Good afternoon,
I own an Atoll AM100 amplifier (built around 2004), with which I am very satisfied. Yesterday I must have come to the speaker output while handling the ground cable of the phono amplifier. After that there was a loud noise from the loudspeaker and then there was silence.
The LED is still on and the relay is energized, but no sound comes out. The transistor in front of the relay gets very hot. The rest stays cold. What could have been broken?
Can the power stage transistors IRFP150 or IRFP9140N be broken? How can I measure this?
Thanks for your help.
I own an Atoll AM100 amplifier (built around 2004), with which I am very satisfied. Yesterday I must have come to the speaker output while handling the ground cable of the phono amplifier. After that there was a loud noise from the loudspeaker and then there was silence.
The LED is still on and the relay is energized, but no sound comes out. The transistor in front of the relay gets very hot. The rest stays cold. What could have been broken?
Can the power stage transistors IRFP150 or IRFP9140N be broken? How can I measure this?
Thanks for your help.
yes, no sound at all. No music playing when it shortend. I touched the positive output of the left channel.
.....have a look at the fuses, are these ok?
can you measure the offset voltage at the outputs of the amp?
can you measure the offset voltage at the outputs of the amp?
It seems very strange to me that only 4mA quiescent current is mentioned in the instructions - go to the attachment. 100-150mA are usual with these MOSFETs. Maybe a very special front end was developed. But according the attached file with only the component side of universal PCB the schematic is similar to those from page 10 under
https://opendata.uni-halle.de/bitst...schewJanko_Entwicklung-Aufbau_Ultraschall.pdf
check also out this schematics
https://www.diyaudio.com/forums/sol...t-power-amplifier-elektor-14.html#post5781768
Hexfet power amplifier
HEXFET amp in Elektor
HEXFET amp - please help me fix it.
Need help with Giesberts HEXFET AMP
Need help with Giesberts HEXFET AMP
In the last URL the developer from
http://www.crimsonelectronics.com
give some interesting advices in post #4+8.
Last edited:
If we start to discuss design decisions forum resources have to be inflated.
Where did you get the schematic ?
Where did you get the schematic ?
This company produces till today similar models with the exact same logic ...
Meaning :
if class of operation is class AB then amplifier will produce some heat when operates
Most of amplifiers have Vbe multiplier function that means one device is monitoring temperature on the heatsink and adjust bias accordingly to preserve electrical and thermal stability and a more balanced behavior /versus temperature for the audio result .
In Atoll there is one thermistor in the enclosure, one per amplifier ch that senses heat from nowhere ....The only creteria is the abient temp that exists in the general area of the amplifier ( by all means not the heatsinks )
in reality the thermistor has actually no idea what exactly is happening on the heatsink of the transistors since also if one transistor gets hot for any reason it will take catastrophic time, and its going to fail far before the rest of the amplifier is too warm for the thermistor to sense and act .
Farther more each transistor has individual heatsink and no one will ever guarantee that the heat is the same for P transistor and N transistor
this picture completes a phenomenon called thermal run away and effects both electrical and thermal stability of the device while as expected amplifier will play far different when cold ( expected ) diferent when in operation temeperature , different when very hot .....
In consumer amplifiers thermistors observe heat on the common heat sink and stop the amp if heat is excesive , common heatsink is used between the P and N transistors to make sure that both operate at the same temperature to ensure stabilty , better performance and lower distortion ...
but it gets worst
in consumer amplifiers there is a compromise in the power supply and the supply is actually not enough for rated power and a specific load Obviously far worst in 4R loads so they make money out of this but also gain that if amp is pushed hard there is not enough power behind the tranistors it to make a damage . Distrotion figures hit the sky at this condition but amplifier gets to be idiot proof in some way .
not in atoll though
Even though rule of thumb says that 2 transistors are good enough for 60 Clean Watts in 8R and bit less than double if power supply and heatsink is enough when at 4 R loads ,Atoll continue to supply the amplifiers with huge trafos rated in a way that one pair of mosfets will have enough PSU behind them to produce 100W at 8R and 140 at 4 ( as they say ) while each industrial mosfet has a heatsink half a packet of sigarets and no temprature compensation ....
We do aythorised service for Atoll and while Greece is a rather hot place we repair more than 20 per year with blown outputs
i try to email them with my findings ( did a study on their machine examined temperature/ bias +ambient and so on ) never got an answer from them
now people change my mind .....
PS
very low bias is actually expected to start up with since their machine suffers from thermal runaway and after some time of operation it will boil and bias will be correct or enough at this point ....
Meaning :
if class of operation is class AB then amplifier will produce some heat when operates
Most of amplifiers have Vbe multiplier function that means one device is monitoring temperature on the heatsink and adjust bias accordingly to preserve electrical and thermal stability and a more balanced behavior /versus temperature for the audio result .
In Atoll there is one thermistor in the enclosure, one per amplifier ch that senses heat from nowhere ....The only creteria is the abient temp that exists in the general area of the amplifier ( by all means not the heatsinks )
in reality the thermistor has actually no idea what exactly is happening on the heatsink of the transistors since also if one transistor gets hot for any reason it will take catastrophic time, and its going to fail far before the rest of the amplifier is too warm for the thermistor to sense and act .
Farther more each transistor has individual heatsink and no one will ever guarantee that the heat is the same for P transistor and N transistor
this picture completes a phenomenon called thermal run away and effects both electrical and thermal stability of the device while as expected amplifier will play far different when cold ( expected ) diferent when in operation temeperature , different when very hot .....
In consumer amplifiers thermistors observe heat on the common heat sink and stop the amp if heat is excesive , common heatsink is used between the P and N transistors to make sure that both operate at the same temperature to ensure stabilty , better performance and lower distortion ...
but it gets worst
in consumer amplifiers there is a compromise in the power supply and the supply is actually not enough for rated power and a specific load Obviously far worst in 4R loads so they make money out of this but also gain that if amp is pushed hard there is not enough power behind the tranistors it to make a damage . Distrotion figures hit the sky at this condition but amplifier gets to be idiot proof in some way .
not in atoll though
Even though rule of thumb says that 2 transistors are good enough for 60 Clean Watts in 8R and bit less than double if power supply and heatsink is enough when at 4 R loads ,Atoll continue to supply the amplifiers with huge trafos rated in a way that one pair of mosfets will have enough PSU behind them to produce 100W at 8R and 140 at 4 ( as they say ) while each industrial mosfet has a heatsink half a packet of sigarets and no temprature compensation ....
We do aythorised service for Atoll and while Greece is a rather hot place we repair more than 20 per year with blown outputs
i try to email them with my findings ( did a study on their machine examined temperature/ bias +ambient and so on ) never got an answer from them
now people change my mind .....
PS
very low bias is actually expected to start up with since their machine suffers from thermal runaway and after some time of operation it will boil and bias will be correct or enough at this point ....
here is what you did ...
1)better heat sink will relief mosfets from excesive heat if and when amplifier is pushed a bit harder .
2) I cannot be sure about the heat transfer characteristics of your construction so i dont know how fast and correct heat can be transfered from mosfet to massive aluminum to original heat sink ....Indeed what you have done is a bit better than the original heat sinks
3) attaching the thermistor to the aluminum ( i will not call it heat sink ) is wrong by all means because the curve of the thermistor is not switable for such an application IE the thermistor doesnt work like the tranisistors you have seen in other amplifiers
IMHO such a simple thing it could be also done at the factory
The reason that they never did it is because this arrangment is a bit more quiet than a transistor and we actually would like to have that while the problem is that when heat appears thermistor senses it and does its thing change the resistance too much ....way too much resulting bias drops to levels that will produce distortion ..... its a known phenomeno called overcompensation and this the reason why manufcturers stop using thermistors for such an application ( they still use them only at safety features IE when amplifiers get too hot to shut them down there overcompensation doesn't matter at all )
SO
reading your post makes me also understand that i cannot take your opinion posted in the other discussion as valid one since you listen from an amplifier that overcompensates two because you compare it with amplifiers that suffer from similar bias problems while SOA is better calculated in Cyrus and NAIM next to Atoll
Poor @Tolu
All that bragging about how brilliant you all are at bettering a construction should be in another thread.
Absolutely nothing of this is helping the guy, who started this thread in a naive hope of help.
Why not try to focus on his problem instead??
Just a thought.
All that bragging about how brilliant you all are at bettering a construction should be in another thread.
Absolutely nothing of this is helping the guy, who started this thread in a naive hope of help.
Why not try to focus on his problem instead??
Just a thought.
because the post is 2 years old so the OP probably had the amp repaired by an expert or trush it anyway
still information written here about procedures , performance thermal conciderations might be usefull to others
Good evening,
i own the old Atoll AM 100 and I question myself why the bias current for IN and AM amplifiers are so different? Do they have diffrent resistor values? I question myself since they have the same transistors and heat sinks. Would be nice if anyone could explain it, because i'd like to run a higher bias. It makes the am 100 sound so effortless.
Further, the electronic part "T17" (left of the Mosfets on the bias current set up chart) always runs very hot on my amp. Is there a way to improve it? And does the bias current affect its temperature?
Would be nice to if anyone could help 🙂
Regards!
i own the old Atoll AM 100 and I question myself why the bias current for IN and AM amplifiers are so different? Do they have diffrent resistor values? I question myself since they have the same transistors and heat sinks. Would be nice if anyone could explain it, because i'd like to run a higher bias. It makes the am 100 sound so effortless.
Further, the electronic part "T17" (left of the Mosfets on the bias current set up chart) always runs very hot on my amp. Is there a way to improve it? And does the bias current affect its temperature?
Would be nice to if anyone could help 🙂
Regards!