![]() ![]() ![]() This will demand somewhere in the +18 to +22dBu range for full scale output and given that you like to clip the A/D you'll need some headroom in hand there. Guitar shed kirkwood Pc#My bench PC is down at the moment but if I can get it repaired next week I'll try to plot THD+N vs Level for the 1646 and see how it looks.įinal thought, re A/D is that yes, the actual chip does run at lower levels but you don't interface your gear directly to the chip, you are connecting to the A/D's analog front end. You'll be presenting easier loads but it's one to watch nonetheless. The other gotcha on the THAT 1646 is the distortion at max output levels, the data sheet says 0.1% THD+N (!) given 18V rails and a 600ohm load (at max levels this is all THD with N contributing little). giving 25.6V peak to peak or 21.35 dBu (not 27dBu Wayne mentions above). So at +/- 15V rails that gives us max swing of +12.8/-12.8V. The THAT 1646 datasheet says Output Voltage Swing positive and negative is rail voltage less 2.2V (with no load). Guitar shed kirkwood pro#The outputs of the 1646 produce +27 dBu with 15V rails and the internal operating level of most pro gear is -2 dBu giving 23 dB of internal HR."I'm confused. Once the signal finally makes its way to the A/D pins it's limited to 2V RMS or about +8 dBu by the A/D itself. "In practice I don't think you'll need the added 4V of headroom. The outputs of the 1646 produce +27 dBu with 15V rails and the internal operating level of most pro gear is -2 dBu giving 23 dB of internal HR." ![]() Regarding the grounding, do you recommend I ground everything to the chassis and then connect that back to the studio ground? Maybe having that as an option if the noise initially measures high will be worth setting up now.Īlso here is Wayne's response regarding voltages and headroom: That's why I'm designing all discrete now To have a big headroom means you don't need to worry about those things anymore, and also increasing your signal to noise ratio aswell. So that's really not a lot, depending on the "moves" you make during the mastering process (eq, gain stages etc). So if you hit your chain say at +12dbu (-6 dbfs peaks) than you end up with an overall headroom of 9.5 dbu.īut as you still have this 6db make up into the THAT 1240 chips which are doing the decoding, and if they run at +/- 15v supply, than you only have 3.5 dbu of headroom left into them. But as the decoding process increases the mid signal by 6db (by design) Wayne placed an 5532 opamp (or anything of that type) after that to drop back the level by 6db.Īs a +/-15v supply in the real world will only support up to +/-13 V peak to peak voltage, this gives you +21.5 dbu of headroom (on paper, reality can be worse). Ok so I need to go into more details here to explain it properly.Īt the time I purchased the first versions of the MS board, three of them, they didn't had the 6/12db trim possibility. I would suggest to unconnect the XLR output grounds if you encounter noise right away. Now if you will use the board as it is meant to be, using the MS insert in balanced mode configuration, you should be fine if everything's setup properly.Īs Ruari and others stated, You will need to take extra caution about your grounding scheme. That way, for this specific design, I could achieve a -96 dbu noisefloor with everything engaged. In effect excluding the MS section Insert (That 1246 / 1646) which I believe added a lot of noise in the signal path. On the MS Tool, I didn't "reversed" the Encode Decode sections for more headroom as it's exactly the same, + 6db will adds up on the mid signal, but because I had crazy noise issues if the processing (passive eq, traffo etc) was put before the insert section. That's why I am suggesting you a +/-17v PSU for the MS board, so you can achieve a +23 dbu headroom, wich is indeed better, and still be in the "safe" zone for the THAT chips which are rated for +/-18v max. Quoting myself (lol) for a bit more explanation here, I should have added : ![]()
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