AndrewT said:
It was in 2000 that ON was spun out of Motorola.
FWIW, I still have some power transistors with the Delco insignia on them.
LME49830
Hi, back again with new problems.. I have assembled and tested the MOSFET/LME49830 amp today. It works, sort of...
Can't get the bais to work, e.g. can't get any bias current through the IRPF240/9240 pair. The VBE and bias adjustment works as far as to the driver stage, I can vary the driver bias from 5-100mA.
The power is there, but of course I have some cross over distortion due to lack of bias current.
Tried just about everything but nothing seems to help. Even removed the driver stage, same-same but different, lot's of distortion w/o drivers.😡
Begining to think that IRFP240/9240 is no good for this amp, seem to require higher VGS than LME49810 and drivers are able to deliver. Does this seem to be a fair conclusion? 😕
I got an advice to move the zener/diode protection from the Gates to the base of the drivers - this does not work at all so I removes the protection all together.
I enclose the schematic of the testversion as it is configured at the moment. Hope to get some advice on this
Hi, back again with new problems.. I have assembled and tested the MOSFET/LME49830 amp today. It works, sort of...
Can't get the bais to work, e.g. can't get any bias current through the IRPF240/9240 pair. The VBE and bias adjustment works as far as to the driver stage, I can vary the driver bias from 5-100mA.
The power is there, but of course I have some cross over distortion due to lack of bias current.
Tried just about everything but nothing seems to help. Even removed the driver stage, same-same but different, lot's of distortion w/o drivers.😡
Begining to think that IRFP240/9240 is no good for this amp, seem to require higher VGS than LME49810 and drivers are able to deliver. Does this seem to be a fair conclusion? 😕
I got an advice to move the zener/diode protection from the Gates to the base of the drivers - this does not work at all so I removes the protection all together.
I enclose the schematic of the testversion as it is configured at the moment. Hope to get some advice on this
if the outputs require a Vgs=3V to pass 100mA of bias then R34 will pass about 27mA when the FETs are correctly biased.
If you are up to 100mA of driver bias then something is not soldered or a component is faulty.
If you are up to 100mA of driver bias then something is not soldered or a component is faulty.
AndrewT said:
I'm not sure, but look at the transistors on the other heatsink. The text is printed the wrong way on them, they are probably fakes...
http://sound.westhost.com/fake/counterfeit-p1.htm#mj15003
I have some "MJ15024" like in the link with the round ring copper heatsink underneath. They blew up at about 1/3 rated power...
In any problem, go back to the beginning -- cut out all of the peripheral stuff in your design and get the amp running in its most simple form.
Then you can add the servo, buffer, nested feedback loops etc.
Then you can add the servo, buffer, nested feedback loops etc.
yes, it's only 1.3V....
I have done that, the buffer and DC-servo are removed.
The chip seem to be off balance by approx. 3V, the voltage between R17/R18 is 3.2V (should be 0V?), the VGS on Q4 is +3.56 and VGS on Q5 is +2.9V. The DC-level on the output is 50mV. I have 1.5mV on IN+ and 1.9mv on IN-.
I noticed that in the AN for 49830 NS have a different set up for the VBE circuit (same as I had in the initial 49810/BJT design that didn't work), 1k2 between BiasP and QVBE) and a 10k trimmer between B-C of QVBE. Maybe I should increase R13 to 4,7-10k?
you need to learn how to do the arithmetic.
Look at your Vbe multiplier.
Ru=1k2
Rl=pot+360r
Maximum voltage from Multiplier = {[1200/360] + 1} * Vbe ~= 4.3*0.6 ~= 2.6V.
Subtract 1.2V for the drop through the drivers and you get ~ 1.4V across R34.
You measured 1.3V.
1300mV/220ohms= 5.9mA (where did 100mA come from?)
Minimum voltage from Multiplier = {[1200/(360+5k)] + 1} * Vbe ~= 1.22*0.6 ~= 0.7V
The two drivers at almost turn off will drop ~400mV each. i.e. no current flows through the drivers and no voltage is developed across R34.
With your existing Multiplier set up the driver bias will vary from 0 to 5.9mA and the output bias will vary from 0 to 0mA.
Look at your Vbe multiplier.
Ru=1k2
Rl=pot+360r
Maximum voltage from Multiplier = {[1200/360] + 1} * Vbe ~= 4.3*0.6 ~= 2.6V.
Subtract 1.2V for the drop through the drivers and you get ~ 1.4V across R34.
You measured 1.3V.
1300mV/220ohms= 5.9mA (where did 100mA come from?)
Minimum voltage from Multiplier = {[1200/(360+5k)] + 1} * Vbe ~= 1.22*0.6 ~= 0.7V
The two drivers at almost turn off will drop ~400mV each. i.e. no current flows through the drivers and no voltage is developed across R34.
With your existing Multiplier set up the driver bias will vary from 0 to 5.9mA and the output bias will vary from 0 to 0mA.
megajocke said:
In the beginning, I actually think that they are maybe remarked.
Although I bought them NT$260/a pear(is upto US$8/pear) in my country.
(I am sure the price don't represent they must be true.🙄 )
That is confused me for much time.
But I don't have enough equipments to measure the transistor is true or not.
In the end, I decided try to use them, because it's too late to return purchase.
On Amplifier running, the sound didn't let me be disappointed.
Compared with I using 2SC5200/2SA1943, the background is actually silent.
I think I will try to use oscilloscope measuring quality next times.
You do have the LED for the clipping indicator connected, correct? This pin can not float. (My wife points out that men rarely read the instruction manuals.)
You're quite right Andrew, I don't (didn't) know how to do the math... But I'm, learning, slowly...🙂
I changed R13 to 5k6 and now the VBE multiplier is working. At a bias current of 45 mA all the cross over distortion is gone and all voltages are as I would expect them to be. Both sine and square waves looks good, but I need a better signal generator than my what I have in the soundcard of my old laptop to do proper measurements. Sounds nice, better than the no-driver 49810/BJT amp, probably due to improved slew rate.
Have anyone used the RightMark Audio Analyzer SW to test amplifiers?
Bias is stabile with temperature as well.
I had to increase R34 to 470R as well since the bias current through the drivers where higher than through the power FET's, the drivers where getting quite hot.
I'm getting 120W RMS @7ohms just below clipping level wich is a bit less than what I was aiming for. 80V P-P is max I can get with +/-55V DC supply. I would expect to loose 12V (6+6) across the FET's and another 2 V across the drivers, but I don't know (yet) where the other 16 V is lost. It might be that I need to increase R34 even more to increase the voltage swing at the Gate's?
I will try to find 2SK1530/2SJ201 as they seem to be a better choice. Finding "exotic" drivers and power transistors for audio isn't very easy here in the dark north,
Thanks again for the help you're giving, it's unvaluable as I have nowhere else to go. "When in doubt -ASK!"
I changed R13 to 5k6 and now the VBE multiplier is working. At a bias current of 45 mA all the cross over distortion is gone and all voltages are as I would expect them to be. Both sine and square waves looks good, but I need a better signal generator than my what I have in the soundcard of my old laptop to do proper measurements. Sounds nice, better than the no-driver 49810/BJT amp, probably due to improved slew rate.
Have anyone used the RightMark Audio Analyzer SW to test amplifiers?
Bias is stabile with temperature as well.
I had to increase R34 to 470R as well since the bias current through the drivers where higher than through the power FET's, the drivers where getting quite hot.
I'm getting 120W RMS @7ohms just below clipping level wich is a bit less than what I was aiming for. 80V P-P is max I can get with +/-55V DC supply. I would expect to loose 12V (6+6) across the FET's and another 2 V across the drivers, but I don't know (yet) where the other 16 V is lost. It might be that I need to increase R34 even more to increase the voltage swing at the Gate's?
I will try to find 2SK1530/2SJ201 as they seem to be a better choice. Finding "exotic" drivers and power transistors for audio isn't very easy here in the dark north,
Thanks again for the help you're giving, it's unvaluable as I have nowhere else to go. "When in doubt -ASK!"
That's right, I DID have it connected - until I read the manual earlier today... In the LME49830 (NOT 810!) on page 3, Connection diagram it says clearly "NC Pin electrically isolated".
😉
Segran said:
Digikey has both devices in stock -- a couple hundred. I think that Swedish is the second language of Minnesota where they are headquartered.
Isn't 55V the unloaded power supply voltage? Try measuring it with a multimeter while loading. It's probably sagging under load.
But it's really the ripple valleys that set the maximum output power so the value given by an average reading multimeter is higher than the value that matters, an oscilloscope gives a better reading.
You also have voltage drop over source resistors.
120W from a +-55V supply sounds about right. I serviced a NAD2200 recently with about +-60V unloaded lower supplies. Clipping was at 150W / 8 ohms after the +-90V boost supply deactivates because of continuous power draw.
But it's really the ripple valleys that set the maximum output power so the value given by an average reading multimeter is higher than the value that matters, an oscilloscope gives a better reading.
You also have voltage drop over source resistors.
120W from a +-55V supply sounds about right. I serviced a NAD2200 recently with about +-60V unloaded lower supplies. Clipping was at 150W / 8 ohms after the +-90V boost supply deactivates because of continuous power draw.
Segran said:
You will definitely learn a lot from Prof. Leach projects http://users.ece.gatech.edu/~mleach/audiothings.html
Thanks for your advice, I have read the Leach pages online before and have now ordered the book as well.
While waiting for the book to arrive I have continued testing and would like to ask yet another question:
With Bias set to 45mA after running idle for 30 minutes I made a full power test ( 200W@4 ohm load) for 15 minutes. The heat sink temp increased to approx 50 C. When checking the bias again it had dropped to 12mA.
It seems to me that the VBEmultiplier (which IS mounted on the heatsink between the 2 power FET's...) is overcompensating for the increased temperature by a factor 4.
Have any of you any advice on this?
While waiting for the book to arrive I have continued testing and would like to ask yet another question:
With Bias set to 45mA after running idle for 30 minutes I made a full power test ( 200W@4 ohm load) for 15 minutes. The heat sink temp increased to approx 50 C. When checking the bias again it had dropped to 12mA.
It seems to me that the VBEmultiplier (which IS mounted on the heatsink between the 2 power FET's...) is overcompensating for the increased temperature by a factor 4.
Have any of you any advice on this?
Is that in the MOSFET amp?
You can put diodes that you keep away from the heatsink in series with the C-B resistor of the bias transistor to decrease the temperature compensation. Observe that each diode will increase bias voltage with 0.6-0.7V if everything else is equal so you will probably need a lower value for R13 than you have now (I guess you increased it a bit to be able to adjust up the bias?) or else you won't be able to adjust the bias voltage low enough. Probably not much is needed, 1 or maybe 2 diodes.
Current falling to 1/4 doesn't mean it has 4 times too much temperature compensation as there is a threshold which makes the function nonproportional. It's probably much less than just 2 times too much compensation.
That is, in series with R13 in this schematic:
http://www.diyaudio.com/forums/attachment.php?s=&postid=1681618&stamp=1228961756
You can put diodes that you keep away from the heatsink in series with the C-B resistor of the bias transistor to decrease the temperature compensation. Observe that each diode will increase bias voltage with 0.6-0.7V if everything else is equal so you will probably need a lower value for R13 than you have now (I guess you increased it a bit to be able to adjust up the bias?) or else you won't be able to adjust the bias voltage low enough. Probably not much is needed, 1 or maybe 2 diodes.
Current falling to 1/4 doesn't mean it has 4 times too much temperature compensation as there is a threshold which makes the function nonproportional. It's probably much less than just 2 times too much compensation.
That is, in series with R13 in this schematic:
http://www.diyaudio.com/forums/attachment.php?s=&postid=1681618&stamp=1228961756