Well, I must say, its been a while since I posed anything here, well over a year by the looks of things, my how time flies. I have been working on some "for sale" projects lately,it seems that a range of guitar pedals I designed and built have been selling, and after running a small pedal custom shop, I can happily say
that making gear for other people is just not for me. Although I love building these things, I get very bored very quickly and instead of building Bass Fuzz number 45, I would much rather be working on some other bit of gear that is just for me and nobody else. So screw everyone! I make enough money without dedicating my life to building Bass Fuzz pedals. Lets not turn my hobby into a job (again!!) and lets build some cool gear for my studio only!!
Some of the projects I have been up to over the last few months include a couple of Pultec EQ's, a GSSL bus compressor, a rack mount JFET Bass Preamp, a Soldano Tube guitar preamp clone and a high end audiophile headphone amp. But apart from that, Ive been designing a lot of stuff. A new power supply, about 20 new guitar pedals and some rack gear. So I thought I would maybe post some of the projects here for you DIY guys to engage with. Potentially, I will post entire projects here including PCB layouts and Schematics. So stay tuned.
My first project here will be a new Mic Pre Amp design based on op amps made available by the various high end chip manufacturers like Analog devices, Burr Brown and THAT corporation. I will be doing some digging and will be posting some of my findings here as a research resource.
The INA217 from Texas Instruments is the chip responsible for the infamous $5 mic-pre blind A/B shootout that left some of the most expensive pre's on the market in runner up positions. Its a very similar design to just about every IC based pre I have seen, but provides some ideas as to what can be done with the design. The best approach would be to develop it piece by piece, perhaps testing a rudimentary version of the pre from a breadboard (despite my hatred for the things). This would give me some sonic perspective before I go all out on this build and it ends up sounding like pants.
First up we have a powerpoint seminar by THAT corporation that was presented at 129th AES convention in 2010. This is a solid state, transformer-less design. And this "tutorial" will take you through the elements required for basic mic pre design. This one is going to be fun!
So after looking at this pdf, I have decided on some specs.
The Pre Amp must have.
- between 60 and 80dB of gain. I would like this to work on ribbon mics.
- Polarity inversion switch
- 20dB pad
- Gain and output level control.
- Balanced output - This might take the form of a transformer.
- Phantom power
- Stereo operation. (Preferably matched)
- Ease of construction - PCB mounted pots and single sided board for home etching.
After a little digging on the above resource, I came across this pdf that gives an excellent implementation of the 1570 and 1246 chips from THAT corporation, and provides a transparent, solid state, transformer-less mic amp that has to be heard to be believed.
This bring me to a point of being torn between using the INA217 and the THAT 1570. I dont have any THAT chips in my box, and ordering small quantity components down here in darkest Africa, is impractical. Perhaps I could make some kind of mash-up of the two, use some of the implimentaiton from the THAT schematic and use some of of the Texas Instruments schematic, make a INA217 pre with polarity inversion and a 20dB pad.
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