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MGH 30th December 2012 07:03 PM

Power supply resistor matching
 
A newbie question here. I've seen people getting matching left and right channel resistors (<1% tolerance) in low level signal section of preamp or amp. I suppose this is even more important in balanced differential preamp/amp. But how important is matching left and right channel power supply resistors in an amp? Seems 1% resistor tolerance is excessive in power supply.

peranders 30th December 2012 07:09 PM

1% is more than enough in most cases but some people like to have 15.000 volts but it is not important.

MGH 30th December 2012 07:19 PM

Thanks. What type of resistors are typically used in power supply...wire wound, metal film, metal oxide, carbon film...?

sreten 30th December 2012 07:33 PM

Hi,

Resistor types (and tolerances) are chosen for the purpose of the
resistor in the circuit, there is no carte blanche simple answer.

Power supplies are are varied as the circuits they feed.

rgds, sreten.

NissanSR20Man 30th December 2012 08:02 PM

Quote:

Originally Posted by MGH (Post 3304664)
Thanks. What type of resistors are typically used in power supply...wire wound, metal film, metal oxide, carbon film...?


The ones that are flame proof and non-inductive. Not sure if both options will fit your needs due to sizes, ratings, etc... This is due to me not wanting to start an inferno in my basement due to a failure, while not wanting to couple any stray magnetic flux from the XFMR and large currents into any stray inductance from a cheap wirewound resistor. I had an ANTEC 1000W PC PSU unit start smoldering in my media server PC (located in my 72" tall rack with all other stuff, xbox, xbox 360, cable box, reciever, etc..). It was smoldering/burning for at least 3-4 days. the wife kept smelling something while i was away. The only reason I am writing this is due to the flameproof components and coatings. If it was a ebay cheapo supply, my house might be missing. PC still continued to run until I pulled the cord, despite the PSU board melting down, smoldering and unsoldering itself. I was damn lucky.

It is a shame to place such precision and materials in the amp section and forget about the PSU. Remember...garbage in is garbage out. If it was me and I was doing a one-off for myself, I would spend the extra $5-10 USD for better components. If it is a mass produced product there will always be the bean counters to throttle the components back to basics.

MGH 30th December 2012 08:41 PM

Yes, I agree good reliable resistors that are overrated should be used. I was thinking high quality noninductive wire wounds from Mills or the like. Any reason not to use them in certain parts of the power supply?

NissanSR20Man 30th December 2012 09:34 PM

A good writeup from here...Resistor Types--Does It Matter?

Read through it, pretty good. I would have chosen incorrectly. There are several articles like this.

"Wirewound resistors are the best choice for noise, followed by metal film, metal oxide, carbon film, and lastly, carbon composition. However, wirewound resistors are not readily available in large resistance values, and are usually inductive, which can cause instability problems in some cases. Bear in mind, however, that many people prefer the "sound" of carbon comps, claiming they sound warmer than film or wirewound types. This is possibly due to distortions generated by the modulation of the contact noise current by the AC signal. Since this noise has a 1/f frequency characteristic (similar to pink noise), it is more pleasing to the ear than white noise. However, pleasing noise is still noise, and in my opinion, it should be reduced to the lowest possible level. The signal distortion is a different topic altogether."

MGH 31st December 2012 08:17 PM

Quote:

Originally Posted by NissanSR20Man (Post 3304808)
A good writeup from here...Resistor Types--Does It Matter?

Read through it, pretty good. I would have chosen incorrectly. There are several articles like this.

"Wirewound resistors are the best choice for noise, followed by metal film, metal oxide, carbon film, and lastly, carbon composition. However, wirewound resistors are not readily available in large resistance values, and are usually inductive, which can cause instability problems in some cases. Bear in mind, however, that many people prefer the "sound" of carbon comps, claiming they sound warmer than film or wirewound types. This is possibly due to distortions generated by the modulation of the contact noise current by the AC signal. Since this noise has a 1/f frequency characteristic (similar to pink noise), it is more pleasing to the ear than white noise. However, pleasing noise is still noise, and in my opinion, it should be reduced to the lowest possible level. The signal distortion is a different topic altogether."

Thanks, I read that article. Seems wire wounds are suited and are favored for most applications if you can find the right value. If you get the noninductively wound WW resistors, you shouldn't have any instability problems, which I assume are high frequency oscillations that can be induced (eg, grid stopper) by inductive resistors.

metalsculptor 1st January 2013 08:30 AM

There is no blanket rule each type has it's advantages, The noisy carbon composition resistor works very well in pulse power or RF circuits also there are many places in an amplifier where a noisy resistor is of no consequence or the noise is heavily filtered by a decoupling capacitor, same goes for instability, a bypass capacitor may move any resonances so far outside the region where the amplifier produces any gain that oscillation is impossible.

MGH 1st January 2013 02:06 PM

Quote:

Originally Posted by metalsculptor (Post 3306445)
There is no blanket rule each type has it's advantages, The noisy carbon composition resistor works very well in pulse power or RF circuits also there are many places in an amplifier where a noisy resistor is of no consequence or the noise is heavily filtered by a decoupling capacitor, same goes for instability, a bypass capacitor may move any resonances so far outside the region where the amplifier produces any gain that oscillation is impossible.

Hi, thanks for your input. So what part of the power supply is a particular type of resistor critical or more important?


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