GC noise and heat issues - Page 4

pacificblue · 8th July 2009, 08:00 PM

As far as I understand those photos and the description of the mute switch the input is left floating. In that case you will get significant DC offset at the IC's inputs. You could try to make R1 = R3 and use the mute switch to ground the amplifier input. That way the DC offset should be the same on both IC inputs, which adds up to something close to zero.

A schematic would help a lot to analyze the exact situation.

If you increase the smoothing capacity the ripple voltage will be reduced, and with it the buzz.
If you connect the ground legs of the smoothing capacitors right next to each other instead of at opposite sides of your ground wire, buzz will probably be reduced as well. The same goes for the ground wires from the rectifiers.
It could also help to create separate grounds for the inputs and for output and power. They should have individual return wires to the star-point.

The easiest solution: don't use the mute switch.

fishski13 · 8th July 2009, 09:42 PM

thanks a lot everyone. i'm learning

.

i now have 18 hrs on the GC, muted. the 1K input resistors and re-doing my grounding scheme seem to have done the trick (fingers crossed). i have no thermal instability issues. i've played a couple of cds in that time and everything sounds great. the buzz is still there when muted, but very faint, even with ears right next to the speakers. i'm just happy that the chips appear to be stable now.

i also contacted AMB Labs re: the CK2III/pre-amp and the mute switch. he sent me a simple schematic for the mute switch so that the inputs of the GC are never left floating.

pacificblue,
DC offset at GC output, un-muted = 5-10mV. when muted, jumps to 32-38mV.

AndrewT,
the NS datasheets spec the with a non-optional 10K pot and a 10uF AC coupling cap inbetween. muted inputs don't meet these component requirements

. after a cursory read, i couldn't find anything specific about floating the inputs.

fishski13 · 9th July 2009, 03:25 AM

i re-wired the mute switch so that when thrown into the "mute" position (amber LED), the pre-outs on the pre-amp are connected to star ground via a 1K resistor per channel. no buzz and thermally kosher.

also, DC offset at the GC output dropped to a more respectable 11mV (R) and 3mV (L) when muted.

Salas,
you were right, they all play in the end

.

[IMG]

[/IMG]

Salas · 9th July 2009, 11:59 AM

And they can look cooler than a DAC1 too.

8th July 2009, 08:00 PM	#31
pacificblue diyAudio Member Join Date: May 2008	As far as I understand those photos and the description of the mute switch the input is left floating. In that case you will get significant DC offset at the IC's inputs. You could try to make R1 = R3 and use the mute switch to ground the amplifier input. That way the DC offset should be the same on both IC inputs, which adds up to something close to zero. A schematic would help a lot to analyze the exact situation. If you increase the smoothing capacity the ripple voltage will be reduced, and with it the buzz. If you connect the ground legs of the smoothing capacitors right next to each other instead of at opposite sides of your ground wire, buzz will probably be reduced as well. The same goes for the ground wires from the rectifiers. It could also help to create separate grounds for the inputs and for output and power. They should have individual return wires to the star-point. The easiest solution: don't use the mute switch. __________________ If you've always done it like that, then it's probably wrong. (Henry Ford)

9th July 2009, 03:25 AM	#33
fishski13 diyAudio Member Join Date: Sep 2008 Location: Minneapolis, MN	i re-wired the mute switch so that when thrown into the "mute" position (amber LED), the pre-outs on the pre-amp are connected to star ground via a 1K resistor per channel. no buzz and thermally kosher. also, DC offset at the GC output dropped to a more respectable 11mV (R) and 3mV (L) when muted. Salas, you were right, they all play in the end . [IMG][/IMG]

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8th July 2009, 09:42 PM	#32
fishski13 diyAudio Member Join Date: Sep 2008 Location: Minneapolis, MN	thanks a lot everyone. i'm learning . i now have 18 hrs on the GC, muted. the 1K input resistors and re-doing my grounding scheme seem to have done the trick (fingers crossed). i have no thermal instability issues. i've played a couple of cds in that time and everything sounds great. the buzz is still there when muted, but very faint, even with ears right next to the speakers. i'm just happy that the chips appear to be stable now. i also contacted AMB Labs re: the CK2III/pre-amp and the mute switch. he sent me a simple schematic for the mute switch so that the inputs of the GC are never left floating. pacificblue, DC offset at GC output, un-muted = 5-10mV. when muted, jumps to 32-38mV. AndrewT, the NS datasheets spec the with a non-optional 10K pot and a 10uF AC coupling cap inbetween. muted inputs don't meet these component requirements . after a cursory read, i couldn't find anything specific about floating the inputs.

9th July 2009, 11:59 AM	#34
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	And they can look cooler than a DAC1 too.

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