The output stage should hold up even with a shorted downconverter, the outputs are 400V devices and the drivers 200V. As long as there is no signal or the output is unloaded they should be fine. The instant blowup of the output stage suggest shorted drivers or an open bias network.
It probably started with a shorted driver or open (intermittent?) diode string. Then this takes out the outputs, and the drivers. The shorted output stage then causes the downconverter fets to blow, the fuses blow after all the semiconductors as usual...
It probably started with a shorted driver or open (intermittent?) diode string. Then this takes out the outputs, and the drivers. The shorted output stage then causes the downconverter fets to blow, the fuses blow after all the semiconductors as usual...
Hi Giaime,
I did get your attention, didn't I?
Still ..........
Hi megajocke,
The first failure may have toasted the downconverter. For sure, non-matched outputs would cause issues with no emitters to force a balance. The bias circuit may have possibly partially failed also. I would expect it to go short.
My guess. An older, powerful sub amp develops broken solder connections. When the amp was moved, flexing of the board caused the failure. The high fault current caused the downconverter to fail short.
Hi nick78,
Normally I check and resolder connections in sub (and car amps) for this exact reason. It's part of my normal service. It's hard to tell other people what you do without even thinking about it.
The beauty of this design, like other Carver amplifiers, is high output power with low dissipation and relative freedom from 2nd order problems. 2nd order issues are reduced, not eliminated with these designs.
-Chris
I did get your attention, didn't I?
Still ..........Hi megajocke,
No way. There is minimal heat sink area and the dissipation would run the outputs into thermal runaway before long. You just need a little bias at that voltage to heat things up and start the slide to destruction.
The first failure may have toasted the downconverter. For sure, non-matched outputs would cause issues with no emitters to force a balance. The bias circuit may have possibly partially failed also. I would expect it to go short.
My guess. An older, powerful sub amp develops broken solder connections. When the amp was moved, flexing of the board caused the failure. The high fault current caused the downconverter to fail short.
Hi nick78,
Normally I check and resolder connections in sub (and car amps) for this exact reason. It's part of my normal service. It's hard to tell other people what you do without even thinking about it.
The beauty of this design, like other Carver amplifiers, is high output power with low dissipation and relative freedom from 2nd order problems. 2nd order issues are reduced, not eliminated with these designs.
-Chris
Of course, if it has a standing current, it will start running away with that voltage as it is not compensated. The OP didn't say if they blew immediately, like power - bang, or after a while (which might not need to be too long). I assumed he meant they blew instantly, which should not happen even with this high voltage.
Hi megajocke,
This is why I suspect an intermittent connection. Next to instant bang if the bias network went open at this voltage. On the Lightstar, the static rest voltage is 13 VDC on the rails. If one got stuck to 125 VDC and the bias network opens briefly, I would expect some damage.
-Chris
True, there should be some time delay. This delay could be very short if the devices were not properly mounted, but there would be some delay.
This is why I suspect an intermittent connection. Next to instant bang if the bias network went open at this voltage. On the Lightstar, the static rest voltage is 13 VDC on the rails. If one got stuck to 125 VDC and the bias network opens briefly, I would expect some damage.
-Chris
The first failure was instantaneous (~ 1/2 second) while moving the sub. I have spoken with NHT and the likely failure is an intermittent connection between the sub's controller and the sub itself (they are connected with a special cable). Basically the two drivers went to max excursion and 1/2 second later the fuse pops.
The 10" drivers are tough birds, I believe they have the same magnet/motor/coil structure of the infamous 1259's. They have shown no apparent damage (measured or observed) from this, and seem to still function perfect.
The second failure (when the outputs blew again after I replaced them) was thermal. After being powered on for a minute, the output heated up enough to thermal short and that popped the fuse again after about 1/2 second. I found that, after replacing the blown output once more, that the amp could be turned on for ~ 10 seconds at a time without additional failures occuring, but the outputs on the (+) side would get nice and warm, much warmer than normal
I don't know yet if anything further is damaged in the outputs. The speaker output has no significant DC offset, so I don't believe that the (+) side outputs are being driven on to any significant level. My understanding is that the downconverters are designed to keep the voltage drop across the CE junction < 6 volts, a safe bias at 6 volts might be deadly at 130V.
fingers crossed.
The 10" drivers are tough birds, I believe they have the same magnet/motor/coil structure of the infamous 1259's. They have shown no apparent damage (measured or observed) from this, and seem to still function perfect.
The second failure (when the outputs blew again after I replaced them) was thermal. After being powered on for a minute, the output heated up enough to thermal short and that popped the fuse again after about 1/2 second. I found that, after replacing the blown output once more, that the amp could be turned on for ~ 10 seconds at a time without additional failures occuring, but the outputs on the (+) side would get nice and warm, much warmer than normal
I don't know yet if anything further is damaged in the outputs. The speaker output has no significant DC offset, so I don't believe that the (+) side outputs are being driven on to any significant level. My understanding is that the downconverters are designed to keep the voltage drop across the CE junction < 6 volts, a safe bias at 6 volts might be deadly at 130V.
fingers crossed.
WARNING!! this is my first post, so go easy on me! I realize this thread is 7 yrs old, but I have a Sub Two that is blowing a fuse as well. The thing is, the fuse is not on the diagram. I see the 2 fuses located on the output board (total amplifier repair newbie!) but not the fuse that is on the power supply board. Is there a second page to the diagram or something that describes the circuit theory/signal flow document that could help me repair this amplifier?
I have a set of both from old pioneer system
Im sitting on a pair of MSA1302 And MSC3281 transistors. Any idea whag theyre worth. i know they come from a mid 90s system that pounded but was all in 1. I never realized the transistors were that good. Im new to this stuff, as in still ramping amps into my idiot fingers twice daily. But learning. Id be interested in letting them go to the right buyer if theyd toss in some info on building my first amp etc. Thanks guys hit me up at 306 700 5221 by text is usually best.
Im sitting on a pair of MSA1302 And MSC3281 transistors. Any idea whag theyre worth. i know they come from a mid 90s system that pounded but was all in 1. I never realized the transistors were that good. Im new to this stuff, as in still ramping amps into my idiot fingers twice daily. But learning. Id be interested in letting them go to the right buyer if theyd toss in some info on building my first amp etc. Thanks guys hit me up at 306 700 5221 by text is usually best.
MJL3281 and MJL1302 are drop-in replacement devices currently produced by On Semiconductor.
MJL3281AG ON Semiconductor | Mouser
https://www.mouser.com/ProductDetail/ON-Semiconductor/MJL1302AG?utm_term=MJL1302&qs=HVbQlW5zcXVTkkXRe2jhZQ%3D%3D&utm_campaign=MJL1302AG&utm_medium=aggregator&utm_source=findchips&utm_content=ON-Semiconductor
I have used them in my Krell KSA-50 MKII clone.
https://www.diyaudio.com/forums/solid-
state/31077-krell-ksa-50-pcb-889.html#post5264496
MJL3281AG ON Semiconductor | Mouser
https://www.mouser.com/ProductDetail/ON-Semiconductor/MJL1302AG?utm_term=MJL1302&qs=HVbQlW5zcXVTkkXRe2jhZQ%3D%3D&utm_campaign=MJL1302AG&utm_medium=aggregator&utm_source=findchips&utm_content=ON-Semiconductor
I have used them in my Krell KSA-50 MKII clone.
https://www.diyaudio.com/forums/solid-
state/31077-krell-ksa-50-pcb-889.html#post5264496
Hi havix08,
They are used, so not that much value as they were not expensive to begin with.
You can look some parts up at DigiKey Electronics - Electronic Components Distributor . Digikey is not the least expensive place to buy things. Also, MSA sounds wrong as a part #, they could be copies of the MJL1302 (= worth even less than nothing).
-Chris
They are used, so not that much value as they were not expensive to begin with.
You can look some parts up at DigiKey Electronics - Electronic Components Distributor . Digikey is not the least expensive place to buy things. Also, MSA sounds wrong as a part #, they could be copies of the MJL1302 (= worth even less than nothing).
-Chris
Only time they're worth more than the DigiKey price is if you have a bunch of matched pairs, but even then they aren't worth much.
Also, 2SA1302s and 2SC3281s were used in lots of amps back in the 90s. When I recently scrapped a Crest CA9 due to "structural damage" (someone genius took it on the road without supporting the back), I saved the output modules since they each have 9 matched pairs on them.
Also, 2SA1302s and 2SC3281s were used in lots of amps back in the 90s. When I recently scrapped a Crest CA9 due to "structural damage" (someone genius took it on the road without supporting the back), I saved the output modules since they each have 9 matched pairs on them.
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