I built a new preamp/limiter from a 3V SSM2167 (with 0.5mm pin pitch) quite a few months ago. I did a little bench testing and could hear its AGC kicking in, and though it didn’t seem as good as the previous ones based on the 5V SSM2165s, I guessed it would be fine. Wrong.
I just went back through some of the recordings to try to recall what the problems were (since it’s hard to fix them otherwise). The recordings it made were useable, but there was a little clipping – which is of course completely unacceptable. The dynamic range is too small somehow. I sort of recall trying to set the gain down to avoid the clipping and having the noise gate cut everything off way before it should have.
I used an IRiver T30 instead of my usual IFP-790 recorders, so that’s another dimension I need to get a handle on. The T30 would only record in stereo – a waste of half its memory – but it should still be very high quality.
The header
I figured I should probably breadboard it so I can play ’til I get it right, but the tiny SMT chip doesn’t lend itself to that. So I made up a little breakout board with 0.1″ spacing pins on 0.3″ centers, just like “normal” DIPs. That was a challenge, and I had to define a custom 10 pin DIL header with near-zero pad on the inside of the middle pin. I had to run some traces at 12 mils – the smallest I can reliably make.
Yeah, it’s really small, but I did an unusually poor job soldering it in. One side is off by nearly half a pin width, and there’s a bent pin on the other side I didn’t notice until looking at the picture. I think it’s electrically sound, but it’s pretty ugly. It’s a good thing nobody will ever see how sloppy it was.
Wearing a magnifier, it’s not too hard to get the chip pretty well aligned on the pads. But you have to hold it down while soldering at least the first couple of leads. I have have to invent a spring wire that reliably pushes only exactly straight down, so I have something to hold chips down after placement.
Anyway, now I have something I can plug into a breadboard to do some more focused testing on.