PCB vs SMT

Discussion in 'Amps and Cabs' started by reaiken, Aug 20, 2005.

  1. reaiken

    reaiken Member

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    Okay, for discussion purposes, let's take PCB technology into the 21st century:

    All tonal comparisons aside for a moment, the biggest complaint people have with PCB amps is the lack of servicablity, right? Through-hole components are a bear to get out and put back in from the top of the board (especially if the bottom leads are clenched to hold the parts in during soldering), and usually a pad gets lifted in the process. The alternatives including desoldering all the connections needed to get the board out to remove the parts from the bottom, or using a bunch of plug-in connections, ribbon cables, and other non-road-worthy mecanical nightmares.

    How about this approach: almost all "modern" electronic products are assembled using surface-mount technology (referred to as SMT or SMD). Surface-mount components have no "legs", just have metal end caps that are soldered directly to the pads on top of the PC board (or on bottom, or both). They are very easy to remove from the board without lifting pads by wicking the solder from both sides of the part and removing it (unless you are dealing with multi-legged devices like ICs, where you need special soldering iron heads that heat all the pins at once). Admittedly, enough desoldering can lift a pad, but it is not nearly as difficult as removing a through-hole part from the top side of the board and putting it back in. Worst-case, you have to buy an SMT tip for your soldering iron that heats both sides of the part at once (these are readily available for most all size components).

    These SMT boards are very vibration-resistant, as the parts are fairly low mass and mounted in low CG positions directly in contact with the board. I've designed many SMT boards for military avionics displays that have to pass strict vibration and hi-G crash tests, so I know they are up to the task of riding around in the back of a band van.

    Most SMT boards use tiny parts, such as 0805, 0603, or smaller size resistors and caps, which are the size of gnat's eyelashes, but those parts aren't compatible with tube guitar amplifier voltages anyway. Here's the kicker: there are tube-amp-compatible surface mount components available. You can get 500V, 1W *carbon comp* resistors in SMT. They aren't cheap, mind you, at around a buck each in quantity, but they are available. There are also carbon and metal film SMT 1W resistors available. You can also get 400V SMT film caps in polyester film (and other film types), ceramic, and silver mica dielectrics.

    Now, the question is, what would the general public reaction be to a tube amp that used all SMT components? Would in instantly be shunned as an "evil" PCB amp or worse, as an even "eviler" SMT PCB amp? Or would it be perceived as "better" than a standard PCB amp, because the parts could be more easily replaced?

    Randall Aiken
     
  2. LaXu

    LaXu Member

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    I think for most people the serviceability is not a big concern. Most of the amp buying public are not electricians and would rather not poke around the insides of their amp in any case. If something fails, they either replace it under warranty or send it to a tech and how easy the amp is to service becomes his/her headache. Sure it might show up in the final bill as a bigger sum, but if you have to spend more on the amp to begin with because it's SMT then the difference kind of negates itself. I imagine finding the tech to service an amp with SMT PCB would be difficult too, at least he'd have to order those special parts and that could really hurt turnaround times.

    So my guess is that the buyers wouldn't think a SMT PCB amp is "more evil" than a regular PCB one, but they sure as hell wouldn't be willing to pay more for one simply for the sake of serviceability. I mean, people here (hopefully) don't buy boutique amps because they are PTP but because they have the sound and features they are looking for.
     
  3. reaiken

    reaiken Member

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    That's the other nice part - SMT assembly is done with "pick and place" machines, rather than hand-assembly, so the labor costs are far less, which should translate to lower amp costs, not higher, even though some of the parts might cost a bit more.

    Although, in the end, the cost of the amp is set by quite a few more factors than just parts cost. For example, some of the highest priced amps out there are built on PC boards (some quite cheap, single-sided ones, some high-quality) and some expensive PTP amps are built using very few components in off-the-shelf thin-aluminum chassis.

    Randall Aiken
     
  4. tedwoods

    tedwoods Member

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    I think that apart from servicability,tone is the other major consideration.
    If the tone is "special" people are going to come along.
    Most of the ptp diehards,myself included,are only in it for what it does "tonally".I couldn't care less about construction if the tone I'm seeking was there.Unfortunately,I haven't heard something in that direction with most pcb offerings.

    Ted
     
  5. Matt Gordon

    Matt Gordon Senior Member

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    Most of the amps I like are voiced close enough for me to tweak to my liking, so for me build quality is the first stop having met those simple tonal requirements. If it's a PCB, then having an option to replace it if something fails would be a benefit. In other words, having replacement PCB's at cost would be a big selling point. But if they all used your advice Randall, there wouldn't be any issue between PCB/PTP construction. As you well pointed out, this issue has legs because of those flimsy PCB's out there on the market. If we're talking about a Randall Aiken designed PCB, well, I wouldn't give it two thoughts. ;)
     
  6. riffmeister

    riffmeister Gold Supporting Member

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    do it Randall!

    move us into the 21st century!!
     
  7. gsf

    gsf Member

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    Yeah, Randall, I agree with Matt. YOU might be the guy to set the new standard in 'guru' designed, boutique tone, breaking the price point barrier. Randall Smith has done fine sticking to his personal opinions about PTP, etc. (I know there are 'market issues' in that case). Your opinion on it is probably the most important one on this board, as you understand what is involved and have seen the manufacturing carried out to a final product (even if not amps). If you can afford to do a couple prototypes, and then calculate your costs, and compare them to your own existing amp line favorably, who's to argue w/you ------- sounds like you aren't concerned with reliability issues. I guess I'm saying you can only 'sell' the process when it's no longer intangible, but a living amp.

    just ramblings
     
  8. aleclee

    aleclee TGP Tech Wrangler Staff Member

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    I think you'd have some education issues. Here are some questions I'd ask:
    • How many amp techs are comfortable working on SMT stuff?
    • How hard is it for me or my tech to get SMT resistors and capacitors to replace or mod the current components?
    • Most SMT stuff I've seen is pretty densely packed. Would these boards be as dense as, say, my computer's motherboard? If so, would there be a tonal impact as currents get induced in adjacent traces?
    • Do SMT components have the same innards as their long-lead counterparts? If not, what sort of impact would that have on tone and reliability?
    • SMT isn't used much on high voltage circuits. Are there any concerns about the technology and components from that standpoint?
    • If SMT was accepted by the market, would the "big guys" like Marshall stand to gain more because of their offshore manufacturing experience? It would be a shame if booteek builders made the concept acceptable only to have the mass producers take advantage to increase the price difference between their products and the boutique stuff.
    Despite all that, it's an intriguing idea and definitely worth investigating.
     
  9. VacuumVoodoo

    VacuumVoodoo Member

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    I agree on the reliability points.

    Through hole PCBs are also stuffed by pick & place machines so this isn't really a big differentiator here. It's more a question of volume and break-even point. What production volumes do you have in mind ?

    Manual assembly of SMD boards is of course out of the question: time consuming and requires skilled certified personnel. Been there, done that.

    Servicing and parts replacement: to do it correctly you need specialised tools. SMD components require short defined soldering time and closely controlled temperature. After removing a part the PCB must be properly prepared and cleaned before new part is glued and soldered in. I can't see an average repairman being capable of doing it properly.
    I'm sure you know all this but thought it worthwhile mentioning for the benefit of non soldering members here.

    Replacing the whole board: will the bad one go straight to garbage bin ? What about environmentally correct disposal ? The RoHS directive makes the manufacturer responsible for that.

    On the other hand, RoHS directive may in fact be an incentive for going SMD: not all components we use today in tube equipment will be available in versions free from lead, chromium and other substances specified by the directive. What about tubes themselves ? AFAIK they do not comply with RoHS...
    Thanks for saying this. I think therein lays a lot of the PCB vs PTP dispute. Some of the stuff out there would have hard time passing standard tests for electrical safety, not to mention the quality and adherence to ground rules of proper PCB design or PTP assembly techniques. Few amps are assembled on quality double sided PCBs with proper separate signal and power ground planes.

    So, my point is that quality and reliability of many amps can be significantly improved by going for well designed doublesided PCBs. Analog PCB design is an art form and letting a professional pcb-designer experienced in analog design do it for you may be a good investment. Just start looking for leadfree components today, the RoHS directive comes into force on July 6, 2006, at least in the EU.
     
  10. riverastoasters

    riverastoasters Member

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    General public? I don't know. Me? If the amp sounds good and doesn't break even under duress then I don't care if it's made out of tubes or turnips.
     
  11. reaiken

    reaiken Member

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    True, but most of the large components currently used by "boutique" guys like myself, are either not available on tape-and-reel, are just too large for the machines used in most board-stuffing houses, or the volume is not there. Most board houses use a slide-line for THT devices. The setup charges for SMT are declining rapidly (or have leveled out), while the cost of manual THT is increasing due to the cost of labor (at least in the board houses I'm familiar with).

    No, it is not out of the question at all. I do lots of contract design work for various manufacturers who get manual SMT work done. In fact, the last board I did recently was a 5 mil trace/space, double-sided, 10-layer SMT board stuffed full of BGAs and 0603-sized components on both sides of the board - we had the first run of boards hand-stuffed to make sure the boards were okay before committing to the first production run of 100 boards. They regularly remove, re-ball, and replace large BGAs manually as well. The board house was quite reasonable on pricing, and if they can manually place a 512-pin 1-mil BGA, I know they can place large high-voltage SMT caps and resistors. Manually-stuffed runs are nearly always done first to avoid having to pay the setup charges for programming the pick-and-place machines in the event of a board design change during the protoype phase.



    Even an inept solder-jockey can do a good enough job to replace a large 2-pad part even without proper prep and cleaning. Techs in all the companies I've worked for replace parts all the time, using standard tools. Although, to be fair, some of the smaller parts and IC's require a hot-air removal tool, but, again, that wouldn't be necessary for the type parts that would have to be used in a tube amp. Most can be removed using the "two soldering iron" technique, cleaned manually, and replaced easily. Obviously, you'd prefer it done by certified techs, but most tech repair work and soldering on normal through-hole pcb's is rather dismal compared to "proper" soldering techniques. We're talking guitar amps here, not military equipment. They'll work fine with minimal attention to soldering/desoldering technique, and I bet the end result would be better than you'd get removing a part from the top of a through-hole board (which is what many techs do!).



    I would never design a product that required board disposal to fix minor problems!

    RoHS and other governmental regulations are going to put everyone except large corporations out of business someday...


    I've been doing high-frequency analog and high-speed digital PCB layouts for 15 years, so I am well-versed in the art! And you are quite correct, sir, it *is* an art, especially in the world of high-impedance vacuum tube circuitry. That is where a good PC layout can actually be better than PTP.

    Thanks for all the great questions, keep 'em coming!

    Randall Aiken
     
  12. reaiken

    reaiken Member

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    Small, 0805/0603 size stuff and SMT ICs? I dunno, probably not many, but I'd bet any tech worth his salt could remove/replace the large-format parts required for tube amp voltages.

    Now, that's an excellent concern. Most, if not all the parts are available through DigiKey, Mouser, Allied, or any of the other distributors commonly used by manufacturers and techs.

    The boards would not be any more dense than a standard through-hole PCB, because the higher-voltage parts are physically larger than your average computer motherboard parts, and there just aren't that many parts on most guitar amp boards (unless you have zillions of features, midi-control, digital displays, and stuff like that, but I'll leave that for Line6 and the other evil solid-state guys. :) ) As for tonal impacts due to adjacent traces/components, that is a factor in *any* layout, not just an SMT layout, and as VacuumVoodoo so accurately pointed out, it is all in the skill of the layout guy.

    Yes, they have the same gizzards. "Purists" could even argue that the removal of the leads and their connections would result in a shorter, more pristine signal path. :D

    As for the parts, as long as the manufacturer used properly rated parts, there would be no difference. The PC board itself is the same, whether it it SMT or THT.

    SMT is already accepted by those guys who play computers...er...modeling amps. It just has never been used (to my knowledge) in a quality "boutique" amp. Of course, larger manufacturers would be able to take advantage of the technology much more easily than a small boutique guy, but, by the same token, it might give the boutique guy a leg up on higher volumes, by farming out his board stuffing and going to PC boards without the fear of the repair issues associated with standard THT PC boards.

    I think so, too. Thanks for all the great questions!

    Randall Aiken
     
  13. reaiken

    reaiken Member

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    Excellent points. I was just sitting around trying to think of ways to be able produce more amps to meet my dealer's demands, and while thumbing through a Digkey catalog, I saw some 1W 500V SMT carbon comp resistors, and a light bulb went off (not in my head, we were having a severe lightning storm here in FL and the power went out. :D). I think it is definitely something worth looking into.

    Randall Aiken
     
  14. reaiken

    reaiken Member

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    Heh, thanks! I don't like the idea of replacement boards. That is reserved for things like computers (i.e. "modeling amps") and consumer electronics which have parts and circuits that cannot easily be repaired by a technician. The average tube guitar amp is about as technically advanced as a light bulb, so a throw-away PCB would be a complete waste.

    Still, PCB is a dirty word among many amp buyers. There are basically three camps: (1) PCB amps are inherently somehow inferior, tonally, and should be avoided like the plague, (2) PCB amps can be made to sound every bit as good as PTP amps, but are a bear to service, and (3) "If the amp sounds good and doesn't break even under duress then I don't care if it's made out of tubes or turnips." (Where have I heard that before???) :D

    Obviously, the guys in camp (1) are probably not going to be interested in the amp from the start, and that's cool, I myself personally prefer a PTP amp just becase I like the looks of them. :) I just want a way to make a reasonably-priced amplifier worthy of putting my name on it, in large enough quantities to keep the dealers and customers happy, and unfortunately, it looks like PC boards might be the only way I can make that happen. I haven't had much luck with outside wiring houses, and, while I have a couple of excellent employees I wouldn't trade anything for, they can only build so many amps a month, so anything I can do to speed up the process is a good thing.

    Randall Aiken
     
  15. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    Randall, if I was going to trust anyone to pull this off, it'd be you. As for the guitar-amp-buying public...there is a tremendous amount of ignorance about the virtues of hand-made amps (well...hand-made anything, really). I think there might be something of an uphill educational battle with those folks...but chances are, most people that liked the way it sounded (and liked the facts and figures that you would have already posted on your website re: the process and it's resulting benefits ;) ), I would guess that a lot of folks would pile on. My impression is that THD, Suhr and even Orange haven't had a lot of trouble attracting a pretty solid (and generally well-deserved) following with PCB-based products.
     
  16. reaiken

    reaiken Member

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    That is true, and it is mainly because guys like Andy Marshall and John Suhr care enough to put a lot of time into designing and building a high-quality product with a great sound. Another great example is Michael Soldano, who has built a world-wide following with PCB amps from the very start.


    Randall Aiken
     
  17. PlexiBreath

    PlexiBreath Member

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    Unfortunately they no longer make turnips that can take 500volts DC. :D

    I love hearing a sane discussion of PCBs like this. Too few are done well and has given the technology a bad name. Regarding SMT, you can get the most pristine signal path with SMT above everything else, but I didn't know there was any SMT devices in values/rating typical for tube musical instrument amplification, this is good news. What are the footprint sizes, can you direct me to some data sheets? Are there film/foil capacitors available in the values/ratings we need?

    A move to SMT on a well designed, quality PCB, has a lot of benefits including testibility with ICT (though limited to what's on the board, not what's off the board on the chassis). A few years ago I tried to source SMT components for tube amps but with no luck, if they are now available that is real cool.

    Here's one idea to sooth the worried customer who can accept PCB but reject SMT, use dual footprints, each footprint in the library for SMT would also have a through hole stuffing option, this way a tech that just couldn't get it together enough to replace a SMD component could remove it and solder in the through hole part as a stuffing option. I'm often having to design boards with alternative stuffing options, usually in areas where second sourcing is next to impossible but a component with a different footprint will do. With such a layout you could then demonstrate an A/B comparison between STD and THT where all variables are the same, the only difference being one amp has though-hole components, the other surface-mount. It's would be a quick myth-buster.
     
  18. Wakarusa

    Wakarusa Member

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    From a technical quality point of view I've no issues whatsoever with SMT (or even PCB for that matter). I think the earlier point about finding a qualified/willing tech is certainly valid. I've got the full hot-air, tweezers, etc. rig for working SMT, but I think I'm unusual in that respect -- particularly in the hinterlands.

    Agreed that a PCB amp is more expensive to fix due to disassembly time. A second contributor is that you almost always have to put the cursed thing back together to test the fix (more time). In high volume production there's the potential for reliability problems, not so much due to the use of a PCB, but due to seeking the absolute lowest cost in production -- current run Marshall and the results of their wave soldering are an excellent example.

    However, as far as the boo-teek world goes, any amp manufacturer has to hit a certain critical mass before SMD (or PCB) becomes a viable solution. Before I spend the setup dough for a run of boards I've got to have the confidence that I'll sell enough of 'em to make it worthwhile. I can think of several boo-teek folks who have gone under from over-investing in a run that didn't ultimately sell. By comparison, I can whip out a turret board pretty quickly and keep the net investment down to a couple of amps at a time. (for the curious, this is also a huge contributor to why you see boo-teek stuff in off-the-shelf chassis. Custom sheet metal ain't cheap)

    The real question is how many amps you need in a run before PCB/SMT makes financial sense. I'm frankly surprised that the big boys haven't already headed in this direction -- particularly Peavey; usually the first to figure out how to do something cheaper in the amp world.
     
  19. Wakarusa

    Wakarusa Member

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    An excellent idea -- solves the issue with techs lacking an SMD rig/skills
     
  20. RL in Fla

    RL in Fla Member

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    As a tech (re: repairs/mods) , I would rather work on a SMT board as opposed to any sort of "eyelet" board , PC or "PTP eyelets" on the size scale we're talking about . (I'm in the terminal strip/actual turret camp Randall ;) )

    SMT would make perfect sense from your standpoint , and the actual boards could be better quality (Cu mil thickness/glass type ) because of it .
     

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