Bias
I use a 2 X 50 vac transformer which will result in 2 X 70 vdc. Sometimes circuit need high voltage before bias works. Turned the potentiometer clockwise and used a vario transformer. Could see when it began to draw current on the display. You can also just measure the temperatur. Approx 35 - 40 Celsius on heatsinks would be fine. I will need another 2 X 50 AC for the other channel. Ordered it from Toroidy - Polen. Have to wait until it arrives to tell how the amp sound. Maybe it only will be used as subwoofer amp. Time will show.
I use a 2 X 50 vac transformer which will result in 2 X 70 vdc. Sometimes circuit need high voltage before bias works. Turned the potentiometer clockwise and used a vario transformer. Could see when it began to draw current on the display. You can also just measure the temperatur. Approx 35 - 40 Celsius on heatsinks would be fine. I will need another 2 X 50 AC for the other channel. Ordered it from Toroidy - Polen. Have to wait until it arrives to tell how the amp sound. Maybe it only will be used as subwoofer amp. Time will show.
Hi, I have bought two PR-800 boards and am experimenting with them. it works well with a Connexelectronics SMPS2000RxE +/- 85Volt power supply. I measured the bias preload on one of the 0.22Ohm cement resistors. I set the bias voltage to 11mV. U = RxI ....... 0.22Ohm x 50mA = 11mV. the heat sink becomes warm. there are no distortions to be heard. the board can also be operated with 100mA. it is then already in class A mode and it gets very hot. then you need large heat sinks. I think 50mA is a good compromise for my application and fun to listen to. it really has a lot of power and i'm a fan.
Self ocillations on a Chinese PR-800 kit,
I mounted power transistors MJL21193G and MJL21196G from Farnell. The driver transistors are MJE15033G and MJE15032G of Chinese origin, those that came with the kit.
For the start-up tests I use a symmetrical 2 x 32V lab power supply limited in current to avoid any problems. Self ocillations occurs by increasing the input signal and also occurs earlier if the supply voltage is lowered to 2 x 20V for example.
I do not have the diagram of this kit of course but an earlier version exists the difference is the protection of the loudspeakers which is different on the first versions. On the one I have, the protection is limited to DC output protection.
Knowing that in the end this amplifier will be powered by a symmetrical voltage of 2 x 80V.
Which way do I have to look to remove this Self ocillations ?
Thanks for your help.
I mounted power transistors MJL21193G and MJL21196G from Farnell. The driver transistors are MJE15033G and MJE15032G of Chinese origin, those that came with the kit.
For the start-up tests I use a symmetrical 2 x 32V lab power supply limited in current to avoid any problems. Self ocillations occurs by increasing the input signal and also occurs earlier if the supply voltage is lowered to 2 x 20V for example.
I do not have the diagram of this kit of course but an earlier version exists the difference is the protection of the loudspeakers which is different on the first versions. On the one I have, the protection is limited to DC output protection.
Knowing that in the end this amplifier will be powered by a symmetrical voltage of 2 x 80V.
Which way do I have to look to remove this Self ocillations ?
Thanks for your help.
Total noob here. I am assuming the oscilloscope is the output, For one, it looks like crossover distortion. I would check Q10 for orientation. And measure across R20 with the input shorted and maybe load the output a little with a small-ish resistor, like 100ohms. Assuming its not oscillating, I would guess V at R20 >1.4V
EDIT: What is the second graph?
EDIT: What is the second graph?
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Yes it is indeed the output on the oscillograms the amp is loaded with a resistor of 8 Ohms for the tests. There is no ocillations without a signal at the input.
Well, the low side (PNP) gain is asymmetrical. And the distortion occurs at ~ -0.6V peak. I would still bet a few small value coins that its at the driver or output, and its not really oscillation, it is a semiconductor dud or connected the wrong way round. Maybe kill the protection by lifting R31 R32 first?
The amplifier part is the same only the protection part is different on that of the green printed circuit! On the green circuit only DC output voltage protection is implemented! It does not advance me in my troubleshooting thank you!
OK you were right, I think it's the drivers transistors that have crappy parameters! So surely fakes because when I remove the 150pF on the base of the MJE15032 and I put a 560pF on the base of the MJE15033 the oscillation disappears even when I increase the input level!
Do you think it is preferable to change the drivers for safe sources or can have to be satisfied with this device with these capacities?
Thanks for your help.