Smeggy Posted March 21, 2009 Report Posted March 21, 2009 It seems you bastards have finally led me to a trail of misery and pain and I feel I should repay you with dumb questions. I plan on this thread growing as my dumbness expands into more areas. I'll start with one question that's been bugging me for a little while.. Resistors. Does the power rating matter as long as they're not underrated for any particular circuit? I've seen 1/8, 1/4, 1/2 watt and so on. Does it matter as far as performance/sound goes?
justin Posted March 21, 2009 Report Posted March 21, 2009 It seems you bastards have finally led me to a trail of misery and pain and I feel I should repay you with dumb questions. I plan on this thread growing as my dumbness expands into more areas. I'll start with one question that's been bugging me for a little while.. Resistors. Does the power rating matter as long as they're not underrated for any particular circuit? I've seen 1/8, 1/4, 1/2 watt and so on. Does it matter as far as performance/sound goes? You should get a resistor rated for at least 3-5x the amount of power used. Physically larger resistors can also be lower noise
Smeggy Posted March 21, 2009 Author Report Posted March 21, 2009 Thanks Justin. so as long as they're the right value bigger voltage ratings don't matter? Sweet.
wrecked_porsche Posted March 21, 2009 Report Posted March 21, 2009 The way I understand it, the bigger the wattage rating on the resistor, it just means that it can handle/dissipate more energy before it goes kaput or gets burnt out/destroyed. Hence why its a good idea to go with a slightly bigger/higher rated one than what's required. Drawback is that it will be bigger(physical size), as Justin already mentioned. Please correct me if I'm wrong.
Smeggy Posted March 21, 2009 Author Report Posted March 21, 2009 As long as they physically fit a board or are doing P2P it's all good with me. Some of these resistors are tiny and I'd prefer working with something a bit bigger where I can. I asked because finding specific voltage/value resistors can be a pain when trying to get stuff locally when I'm in a hurry. I know, rat shack and the like aren't the best option but at least they're there and have what I need even though tolerances are at about 5%. I can live with that in a push.
wrecked_porsche Posted March 21, 2009 Report Posted March 21, 2009 I know, rat shack and the like aren't the best option but at least they're there and have what I need even though tolerances are at about 5%. I can live with that in a push. Heh.... just buy a bunch and spend the afternoon sorting through them and try to match them as close as you can... I'm pretty OCD that way sometimes, but yeah, I could live with them being +- 5% too. Yeah, I get you, finding specific voltage/value resistors are a real PITA when you want them locally and when in a hurry. Been there before.
spritzer Posted March 21, 2009 Report Posted March 21, 2009 Using larger resistors is much easier when doing P2P work but you can always drill out the holes on a PCB. I had to do that on the BH boards I was working on as I was using resistors with higher wattage rating.
Smeggy Posted March 21, 2009 Author Report Posted March 21, 2009 Yeah, I already bought a bunch but was unsure if it would screw anything up using mixed wattage parts.
swt61 Posted March 21, 2009 Report Posted March 21, 2009 That's funny timing because I was at RatShack looking at resistors yesterday, and had the same question. None of the RatShack resistors had anywhere near the 3W rating I was looking for, so I opted to wait and lean on luvdunhill to help me with an order. From my point of view however that wasn't a dumb question. But great thread, because I too plan on asking many really stupid questions now that I've also been sucked in. BTW, who can steer me to a nice IEC w/fuse and power switch at a decent price?
spritzer Posted March 21, 2009 Report Posted March 21, 2009 BTW, who can steer me to a nice IEC w/fuse and power switch at a decent price? A quick search turned up this one for 34$.
luvdunhill Posted March 21, 2009 Report Posted March 21, 2009 (edited) That's funny timing because I was at RatShack looking at resistors yesterday, and had the same question. None of the RatShack resistors had anywhere near the 3W rating I was looking for, so I opted to wait and lean on luvdunhill to help me with an order. From my point of view however that wasn't a dumb question. But great thread, because I too plan on asking many really stupid questions now that I've also been sucked in. BTW, who can steer me to a nice IEC w/fuse and power switch at a decent price? Steve: I'm sorta out of commission until later today, hopefully I'll survive some fireworks at pabbi1's house.... I'll give you a ring when I'm on the road back to Austin. With regard to IEC w/fuse and power switch, new it's hard to find something under $10 or so. One option is the below surplus part, which also includes a EMI/RFI filter... kinda like an integrated power conditioner. Since you have some mad square hole cutting skills, you could go this route. I've purchased several of these in the past: DELTA LINE EMI FILTER 6 AMP 06AK2D Lightly Used - eBay (item 330084141165 end time Jan-31-09 10:03:28 PST) Problem is, shipping nails you on these, unless you get 3 or so. The deal is, new these are probably >$25 each when purchased new. Anyways, this is one option. I'm sure others around here will have some good choices. If you like the one I used on your Pearl, it is Digikey part 486-1084-ND for $10.01. The deal with this, is it uses dual fuses. This is easily fixed with some solder, or actually using two fuses. A single fuse version of this would be more suitable in some senses. Edited March 21, 2009 by luvdunhill
swt61 Posted March 21, 2009 Report Posted March 21, 2009 OK Marc, sounds great. Just give me a call when you get home, no need to talk on the road. Or we can do it tomorrow. I just ordered the IEC on ebay, thanks. It'll just be easier than three separate holes, as you already knew.
Smeggy Posted March 21, 2009 Author Report Posted March 21, 2009 Awesome... ok this is, of curse, open to all dumb newb questions as I'm sure many of us have questions about the little things that are so frustrating.
TomB Posted March 21, 2009 Report Posted March 21, 2009 Hmm ... I usually size resistors for 2X power rating. That should be plenty safety factor, assuming you know for certain the voltage involved and you use quality resistors. I've not heard that larger resistors might have less noise, either. Seems that if that were true, SMD resistors would be the noisiest.
Dusty Chalk Posted March 22, 2009 Report Posted March 22, 2009 Yeah, I already bought a bunch but was unsure if it would screw anything up using mixed wattage parts.Fellow n00b here, so non-n00bs, feel free to confirm or deny -- two pieces of advice I've received: - try to be symmetrical about it, if you're going to use a higher wattage resister in one place on the left channel, try and use a higher wattage resister in the same place on the right channel; - as to whether or not one sounds better or not -- heck, try it for yourself, and see if you can hear a difference -- I doubt it in the case of only one, so the real test would be to swap them all out (this one is not advice I've heard, but rather, a conclusion I've seen several people come to on their own); - there are better places to use higher wattage resistors -- try and find out what they are (perhaps by asking).
Smeggy Posted March 22, 2009 Author Report Posted March 22, 2009 I think matching both sides makes sense.
fordgtlover Posted March 22, 2009 Report Posted March 22, 2009 The Wikipedia article on resistors is quite informative. I'd be interested to hear more about the benefits of using a resistor with a higher power rating than specified. I've only been doing DIY for a few years - mainly as a board stuffer - and have not seen or heard anything about this. This website shows how to calculate resistor noise. I couldn't see anything relating to power rating and its impact on noise. As best as I can understand, metal film resistors are more stable across temperature ranges and age and are less noisy than carbon resistors. But here's the rub, metal film resistors seem to be only available in relatively small power ratings (less than 2 or 3 watts). If you were to want higher powered resistors in your circuits, you would need to use carbon film resistors, with their higher noise and lower stability over time, or wirewound resistors that are significantly larger. And, of course, circuit boards would all need to be much bigger than (possibly/probably) required. As for symmetry in circuits, I would use the same type of part in both channels and match the resistance value as closely as possible. I don't know if there is any real value in doing this, but it makes me feel better. I'm hoping someone like Kevin Gilmore can chime in on this whole issue (no disrespect to anyone else who knows the answer).
TomB Posted March 22, 2009 Report Posted March 22, 2009 Resistor Types--Does It Matter?Sorry, but I'm still skeptical. Thermal/Johnson-Nyquist noise is familiar to all, but focuses on resistance, not physical size. This reference seems to focus on something called "Contact Noise" to justify that larger resistors have less noise. Yet, there's no reference for that section, no derived basis in predictably or proof. Plus, he references mainly carbon comp resistors in guitar amps. Carbon comp have many issues all on their own - it might be quite possible that larger is better in that case. However, I'd like to see more evidence before believing this for metal films or that a 1206 SMD resistor would have less noise than an 805, for instance. EDIT: It looks like there are some other references to contact noise, but it appears to have to do with the fluctuating "contact" between materials, otherwise known as "flicker noise." It's probably called "contact noise" because the effect is predominate in metal contacts (again, where larger is better seems to make common sense). If someone has an IEEE membership, perhaps they can look up the complete article on this reference: http://ieeexplore.ieee.org/Xplore/login.jsp?url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel6%2F33%2F25361%2F01136638.pdf%3Farnumber%3D1136638&authDecision=-203 Again, the issue seems to have a great effect in carbon comp resistors due to the granular nature of the composition material - lots of miniature contact surfaces between the granules. It makes sense that if a resistor was bigger for a given resistance value, then the contact surfaces would be maximized, lowering the potential noise. I'm still skeptical that this applies to metal films and the way in which they're constructed, however.
fordgtlover Posted March 22, 2009 Report Posted March 22, 2009 I found this reference on Google books in Practical electronics for inventors By Paul Scherz (pp. 323 - 324) Practical electronics for inventors - Google Book Search So if we use metal film resistors, contact noise should not be a problem. Is that correct?
TomB Posted March 22, 2009 Report Posted March 22, 2009 Well, that's interesting and sort of what I was surmising from the references I found. Your reference goes so far as to say that "Wire-wound resistors do not have this noise - only those with carbon particles." (contact noise). Again, that also sounds like metal films are completely immune to this larger size/less noise phenomenon.
luvdunhill Posted March 22, 2009 Report Posted March 22, 2009 with all due respect, this conversation doesn't belong in a intro to DIY thread. I'd excise it if I could. This is way down in the weeds.. you new guys need to get your hands dirty and start to form your own opinions on what makes a difference
TomB Posted March 23, 2009 Report Posted March 23, 2009 with all due respect, this conversation doesn't belong in a intro to DIY thread. I'd excise it if I could. This is way down in the weeds.. you new guys need to get your hands dirty and start to form your own opinions on what makes a difference Are you asking for moderation?
Smeggy Posted March 23, 2009 Author Report Posted March 23, 2009 Are you asking for moderation? No, just simplicity, and less arguing the intricacies of theoretical stuff us nubs don't understand anyway We want basic answers to basic questions.
Duggeh Posted March 23, 2009 Report Posted March 23, 2009 I have a basic question. Should I put the mayo between the bread and the ham, or between the ham and the salad?
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