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Any interest in designing a USB ADC?
Any interest in designing a USB ADC?
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Old 1st December 2008, 05:46 AM   #1
TheSeekerr is offline TheSeekerr  Australia
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Join Date: Jan 2008
Default Any interest in designing a USB ADC?

Hi all,

I know around here, reproduction is the name of the game, however, my main interest is in the beginning of the chain, not the end - recording.

So, as a result, in addition to building up a good quality output chain for my PC (eventual plan is to have an Opus driving a buffer driving a Joshua Tree driving whatever headphone amplifier I'm using by the time it's all finished :P ), I'm interested in doing up a set of inputs. I've got an active DI in the works, and some mic preamps, but right now, the weak link in the chain is the Analog to Digital Conversion. I'm not interested in USB powered multifunction external soundcard gadgets, I just want 2 channels of high fidelity input. To me, that means dedicated chips and a clean power supply.

So, this is a DIY forum. I'll admit right now, I don't yet have the skills to do this - I have only played around with PCB layouts, and I can't solder SMD's for peanuts. But that said, perhaps, with a little bit of help from a lot of people, and a lot of time, we can design something really nice.

I'm not asking anyone else to do this for me, I just want the benefit of your collective wisdom. I've got a lot to learn.

So, first questions first:

- Is there anyone else interested?

- What, right now, is the best audio ADC chip? What format does it output? Does there exist such a thing as an I2S (or whatever format it does output) to USB bridge chip? Or, even better, the same thing, but with a Firewire interface?

Thanks for any help.

Maybe I'm just completely mad,
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Old 1st December 2008, 11:14 PM   #2
dangus is offline dangus  Canada
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Join Date: May 2004
Location: Vancouver Island
There are worse things than a setup consisting of an Audigy 2 ZS fitted with an optical input, and a Behringer SRC-2496 used as an outboard ADC. The Audigy is capable of bit-accurate capture of S/PDIF streams, so you can't ask for better quality than that. There must be scope for improving the Behringer's power supply and maybe analog input components, but (if they're true) the out-of-the-box specs look pretty good. USB is convenient, but I have more faith in something that's sitting right on the PCI bus.
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Old 1st December 2008, 11:53 PM   #3
cuibono is offline cuibono  United States
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Join Date: May 2006
Location: City of Angles
I record too, and used to be interested in building my own ADC. I don't know how you define "quality or clean", but I prefer technical measurements. There are ADCs on the market that are far beyond what you and I are capable of building, in terms of technical performance, and they are way cheaper, and way easier to obtain (buying versus building). Kind of made DIYing it a moot point for me. I've definitely gotten to the point where I avoid DIYing unless there is substantial money to be saved/quality to be obtained (hint - speakers).
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Old 2nd December 2008, 03:25 AM   #4
TheSeekerr is offline TheSeekerr  Australia
diyAudio Member
Join Date: Jan 2008

Input via SPDIF to a PCI card is an idea I don't mind - once it's digital, the signal is pretty safe from any of the crap going on. It's the other stage I'm worried about, the analogue to digital stage proper. I've worked for years with behringer gear on stage, and it's typically garbage - the specifications, when they aren't outright fabrications, only apply to the product when it is new. 6 months or a year later, they tend to have degraded to a point of uselessness, and invariably seem to develop the infamous "Behringer Hum".

That said, most of those issues can probably be resolved by replacing the garbage electrolytics and upgrading the powersupply.

As far as "quality" and "clean" go, I'm absolutely in favour of measurements vs subjective impressions. When I talk about a "clean" power supply, I mean one that is free of noise and ripple. When I say "quality", I mean just that - that the gear is well built and high performance.

I shall look into the behringer, and see how cheap I can get hold of one to have a look at.
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