Reliqua 312 DI noisy

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bobschwenkler

Well-known member
Joined
Dec 8, 2005
Messages
483
Location
Olympia, WA
Who else has built this circuit with the DI? I made an 8 channel unit years ago and never got around to really figuring out why the DI is as noisy as it is. The noise floor is not overpowering or anything, but it's clearly audible, perhaps 30-40dB down with an old Epiphone guitar plugged in. Other sources give similar results.

I've tried a little bit of experimentation with no improvement. I dropped the 2.2M input R to ~.5M, my input signal goes up accordingly (it forms a volts divider with the 1M to ground at the amp input) but the noise floor seems the same.

I thought perhaps it has to do with poor matching of OSI for the op amp but noise remains the same with signal generator plugged in.

Any thoughts?
 
You already checked/replaced the maybe leaky zeners Z1 and Z2 ? (maybe lift kathode side of Z1 and listen for a change. These 24V zeners probably would be replaced with max.12V or half rail-voltage parts).
500K still seems on the high side. Do you need the -10dB or now -3.5dB pad at all ? You could switch/short out the 2M2 or your 500K substitute and put a maybe 10K .. 20K in series in front of the 100nF CD12 to get resistive noise down. (alternative with increased CD12 to get this 1st order hpf lower).
 
I'm using Fabio's 2520s. There are a couple 1731s in there also, but I think they're not on the channels with DIs. I haven't tried different amps.

I took the series input resistance down to I think 15 or 20k and swapped the coupling cap for a .068 Panasonic film cap. I wasn't doing very scientific comparisons, but that R seemed to give good noise performance and the coupling caps I had may have been both too small and too crappy, I noticed a marked difference with the new ones.

I'll have to give them a more detailed listen, but they're sounding better for sure, I think a lot closer to what they should be sounding like.
 

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