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Hi, I have a Buffalo II/legato II combo. The legato is powered with a lcbps. I also use a volumite for volume control. This goes into my own "pseudo balanced" gainclone with a gain of 11. With this hookup i can certainly hear the noise-floor of the system if i put my ear to the speaker cone or on a quiet night even a foot or two away.
I don't think any sane person would dwell upon this seeing as the noise floor is totally inaudible from the listening position, but I still find myself wondering if this is normal or if the situation can be improved upon. especially since I found this quote by Russ on a forum regarding the legato noise floor:
"I have many hours listening to it now. The noise floor is surprisingly low for a discrete cct. When I put my ear to the cone of a full range driver with the DAC directly coupled to a balanced power amp with about 20db gain I can't detect any noise at all."
In short: I was wondering if upgrading to a more quiet power supply (like I presume the placidHD is) would mitigate/eliminate this noise.
Thank you!
/sebastian
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Well it really comes down to what is producing the noise. The LCBPS noise floor is very low. I doubt that is where you are getting your noise. For esample, in my setup I have the same low (can't hear it at all) noise floor when I use either placidBP or LCBPS.
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Alright thanks that is good to know! I might get this thing absolutely quiet then perhaps.
It still leaves me puzzled though. The problem (if there is one) is either with the legato/lcbps, since it is still present with the buffalo left unpowered, or possibly with my poweramps CMRR. (The amp is perfectly quiet by itself. It is a chipamp design with imput impedances matched at 10Kohm between the + and - imputs using 0,1% resistors.) I don't have any other balanced input amp to try it out with.
I have basically ruled out faulty components on the lcbps since I tried with another LCBPS that I originally bought for dual mono configuration of the legato somewhere down the line. I have also tried with different interconnects but the problem is persistent. If it was a component issue on the legato board it "should" most often affect one channel only. That is why I originally thought about the power supply as a contributor.
Guess it could be some kind of general RFI pickup.
Oh, and I don't have super-sensitive speakers either...
What sounds most likely to you? Where would you start looking to make this thing just that little bit more quiet?
Oh, and I don't have super-sensitive speakers either...
/seb
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How does the noise sound?
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I believe a hiss would be the correct English description :) Just a high frequency "gaussian" noise heard from the tweeter.
Look, I realize that this can probably depend a lot on the specific implementation, interaction with other gear, casing, signal path and shield soldering etc. etc. And I realize that I cant be held in the hand all the way with this, especially since I cant be certain it isn't in reality a problem that rather has to do with my power amp, or if it really should be classified as a problem to begin with.
Basically I just wanna say that I am grateful for any tip or pointers you guys might have!
One thing I was thinking of is to upgrade the legato transistors to the type that is used in legato III. That way I would at least get a nice upgrade even if it still hisses! And I would rule out another possible source of error. What else do you think I should consider.
/seb
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Have you tried having the buffalo connected directly to the amp?.
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No. Great idea!
Is there anything I have to keep in mind when I do this? For example I have a couple of off board MKP caps for coupling inserted right now. Just to be absolutely sure: it wouldn't be a problem to take the signal from the DAC through them would it?
/seb
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Another test to perform. Keep powering the Legato and unplug the Buffalo from power. You can keep the Buffalo sitting stacked ontop of the Legato during this test.
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sebastian wrote:No. Great idea!
Is there anything I have to keep in mind when I do this? For example I have a couple of off board MKP caps for coupling inserted right now. Just to be absolutely sure: it wouldn't be a problem to take the signal from the DAC through them would it?
/seb Yes, use the DC blocking caps. I have the BII directly connected to hypex amps (with blocking caps just in case) and they are completely silent. The Hypex have a gain of 26 dB and the speakers are 90 db
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Right! I tried to listen directly to the output of the buffalo II itself and it works a treat! The background noise is gone. So it seems I have really isolated this hiss to the legato board itself, since I can now practically write off the power amp as the troublemaker.
It would probably be some kind of malfunctioning component issue then i guess. Is there any conclusions to be drawn from the fact that the hiss is equal on both channels? Could I perhaps have driven the board to hard so that components on both channels were damaged? (I have previously used a voltage of +15 to -15 but that should be alright shouldn't it?).
I was also surprised at how relatively loud the signal directly from the buffalo was. I would have thought that the buffalo signal would be considerably lower in amplitude compared to the legato output. The buffalo outputs seem to be not miles below the legato though. Does this sound strange or is it that the i/v stage is just not designed to provide a lot of gain?
As always, most thankful for any thoughts on this!
/seb
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A couple of possibilities: 1) Simpler wiring. 2) Impedance mismatch between + and - inputs on your power amp. The DAC directly would not be bothered, but the legato could. The reason being that this will negatively impact CMRR. I can't rule out a problem on the legato, but I have not run into one like this. 15V rails is just fine as long as ventilation is good. Edited by user Monday, January 16, 2012 3:58:02 PM(UTC)
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Well, alright then the amp doesn't get off the hook quite that easy :) Because of the legato output impedance being higher than the buffalo i guess? I don't think its a wiring issue since I simply refitted the same wires to the buffalo. Plus that I have tried with several different wiring configs within the enclosure in the past. Shielded and unshielded hisses just the same. If anything this kind of noise pickup would certainly affect one channel more than the other in my box. I realize I haven't mentioned that i have omitted the buffers on the legato. Perhaps this is useful information. Even if I've been led to believe this would not cause a problem with an amp input impedance of 10K, perhaps it can still be an issue? As for the amp I attached the schematics: All resistors are 0.1% tolerance. My implementation overshoots the ideal value of the impedance matching resistor (10453 ohm) by 2-3 ohms. This is well within the tolerances mentioned by Thorsten Loesch in this thread. Can you guys see any reason why this thing would not work well? That leaves the general build quality and soldering skills and so on as a potential lurker. If I may say so myself, I am pretty handy with the soldering gun and I like my stuff to be well laid out, power and audio well apart physically, well ventilated etc. I'm not saying I'm a genius, just that I would be surprised if general build quality turned out to be the culprit. I'll post some pics if you think it would help... /seb sebastian attached the following image(s):  pseudo balanced gainclone.png (17kb) downloaded 50 time(s).You cannot view/download attachments. Try to login or register.
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