Dear all,
I searched but couldn't find any comments on this one. I guess I'll continue searching... but:
Why would anyone use the non-isolated version of the amp chip under normal circumstances? I've read probably twenty complete threads about the Gainclone, and no one is doing anything interesting by using the heatsink as part of the supply rail. This means that no one actually seems to need this electricity flow.
On the other hand, having an isolated version of the chip could improve the thermal coupling between chip and heatsink dramatically. One of the problems of chip amps is that there's insufficient surface area for power dissipation compared to discretes, leading, in some cases, to lower reliability long-term. In that case, the use of a Sil-pad or equivalent becomes even more of a serious problem here, and the isolated version can totally eliminate this layer.
So, why do people use the non-isolating version? I guess I'm missing something obvious. Don't tell me it's the "warmth of the Sil-pad sound"?
Tarun
I searched but couldn't find any comments on this one. I guess I'll continue searching... but:
Why would anyone use the non-isolated version of the amp chip under normal circumstances? I've read probably twenty complete threads about the Gainclone, and no one is doing anything interesting by using the heatsink as part of the supply rail. This means that no one actually seems to need this electricity flow.
On the other hand, having an isolated version of the chip could improve the thermal coupling between chip and heatsink dramatically. One of the problems of chip amps is that there's insufficient surface area for power dissipation compared to discretes, leading, in some cases, to lower reliability long-term. In that case, the use of a Sil-pad or equivalent becomes even more of a serious problem here, and the isolated version can totally eliminate this layer.
So, why do people use the non-isolating version? I guess I'm missing something obvious. Don't tell me it's the "warmth of the Sil-pad sound"?
Tarun
Hi Tarun,
I personally would never use the heatsink as conductor only
cause I like it properly soldered for good contact and don´t want my heatsinks which are most probable external to sit on one of the voltage rails (safety!).
Even if you do like you describe you´d have to use thermal grease which makes the contact even worse (OK, you could use silver grease).
Your arguments about the ability to dissipate are actually the other way round.
The non-isolated package has lower thermal resistance than the isolated!
With the isolated version it´s recommended not to exceed a certain power dissipation. Can´t remember the figure but it´s in either the datasheet or the calculation tool from National S.
Here is the thread about the calculation tool.
Cheers
Jens
I personally would never use the heatsink as conductor only
cause I like it properly soldered for good contact and don´t want my heatsinks which are most probable external to sit on one of the voltage rails (safety!).
Even if you do like you describe you´d have to use thermal grease which makes the contact even worse (OK, you could use silver grease).
Your arguments about the ability to dissipate are actually the other way round.
The non-isolated package has lower thermal resistance than the isolated!
With the isolated version it´s recommended not to exceed a certain power dissipation. Can´t remember the figure but it´s in either the datasheet or the calculation tool from National S.
Here is the thread about the calculation tool.
Cheers
Jens
I said "could"Peter Daniel said:
That means that with crappy pads, you could end up with worse thermal resistance that the ready-to-use isolated version
but that you also can have a better one, with good pads
I just wanted to say that you can't compare the raw numbers of the thermal resistance of the isolated and the non isolated, you have to consider the pad too
If I get you right Ron you´re just lucky that your heatsink is eloxated which isolates to a certain extent.
Slight scratches on the heatsink or some higher voltage and a "fault current" (don´t know the correct expression) will flow from V- to earth-ground (in case your heatsink is earthed).
Of course then the "fault current breaker"
will become active and switch of your electricity in the apartment or whatever. (that´s at least how it works in our country)
Cheers
Jens
Slight scratches on the heatsink or some higher voltage and a "fault current" (don´t know the correct expression) will flow from V- to earth-ground (in case your heatsink is earthed).
Of course then the "fault current breaker"
will become active and switch of your electricity in the apartment or whatever. (that´s at least how it works in our country)Cheers
Jens
roncla said:
I don't know if this idea is something to be too proud about...
yes, anodized Al is an insulator but it seems to me you are flying too close to the skyscrapers here. A pad is not such a big deal and it puts a nice level of safety between the chip and the heatsink. That way you could use a metal screw and tighten the chip a bit more against the HS.
Banned
Joined 2002
Banned
Joined 2002
Someone should try the following. Take the unisolated one, and lap the contact surafce to the heatsink very carefully till it is perfectly flat and smooth. Similarly, also lap the heatsink contact are till it is also perfectly smooth. When you drop the chip on the heatsink it might " stick" because of the perfect contact. Now you can mount the chip with very little heatsink and have the best thermal contact. See if the heavy bass lines improve.
I suggest taping 600 grit emery on a flat pice of glas to do the above. The thermal resistance or lack of will be vastly superior to mica or sil pads. That way, the thermal and current protection doesn't begin to kick in and generate non linearities and compression.
I suggest taping 600 grit emery on a flat pice of glas to do the above. The thermal resistance or lack of will be vastly superior to mica or sil pads. That way, the thermal and current protection doesn't begin to kick in and generate non linearities and compression.
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