Stereo ADC with the most headroom for under $2K

[neonaudio]

I currently have an Antelope Orion handling all conversion for my mix room, and although I'm very happy with the sound, I wish it had more headroom for the stereo AD return from the mixer. See, I'm often pulling the master fader down 5 to 7.5 dB to prevent digital clipping, and I would rather have the option to leave it at unity and drive the transformers a bit more.

The Orion can take a max of +20 dBu input, so I've been looking around for stereo converters that can go higher, without spending a fortune. The Benchmark ADC1 is the only thing I've found under $2K that will fit the bill, with a max input of +29 dBu. Are there any other options?

[Jim Williams]

Since most ADC's clip at +20 dbu, it's really dynamic range you need to look at. What you see are various gain staging around those converter chips. Adjust levels and go, you won't buy anything using a ADC that attenuates the input signal so it can take +24 dbu or more. You can attenuate the signal yourself with some resistors.

[neonaudio]

I've thought about resistor attenuation before, just concerned about detrimental effects to the audio. I'll look into it more.

As for dynamic range, are you saying this in regards to noise floor? That's how they seem to measure dynamic range with converters... so better DR would mean less noise so more attenuation flexibility?

There do seem to be several ADC that offer input up to +29 dBu, I guess through attenuation before conversion. I already mentioned the Benchmark ADC1, but the Prism Dream lists the same in it's specs. I'd imagine other high end converters might offer this flexibility.

[The Scum]

The converter chips in any such device are probably running on unipolar 5V or 3.3V supplies. The max input is constrained by the supply voltage.

I've been using Analog Devices' Sigma family, which are 3.3V parts. 3.3V peak-to-peak is about 3.5 dBu.

Wrapped around the converters are stages that scale and offset the analog voltages to fit within the 3.3Vpp limit. The input scaling part of that looks a lot like any ol' attenuator - a resistor divider. We could design an input stage that accepted 100 dBu input, simply by applying enough attenuation...

...there's also the practical matter that such a stage isn't very useful, because we don't encounter 100 dBu signals in the wild. 22 dBu is a practical limit.

So go ahead and build an attenuator for your current conversion. Use 1% metal film resistors, keep the Zin and Zout in a sensible range, and it won't be significantly different from what happens inside an ADC.

[neonaudio]

Good stuff. I had looked up the converter in the Benchmark and it is running on 5V. So obviously attenuation is achieving the greater headroom.

Building an attenuator should be well under $2K...

[norton]

Sound devices 700 series recorders have extremely high resolution conversion. Don't know if it'll fit into your workflow, but they do sound fantastic.