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surface mount resistor advice, smt resistors vs through hole audio quality
john11
post Mar 4 2013, 08:47
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Hi and thanks for reading this post.

I have a few blown one watt resistors i want to replace in my power amp and am thinking about using surface mount resistors.

Do you think this is a wise move switching from through hole to surface mount, has anyone done this and what are your experiences concerning sound quality changes.

Many thanks in advance. John.
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Light-Fire
post Mar 4 2013, 10:07
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Unwise move. There will be no sound improvement.
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Glenn Gundlach
post Mar 4 2013, 10:50
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You don't mean 1 Watt surface mount right? They don't exist at DigiKey which means they may not exist at all.

Why would you think of changing through hole resistors to SMT? If you were designing a new board it would make sense but to try to replace axial resistors with SMT would be extraordinarily tedious. After all that trouble what would you accomplish besides voiding the warranty?

If you were suggesting replacing carbon films with metal films MAYBE it _could_ be worth the effort but if designed properly it shouldn't be a carbon vs metal because the operating impedances internally would swamp out the Johnson noise of the resistors.

Bottom line - if it works leave it alone but you should find out WHY the 1 Watt resistors failed as that is not at all typical.

G
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Arnold B. Kruege...
post Mar 4 2013, 14:29
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QUOTE (john11 @ Mar 4 2013, 02:47) *
Hi and thanks for reading this post.

I have a few blown one watt resistors i want to replace in my power amp and am thinking about using surface mount resistors.

Do you think this is a wise move switching from through hole to surface mount, has anyone done this and what are your experiences concerning sound quality changes.


PC card design for SMT parts is vastly different from that for through-hole parts. It is sometimes thinkable to replace SMT parts with through-hole parts in a pinch. The inverse is generally pretty impractical.

Most of the concern in this area has been that SMT parts don't sound as good as traditional parts.

The real concern is servicability as SMT parts replacement in the field takes new tools, supplies, and procedures.

In fact for audio, it hardly matters one way or the other for final performance of the finished piece. It has been possible to easily build great-sounding equipment either way for well over a decade.

SMT's primary advantage is equal or better total quality for the price including reliability of finished product both initially and over the long term. IOW, its all about money not sound quality.

Like all new technologies there have been teething problems with SMT, but those are in the distant past.

SMT may be more susceptible to tin whisker problems due to ROHS compliance because it tends to put conductors closer together on circuit cards. But again that is not really a problem inherent with SMT, but rather a problem with soldering.


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john11
post Mar 5 2013, 03:51
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Hi. Thanks for the replies, much appreciated.

The reason i am thinking of switching to surface mount resistors is that the blown resistors i want to replace are tiny they only occupy 8.5mm on the board, i have searched digikey, mouser farnell and cannot find any high quality resistors with such a small footprint, except that is of course the surface mount type but i don't know how surface mount sound, are they any good for within a power amplifier.

Many thanks. John.
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splice
post Mar 5 2013, 05:32
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I doubt you'll find SMT 1 watt. That power dissipation is better handled from an axial resistor that sits up from the board, allowing air to circulate on all sides.
Either:
- Bend the leads back under the resistor before bending them down to fit the holes
Or:
- Mount the resistors "on end" (standing up). Put a piece of insulating sleeve over the exposed lead.


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john11
post Mar 5 2013, 08:34
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Hi. Thanks for the replies.

I've found a few surface mounts on mouser but cannot understand the datasheet, usually when purchasing through hole resistors i look for descriptions such as low noise or military or suitable for audio etc but there is no mention.

Does anyone understand datasheets better than me or has an opinion on the caddock mk 132 series,vishay dralorik crcw-hp, vishay wsc/wsn series.

Are these suitable for audio amps.

Thank you. John.
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DVDdoug
post Mar 5 2013, 22:43
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QUOTE
...the blown resistors i want to replace are tiny they only occupy 8.5mm on the board,
Physical size is related to the power rating. All 1W resistors will be about the same size.

If the resistors are burned-up, it's very likely that an active component (Transistor, MOSFET, IC) is also fried.

QUOTE
Are these suitable for audio amps.
Just get the right value, power rating equal or greater than or the original (as long as it will fit physically), and tolerance equal to or less than the original.
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Arnold B. Kruege...
post Mar 6 2013, 13:37
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QUOTE (john11 @ Mar 5 2013, 02:34) *
Hi. Thanks for the replies.

I've found a few surface mounts on mouser but cannot understand the datasheet, usually when purchasing through hole resistors i look for descriptions such as low noise or military or suitable for audio etc but there is no mention.

Does anyone understand datasheets better than me or has an opinion on the caddock mk 132 series,vishay dralorik crcw-hp, vishay wsc/wsn series.

Are these suitable for audio amps.


Given the uniformity of advice to not use SMTs, why do you think that anybody will pay any attention to your continued attempts to disregard our advice? You've implicitly said that our advice is useless, so why should we help you waste our time and your time and shoot yourself in the foot?
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pdq
post Mar 6 2013, 14:23
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One point to consider - If the through-hole resistor made contact with a trace on the bottom of the board, and if you replace it with a surface-mount resistor that only contacts the top of the board, then you are depending on the through-hole plating, plus solder, if any, that fills the hole, for electrical contact. This could make for a very unreliable connection, especially if the act of removing the old resistor damages the through-hole.

In other words, don't do it.

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Glenn Gundlach
post Mar 7 2013, 04:43
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If the vias (those holes for the sole purpose of changing layers on a PC board) were unreliable, your computer absolutely would not work because it can't be done as a 1 layer board. I used to lay out PC boards and 2 and 4 layer boards are pretty common particularly in computers. The only time I find problems with the actual PC boards is from capacitor leakage that doesn't get cleaned off. At that it takes years to rot the board.

I agree with the "don't do it" advice but not because of the plated through holes on boards.

G
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greynol
post Mar 7 2013, 05:23
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I have the same experience with designing layouts plus dealing with manufacturing PLUS servicing/reworking populated boards. It is this last point that pdq is addressing. This is not about the integrity of vias and plated through-holes; it is about what becomes of them after less-than-delicate work has been performed.


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wood11
post Mar 27 2013, 14:54
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QUOTE (Glenn Gundlach @ Mar 4 2013, 10:50) *
You don't mean 1 Watt surface mount right? They don't exist at DigiKey which means they may not exist at all.

Why would you think of changing through hole resistors to SMT? If you were designing a new board it would make sense but to try to replace axial resistors with SMT would be extraordinarily tedious. After all that trouble what would you accomplish besides voiding the warranty?

If you were suggesting replacing carbon films with metal films MAYBE it _could_ be worth the effort but if designed properly it shouldn't be a carbon vs metal because the operating impedances internally would swamp out the Johnson noise of the resistors.

Bottom line - if it works leave it alone but you should find out WHY the 1 Watt resistors failed as that is not at all typical.

G

I also totally agree with you. Replacing Carbon film resistor with metal films could be worth effort than replacing axial resistor with a SMD resistor.
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