thanks for sharing, knutn😀
by the way, i can't get 24.6v but only 22.50v😕
An externally hosted image should be here but it was not working when we last tested it.
by the way, i can't get 24.6v but only 22.50v😕
Hi,
I had a problem on the negative supply, which people above suggested was likely the zener. Turned out to be the case. Seems to methe same would apply to the positive supply, so can you check the voltage drop across the zener? If it's not quite right that would change the output voltage, wouldn't it?
Cheers
Nigel
oh now i see, times 1.4... haha, i am still very new into this.
another question, for the preamp stage, both dual mono channel sharing single shunt regulator circuit board, or one shunt reg circuit is needed for each single channel?😱
yes, they are a current mirror, but what does the mirror action achieve?
Does Q2 and R8 do anything, or do they enhance the performance?
Keep in mind the zener is quite noisy, and 10uF doesn't do much to filter that noise. When I used a zener in the reg I measured acceptable noise reduction with a 1000uF bypass cap. Otherwise it sort of defeats the purpose of using a low noise jfet like the BF862, similar to using dirty water with a very clean pot.
Just my 2c.
Just my 2c.
Ah, I see where the error is. In the schematic, given above, instead of diode symbol should be a zener diode symbol. That's why Andrew raised the question about current mirrors.
Blue Sky, there is a 1N4749 mark beside the diode so it's clearly a 24V Zener.
Iko, in my experience, zeners are noisy only with insufficient current running through them. With R7=220R there will be about 5.2mA flowing through zener diode which is quite enough. The shunt is totally silent - my scope is 20MHz device and I see no trace of noise.
I don't know how you can give all those fact-buffed lectures to DIYers without being able to understand such a simple concept ?
would you care to take the time to explain it to me and any others that want to know, rather than posting the put down that we can all see.
BTW,
I can see that the upside down diode could only be a Zener.
It holds the Q3 base at a near constant voltage and the near constant Vbe of this transistor sets the control voltage coming out the right hand side to feed M3.
What does the Q2 R8 combination add to that?
I was just saying, that's all. I could measure an increase of "grass" type of noise of a few hundreds microvolts peak to peak, with good current (7mA) going through the zener, and not large enough bypass cap. Whether that's acceptable or not, that's another thing, and it depends on the application. When I stopped using the zener the noise has become less than 40uV pk-pk.
Member
Joined 2002