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Dear all, I have used the single ended output so far, but I've always recognize a sort of veil on the music. But this works perfectly and It's very quite. I've then decided to take the single ended output from the balanced output (+ and GND) or, same, (- and GND) to avoid the IC. The results: the veil is disappeared (great sound now, really!) but some "frying" random noise (every second or less) very udible on both channels is coming out... This is not hum noise, nor something caused by the transformers or power supplies: I've checked them, tried to put far away etc... I've tried many pre and amplifiers: it is the legato 2 that generates it. I've tried to reduce the supply from +15 -13 to +12 -12 but the effect is the same. I'm using 2x680R and 1x150R I've tried to disconnet the digital input (SPDIF), Buffalo goes on mute, the random noise still remains... May you please help me to solve the problem? Thanks a lot! Andrea Edited by user Monday, March 14, 2011 5:19:03 AM(UTC)
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Rank: Administration
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Hmm, sounds like you might have a damaged FET possibly? I definitely would never recommend using that configuration. The legato is not designed to be used like that. Edited by user Monday, March 14, 2011 3:58:40 PM(UTC)
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Rank: Member
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Thanks Russ! The problem is on both channels... this is the odd issue if it is a fet. And in common they have only the Placid BP Yesterday I tried again and it seems than when you touch (actually try to move a little bit) the Vreg (Vr3 Vr4) 10K trimmers of the Placid BP you will have an increase apparently of the same kind of noise. As soon as I have time I will try to change both and use a resistor. I will however investigate deeper and I will report you my findings... About the use of the balanced out to feed a single ended, I ask: is there another way to convert balanced into single ended without using an IC and feedback etc...? There is, believe me, really a huge difference in sound, and the spectrum measuring are very close... Edited by user Tuesday, March 15, 2011 1:14:59 AM(UTC)
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Rank: Advanced Member
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Joined: 7/22/2009(UTC) Posts: 81  Location: Norwich, UK Thanks: 2 times
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Hi Andrea
I understand why you are trying this (some people round here will think you mad, I think :-) ), and I've tried the same, with the same result- except my frying noise doesn't ever stop! And I don't think there's anything wrong with your Legato. A while ago I built an alternative I/V stage for buffalo II, based on a circuit I've used with a single ended DAC in the past, which also uses a complementary feedback pair (though both devices were bipolar transistors ; and the latter were later upgraded to a triple of devices- a complementary feed back triple), albeit with the constant current sources needed for good single ended operation, and some other differences. I just used four of these circuits, one for each "half" of each DAC channel's balanced outputs. At first I used an op amp (same as in Legato and IVY III) on its outputs ,for balanced to SE conversion. It worked well- I preferred it at the time to IVY (though this may have just been my bias!). Then I took a single ended output from half of each channel, after the I/V stage - same sizzling noise! (I left the + and - DAC's outputs, on each channel, connected to the I/V stage- I just took an output from one half the I/V circuit and ground). I think I also tried with IVY III- or perhaps Buffalo 32S?- with the same result.
I must admit I'm getting stupendous results from my somewhat modified Legato- now using triples the TP0604 FETs that Russ is using in Legato 3 (thanks Russ!), "despite" using an op amp for BAL to SE conversion. The alternative to the latter would some sort of unity gain, differential amp built of discrete components (which might or might not sound better), or a transformer
Hope this helps
Paul
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