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.
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.
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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."
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."
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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.
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?
Anything after the final filter capacitor or affecting a ground reference is more likely to introduce noise. In the main power circuit heat dissipation is probably going to be a major selection criteria, that is easily calculated. Metal cased wire wound resistors are compact with moderate temperature rise for their dissipation rating and OK for the voltages usually found in audio amplifiers. High voltage power supplies often use long ceramic carbon film or carbon composition resistors for voltage division. Precision voltage references often use constantan wire wound resistors for any precision voltage dividers or gain setting. For Audio metal film for the signal handling and Metal cased wire wound for any power handling should cover most applications. You should always read the manufacturers data sheets and any application notes before using any component in a design. For a resistor, dissipation and voltage rating would cover most applications. Case isolation voltage and capacitance to case are things to look out for with the metal cased resistors. Inductance should be minimised in the supply lead to a voltage regulator and these devices should have bypass capacitors in accordance with manufacturers recommendations. There is so much to cover I can only scratch the surface. Needless to say you will end up reading many documents in any electronic design process and these are usually the best source of information.
Wow, thanks for the info! I will try to digest all this. Please see your PM box.
I got the PM but for whatever reason the messenger could not find you user name anyway the reply: That is fine, I grew up with tube circuits so I know my way around them. I do need to know relevant voltages and design current. If you do not know the total current, the total maximum plate dissipation of the tubes will do
I guess one way of approaching the question of whether matching matters, is that It may not matter at all, but it certainly won't hurt if you do 
so if it is not going to cost very much to do it then why not
for example some suppliers offer a matching service at reasonable cost ( I got some matched pairs of caps and resistors for my preamp at a cost of $1 extra per matched pair). Which in the long run is probably cheaper than buying 50 or more and matching myself when it is only a small quantity.
Tony.
so if it is not going to cost very much to do it then why not for example some suppliers offer a matching service at reasonable cost ( I got some matched pairs of caps and resistors for my preamp at a cost of $1 extra per matched pair). Which in the long run is probably cheaper than buying 50 or more and matching myself when it is only a small quantity.
Tony.
if you are going to match resistors, make shure you dont get thermal mismatches between the matched resistors or all your matching will nulled depending on the change of resistance do to thermal issues. This is a layout , build issue, but I have seen matched circuitry where some resistors were nearer a heat source than there respective resistors on the other channel. This buggered things up a bit! they were 0.1% tolerance resistors though, and in cuitrity that had to work -40/+85. But it is worth noting if you are going to o to the effert to match components.
Hi, by bias setting resistor do you mean grid blocker? gain setting resistor meaning plate resistor? I have a feeling I'm wrong about these.
A grid blocker AFAIR refers to a capacitor, you probably mean grid leak Bias setting resistors can be a resistor in series with the cathode, a voltage divider in a dedicated bias power supply or in a less direct way, a grid leak resistor. Gain setting resistors can be a feedback voltage divider or to a lesser extent a plate or cathode load resistor. Note this only applies to sections of an amplifier which use differential or complimentary amplification stages, for example most of the McIntosh MC75. If you are planning on building an amplifier consisting entirely of single ended gain stages none of this applies. Metal film and wirewound resistors have reasonably low temp coefficients. Marce's point was more about layout, for a differential circuit it is good practice to put the components of both halves of the differential pair in close thermal proximity.
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