Hi all,
Refurbishing an old defective Luxman 308 amp, I found the main amp boards schematic is like the following (of the l80) and although there may be more, my first questions are:
1. why is the r115 resistor supplying the zener so low (zener gets some 15 milliamps as supply voltage is around 45 and it will run quite warm, as does the resistor). Note, in a newer amp (l85v) they do not not have the r116 470 Ohm but the 1k5 resistor is 8k2 there.....
2. Just drilling 2 little holes, I can bypass the zener with a little cap, would this be beneficial? read: will zener noise affect operation much, here?
Luxman did this in a later mode L85v having same input circuit (although the mentioned 5k6 resistor is 4k7 there)l, they put in a 40 nf ceramic cap.
I presume they just standardized on 40nf caps, as they used this value as ceramic bypass on several positions in different amps. I could put in a nF range ceramic cap, there is not much space for anything else, or a little tantalum electrolytic of a few microfarads, which could fit.
Refurbishing an old defective Luxman 308 amp, I found the main amp boards schematic is like the following (of the l80) and although there may be more, my first questions are:
1. why is the r115 resistor supplying the zener so low (zener gets some 15 milliamps as supply voltage is around 45 and it will run quite warm, as does the resistor). Note, in a newer amp (l85v) they do not not have the r116 470 Ohm but the 1k5 resistor is 8k2 there.....
2. Just drilling 2 little holes, I can bypass the zener with a little cap, would this be beneficial? read: will zener noise affect operation much, here?
Luxman did this in a later mode L85v having same input circuit (although the mentioned 5k6 resistor is 4k7 there)l, they put in a 40 nf ceramic cap.
I presume they just standardized on 40nf caps, as they used this value as ceramic bypass on several positions in different amps. I could put in a nF range ceramic cap, there is not much space for anything else, or a little tantalum electrolytic of a few microfarads, which could fit.
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Zener won't start making alot of noise if run over 5mA , 15mA should be >-100db (white noise). Analog synths use zener
noise generators at <1mA current to make pink/white generators - then amplify 100X.
At over a hundred db noise , you could bypass the zener with .01-.022uf poly cap. I do this on my series regulated zener
stages. I doubt you would notice the zener noise. A more current Zener could be quieter ?
OS
noise generators at <1mA current to make pink/white generators - then amplify 100X.
At over a hundred db noise , you could bypass the zener with .01-.022uf poly cap. I do this on my series regulated zener
stages. I doubt you would notice the zener noise. A more current Zener could be quieter ?
OS
Thanks, I think I settle for a resistor taking care for a zener current of around 7 milliamps.
Gerard
Gerard