There are
two schools of thought on how to handle the signal ground in audio components. Some believe it is best to leave the signal ground floating-Ayre, for instance floats the signal ground in all their products, Ayre goes one step further, and does not connect the AC ground to anything. I believe the argument for the floating approach is that it does not allow noise on the AC ground to be introduced into the system, and there are also no ground loops when the signal ground is floating.
Others connect the signal ground to the chassis and AC ground of the system. Some seem to believe that grounding the signal gives better sound, why, I do not understand.
I have had no issues with keeping the signal ground floating with my Legato in my balanced system. It is dead quiet, and sounds great. I am interested in reading about the different approaches, and theories people ascribe to them.
two schools of thought on how to handle the signal ground in audio components. Some believe it is best to leave the signal ground floating-Ayre, for instance floats the signal ground in all their products, Ayre goes one step further, and does not connect the AC ground to anything. I believe the argument for the floating approach is that it does not allow noise on the AC ground to be introduced into the system, and there are also no ground loops when the signal ground is floating.
Others connect the signal ground to the chassis and AC ground of the system. Some seem to believe that grounding the signal gives better sound, why, I do not understand.
I have had no issues with keeping the signal ground floating with my Legato in my balanced system. It is dead quiet, and sounds great. I am interested in reading about the different approaches, and theories people ascribe to them.
Oh my good I discovered other thing: to get the best sound all preamps must be powered & when I hear the preamp SE with the preamp balanced with a switch for bal/unbal when connected balanced the voice moves extremely to the right & when connect unbalanced the voice moves lightly to the left not extremely so more centered all heard with the SE preamp
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Hi Barrows,
Do check though that your signal ground is not connected to your AC supply ground somewhere else in your system. For instance, my Manley Stingray amp has it's signal gound connected to AC ground. You are right though, a lot of modern equipment that is double insulated has no power ground connection. If I connest up my old CD player and Lavry DAC, the signal is conected to ground in 3 places - not ideal!
On my Buffalo, (which is a 2 box set up), the AC incomming ground is only connected to the cases.
Indeed...
Martin: In my system the only component which grounds the signal to the AC ground is my Pass amplifier-it shows about 6 ohms from XLR pin 1 to IEC ground pin (probably a 5 ohm resistor in there somewhere). But, I have also had an Ayre amp in my system, with it the entire system is floating, and the system is noise free (virtually) and sounds great either way. BTW, Ayre does not even ground the chassis to the IEC; as Charlie Hansen is well known to be very suspicious of any path for RFI to get into the system, my guess is that Ayre floats the grounds in an effort to keep AC ground borne RFI out of the components.
Martin: In my system the only component which grounds the signal to the AC ground is my Pass amplifier-it shows about 6 ohms from XLR pin 1 to IEC ground pin (probably a 5 ohm resistor in there somewhere). But, I have also had an Ayre amp in my system, with it the entire system is floating, and the system is noise free (virtually) and sounds great either way. BTW, Ayre does not even ground the chassis to the IEC; as Charlie Hansen is well known to be very suspicious of any path for RFI to get into the system, my guess is that Ayre floats the grounds in an effort to keep AC ground borne RFI out of the components.
Thanks Barrows, I am certainly not in a position to question Mr Hanson, but I would expect that airborne RF would also come in to play. Certainly if I put a scope on an ungrounded chassis, it shows a ton of RF junk, grounding that chassis eliminates it. I suppose that it's a trade off. If my case is an ungrounded RF antenna, there will be some capacitive coupling to the circuits inside, however, if I ground it and that ground is alo connectied to the signal ground, I will be injecting RF into the signal ground IF the ground connection carries any significant resistance to ground. Either way, I would expect that grounded vs ungrounded signal line will be extremely system dependent, hence my thought of adding a 'ground lift' option to the Buffalo.
Happy listening!
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If you are using the SE outputs, the balanced outputs are always loaded by the BAL/SE stage. About 4.7K load. This is in addition to the load of the I/V resistors themselves.
Thanks Russ
Hi I've just completed my Legato II board. I'd like to have some advice.
1)I set the PlacidBP at +-12DCV and trimmed R1 and 2 at 0,25V, so I have at V Out 300 mA. Whith Legato connected I set R13 and 14 at 0,06V...but at this point at V+ there is 250mA and at V- 200mA. I have to counterbalance or is it normal?
2)To trim + and – inputs to 0 I had to unscrew completely VR's to the top stop...again is it right?
Thanks for your help and patience
Regards
gianluca
1)I set the PlacidBP at +-12DCV and trimmed R1 and 2 at 0,25V, so I have at V Out 300 mA. Whith Legato connected I set R13 and 14 at 0,06V...but at this point at V+ there is 250mA and at V- 200mA. I have to counterbalance or is it normal?
2)To trim + and – inputs to 0 I had to unscrew completely VR's to the top stop...again is it right?
Thanks for your help and patience
Regards
gianluca
Is there a reason for the 4K7 ohm value for R17-R24 for the BAL/SE opamp?
Is it to meet an ultra low S/N spec?
In an SE only output system, if the value could be raised to say 100K, C5-C8 could be sized smaller and high quality film caps could be substituted for the electrolytics supplied as well.
Is it to meet an ultra low S/N spec?
In an SE only output system, if the value could be raised to say 100K, C5-C8 could be sized smaller and high quality film caps could be substituted for the electrolytics supplied as well.
I am sure many of you will be very interested in this:
http://www.diyaudio.com/forums/twisted-pear/183663-legato-3-look-ma-no-caps.html
http://www.diyaudio.com/forums/twisted-pear/183663-legato-3-look-ma-no-caps.html
Steve, as you point out, lower resistor values give a lower noise. However these resistors also load the opamp output, so they can't be too low. 4K7 is a good middle point. They are actually nothing to do with the 100uF coupling caps, so will have no effect on the bass -3dB point.
No reason not to go with film caps or bypass the caps altogether, provided DC offset isn't too high. It's quite possible to null out the DC offset on the Legato 1 & 2s - you need to vary the current through the one of the current sources. Just takes a little imagination in mounting a variable resistor.
The 4.7K actually do come into play after the 100uf caps and do effect the corner frequency.
And yes nulling the DC is not too hard if you have the gumption. The best place to do it is at the BAL/SE stage if your using SE output. Not at the CCS.
Cheers!
Russ
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