Hey, All!
I can't hear a difference with my current set-up either way, but is there a reason channel grounds are normally connected together?
My GC (which is nearly done -- it needs heatsinks, rubber feet and a faceplate) is the typical two-PS BrianGT LM3886 kit.
The only difference I can think of when the channel grounds are shorted together is that this would provide a ground loop path for whatever's connected on the inputs. How can this possibly be good?
With the channel grounds *not* connected, I effectively have two completely separate amplifiers in one chassis, which happen to share transformer secondaries.
The "star ground" point I decided for each channel is the ground plane of the PCB. As it stands right now, the amp is quieter than my source.... with the inputs shorted, I can't decide if the hiss I hear when pressing my ear against the tweeter is seashell-ocean noise or if it's coming from the amp.. so as it sits right now, this is the quietest amp I have ever owned, including my much-loved Harmon-Kardon HK440.
Wes
I can't hear a difference with my current set-up either way, but is there a reason channel grounds are normally connected together?
My GC (which is nearly done -- it needs heatsinks, rubber feet and a faceplate) is the typical two-PS BrianGT LM3886 kit.
The only difference I can think of when the channel grounds are shorted together is that this would provide a ground loop path for whatever's connected on the inputs. How can this possibly be good?
With the channel grounds *not* connected, I effectively have two completely separate amplifiers in one chassis, which happen to share transformer secondaries.
The "star ground" point I decided for each channel is the ground plane of the PCB. As it stands right now, the amp is quieter than my source.... with the inputs shorted, I can't decide if the hiss I hear when pressing my ear against the tweeter is seashell-ocean noise or if it's coming from the amp.. so as it sits right now, this is the quietest amp I have ever owned, including my much-loved Harmon-Kardon HK440.
Wes
Thanks, Mick.
Any idea why this seems to be a common recommendation?
I'm trying to figure out any advantages to the configuration... the only one I've come up with is that a half-broken input connection might still sound okay..
For now, I think I will just leave them disconnected, I suspect that will make for a quieter amp when hooked up to crappy gear.
Oh, one more thing -- does it make a difference for bridging?
Wes
Any idea why this seems to be a common recommendation?
I'm trying to figure out any advantages to the configuration... the only one I've come up with is that a half-broken input connection might still sound okay..
For now, I think I will just leave them disconnected, I suspect that will make for a quieter amp when hooked up to crappy gear.
Oh, one more thing -- does it make a difference for bridging?
Wes
Hey, Mick!
Great site, I wish I had found that a while ago!
Your grounding scheme is nice and a tight, going with a P2P construction really helps in that regard. You P2P guys must be very patient, that is some nice intricate work!
Your grounding scheme does keep the channels at the same ground potential, though; the single power supply enforces this.
Is that hunk of aluminium enough for a heat sink, or did you have to add some more? I have a similar-sized piece of stainless steel I am using, it gets quite warm even though it is connected to the rest of the chassis. I had planned on adding more heat sinking, but I snapped my #6 tap trying to put a blind hole in copper. GRR!
I also find the oscilloscope views interesting, I have a 'scope and an audio signal generator here -- but I've never actually tested an amplifier in more detail than 'does it work? Yup!' before.
Wes
Great site, I wish I had found that a while ago!
Your grounding scheme is nice and a tight, going with a P2P construction really helps in that regard. You P2P guys must be very patient, that is some nice intricate work!
Your grounding scheme does keep the channels at the same ground potential, though; the single power supply enforces this.
Is that hunk of aluminium enough for a heat sink, or did you have to add some more? I have a similar-sized piece of stainless steel I am using, it gets quite warm even though it is connected to the rest of the chassis. I had planned on adding more heat sinking, but I snapped my #6 tap trying to put a blind hole in copper. GRR!
I also find the oscilloscope views interesting, I have a 'scope and an audio signal generator here -- but I've never actually tested an amplifier in more detail than 'does it work? Yup!' before.
Wes
Interesting -- can you estimate the running temperature?
These are just guesses, but my chips seem to run at about 50C, the heatsink at 40C near the chip, at about 25C at the extremities (suggesting stainless steel is not a great heat conductor). Ambient is about 17C.
It doesn't seem to alter much between quiet and loud listening levels, although I haven't listened to it loudly for more than a couple of minutes -- I'll get a chance to do that this weekend, though.
Wes
These are just guesses, but my chips seem to run at about 50C, the heatsink at 40C near the chip, at about 25C at the extremities (suggesting stainless steel is not a great heat conductor). Ambient is about 17C.
It doesn't seem to alter much between quiet and loud listening levels, although I haven't listened to it loudly for more than a couple of minutes -- I'll get a chance to do that this weekend, though.
Wes
Hi Mick_f,
that rapid fall in temperature is a high thermal gradient in the aluminium heatsink. A good conductor of heat would hold almost the same temperature across the heatsink.
That temperature gradient is telling you that the sink is too thin.
A rough estimate for your heatsink thickness is a tenth of the radius to which you wish to dissipate your heat. i.e. 2mm thick works out to 40mm diameter. 3mm thick out to 60mm diameter. 10mm thick out to 200mm diameter. after you go beyond a sensible radius then the temperature does indeed fall and the sink becomes less efficient. Large increases in radius give little increase in dissipation. Stainless steel will be a lot worse in this respect. I don't have data to hand, but it would be mighty thick, but a big advantage would be thermal inertia.
that rapid fall in temperature is a high thermal gradient in the aluminium heatsink. A good conductor of heat would hold almost the same temperature across the heatsink.
That temperature gradient is telling you that the sink is too thin.
A rough estimate for your heatsink thickness is a tenth of the radius to which you wish to dissipate your heat. i.e. 2mm thick works out to 40mm diameter. 3mm thick out to 60mm diameter. 10mm thick out to 200mm diameter. after you go beyond a sensible radius then the temperature does indeed fall and the sink becomes less efficient. Large increases in radius give little increase in dissipation. Stainless steel will be a lot worse in this respect. I don't have data to hand, but it would be mighty thick, but a big advantage would be thermal inertia.
Hi Andrew,
I dont completely agree with you. First, a good thermal conductor will effectively carry the heat away from the chip and therefore will give rise to a thermal gradient. Second, whether or not a heatsink is held at the same temperature is strongly depending on the size of the heatsink, which for a given material determines its heat capacity, and by the power dissipated by the chip which is used to heat the heatsink. If only a small amount of heat is produced by the chip, the "hot radius" will be small and all you observe is the strong thermal gradient at its borders.
Actually my heatsink is grossly oversized. The chip is directly attached to an aluminium plate of about 2mm thickness and about 600 cm^2 surface area.
Mick
I dont completely agree with you. First, a good thermal conductor will effectively carry the heat away from the chip and therefore will give rise to a thermal gradient. Second, whether or not a heatsink is held at the same temperature is strongly depending on the size of the heatsink, which for a given material determines its heat capacity, and by the power dissipated by the chip which is used to heat the heatsink. If only a small amount of heat is produced by the chip, the "hot radius" will be small and all you observe is the strong thermal gradient at its borders.
Actually my heatsink is grossly oversized. The chip is directly attached to an aluminium plate of about 2mm thickness and about 600 cm^2 surface area.
Mick
Hi Mick,
if the chips are running at 60 deg c then I'd question your assertion that the sinks are grossly oversised
personally I'd say that they are marginal.... but then I like things to run cool
Tony.
edit: I'm assuming that the 60 deg C is at normal listening levels not when pushed to the limit.
edit2: and back on topic..... I assume that when you say the input grounds are connected together you mean one is connected to the other and then that one is connected back to the main star... not both go to the star and then there is a link between them as well!!!!
if the chips are running at 60 deg c then I'd question your assertion that the sinks are grossly oversised
personally I'd say that they are marginal.... but then I like things to run cool Tony.
edit: I'm assuming that the 60 deg C is at normal listening levels not when pushed to the limit.
edit2: and back on topic..... I assume that when you say the input grounds are connected together you mean one is connected to the other and then that one is connected back to the main star... not both go to the star and then there is a link between them as well!!!!
Hi Mick,
your 2mm thick aluminium plate loses temperature quickly as you move away from the chipamp.
This indicates a poor conductor (sorry to repeat myself). A high temperature gradient (rapid fall in temperature with increasing distance) indicates a poor conductor.
A high temperature gradient also inducates a high thermal resistance.
Your material (aluminium) is potentially a good conductor, but you have chosen too thin a section to spread the heat effectively over a 200mm width, you need about 10mm thick. If you want (or need) to spread the heat along the 300mm length then you should choose even thicker, try about 15mm thick.
If you need a further explanation, I could compare your heat flows to electrical flows through a resistor. But maybe you can think this through yourself.
your 2mm thick aluminium plate loses temperature quickly as you move away from the chipamp.
This indicates a poor conductor (sorry to repeat myself). A high temperature gradient (rapid fall in temperature with increasing distance) indicates a poor conductor.
A high temperature gradient also inducates a high thermal resistance.
Your material (aluminium) is potentially a good conductor, but you have chosen too thin a section to spread the heat effectively over a 200mm width, you need about 10mm thick. If you want (or need) to spread the heat along the 300mm length then you should choose even thicker, try about 15mm thick.
If you need a further explanation, I could compare your heat flows to electrical flows through a resistor. But maybe you can think this through yourself.
back to the topic of grounding
hi folks,
I'm in the process of building an integrated amp using the Brian GT 3886 kit with single rectifier.
I need to include a phono stage and switching for two phono inputs. So, if I want to switch between the two phono sources and the line level sources with a single switch, I'll need to switch both the input to the phono stage and the output from it on the same switch.
I have a 6 pole 8 way rotary that I'd like to use. I was thinking of using three poles for input and three for output. ie: Left hot, right hot, and left and right ground tied together at the switch. This way each source would be grounded only to itself and all other sources would be completely disconnected when not switched on. Does this seem like a good idea?
Oh, and my heatsink is 11 lbs of finned anodised aluminum, so no issues there.
Max
hi folks,
I'm in the process of building an integrated amp using the Brian GT 3886 kit with single rectifier.
I need to include a phono stage and switching for two phono inputs. So, if I want to switch between the two phono sources and the line level sources with a single switch, I'll need to switch both the input to the phono stage and the output from it on the same switch.
I have a 6 pole 8 way rotary that I'd like to use. I was thinking of using three poles for input and three for output. ie: Left hot, right hot, and left and right ground tied together at the switch. This way each source would be grounded only to itself and all other sources would be completely disconnected when not switched on. Does this seem like a good idea?
Oh, and my heatsink is 11 lbs of finned anodised aluminum, so no issues there.
Max
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.