Surface Mount Transformer?

[Onion Ring Modulator]

Hello,

Google has failed me. Is there such a thing as a surface mount audio transformer? Wondering about the 42TM018 in particular.

Thanks!

[FiveseveN]

Yes, tiny ones.


Why does it have to be SMD?

[R.G.]

As FiveseveN notes, yes, SMD transformers do exist, but the ones that exist are maybe not the ratings and windings you're looking for. As for iron core ones like the 42TM018, that may be very hard to find, as you're finding out. I think this is caused by a couple of things; the market is no longer big for small audio transformers, so not many get made, and they're physically difficult to mount securely on an SMD-only PCB. They weigh enough to rip up pcb traces if, for instance, the PCB gets dropped on its edge. The mounting tabs and leads in through-holes are much more secure mechanically.

You could always splay the mounting tabs and wire leads out to tops-side pads and hot glue, epoxy, or silicone sealer glue the body of the transformer down.

[Onion Ring Modulator]

Yes, tiny ones.


Why does it have to be SMD?

It doesn't really have to be. I am trying my hand at designing a surface mount PCB for the first time, with the idea that I would order some completely populated. I think I've decided to just leave the appropriate spot for the transformer, and then all I have to do is add that and do the wiring and I'm done.

[Govmnt_Lacky]

It doesn't really have to be. I am trying my hand at designing a surface mount PCB for the first time, with the idea that I would order some completely populated. I think I've decided to just leave the appropriate spot for the transformer, and then all I have to do is add that and do the wiring and I'm done.

I have found it extremely difficult to find low-voltage output (100-200mA) transformers in a 'small' package for designs. Something that will be AC-AC or AC-DC. Even transformers that go down to 9 or 12V AC or DC are around 20+mm height off the PCB 

[PRR]

If you mean 120VAC/240VAV transformers: you need enough iron inside so the winding does not act as a near-short on the power line. This interacts with practical wire diameter- small wire costs very much more per reel, and is much harder to wind without breaking, also self-corrodes over the years (why most 500 Ohm speakers are found dead today).

Yeah, 20mm may be about as small as I have seen.

"Audio" transformers can be smaller if you accept less bass. The old "modem" transformers must have been made SMD. While large examples like R.G. specced for his splitter can be forced below 100Hz, the truly tiny ones won't take much power without distortion. (In modem duty the bleeps could be pre-distorted to compensate.)

[Ice-9]

In my honest opinion and for a couple of different reasons I would say, have you PCB's fabbed wit hall the SMD parts but be prepared to hand solder the transformers yourself using through hole parts.
1. As noted above by R.G . the transformers will be quite heavy so to rely on SMD soldering as a point of mounting might not be the best option.
2. When it comes to shipping the assembled PCB the extra weight and size of the package will cost a lot more, especially if you are going to order from China (import duty and shipping).
3. Because of No1. you may get failures which will lead to repairs and further shipping costs to customers.

My approach on PCB assembly is to only get the SMD assembled by the fab and then hand assemble all the through hole components myself.

[FiveseveN]

I think I've decided to just leave the appropriate spot for the transformer, and then all I have to do is add that and do the wiring and I'm done.

Yup, that would be the way to do it.

[Nitefly182]

I agree with all the above comments about using a TH transformer regardless of other components that may be surface mount. The pedal will be much more durable and its not going to add dramatically to assembly time if you are already soldering pots and wires anyway.

[amptramp]

If you are using signal transformers as isolators, there are better ways to do this.  There is a linear optoisolator circuit:





This would be smaller than a transformer with equivalent bass response and it wouldn't fall off the circuit board because it would be lighter and smaller.  Other op amps could be used and the pots could be replaced with fixed resistors.