I was wanting a cheap, lightweight (my racks are mobile) 51x preamp to fill out the empty part of my 51x racks for my mobile recording rig.
I have been adding various flavors of preamps, but I don't want to just build a bunch of something. I want to be able to wait, and take selective advantage of all the great ideas that seem to be rolling through GroupDIY. I will continue to add clones and stuff that looks interesting to add to my bag-o-tricks, but right now, I want to get the empty channels populated with a high quality clean fast cheap build (yes, I said those in the same sentence).
I looked around for a transformerless design. Bruno's 9k5's are good and i built 3, but they are one flavor, and not cheap, simple or fast to build.
No transformers - light weight.
Lots of headroom (so I can make mistakes and not pay for them in the field)
Super low noise - ideally fully balanced operation ( to be more forgiving in the field).
Low parts count or at least fast to build.
I am thinking simple - Gain, Phantom, mic/line switch (perhaps as an option), phase (I thought I might lay out the card with option space, headers, maybe standoff holes, to add other capability (High Pass, Limiter, etc) so I could evolve future versions if I wanted.)
Oh yeah and I want to get at least 8 in the racks by summer.
Is there anything out there now that fits that bill?
I was thinking about a 51x green pre, or a 51x fully balanced Amek 9098 clone. But then I started looking at the THAT 1570 chip. Other than the one major drawback (no pins - qfn-16 smd only) it seems like a good fit.
There are several example schematics for this chip. THAT publishes a well spec'd out, which I could use and Rane has a simpler one (once you throw away the clip lights - I have meters.
I know there is a digital project getting rolling out there using the 5170 digital preamp control chip, but I don't need that. The 1570 runs analog, and it will add expense and a whole bunch of stuff to learn (One reason I like analog gear is that it doesnt HAVE software!).
What I am wondering is, before I re-invent the wheel.
Is what I want out there now? A board I can just stuff, solder and go?
What do you all think of the 1570?
Any thoughts on the design? ( I have read all the 1570 data sheet, and the two AES presentations THAT made, and the DN140 THAT design note ( it has some almost complete preamp designs in it)). I was thinking of modifying one of those, perhaps with a CMR choke, and maybe metering.
Related topic. Anybody have a good 1570 QFN-16 eagle footprint? I have been looking into the whole surface mount thing, and putting a QFN-16 eagle footprint together (there doesn't seem to be a good one in place). That wants a thermal pads with 5 tented vias (not eagles favorite task) under a single pad to drag heat to the opposite side of the board. And then the thermal pad is not at ground it is at V-, so you have to separate the bottom side heat sink from the ground plane. Anybody want to share a footprint.
I noticed in the digital thread a comment that said that the THAT demo board was 4 layer for better performance, but the design notes don't mention that, in fact they talk about managing parasitic capacitance a task where I would think a 4 layer board would add complexity. Any truth to the four layer need, and what is that about?
Anyway... I was thinking I could keep the parts count low, keep the layout small, I think I can surface mount that one chip with a cheap reflow station, and do the rest with through hole components.
Thoughts and suggestions please.