open question is how to most easily mount them like the originals, which use a T nut epoxied in the center.
I think I'm going to get the Toroidys, in 58V CT, or 2x28V. Only open question is how to most easily mount them like the originals, which use a T nut epoxied in the center.
Attachments
OK... so, got the Toroidys today, and, either their transformers are a bit bigger for the same VA, or the Brystons are actually only 80VA. I think I can still make these fit. I will have to drill new mounting holes in the bottom of the case, though, and I may need to cut a bit out of the L shaped brackets that hold the inner module rails, in order for the new transformers to sit flat on the bottom of the case (and low enough in the case). 
twiiii
Lunatic Member
Remember depending on the type of power supply rectification and filtering the DC voltage can easily be 1.5 times higher than the AC voltage coming out of the power transformer.
As others have said Bryston is a well respected amplifier and easily meets it specs in RMS power from 20 to 20 KHZ with room to spare. When we had Mcintosh amplifier clinics as a dealer and when we had a few come into our shop that had been abused they always met specs over 90% of the time. The ones that didn't definitely been damaged. Exposed to liquids or power surges and voltage fluxuations from the power company. OLD Mexico at night the wall voltage could easily drop down to 90 or 95 volts while reaching over 135 volts at other times. Our side of the border stays between 122 to 127 volts as we are close to a power sub-station.
As others have said Bryston is a well respected amplifier and easily meets it specs in RMS power from 20 to 20 KHZ with room to spare. When we had Mcintosh amplifier clinics as a dealer and when we had a few come into our shop that had been abused they always met specs over 90% of the time. The ones that didn't definitely been damaged. Exposed to liquids or power surges and voltage fluxuations from the power company. OLD Mexico at night the wall voltage could easily drop down to 90 or 95 volts while reaching over 135 volts at other times. Our side of the border stays between 122 to 127 volts as we are close to a power sub-station.
So, if someone had brought in a 2B-LP you would have tested it to see that it could continuously produce 100WPC into 4 Ohms? How long is continuous? Rectification gains don't buy you anything in terms of secondary sag under load when the core is saturated.
whoaru99
Epic Member
Have you done any testing or have reference to a test that shows the amp does not meet published output specs with the original transformers?
No. It's just based on math and design principles.
A few other things to note, though:
1. It's conceivable that transformers made to run only off of 60Hz, rather than 50/60Hz, could be smaller for the same VA rating... but my 2B-LP is marked 50/60Hz.
2. It's conceivable that the VA rating system used by Toroidy today is stricter than the one used by Bryston (Harris?) at the time my amp was made (1987).
3. VA rating is based on the power a transformer can provide continuously without overheating or drooping too much. How much is too much? How long is continuous?
4. The new Toroidys weigh about 10% more than the originals, and have 1.7 Ohm secondary resistance vs 2.5 Ohm in the originals.
5. I did not find any old Audio magazine tests of this amp, but I did find this review that tested it including 4 Ohm 100W delivery, and it was able to deliver for whatever the length of the test was. The main issue the reviewer found was that the amp fell pretty short of its claimed 500 damping factor at 20 Hz. https://www.google.com/search?q=bry...e=ive&vld=cid:afcf12f5,vid:_VNyW5azngA,st:235
Overall, I think what likely is happening here is that Bryston did an excellent job of leveraging the safety factor over VA rating of the transformers. Squashing the transformers between the top and bottom of the case probably helps them dissipate heat - using the case as a heat sink, which may extend the effective VA capacity of the transformers as well.
A few other things to note, though:
1. It's conceivable that transformers made to run only off of 60Hz, rather than 50/60Hz, could be smaller for the same VA rating... but my 2B-LP is marked 50/60Hz.
2. It's conceivable that the VA rating system used by Toroidy today is stricter than the one used by Bryston (Harris?) at the time my amp was made (1987).
3. VA rating is based on the power a transformer can provide continuously without overheating or drooping too much. How much is too much? How long is continuous?
4. The new Toroidys weigh about 10% more than the originals, and have 1.7 Ohm secondary resistance vs 2.5 Ohm in the originals.
5. I did not find any old Audio magazine tests of this amp, but I did find this review that tested it including 4 Ohm 100W delivery, and it was able to deliver for whatever the length of the test was. The main issue the reviewer found was that the amp fell pretty short of its claimed 500 damping factor at 20 Hz. https://www.google.com/search?q=bry...e=ive&vld=cid:afcf12f5,vid:_VNyW5azngA,st:235
Overall, I think what likely is happening here is that Bryston did an excellent job of leveraging the safety factor over VA rating of the transformers. Squashing the transformers between the top and bottom of the case probably helps them dissipate heat - using the case as a heat sink, which may extend the effective VA capacity of the transformers as well.
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restorer-john
Addicted Member
Get a pair of dummy loads, feed in a sine, drive the amp to rated spec, view the output on a decent 'scope and report back. Then you will know if your bodge transformers are up to the task or not.
Bryston amplifiers are probably one of THE most conservatively rated products on the planet. They rate to FTC spec with plenty of reserve. I've had only a few over the years and they delivered nearly 30% above their continuous rated power and THD ratings.
Bodge? Really? These guys make some really nice power and output transformers. There's no need for slander here.
I have an HP distortion analyzer. No need for guessing what something sort of looks like on a 'scope.
I bought this amp new in 1987. I have used it in a number of systems over the years. You don't have to convince me it's good product. But Bryston doesn't have access to any physics not available to other companies. Transformers this size cannot be more than 100VA, and are probably less.
Update: I did one quick test on the transformers:
Original:
115VAC 60Hz input stabilized with Variac, verified supply voltage no load and with load
No load: 58.8V
32 Ohm load: 55.2V = 6.1% droop
Toroidy:
230VAC (theoretical, but actually measures 236V with only about .1V difference for load) 50Hz, just plugged into the wall.
No load: 63.3V
32 Ohm load: 58.4V = 7.8% droop
I would have liked to have tested them for heating with this roughly 100W load, but my IR camera seems to be dead. Hopefully it will come back after a bit of charging.
Some of that extra droop is due to the higher input voltage and higher no-load voltage, but I'm interested to see what the output is from the transformers at idle in the amp.
Update 2: IR camera did just need to be charged. This was done with both transformers just sitting on the tile floor, so no advantage in heat dissipation for either of them.
Original: 32 Ohm load = about 95W
Initially: 23C
After 5 minutes: 32C
Toroidy: 32 Ohm load = about 105W
Initially: 23C
After 5 minutes: 30C
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whoaru99
Epic Member
There is a (not Amir) review/test on ASR that includes data. In a quick look it generally seems to meet or exceed rated power/THD at 8 and 4 ohms.
I see. My mistake. I did not realize that FTC power claims only needed to be continuous for 8 Ohm loads. At 4 Ohm, just delivering the power for a short period of time is fine. So, the transformers, even if they are only 80VA, are still (just) sufficient to deliver full 8 Ohm power continuously.
whoaru99
Epic Member
Hey, it's your amp. Personally I don't care if you connect it to external 1000VA transformers if that would trip your trigger.
The point is I don't believe the assertions the Bryston amp wouldn't meet or exceed published specs as designed. If it didn't that would be considered broken and they'd repair it under warranty... albeit the 20 year warranty is long past on your 1987 purchase.
The point is I don't believe the assertions the Bryston amp wouldn't meet or exceed published specs as designed. If it didn't that would be considered broken and they'd repair it under warranty... albeit the 20 year warranty is long past on your 1987 purchase.
Like I said, it's my misunderstanding of the published spec. I thought 50@8, 100@4, 200@8 bridged, meant continuous for all of these... but it does not. It's only for the 50@8. That's a bit disappointing compared to my other amps which do have sufficient power supply to continuously deliver their 4 Ohm rated output.
I'm also a bit surprised at Bryston going with just thermal switches on the heat sinks as the only protection for overloading the transformers. I'm sure they tested it, but it still seems odd.
whoaru99
Epic Member
I'd think rather than a design deficiency, I view it as overloading the transformers wasn't a durability or performance concern for their engineers.
First let me be clear I think an amp should meet or exceed published specs under the conditions of the rating method.
That said, the general fixation (not just/only you) on "continuous power" has always been red herring to me. That is not how an audio amplifier is taxed in the normal function of an audio amp passing music.
First let me be clear I think an amp should meet or exceed published specs under the conditions of the rating method.
That said, the general fixation (not just/only you) on "continuous power" has always been red herring to me. That is not how an audio amplifier is taxed in the normal function of an audio amp passing music.
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I see what you mean. Undersized transformers, in this case, along with a common collector output, seems to be more about durability, while meeting the letter of the published spec. A bigger transformer would make it harder for the output section to crowbar the power supply without being damaged. The circuit board calls for AGC 2 for 200-220V and AGC 1 (point something? - hard to read) for 240V. I think I'll try a T1 or an AGC 1.5, and see how that goes.