Does anyone care to ask an amplifier designer a technical question? My door is open.
Can you please tell me the purpose of resistors R1 -> R8 in the power supply shown below in the URL ? Is it to reduce the resonant frequency in case the supply oscillates with the stray inductance of the smoothing caps ? https://www.passdiy.com/project/articles/burning-amplifier-1 Thanks |
Hi ramtubes, Thanks for answering my previous question. I appreciate it. I do have another question please... I am building a symmetric plus/minus 70 volts dc (2 x 50 volt ac secondaries) power supply for an amplifier I am building. Mechanical issues are giving me more trouble than electronics such as drilling holes accurately etc. To this end, I want to build this so I do not have to change the smoothing capacitors for a LOOOONG while so I dont have to re-drill holes etc if and when they break. I am concentrating on those specific capacitors since they are large electrolytics and hence are most likely the least reliable of the components. In your experience & opinion, which make (and series/types) of such large electrolytics are the MOST reliable in the long term ? I am considering about 40 to 80 milli farads at 100 volts per each side of the supply, depending on the price & physical dimensions. I predict that these capacitors will be in a vicinity with a temperature of about 60 - 65 C most of the time. Thanks |
I am also looking for a lab/bench symmetric power supply of up to +/- 100 volts DC at about 2 - 3 amps (so about 500 - 600 watts) and having a very difficult time finding it. The very rare ones I have seen are in excess of $1500. I need such a supply for testing purposes. I do not want to build one. Does anyone know of one around a max of $500 ? Thanks |
Thanks again ramtubes. Sorry did not get back to you in time. I was the one asking about the reliable electrolytics. The amp I am building is about 300 rms watts/channel int 8 ohms. I usually like over engineering things mostly for purposes of reliability and longevity rather than sound quality since after a certain point sound difference becomes indistinguishable. I am therefore using 1800 VA toroidal and a 270 amp rectifier. Caps are 4 x 47,000 uF but s I mentioned, at 85 degrees C the caps are rated at 2000 hours. Therefore they are the weakest links in the amp. I saw some Nichicons with 105 degrees C at 10000 hours but they were about $250 EACH (phew). The rectifier, altho likely to be used for welding applications, has soft switch characteristics AND it is quit fast, so would be suitable for audio. I over sized the rectifier so that it would easily handle the initial short circuit of the caps when the amp is first turned on. I am also using an inrush current limiter, composed of Airotronics MC1004531J (rated to 25 amps AC) and a flame proof 33 ohm 25 watt wirewound resistor as the current limiter. I could not decide between a thermistor and a resistor so decided to go with a resistor. My concern was that if the relay did not engage due to a fault, the thermistor would run at about 150+ degrees, which in my opinion is NOT safe in a solid state enclosure. The resistor would most likely burn out open circuit and I would either smell it or notice it the next time I switch the amp on, when the lights dim :-) Thanks |
Hi ramtubes, About your variac suggestion :-) Funny you mentioned that since I also came to the exact same conclusion. I have rectifiers & capacitors already lying around with which I can build an un-regulated variac based power supply. All I have to do is add 2 voltage meters to it and an enclosure and voila, it works. I dont need extreme regulation anyway so it would be fine. For isolation also, I have a 1000VA toroidal with 2 x 50 volts ac lying around which will use. This will easily give me 2 x 70 - 75 volts DC. It will be a bit heavy but will successfully work with gobs of spare power. I will have to add an inrush current limiter too unless I turn the variac down before I turn the power on, every time. I also play around with DC motors too, so this supply could also easily be used to test them. Thanks |
