The only remotely creative aspect of the preamp was the use of discrete voltage regulators for almost every component in the audio path. It has a comical number of voltage regulator ICs.
There hasn't been much commentary about the electronics, but I found it amusing myself about the amount of overkill on the multi-stage voltage regulation scheme. Those components drawing more wasted power from the external supply than the audio circuits themselves.
I know overkill is important in some audio circles, but did I say massive external supply for a preamp?
This kind of signal handling does not require a high-current audio circuit where there may need to be a very sizable power supply. When that happens it may be the best idea for the power components, especially transformers and other potentially noisy components like voltage regulators to be enclosed in a separate chassis from the sensitive audio semiconductors and their carefully laid out signal connections. You don't have to be an audiophile to recognize when this might be needed, don't ask me how I know ;)
What I like to do is make the external supply good enough so that no significant power components are needed inside the instrument chassis, other than ferritics and capacitors for local storage/delivery and filtration of anything that might come in on the (well-shielded) cable like it was an antenna or something.
I figure I'm not the only one around here to have designed their own personal phono preamp after looking at numerous opamp datasheets, these are actually not easy.
I needed one to work with 78 rpm records, not audiophile material :\
Actual vinyl polymer at 33 1/3 rpm was even more challenging even though the RIAA equalization was standardized by then. I figured might as well, if I'm going to do some serious soldering it would be good to exceed minimal objectives.
RIAA is functionally a very steep well-defined mathematical curve[0]. Traditionally implemented using all analog components in a much lower-noise arrangement than usual. It requires quite a high gain preamp to recover the bass from the microgrooves where it has physically been pressed so much more lightly than the other frequencies.
I just used one audio circuit board since I was indulging in the opposite approach to overkill. From what I've heard, the fewer active analog components that your signal passes through, the fewer compromises it may be subject to anyway ;)
Audiophiles would think I took a lot of short-cuts which is true, I could surely have gotten better channel separation using two boards instead of one. But it did take a little rig about twice as complex just to perform the development experiments on, which was re-architected a number of times, one of the advantages of a non-PCB free-form soldered breadboard.
Well I have nothing to brag about the way I cheated on my own power supply for this project. I would say it really does take about as complex a power supply PCB or more than it does for the audio PCB. Screw that, I used batteries :) Needed to be portable anyway like a laptop. Plus batteries have no hiss or hum, that was easy. Actually I got lucky because I was able to achieve my goal of digitizing vinyl at the standard CD format of 44.1 KHz 16-bit, while introducing lower analog noise than a CD can reproduce. IOW transparent for that application, and see what collateral damage there is otherwise :) There was plenty of headroom with two 9V batteries giving 18V peak-to-peak before clipping. Plus the batteries lasted a long time since very few components were on the final board, and it's just a preamp.
Now I shouldn't complain about having loads of PCBs stacked in overkill configuration until it almost topples under its own weight, using blank copper boards for shielding within a plastic enclosure. Not when mine sits on a teflon sheet inside a mere small cookie tin, and the shielding is still usually OK when the top is removed :)
For a while there you could even still smell the cookies.
and a single-board amateur project to learn from where it looks like there are some power components on the PCB, probably not much more complex than my lab effort otherwise. They cover using a single 9V battery during their prototyping as well as the migration to A/C adapter and virtual ground for the opamps. I used a pair of batteries wired for true bipolar +/- 9VDC and stopped there. Also notice how much bigger the plastic caps are than tantalum would be:
Edit: Left out the part where I would use a Dremel to cut out the RIAA section from the populated PCB of cheap scrap record players that people were once discarding quite commonly. These were small little "partial" PCBs too and quite dissimilar, but made them work on their own before building to my final specs.
