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USB recording interface for multi-track use

I have been looking at your “USB Stereo Recording & Playback Interface” (SILICON CHIP, June 2011) and wonder whether there would be any problems if I use it just for the ADC function, ie, input only at S1? This could simplify construction if I omit the microphone preamps. Would it then be sensible to put a volume control at the input? Perhaps 15kΩ pots at the line input would do the job?

I have a very good 8-channel mixer with balanced and stereo line outputs but I would like to run it into a PC. Perhaps SILICON CHIP has done just the A-D bit for that very purpose or would the June 2011 circuit do a better job?

Another question is how can I get multi-track recording on a PC? Can just one USB input, with appropriate software, give me a multi-track outcome in the PC for editing and production? It seems the best way to do multi-track recordings is to use hardware like Zoom R16 etc and then transfer the tracks into the PC for editing (eg, with Reaper etc).

Conceptually, it should be possible to assign each channel of a mixer to a separate track in a PC with a DAC and a USB connection but this would require some kind of “tagging” of each channel in the mixer and separation in the PC. I don’t know if anyone does that.

I have been told that the clock for the DAC can be a critical issue for high-end recording. Mention has been made of “jitter” and software (eg, Apogee’s “Big Ben”) that gets down to just tens of picoseconds of error in clock speed. Apparently (young) audio engineers can hear the difference and look for very accurate control of the DAC.

Can you comment on the accuracy of the clock for the June 2011 DAC? Has SILICON CHIP done an article on a digital audio work-station (DAW), especially on multi-track recording and editing? (J. K., via email).

• If you need only line inputs on the USB Recording & Playback Interface of June 2011, it would be OK to omit all of the mic preamp circuitry. It would also be OK to fit 15kΩ or 10kΩ pots at the line inputs, as you propose. We have not described any other stereo ADC projects which would be more suitable for your application.

For multi-track recording on a PC, you would need a somewhat different set-up. It would be able to use a single USB 2.0 port but the ADC would need to be a specialised multi-channel device which would be able to “tag” the samples for each channel before they are interleaved in the bitstream sent to the PC.

We cannot answer your questions about clock jitter in ADCs and DACs. You’ll need to talk to specialists in high-end digital audio processing. We have not produced a digital audio work-station.

More injectors with the Digital Pulse Adjuster

Your Digital Pulse Adjuster (from SILICON CHIP’s “Performance Electronics For Cars”) will run two fuel injectors, each with a minimum of 10Ω. I’m looking at running four injectors (minimum) by adding another Mosfet (STP16NF06).

The question is, do I need to add or increase the values of diode D1 or the 100nF & 100µF capacitors? (T. E., via email).

• You should not need to use more than one Mosfet if you change it to an IRF1405N. Also change the fuse to 6A and thicken the PCB tracks leading to the Mosfet and diode using solder or tinned copper wire.

In addition, the 100µF capacitor could be replaced with a 220µF low-ESR type (16V). And the cathode of diode D1 should be connected directly to the injector’s 12V supply.

If you use two Mosfets, then separate diodes (D1) and 10Ω gate drive resistors will be required. In addition, another gate protect zener diode (ZD3) should be included across the second Mosfet’s gate and source terminals.

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