View Full Version : Whee! (homebrew ADCmaker)

April 17th, 2007, 01:34 AM
So, I've been doing a lot with a weird piece of ADC junk- namely, a Lexicon MPX-100. I don't use it for reverb anymore, I wired some TRS jacks directly to the converters and I drive them with good pres. I've got a pretty fucked-up arrangement that way- two API 3124, and the Lexicon. I've been patching stuff using a patch snake with TRS plugs into the jacks on the mpx-toy :)

Well- I have another cheesey piece around- an ADAT LX20. I'd already butchered the analog board completely in efforts to make it sound okay, years ago. So I figured, eight ADCs- yeah, it's only 20 bit, but who knows, why not try to do the same trick on a larger scale?

The LX runs on AK4520 chips, and I got a datasheet for them, and tracked down the pinouts. Two neat discoveries- one, these are just as much balanced chips as the ones in the Lexi, it's just that the - inputs are floating with a cap to ground. Removed. The other neat discovery is that there's a voltage reference on the chip that requires a capacitor to smooth out digital noise on the analog inputs. It was using crappy surface mount ceramic caps, as cheap as possible. I already had some big electrolytics replacing other cheapies, and I threw in polystyrene 680pf caps. The ceramic caps to ground got thrown away (the chip oversamples anyway) and the pads where the caps were became the attaching points for simple wires to TRS jacks.

Tested it out, all eight channels working. As before, everything's being driven by API 3124 pres (transformer outs). But, was the 20 bit raw-converter ADAT rig as good as the 24 bit raw-converter Lexicon rig?

Oh hell no- it's WAY BETTER. I don't know whether it's better clocking somehow, or if it's the polystyrene caps on that reference-voltage pin, or what, but this rocks. Specifically, the highs are better, the lows are better too, and all the textures of everything are more believable. This and eight channels at once of it...

GOOD work day.

Anyone with similar crap they feel like playing with? The great thing is that there's no real risk as ADAT LX20s are worth like $30 on ebay anymore :)

Actually the great thing is, this is all on an analog board that's removable. So not only is it easy to work on, but if I feel like recording on the actual ADAT tapes and the mechanism breaks, I can get another LX20- pop in the analog board upgrade- and be ready to go.

Happy ChrisJ :D and just in time for final CaPE tracking, too.

April 18th, 2007, 06:18 AM
Okay, this is about the stupidest thing I've ever recorded. Enjoy.

First, I recorded drums into the new ADC, using Studio Projects C4s for overheads, Audix D6 for kick and SM57 for snare. I've modded the C4s, mainly to unveil the highs so I don't need to ever boost them. All through API 3124 pre.

Then, I modded a Studio Projects C1- and made rude comments about the drum track all the way through. "Yay, cowbell! :lol: " "Wait, do that fill again- I really need to hear THAT one again. :Roll eyes: " etc etc. The basic idea being that I wanted to hear what the new C1 sounded like- and when I listened to the whole mess, it reminded me of 'A Little Green Rosetta' off Joe's Garage Act 3 so I did an mp3 of drums plus sarcasm :D

I think the drums have never sounded better in any recording I've ever done, and the voice really conveys attitude- all of which is better thanks to the condenser mic mods and the ADC mods. So if you want to hear (an mp3) of this wizzy new ADC hack, and/or the cheap-condenser-mic hacks, here you go. Or if you just want to hear me fucking around being stupid on mic :lol:

April 18th, 2007, 04:16 PM
Chris, that was fun. :)

Dood, sounds really clean.

April 18th, 2007, 06:10 PM
It's like I said- if you patch right into the _chip_ on various crap ADCs, using a really good pre, neat things happen. Not only is it 20-bit, it's the crap level ADAT of that generation, an LX20. Except, what it really is, is eight channels of AK4520 converter- and the thing is, if you get the clocking and the voltage reference okay, and you bypass pretty much the whole analog stage and go straight to the chip- the actual digital signals don't mind being on an ADAT. That part doesn't care what it's on as long as it's passing the bits, and you get lightpipe optical 8-channel out, plus it comes with a marginally competent tape data-recording system making it standalone :D

Food for thought, definitely food for thought.

Now if I could do that WITHOUT the two API 3124s, then I'd be ruling the world ;) but I think this is an argument for 'spend your money on good pres, hack with a soldering iron on cheap ADCs, recorders, mics etc'. The ONLY upscale thing in the whole recording is the pres. Not even the mics are fancy- it was all about modding the C4s, and the D6 and SM57 are dynamics, nothing to 'em.

April 19th, 2007, 01:53 PM
i don't suppose the sm57 is modded too?

April 19th, 2007, 07:29 PM
Nope. I've decided I want stock SM57s and no-xfmr SM58s. I have a no-xfmr 58 but you're not hearing it here. Stock 57 into the API.

April 19th, 2007, 09:56 PM
Okay, this is about the stupidest thing I've ever recorded. Enjoy.

I like it...too bad nothing went wrong during the recording...had that happened, you would've had the drummer's answer to Slippy's beloved Palmer box fiasco.