ok ....misunderstanding solved English is not our native language neither danish sarkasm...so some things might not be easy to understand ...
So ..do your reading about Vbe multipliers on CFP amplifiers observe your amplifier and we talk again Monday ..\
Picture of one board might also help others to join in
So ..do your reading about Vbe multipliers on CFP amplifiers observe your amplifier and we talk again Monday ..\
Picture of one board might also help others to join in
No hard feelings
I don't have the amplifier any more, I sold it long ago and it is working fine.
Well it is difficult to know exactly what the temperature is when he said " I think it is too low".
It is also difficult to know the exact temperature of the difference between your definition of "hot", "boiling hot" and "lukewarm"
What I tried to tell him (Chris68 in post #6 + #7) was, that if he got the idle adjustment correct, then the temperature will come up by itself. I never said that it should run cold.
Besides: Amplifier temperature is both ambience temperature + temperature increase from idle current. In northern Europe ( Denmark & UK) the temperature indoors can be 12-18 degrees in winter.
In Greece? I don't know.
The 10 degrees difference between 40,50 and 60 degrees is probably what most people would consider as the difference between lukewarm, hot and boiling hot respectively.
Chris68 wrote in december ( = winter)...so unless one measures the exact temperature, one cannot know for sure.
Would Nakamichi PA5 MKII be performing equally in a living room in the UK of 15 degrees with 40mA per transistor and a heatsink temperature of 40 deegrees,
as it would in a living room in Greece with a temperature of 25 degrees with with 40mA per transistor and a heatsink temperature of 50 deegrees?
...probably close enough, the temperature would probably mean more to your blood pressure and thereby your hearing.
Close enough but not correct ...
Here is your story
1) one thing to notice before all is operating voltage It is not that simple like 110 or 220 there is plenty of models that are out there that are designed to operate in 220 mains but now days operating voltage in most EU countries is 230-240 ..These few extra volts can and will stress the amp since eventually bias will be altered .
Not much you can do unless you can afford a new trafo..On the other hand tuning the bias just something like 10% lower as a precaution might help a bit but if ( any) amplifier is based in strict rail voltage will be stressed .
2) the twist in these amplifiers is that like most CFP amplifiers the Vbe multiplier doesn't sense on the main heat sink . Usually it senses on the drivers but for his own reasons the designer chooses to locate the vbe sensing heat from the inner space of the amplifier (??? ) It also looks like that something went wrong and even though there is accommodation for the transistor on the board in all models Vbe is located on the copper side facing the power supply .
My guestimation is that if Vbe was too close to the heat sink was overcompensating and bias dropped to an undesired level .
What actually happened to you and probably others is that you tuned the amplifier according to specs put the cover on and ready to go .
In reality what actually happened is that after you put the cover on temperature rises inside the amp enclosure vbe will sense that and drop the bias to an undesired level so eventually the amp will run relatively cold even though originaly tuned according to specs but with the cover open .
For this amplifier you need to warm up the amp tune it according to specs but with the cover closed in order to achieve proper biasing and preserve it ....
Drill ventilation halls on the top cover and bias will rise till blow. Add a ventilator on the top cover and then it will blow even faster If you like to ventilate for any reason and any amplifier then this has to be done strictly on the main output heatsink nowhere else ...( As a general information)
Are we done ?
Kind regards
Sakis
Here is your story
1) one thing to notice before all is operating voltage It is not that simple like 110 or 220 there is plenty of models that are out there that are designed to operate in 220 mains but now days operating voltage in most EU countries is 230-240 ..These few extra volts can and will stress the amp since eventually bias will be altered .
Not much you can do unless you can afford a new trafo..On the other hand tuning the bias just something like 10% lower as a precaution might help a bit but if ( any) amplifier is based in strict rail voltage will be stressed .
2) the twist in these amplifiers is that like most CFP amplifiers the Vbe multiplier doesn't sense on the main heat sink . Usually it senses on the drivers but for his own reasons the designer chooses to locate the vbe sensing heat from the inner space of the amplifier (??? ) It also looks like that something went wrong and even though there is accommodation for the transistor on the board in all models Vbe is located on the copper side facing the power supply .
My guestimation is that if Vbe was too close to the heat sink was overcompensating and bias dropped to an undesired level .
What actually happened to you and probably others is that you tuned the amplifier according to specs put the cover on and ready to go .
In reality what actually happened is that after you put the cover on temperature rises inside the amp enclosure vbe will sense that and drop the bias to an undesired level so eventually the amp will run relatively cold even though originaly tuned according to specs but with the cover open .
For this amplifier you need to warm up the amp tune it according to specs but with the cover closed in order to achieve proper biasing and preserve it ....
Drill ventilation halls on the top cover and bias will rise till blow. Add a ventilator on the top cover and then it will blow even faster If you like to ventilate for any reason and any amplifier then this has to be done strictly on the main output heatsink nowhere else ...( As a general information)
Are we done ?
Kind regards
Sakis
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Hi Henrik,
They do get fairly warm compared to other amplifiers in idle. The closest amplifier I can think of for running temperature would be a mosfet amplifier about the same power output.
Because the negative feedback take off point is before the output stage, these amplifiers sound better with 8R speakers compared to lower impedance types. Also the impedance curve would be better flatter than with lots of peaks and valleys. I have a Stassis type receiver here that shows a distinct preference for easier loads. It will happily drive low impedance loads, as will these amplifiers. They just have higher distortion levels because the THD from the output stage is not within the feedback loop.
-Chris
They do get fairly warm compared to other amplifiers in idle. The closest amplifier I can think of for running temperature would be a mosfet amplifier about the same power output.
Because the negative feedback take off point is before the output stage, these amplifiers sound better with 8R speakers compared to lower impedance types. Also the impedance curve would be better flatter than with lots of peaks and valleys. I have a Stassis type receiver here that shows a distinct preference for easier loads. It will happily drive low impedance loads, as will these amplifiers. They just have higher distortion levels because the THD from the output stage is not within the feedback loop.
-Chris
Sakis : The variating mains voltage was the next thing I would bring into the discussion.
Good point regarding putting the lid back on, regarding optimum bias.
I always do this anyway, I just never thought to mention it.
Yes - we are done
Chris anatech :
Good info, but the CFP out stage sounds wonderful anyway.
Good point regarding putting the lid back on, regarding optimum bias.
I always do this anyway, I just never thought to mention it.
Yes - we are done
Chris anatech :
Good info, but the CFP out stage sounds wonderful anyway.
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