Electronics > Beginners
smd resistor in power audio amplifiers
mrjoda:
Hi guys, as HW designer i should know it but :-\ ... i need advice.
Are there any "no go" for SMD resistors/capacitors in power audio amplifiers ? Maybe some noise, power capabilities ... ? At input stage. Power resistor will be wounded welwyn or so.
I am currently working on update of one of my projects and i need to decrease dimensions under the 100x100mm. And is it quite old project made for DIY production (i made almost 100pcbs at home of this) so it needs some modernisation.
Based on this page https://www.beis.de/Elektronik/ResistorCurrentNoise/CurrentInducedResistorNoise.html , the difference between 1206 smd and tht metal film resistor is almost 10dB.
The graph shows that noise is voltage dependend and voltage of that amplifier is around +/- 30V . I uploaded schematics, i was thinking about usage of smd parts up to VAS. Overcurent sould be OK with SMD parts, bias controller also.
I am not sure about it. What do you think ?
Thanks
magic:
Look for teardowns of audio gear, it seems everybody uses SMD these days.
There are two SMD resistor technologies: thick film and thin film. The former are noisy and nonlinear, the latter are similar to through hole metal film resistors, although IIRC there were some complaints about silght voltage coefficient in the smallest package sizes. Maybe thermal modulation? Stronger field gradient?
As for capacitors, small values in C0G/NP0 dielectric are OK, all the X7R, Y5V stuff is highly nonlinear and microphonic so not really suitable for coupling, filters and such.
exe:
I'd say resistors totally fine if they can handle power you need. As of smd caps, depends where and what they do, DC bias being, probably, the biggest problem. I wouldn't use smd caps smaller than 0805, but bigger packages, while having better specs, are more fragile and can cause a short.
Anyway, I wouldn't care much about distortion, etc. Unless you have "golden ears", I doubt it's audible to have 0.1% or 0.01% distortion, let alone making a difference in experience. I know the pressure in audio community for "special" cables, resistors, capacitors, opamps, etc. Probably that's why you are here asking this question. But look critically at the plots you showed. Are you really care about resistor noise of <-110db?
My advice: get an audio analyzer if you really care and see yourself how different components affect distortion and noise. Otherwise just use normal components and save yourself a lot of time and trouble.
mrjoda:
thank you guys.
My question was pretty much general about power amplifiers. Audio is not my field of interest, i don't care about seventh place of distortion. My scope is to publish my old project as open source in smaller form factor with the newest parts.
I decided to use 1206 resistors and parallel combination if power rating is too high for one. For capacitors, the best choice is NP0 for stability and X7R as general for power rails blocking.
I don't have access to audio analysers, just bode100 and i am not sure, if input dynamic range is sufficient for audio measurements. My knowledge in this field is minimal.
mariush:
If you just want to reduce the size, you could place the resistors on some small boards and connect them like SIMM sticks to the board (like ram sticks but without connectors).
You could solder a right angle 0.1" (or 2mm or 2.5mm) spaced header and then plug the header on the base board.
With double sided circuit boards you could route things quite nicely that way.
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