[intlplby]

i'm sick of using a crappy soldering iron so i am in the market for a new and better soldering station......

i was curious about trying to make some of the amp designs, but with smd/smt components...

from everything i have read it doesn't seem that much harder to do SMD/SMT work especially once you get the hang of it

two big reasons i am considering SMD/SMT are:

1) I have very good eyesight especially when working with very small things.

2) I am very good with my hands when working with very small things. very steady and very precise.

other than the added cost of buying an SMD/SMT station are there any specific considerations for DIY audio?

is it easy to find high audiophile grade quality smd/smt components such as resistors, capacitors, diodes, op-amps etc? are the smt/smd components cheaper or more expensive

 

[nkd]

Op-Amps are just as easy to find as the DIP versions. As for the other components, you'll probably have to keep using the conventional types.

 

[tangent]

Quote:

the added cost of buying an SMD/SMT station

You don't need a reworking station for most SMT assembly work. The hot air rework stations are for removing many-pin parts without damaging the parts or the board. For removing even op-amps (8 pins) you can manage that with a standard iron if there isn't anything nearby on the board.

Quote:

is it easy to find high audiophile grade quality smd/smt components

I'm not aware of any exotic SMT components. They're the same components used in commercial products, not strange things you never see in anything but high-end audio equipment. There are differences in grade among SMT components, of course, but nothing beyond what you'd expect. The differences are all (gasp, horror) measurable.

Quote:

are the smt/smd components cheaper or more expensive

In my limited experience, they're always the same or more expensive, all else being equal.

 

[DCameronMauch]

I believe Vishay bulk metal foil resistors are available in SMD versions. The new popular resistors are tan film. They are more environmentally rugged, especially with respect to moisture, but seem to have inferior noise specs. I stick to 1208 sized resistors. Larger has less noise and easier to solder. But smaller lets me get so much more done in a small space and keep traces nice and short. So given these factors, I went middle of the road with the 1208 package. For close power supply bypass, I have been using .1uF X7R 1208 ceramics. Their tolerance and stability is good enough I guess. And they have a low ESR past RF frequencies. The only other choice I have seen at or near that size is tantalums. But they have a high ESR even at low frequencies. At roughly 6 times the footprint, there are .1uF metal films. Awesome specs, but they are just too big to be useful in my designs. I think in the Digikey catalog I saw some surface mount aluminum electrolytics at 6.3mm square (I think) which were designed specifically for audio. But I have been sticking with regular audiophile approved through hole caps for those larger values. That is pretty much everything I know about SMD component selection.

The other methodology I have been using: Since everything is on the top, including the traces, make the bottom a big 'ol ground plane. But I make every effort to keep any and all currents off the ground plane. Where necessary I use local ground buffers. All power supply caps are rail to rail. This way, my master ground reference stays nice and clean.

I have been using a little 15 watt ratshack pencil iron. Ground the tip to a near point and tinned. Soldering SO8s and even 0805s with well thought out technique, a steady hand, and some dorky head band mounted magnifying glasses (like what jewelry repair guys use) has been quite good. Haven't made any attempt at removing anything. Really gets you in that "do it right the first time" mentality.

 

[Sycraft]

The thing of SMD is, it wasn't made to be better acuostically or electrically or anything, it was made because machines have an easier time doing SMD in many cases. Also it is for boards with more than two layers. If you look at computers, you'll find that most boards don't just have a front and a back, they have multiple layers with different traces (six layers is fairly common). Well, you can't have pins sticking all the way through, since it sould often mean peicering a trace. Even more so if you have two components on opposite sides of the board. SMD also makes smaller spacing a possibility. Look at some ICs on a PC card someday, some od the spacings on the leads are such that there is no reasonable way to do it DIP.

SMD is a design choice for certian kinds of layouts. If you have a layout that supports all DIP, I can't see a reason not to use it. I am not aware of any superiority in performance that would in any way translate to an audible difference.

 

[DCameronMauch]

I see no reason why SMD doesn't work well with 2 layer board. I have been doing it with no problems. SMD does have another advantage over large through hole stuff - high frequency. You get better high frequency performance with SMD because everything can be kept small and tight including the traces. Which means you can use higher bandwidth parts and get at least superior harmonic distortion performance. You can't get these circuit stable with large parts and long traces. And some of the best parts are ONLY availabe in SMD. Like the AD8610/20 or OPA1632 or TPA6120A2. In my latest designs, there are hardly any holes through the board at all. With very carefull placement and routing, I keep most all the traces on the top with the components.

 

[drewd]

Quote:

Originally Posted by DCameronMauch I see no reason why SMD doesn't work well with 2 layer board. I have been doing it with no problems. SMD does have another advantage over large through hole stuff - high frequency. You get better high frequency performance with SMD because everything can be kept small and tight including the traces. Which means you can use higher bandwidth parts and get at least superior harmonic distortion performance. You can't get these circuit stable with large parts and long traces. And some of the best parts are ONLY availabe in SMD. Like the AD8610/20 or OPA1632 or TPA6120A2. In my latest designs, there are hardly any holes through the board at all. With very carefull placement and routing, I keep most all the traces on the top with the components.

I agree that some of the best stuff is available only in SMD, but I'm not sure that there is much of a difference frequency-wise. The frequencies that we are working at are really quite low in terms of PCB design. The traces aren't transmission lines, even at 20KHz because of the huge wavelengths. The difference in trace length between a DIP and SOIC on a well-designed PCB shouldn't be all that great. I've never had a DIP (or SOIC on an adapter) oscillate or even sound worse than its surface mounted equivalent.

But - when space is at a premium, surface mount devices are a boon. That's why I shifted to all surface mount ICs in my amps. But I still use through hole discretes for a couple of reasons. The first is that, other than electrolytic caps, they don't take up that much room and the second is that I haven't found any that match the noise specs of through hole parts.

Anyway, to me, the real test is my ears. I cannot hear the difference between a surface mounted or through hole opamp. But I sure do appreciate the space that an SOIC saves me!

-Drew

 

[SHLim]

A question about SMD soldering.
My Pioneer DVD player have a thick layer of lacquer all over the analog board including the opamp. What is the safe way of removing these lacquer from the opamp surrounding so that I can safely desolder it?

TIA,
Sam

 

[tkerby]

One advantage of smd is that everything is smaller so there is less chance of audible noise pickup or losses in the pcb tracks. This does, however, assume good layout practices. The main advantage is that solid ground and power planes can be provided on a 4 layer board with these forming the inner layers. This allows for much improved noise performance, especially when building with a mix of analogue and digital such as a DAC