Franz,
I have shorted one internal thermal track diode.
The initial value of the voltage drop over an emitter resistor (with the trim-potentiometer being set to 0 Ohm) is now 0V,
and I can very easily adjust the voltage drop to 18mV as Mihai suggested.
And, as you said: the quiescent current flowing through the backend decreased a lot. The light-bulb is ony "glowing".
What problem do I have?
Best regards - Rudi
I have shorted one internal thermal track diode.
The initial value of the voltage drop over an emitter resistor (with the trim-potentiometer being set to 0 Ohm) is now 0V,
and I can very easily adjust the voltage drop to 18mV as Mihai suggested.
And, as you said: the quiescent current flowing through the backend decreased a lot. The light-bulb is ony "glowing".
What problem do I have?
Best regards - Rudi
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You're welcome Rudi.
I'm happy if i can contribute to this nice project.
being a little bit off have you playd PL comp?
It shows nice phase margin and Aksa find it to sound nice.(and JCarr too)
In the beginning of the rmi-fc100 thread Aksa gave some comp. mode which are interestings.
Maybe if you play with it on the real amp and find it to be good sounding would be nice to give place on the next pcb (just an idea).
View attachment rmi_fc100_loopgain_pl_comp.zip
Regards,
zsaudio
I'm happy if i can contribute to this nice project.
being a little bit off have you playd PL comp?
It shows nice phase margin and Aksa find it to sound nice.(and JCarr too)
In the beginning of the rmi-fc100 thread Aksa gave some comp. mode which are interestings.
Maybe if you play with it on the real amp and find it to be good sounding would be nice to give place on the next pcb (just an idea).
View attachment rmi_fc100_loopgain_pl_comp.zip
Regards,
zsaudio
I feel quite relieved now. 
I will remove the backend PSU from the light-bulb now, adjust the quiescent current once more and leave the AMP for an hour or so.
Then I will measure again and apply a sine wave, a square wave,..., and "listen" to the oscilloscope.
And then ...
But I still have to find out, why I have to short a thermal track diode to make this AMP running.
I will be back in some hours.
Best regards - Rudi
I will remove the backend PSU from the light-bulb now, adjust the quiescent current once more and leave the AMP for an hour or so.
Then I will measure again and apply a sine wave, a square wave,..., and "listen" to the oscilloscope.
And then ...
But I still have to find out, why I have to short a thermal track diode to make this AMP running.
I will be back in some hours
.Best regards - Rudi
What's your +- current draw of the frontend from your shunt psu?
Did you measure the current of the ltp and the vas?
According to the real built of the amp (by Mihai and several forum members) and to LTspice simulation the amp should work with one NJL diode bypassed.
The jfets work on about 6.1mA per device the vas about 2.16 mA per device.
If your set-up similar to this maybe your NJL's TC diodes differ. Would it be possible i do not think so but who knows.
Did you run the simulation and compare the values (voltages and currents) on every devices?
Regards,
zsaudio
Did you measure the current of the ltp and the vas?
According to the real built of the amp (by Mihai and several forum members) and to LTspice simulation the amp should work with one NJL diode bypassed.
The jfets work on about 6.1mA per device the vas about 2.16 mA per device.
If your set-up similar to this maybe your NJL's TC diodes differ. Would it be possible i do not think so but who knows.
Did you run the simulation and compare the values (voltages and currents) on every devices?
Regards,
zsaudio
Rudi,
please check the collector current of the VAS and see Fig. 12 from the datasheet http://www.onsemi.com/pub_link/Collateral/NJL0281D-D.PDF
Perhaps your transistors have a little bit different specs. Lets hope they're not fakes. Those branded ISC are not trustworthy.
please check the collector current of the VAS and see Fig. 12 from the datasheet http://www.onsemi.com/pub_link/Collateral/NJL0281D-D.PDF
Perhaps your transistors have a little bit different specs. Lets hope they're not fakes. Those branded ISC are not trustworthy.
Franz,
the NJL transistors are absolutely integer and authentic.
I bought them from a DIY-friend whom I know for a long time.
In contrast to my post #198, where I measured only about +/-15 V at the collector of the 2SC / 2SA transistors,
I am now (with only 4 diodes in the string) measuring +/- 35V at the collectors.
It looks like the 2SC / 2SA transistors that I use, do not supply enough current to turn all 5 diodes on.
To replace these 2 transistors Q19 and Q20 (I use 2SA1360 and 2SC3423 throughout the build) will be a very hard job,
since these 2 transistors are mounted beneath the PCB (which is plated-through).
I have still a whole bunch of 2SA1360 and 2SC3423 at hand.
How can I make sure that these are "fakes", before I try and solder them out?
Best regards - Rudi
the NJL transistors are absolutely integer and authentic.
I bought them from a DIY-friend whom I know for a long time.
In contrast to my post #198, where I measured only about +/-15 V at the collector of the 2SC / 2SA transistors,
I am now (with only 4 diodes in the string) measuring +/- 35V at the collectors.
It looks like the 2SC / 2SA transistors that I use, do not supply enough current to turn all 5 diodes on.
To replace these 2 transistors Q19 and Q20 (I use 2SA1360 and 2SC3423 throughout the build) will be a very hard job,
since these 2 transistors are mounted beneath the PCB (which is plated-through).
I have still a whole bunch of 2SA1360 and 2SC3423 at hand.
How can I make sure that these are "fakes", before I try and solder them out?
Best regards - Rudi
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Rudi, I,ve just finished doing a little test on the diodes only on the njl0281dg transistors and I,ve discovered that there is a big difference in voltage drops across the diodes and different current levels,,enough so 1 device can cause a problem. I,m going to test other devices I have to see if the same condition occurs.. Evette
Use the diodes with the lowest voltage drop. If this will not work, bypass one of the five diodes with a small Schottky diode. (BATxx type will be fine.) With only four TT diodes bias voltage could be undercompensated. Schottky diodes have negature temperature coefficient and are used in some Sanken SAP devices.
The transistors aren't counterfeit, they're genuine chinese stuff. ISC is a chinese manufacturer and their process could differ from the japanese one.
Don't trow them away. Let's see if we can fix the problem as suggested above.
The transistors aren't counterfeit, they're genuine chinese stuff. ISC is a chinese manufacturer and their process could differ from the japanese one.
Don't trow them away. Let's see if we can fix the problem as suggested above.
I have used these transistors in the past and had nothing but problems with them,osc burn outs you name it I could never get them to work right. Evette
good to know. that's why i always try to buy orig japanes parts. It's sometimes very hard to find a trustable dealer and you need to pay extra. I started to buy Sanyo video transistors for my diy store, because of OnSemi.
zsaudio
good to know. that's why i always try to buy orig japanes parts. It's sometimes very hard to find a trustable dealer and you need to pay extra. I started to buy Sanyo video transistors for my diy store, because of OnSemi.
zsaudio
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