Hi,
The Pearl has 60,000uF of power supply capacitance on the main boards, plus another 20,000 in the power supply box if it is built as suggested. (I hope I got that right - it looks pretty high, but I've checked and re-checked that several times.) I know this is "only" 40V, but I've never built anything with this much capacitance before. Would it make sense to put in inrush current limiters or anything like that? I've never heard of a current limiter in a phono stage, but I'm a complete beginner at this, so that doesn't mean anything. I wll be using an Avel Lindberg transformer with the same rating as the recommended part number, if that makes any difference.
I'm just trying to get a perspective on this from people who know more about this circuit. I'd appreciate any advice.
Thanks,
Saurav
The Pearl has 60,000uF of power supply capacitance on the main boards, plus another 20,000 in the power supply box if it is built as suggested. (I hope I got that right - it looks pretty high, but I've checked and re-checked that several times.) I know this is "only" 40V, but I've never built anything with this much capacitance before. Would it make sense to put in inrush current limiters or anything like that? I've never heard of a current limiter in a phono stage, but I'm a complete beginner at this, so that doesn't mean anything. I wll be using an Avel Lindberg transformer with the same rating as the recommended part number, if that makes any difference.
I'm just trying to get a perspective on this from people who know more about this circuit. I'd appreciate any advice.
Thanks,
Saurav
Saurav,
You have better questions than I did...
I built the Pearl exactly as described in the article, including the recommended PS. I've had no problems. The DC supply voltage comes up to +42V over 8 to 10 seconds after turn-on.
Ren
You have better questions than I did...
I built the Pearl exactly as described in the article, including the recommended PS. I've had no problems. The DC supply voltage comes up to +42V over 8 to 10 seconds after turn-on.
Ren
Saurav, the reasons to have inrush current limitation is:
Some components can get damaged due to the high currents
It can be hard to find a fuse which really protects
The suggested PS can take the power up without problems and I believe there is no fusing problem.
You have R's in a few places with limits the current somewhat.
Inrush currents is a bigger problem when you have a rectifier bridge directly connected to the mains and 230 V. Then you can talk about malign currents. It's also important to observe large (>300 VA) toroids (not "normal" ones), they can really test the fuses! It's not so much the huge capacitor battery, it's the transformer itself. Try to (I have done it myself) connect a toroid with abolutely no load. Take a current probe (or shunt) and freeze the current with a oscilloscope. I got 77 A at 230 V mains. Eventually you will blow your main switch if you don't do anything.
Conclusion: Not neccessary to do anything unless you experience fuse blowing now and then.
BTW: 60000 µF IS really much for a low current circuit but you can choose any value you like, not too low though. Bare in mind that the power supply rejection ratio PSRR, is rather low, by nature, so you need a quite power supply voltage in order to get low hum levels. The Pearl stage isn't a opamp with 100 dB PSSR, you know. I have the same problem in my discrete designs.
Some components can get damaged due to the high currents
It can be hard to find a fuse which really protects
The suggested PS can take the power up without problems and I believe there is no fusing problem.
You have R's in a few places with limits the current somewhat.
Inrush currents is a bigger problem when you have a rectifier bridge directly connected to the mains and 230 V. Then you can talk about malign currents. It's also important to observe large (>300 VA) toroids (not "normal" ones), they can really test the fuses! It's not so much the huge capacitor battery, it's the transformer itself. Try to (I have done it myself) connect a toroid with abolutely no load. Take a current probe (or shunt) and freeze the current with a oscilloscope. I got 77 A at 230 V mains. Eventually you will blow your main switch if you don't do anything.
Conclusion: Not neccessary to do anything unless you experience fuse blowing now and then.
BTW: 60000 µF IS really much for a low current circuit but you can choose any value you like, not too low though. Bare in mind that the power supply rejection ratio PSRR, is rather low, by nature, so you need a quite power supply voltage in order to get low hum levels. The Pearl stage isn't a opamp with 100 dB PSSR, you know. I have the same problem in my discrete designs.
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