Designing SMD AMplifier Board, please suggest & Comment ?  - Page 1
Forum section: electronics / projects

author: dashpuppy
author_rank: Regular Contributor
timestamp: March 17, 2018, 10:44:47 pm
content: This isn't totally done yet but i'm looking for some suggestions and improvments remarks maybe some positive and bad feedback ? This is the driver stage of the amplifier, the outputs are on another board..

author: dashpuppy
author_rank: Regular Contributor
timestamp: March 18, 2018, 06:40:38 pm
content: NO advice from all the good guys on here ?

author: ejeffrey
author_rank: Super Contributor
timestamp: March 18, 2018, 07:07:14 pm
content: You haven't specified your goals/specs, provided a schematic, or talked about why you did it this way or what else you considered. So there isn't much for anyone to comment on, and there is a fairly big barrier to trying to reverse engineer a schematic from your layout.

author: dashpuppy
author_rank: Regular Contributor
timestamp: March 19, 2018, 12:30:51 am
content: Quote from: ejeffrey on March 18, 2018, 07:07:14 pmWell that makes senseThe goal is to keep it compact. It's an Nelson Pass Aleph 2 SMD PCB layout, the board shown is the driver stage. I have the IRF9610's in the center with holes in the middle of the 3 so i can push a pair of small bolts through and mount to a small thin heatsink and clamp against the fets. They don't get tooo too hot, but they get warm, if i pull the heat away they will last longerThe board uses all SMD devices and using 0204 MELF resistors @ 1% precesion. The power resistors are at the top because those are 3watt SMD dale units. They don't get hot..Schematic AttachedOutput Board

author: dashpuppy
author_rank: Regular Contributor
timestamp: March 26, 2018, 02:17:43 am
content: TTT

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 26, 2018, 12:34:29 pm
content: I don't really like the trace between R52 and R7. It's a mess and gets too close to a plated hole for my taste.I would probably route it on the bottom layer.

author: dashpuppy
author_rank: Regular Contributor
timestamp: March 26, 2018, 02:48:25 pm
content: Quote from: SiliconWizard on March 26, 2018, 12:34:29 pmYUP ! that part is a nasty mess LOL ! I have better plans for that area, like you suggested under side it wil go !

author: schmitt trigger
author_rank: Super Contributor
timestamp: March 26, 2018, 03:20:12 pm
content: Fill all the unused real state with a low impedance ground plane.

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 27, 2018, 02:36:24 pm
content: Yep.Just one tip: provide sufficient clearance around wide traces if you fill the void with a ground plane (which you should do). Depending on the PCB class and the manufacturer, you may get subtle short-circuits between wide traces and the ground plane if you don't give enough clearance. Got bitten with this once

author: Audioguru
author_rank: Super Contributor
timestamp: March 27, 2018, 06:00:33 pm
content: I notice that your schematic is completely wrong:

author: dashpuppy
author_rank: Regular Contributor
timestamp: March 28, 2018, 03:11:04 am
content: Quote from: schmitt trigger on March 26, 2018, 03:20:12 pmI will be using a Ground plane Here is a screen shot.

author: dashpuppy
author_rank: Regular Contributor
timestamp: March 28, 2018, 03:12:13 am
content: Quote from: Audioguru on March 27, 2018, 06:00:33 pm

author: Audioguru
author_rank: Super Contributor
timestamp: March 28, 2018, 03:42:35 am
content: The Nelson Pass Aleph 2 amplifier is a room heater (class-A dissipation is 300W). It produces an output of 100W into 8 ohms. Its distortion is fairly high compared to modern amplifiers.

author: dashpuppy
author_rank: Regular Contributor
timestamp: March 28, 2018, 04:08:53 am
content: Quote from: Audioguru on March 28, 2018, 03:42:35 amActually you are incorrect.I know what it is, I have built TONS of nelson's designs.

author: schmitt trigger
author_rank: Super Contributor
timestamp: March 29, 2018, 07:25:22 pm
content: Quote from: SiliconWizard on March 27, 2018, 02:36:24 pmVery Correct!Most PCB design packages allow to set the default clearance between planes and other traces.

author: dashpuppy
author_rank: Regular Contributor
timestamp: March 30, 2018, 03:37:23 pm
content: Quote from: schmitt trigger on March 29, 2018, 07:25:22 pmYup i have a default gap between all the pcb traces. And have Eagle to remind me that things get to close to each other..

author: dashpuppy
author_rank: Regular Contributor
timestamp: March 31, 2018, 03:28:28 am
content: Quote from: Audioguru on March 27, 2018, 06:00:33 pmSorry you are correct, i fixed this! Thought you were thread crappingSent pm

author: dashpuppy
author_rank: Regular Contributor
timestamp: April 01, 2018, 04:32:39 pm
content: Totally re-vamped the board.

author: schmitt trigger
author_rank: Super Contributor
timestamp: April 04, 2018, 01:55:39 pm
content: There are a couple of taces, close by the N$2 label in yellow, which could benefit from a little more clearance.

author: dashpuppy
author_rank: Regular Contributor
timestamp: April 04, 2018, 02:59:38 pm
content: Quote from: schmitt trigger on April 04, 2018, 01:55:39 pmThanksIm thinking about trashing this and trying again .. Wish i could pass the file around and see what others can do..

author: Zero999
author_rank: Super Contributor
timestamp: April 05, 2018, 09:56:10 am
content: Quote from: dashpuppy on March 28, 2018, 04:08:53 amI can't comment on the distortion because I haven't seen the whole schematic or done any tests/simulations, but he's almost right about the power dissipation. Note I said almost right, because an efficiency of 30% is optimistic. The theoretical maximum efficiency for a class A design, without a transformer, is 25%. In reality, it will be much lower than, probably around 2% under typical operating conditions.No doubt there are plenty of cheaper, modern class AB and even class D amplifier designs, capable of the same output power level, using a fraction of the input power of this design, with similar or better distortion and noise figures.

author: dashpuppy
author_rank: Regular Contributor
timestamp: April 05, 2018, 02:48:55 pm
content: Quote from: Hero999 on April 05, 2018, 09:56:10 amPower dispation is correct. BUT people don't buy a Class A amplifier for it's effeciancy. They buy / BUILD them becuse they sound goodI've tried Class d and many high end brands IMO they all sound like CRap! IMO They should be used for one thing, and one thing only. Subwoofers thats it.

author: Audioguru
author_rank: Super Contributor
timestamp: April 05, 2018, 07:12:20 pm
content: The Nelson Pass Aleph 2 amplifier costs $14,000 dollars (!!) a pair. It is a box covered with heatsinks.A reviewer said it caused his electricity bill to increase 40%. The review was full of audiophool remarks.Its spec's say its distortion is <1% which is very high but the distortion is mostly second and other even harmonics that sound musical like an old vacuum tubes amplifier.

author: dashpuppy
author_rank: Regular Contributor
timestamp: April 06, 2018, 12:27:16 am
content: Quote from: Audioguru on April 05, 2018, 07:12:20 pmName a good class A amplifier that doesn't suck up power. They all do, Infact the Krell KSA 50 & 100 eats even more power. I'm a Nelson Pass fan so thats what I use

author: Zero999
author_rank: Super Contributor
timestamp: April 06, 2018, 08:28:43 pm
content: Quote from: dashpuppy on April 05, 2018, 02:48:55 pmOr people might buy/build them because they believe they sound better. It highly subjective and could even be the placebo effect, if the amplifiers are good enough and are operated well within their power ratings. See the study linked below, which tested whether audiophiles could tell the difference between three different amplifiers: one very old solid state design, a new (back then) solid state design and a valve/tube design. The volume was set the same, taking care not to overload the amplifiers. The same speakers were used and someone, in another room, switched between different amplifiers, randomly. The end result was no one could tell the difference, any better than chance, meaning all of the amplifiers sounded the same!http://www.keith-snook.info/wireless-world-magazine/Wireless-World-1978/Valves%20versus%20Transistors%20DCD.pdfThe senses can easily be tricked. Aesthetics, brand and marketing are very influential. It's almost certain that, if I put the same amplifier circuit inside two enclosures, one which looks nice and high quality and another which looks cheap and nasty and asked people to rate how they sound, they'd pick the nicer looking amplifier, as the one which sounded better. Similar experiments have been conducted with the same food on different plates and in different packaging, with similar results: nicer packaging and crockery make it taste better!Of course in real life, people do drive their amplifiers into clipping (overload) and that's where the differences start to appear: an old valve design might distort subtly, in a pleasing manner, whilst a modern transistor amplifier will harshly clip the signal, resulting in nasty distortion. This is why many musicians prefer old valve/tube amplifiers and your class A amplifier might sound similar.It's true that class D amplifiers weren't very good when they were originally introduced, but some modern ICs have imperceptibly low levels of distortion, when operated within their ratings. Of course, lower distortion doesn't mean it will sound better to everyone. As I mentioned before, it's highly subjective. Some people like certain types of distortion.If you want low distortion, your best bet is to over-rate the amplifier so it's never driven into clipping. The main source of distortion then becomes the speakers and room acoustics, which are far more important, than the amplifier design.

author: dashpuppy
author_rank: Regular Contributor
timestamp: April 07, 2018, 02:38:43 am
content: If you want low distortion, your best bet is to over-rate the amplifier so it's never driven into clipping. The main source of distortion then becomes the speakers and room acoustics, which are far more important, than the amplifier design.Well i would never use a full 100-watts with the effecient speakers i run. HOWEVER having some headroom so if i wanted to turn them up is a proper thing to do.

author: Audioguru
author_rank: Super Contributor
timestamp: April 07, 2018, 03:09:42 pm
content: Clipping is not the problem.A class-A amplifier uses a single or some paralleled transistors doing the entire output voltage swing that is non-linear. The output voltage swing becomes compressed when the transistor approaches cutoff.Its spec's say "its distortion is less than 1%" which is awful today for any amplifier cheap or expensive.A class-AB or class-D amplifier uses push-pull transistors that always has a transistor conducting when the other transistor approaches cutoff so they do not produce this distortion.

author: mariush
author_rank: Super Contributor
timestamp: April 07, 2018, 03:40:39 pm
content: Quote from: dashpuppy on April 01, 2018, 04:32:39 pmWhat I would think of doing ....Change C5, C9 and C10 footprints for both smd AND through hole. I found that in general, surface mounted electrolytics are not as reliable as through hole and their technical specs are also not as good.Your design is not 100% surface mount, as you still have through holes for some components like those lonely MPSA18 transistors (really, can't find something similar in a surface mounted package?) and you have what seems to be hole for leads or for pinouts.You're using rounded corners and you're not using 45 degree when routing the traces, it looks ugly to me. You also have some 90 degree angles. It's not necessarily bad, but it looks ugly to me and others would probably be able to bring arguments as to why it would be better to not have a trace coming out of a pad at weird angles (like the trace from Q3 to the R10 resistor)Are those holes between the Q1 , Q2 , Q3 and Q4 ? If so they seem like some pretty big holes compared to the circuit board... must those be really that big?I'd think about rotating Q1 90 degrees to the right and Q3 90 degrees to the left, and if you move the whole set lower (unless you have the holes to install heatsink or something) it would allow having a continuous block of copper fill on the board to spread heat better.You also have a bunch of resistors of same size, like 220 ohm , 10k ohm etc ... my mind went right to how about using a "4 resistor array" components instead of 4 separate resistors, on each side of the board, to keep the design symmetrical? I see 4 x 10k, i see at least 2 x 3 220 ohm resistors ...Looks like you would be able to move Q4 and Q5 towards the edges so the traces from those don't go directly under those mosfets if it can be avoided ... maybe have there another copper fill and use a bunch of vias to increase the heatsinking ability?Lots of empty pcb space on the bottom right ... why ..That ^ in the thick trace looks really ugly to me, like an afterthought or something.

author: dashpuppy
author_rank: Regular Contributor
timestamp: April 07, 2018, 05:19:20 pm
content: Quote from: mariush on April 07, 2018, 03:40:39 pmI don't want to do through hole parts. The whole point of the project is to do SMD I have spent months & almost a year finding parts and researching so everything is SMD now it's 100% possible so im going that route.I can't move the SMD irf9610's another way because if you look at the 4 holes that allows me to push a bolt through the back side and bolt to a small heatsink strip.I built these smd amplifiers 14 years ago all 4 of them running 100% strong and not a sign of issues.

author: mariush
author_rank: Super Contributor
timestamp: April 07, 2018, 07:32:05 pm
content: Quote from: dashpuppy on April 07, 2018, 05:19:20 pmBut you just showed me you DO through hole parts. And your project is NOT 100% SMD and it's not an all-smd circuit board just because you say it is. IMHO an all-smd circuit board would be one where there's only VIAs going from top to bottom, and everything is surface mount pads.You're using through holes to solder wires to your board in the picture above, you're using leaded axial resistors that you solder to through holes and you're just not inserting the lead through the hole ... same for those MPSA transistors.if you truly wanted a smd only board, you would find surface mounted connectors, plenty of those around... you would even find proper surface mounted resistors, in packages like DPAK or D2PAK ( to-252 / to-263 etc ) here'ssome examplesMakes me wonder in your last picture how hot those four axial resistors are during regular use, how that heat goes through the board and cooks those electrolytics and degrades them (though they seem to be quality panasonic ones they will suffer) and also makes me think how those two transistors being heated unevenly (as one is closer to those resistors) affects your amplifier.What I was saying was that you could have radial (leaded) electrolytics sitting flat (horizontal) on the circuit board , and you shape the leads so that you have a L or U at the pcb level, solder that U to the surface mount pads and use a drop of glue /selastic/whatever to prevent the capacitors from vibrating and you're done.

author: dashpuppy
author_rank: Regular Contributor
timestamp: April 07, 2018, 07:45:45 pm
content: Quote from: mariush on April 07, 2018, 07:32:05 pmThe resistors on my "front" end board do not get hot, the Dale resistors on my output board pic above get slightly warm..The only thing that really creates heat are the IRFp240's & IRF9610's The 9610's don't get that hot but putting a heatsink ontop of them just removes the heat from them and away from the board.The board above is 15+ years old when some SMD things were not available for the sizes and values we use.Maybe you want my pcb & sch file to have a look and show me ? I don't like the to-252 resistors, i like the Dale ones

author: Zero999
author_rank: Super Contributor
timestamp: April 07, 2018, 08:48:11 pm
content: Quote from: dashpuppy on April 07, 2018, 02:38:43 amI hope you realise that efficient speakers tend not to have the lowest distortion, which is why they tend to be used in public address systems, where distortion and sound quality are less important, than efficiency.Quote from: Audioguru on April 07, 2018, 03:09:42 pmI can't comment on this design, as I've not seen the entire schematic, but this isn't an inherent flaw in class A amplifiers, only in very simple designs which only use one transistor, with very little negative feedback. It's fairly easy to design a class A amplifier which doesn't have the distortion due to the change in transconductance vs current, by using a constant current source and plenty of negative feedback.

author: Audioguru
author_rank: Super Contributor
timestamp: April 07, 2018, 09:26:20 pm
content: The $7000 amplifier ($14000 for stereo) doesn't even look good. It was designed with Mosfets to produce the same (distorted) sound of an old vacuum tubes amplifier.The high cost goes into the designer's pocket and weighs 60 pounds.

author: schmitt trigger
author_rank: Super Contributor
timestamp: April 08, 2018, 01:29:57 am
content: Audio amplifiers are like wine.I would bet that almost all wine lovers would be perfectly capable in distinguishing between an $8 US and an $80 bottle.But how about between an $ 80 and an $ 800 bottle? I would think that most won't, but there will be a few privileged individuals who certainly can.I am in the first group, and as such, I'm perfectly content with spending $ 80 on a bottle. Max.But if you are in the group that DOES distinguish the difference, AND have the economic means to afford it, then I sincerely say: By all means enjoy it. Its your money after all, you can spend it in anything that gives you pleasure.Likewise with audio amps.

author: dashpuppy
author_rank: Regular Contributor
timestamp: April 08, 2018, 02:26:30 am
content: Quote from: schmitt trigger on April 08, 2018, 01:29:57 amThere are a few Class a/b amps on the market I have heard and like. Bryston & Parasound. I have also heard some really high end ones that sucked ass too! I personally really like Class A. So that's what i build and use !

author: Audioguru
author_rank: Super Contributor
timestamp: April 08, 2018, 02:56:58 am
content: Here is what $7000 looks like:

author: dashpuppy
author_rank: Regular Contributor
timestamp: April 08, 2018, 03:02:20 am
content: Quote from: Audioguru on April 08, 2018, 02:56:58 amSold lots of them too, and still people talk highly about them! Sure they make heat, but they also make very good sound.

author: EEVblog
author_rank: Unknown
timestamp: April 08, 2018, 09:18:39 am
content: Quote from: schmitt trigger on April 08, 2018, 01:29:57 amI bet they can't consistently in a true double blind test.

author: dashpuppy
author_rank: Regular Contributor
timestamp: April 08, 2018, 05:19:17 pm
content: Some changes.

author: Zero999
author_rank: Super Contributor
timestamp: April 08, 2018, 07:46:22 pm
content: Quote from: EEVblog on April 08, 2018, 09:18:39 amI agree. Also I'd bet there are some $800 audiophool amplifiers, which sound no better than an 8$ amplifier, when subjected to a double blind test.

author: dashpuppy
author_rank: Regular Contributor
timestamp: April 08, 2018, 07:52:02 pm
content: Quote from: Hero999 on April 08, 2018, 07:46:22 pmThats why i like to DIY my own, I would never drop 10k on an amplifier. Would rather build it..