there are some tapped holes. Can't they be used to clamp the TO220 packages via a metal strip and a rubber washer?
Or use something like https://www.farnell.com/datasheets/2182592.pdf
Or use something like https://www.farnell.com/datasheets/2182592.pdf
The holes are too big and not in the right places. But it could be done. Given the enormous thermal mass of this heat sink it won't matter that the heat sources aren't perfectly centred. The Max Clips are great! Also, I've seen SilPad material in tubular form. Drape it over the TO-220 and apply pressure with a clamping bar. That'd work. I'd use a bit of U channel for the clamping bar.
Tom
Tom
Firstly the LM1875 needs an insulating pad to mount to the heatsink (the datasheet is fairly coy on this but talks of mica washers in the heatsink section).
Secondly if your aluminium is pure (soft as cheese), don't even think about tapping it - drill a hole and bolt through, and expect to have trouble drillling a deep hole (use cutting lubricant, and peck-style drilling). If its an aluminium alloy designed for machining then tapping is an option. You really need a drill stand to drill deep holes, its so much more tractable.
Pure aluminium will try to weld itself to the drill bit, so be prepared to scrape it off with a wire-brush from the drill cutting faces regularly. If you don't it will jam, and you won't be able to get the drill bit out...
Secondly if your aluminium is pure (soft as cheese), don't even think about tapping it - drill a hole and bolt through, and expect to have trouble drillling a deep hole (use cutting lubricant, and peck-style drilling). If its an aluminium alloy designed for machining then tapping is an option. You really need a drill stand to drill deep holes, its so much more tractable.
Pure aluminium will try to weld itself to the drill bit, so be prepared to scrape it off with a wire-brush from the drill cutting faces regularly. If you don't it will jam, and you won't be able to get the drill bit out...
for testing purpose only, I drilled a small aluminum case top from a previous project and attached the LM1875 chips with nylon nuts and bolts, and with a heat transfer insulator sheet between the chip and the aluminum plate.
Then while testing I sit one of the overkill heat sinks on the aluminum case top.
Took over an hour of listening to the LM1875 amp for the big sink to get slightly above ambient, and another hour for it to get fairly warm.
For long term in a chassis I am still thinking some type of clamping arrangement although the nylon bolt and nut seem pretty strong.
The LM1875 amp sounds damn good, and it came with speaker protection relay on the board. $30 delivered!
I think I would put it up against my $1300 QUAD909 and it would be debatable which sounded better!
What a difference 50 years makes 😆
Then while testing I sit one of the overkill heat sinks on the aluminum case top.
Took over an hour of listening to the LM1875 amp for the big sink to get slightly above ambient, and another hour for it to get fairly warm.
For long term in a chassis I am still thinking some type of clamping arrangement although the nylon bolt and nut seem pretty strong.
The LM1875 amp sounds damn good, and it came with speaker protection relay on the board. $30 delivered!
I think I would put it up against my $1300 QUAD909 and it would be debatable which sounded better!
What a difference 50 years makes 😆
Personally, I would not rely on a nylon nut and bolt. The nylon may experience elastic behavior due to heat, in which it expands and never recovers to its former length. This would eventually result in reduction of the clamping force imposed on the chip and the aluminum mounting plate. I recommend steel nuts and bolts, insulated with nylon shoulder and flat washers.
The LM1875 is a great chip but it's quite an old design. I have some in my collection with 1984 date codes.
I know there are newer class a/b chips that offer more power but I doubt I would find one that sounds better. It would be nice to have the master/slave functionality and the clipping indicator, but the sound qualities are numero uno for me.
@Mark Tillotson: I had to do a search for PPS. They are not inexpensive, but I see that they are a value proposition when figuring out the time and extra installation hassle of using metal screws/bolts and insulating should and flat washers. Thanks for the education!
PPS can degrade, and fiber glass is a health hazard.
Metal, preferably stainless steel is better.
Metal, preferably stainless steel is better.
Best is get silicon sheets, and cut to size.
Ready made kits for 2030 are about 5 Rupees here... screw, metal washer, nut, mica strip, plastic stepped washer.
Enough to use, the washer is usually Nylon or Delrin, or similar material.
Ready made kits for 2030 are about 5 Rupees here... screw, metal washer, nut, mica strip, plastic stepped washer.
Enough to use, the washer is usually Nylon or Delrin, or similar material.
Silicone perhaps, not silicon! Not the same thing at all...
Yes PPS might have reduced strength with temperature, but it will be much better than nylon, and its an insulator and they sell hardware made from it!
Yes PPS might have reduced strength with temperature, but it will be much better than nylon, and its an insulator and they sell hardware made from it!
Nylon and Acetal are softer than PPS, so some wiggle room is available when fixing, sometimes the holes are slightly out of alignment.
Dielectric strength in a low voltage <100V environment, or temperature resistance <100 Celsius does not matter much here, in the choice of material for heat sink fixtures.
PPS is used for fasteners in chemical plants, small fasteners below 12 mm will be an oddity here.
PPS is about 2.5x the price of Nylon and Acetal here. And it is more difficult to process, requiring higher temperatures, so the product cost goes up.
I have made submersible pump parts from a modified PPS material, trade name Noryl, it was 30% glass fibre filled. So I can claim hands on experience.
No ties to any brands here.
Dielectric strength in a low voltage <100V environment, or temperature resistance <100 Celsius does not matter much here, in the choice of material for heat sink fixtures.
PPS is used for fasteners in chemical plants, small fasteners below 12 mm will be an oddity here.
PPS is about 2.5x the price of Nylon and Acetal here. And it is more difficult to process, requiring higher temperatures, so the product cost goes up.
I have made submersible pump parts from a modified PPS material, trade name Noryl, it was 30% glass fibre filled. So I can claim hands on experience.
No ties to any brands here.
I just checked, 6 days delivery for small PPS screws, 2.5 mm upwards, for chemical lab use, and exotic prices.
I will stick to metal here in India.
I can get stainless steel screws at 1/3 the price of PPS, and for the asking...at specialist fastener shops some 3.5 km from home, in the city centre, which I visit twice a week on average.
Ordinary mild steel, they are cheap, some shops also keep small brass screws.
I will stick to metal here in India.
I can get stainless steel screws at 1/3 the price of PPS, and for the asking...at specialist fastener shops some 3.5 km from home, in the city centre, which I visit twice a week on average.
Ordinary mild steel, they are cheap, some shops also keep small brass screws.
Tom, how did you get McMaster-Carr to ship to you? Whenever I've attempted an order with them, as soon as it gets to a Canadian address, they say 'nope. no can do'. Now, given I'm trying to not shop anything from the US, this is a moot point, but still am curious.
JB WELD two-part high-temperature epoxy will do the job and THEN some. The work must be clamped. Thermal transfer is exceptional into steel, copper and aluminum. The problem is, it is a one-way ticket. If you want to undo the bond, you will destroy some portion with a grinder or such.
If you want it to bond faster, apply heat during the set-up. Or wait overnight.
Attachments
You get metal powder filled two part adhesives, that has been used as thermal adhesive for a driver on board LED bulb circuit by me.
That has to be broken to remove, the lamp circuits are very cheap here, about 10 Rupees for a 220V / 9 Watt unit.
I would use a less permanent method on a chip amp.
Work around is to coat the chip with a release agent like mold release spray, or waxed paper, so it will not stick, the adhesive will work as a gasket, filling gaps.
In fact, the red high temperature silicone adhesives used for head gaskets will also work, and are easier to take apart.
That has to be broken to remove, the lamp circuits are very cheap here, about 10 Rupees for a 220V / 9 Watt unit.
I would use a less permanent method on a chip amp.
Work around is to coat the chip with a release agent like mold release spray, or waxed paper, so it will not stick, the adhesive will work as a gasket, filling gaps.
In fact, the red high temperature silicone adhesives used for head gaskets will also work, and are easier to take apart.