Salas DCG3 preamp (line & headphone)

[Russellc]

Are the screws too thick? Don't tighten them too much.

M3, I did snug them pretty darn tight, I figured they needed clamped against heatsink tightly. Whoops.

 

[Salas]

The bar is a good idea. I hope the goop isn't conductive like some types made for CPU.

 

[Russellc]

Here is a pic of MOSFETs.

Russellc

 

[Russellc]

This is the goop. It is new, and this is first time to use.

Russellc

 

[Salas]

The bits themselves should had been good. But we have had wrong insulation assembly initial incidents. Usually deformed washers from too much pressure. But everyone was able to eventually sort out such mechanical mishaps.

 

[pfarrell]

Keep it up Russell! This amp is worth the effort! (IMO)

 

[Salas]

This is the goop. It is new, and this is first time to use.

Russellc

It's proper good quality goop for the job

 

[Salas]

Here is a pic of MOSFETs.

Russellc

Huge sink for this. But it will never go hot. You only need a bead of goop behind a mica or a tab and then the pressure spreads it. Too much is messy and doesn't add to thermal transfer. But it doesn't hinder it either.

 

[Salas]

The goop works by filling micro anomalies. It maximizes the mating surface for heat to transfer more efficiently.

 

[Vunce]

Russellc,
It doesn’t look like the legs of M1,2,3 (both channels) are through the pcb and soldered properly. But instead are connected by solder blobs on top of the pcb, I would check all those spots for solder bridges creating a short.

 

[Salas]

M3, I did snug them pretty darn tight, I figured they needed clamped against heatsink tightly. Whoops.

https://www.vishay.com/docs/72674/72674.pdf

 

[Russellc]

Should I try a screw smaller than M3?

 

[Russellc]

Russellc,
It doesn’t look like the legs of M1,2,3 (both channels) are through the pcb and soldered properly. But instead are connected by solder blobs on top of the pcb, I would check all those spots for solder bridges creating a short.

Its just the way it looks, they are through the holes.

Russellc

 

[Russellc]

https://www.vishay.com/docs/72674/72674.pdf

That's quite a range of tightness! 1 inch pound to 15 inch pound. No idea of how tight that is, typically I turn them snug, then a little more. I did notice improvement when loosening them, so I will adjust a bit like that. how small amount of "snuggness" can I get away with? i turn until it snugs, then more.

Let me try, otherwise the bar method will be used.

Russellc

 

[Salas]

Should I try a screw smaller than M3?

The typical is M3. But if the smaller still has wide enough head not to sink inside the nylon shoulder washer, you can try it.

 

[Salas]

That's quite a range of tightness! 1 inch pound to 15 inch pound. No idea of how tight that is, typically I turn them snug, then a little more. I did notice improvement when loosening them, so I will adjust a bit like that. how small amount of "snuggness" can I get away with? i turn until it snugs, then more.

Let me try, otherwise the bar method will be used.

Russellc

7-10 In lb seems good enough already in the chart. Finger tight is surprisingly powerful: https://en.wiktionary.org/wiki/finger_tight

 

[Russellc]

Ok, backing them off, then snugging forward without the extra ump has them all quiet. Just turned until good snug, without the extra twist
like I would do an output mosfet on a power amp. I guess I will find out monitoring their heat with a laser thermometer tool.

I dont have this fuse on hand to replace so fireups will have to wait.
Russellc

 

[Russellc]

7-10 In lb seems good enough already in the chart. Finger tight is surprisingly powerful: https://en.wiktionary.org/wiki/finger_tight

Whow. This isnt super tight but beyond finger for sure. Thinking I just pressed them too hard. the smallest slow blo fuse I have is 2.5 but I am still digging around, thought I had some .5 amp. Looks like fuse buying time!

Russellc

 

[Salas]

I found yet another reference for finger tight is about 15 in-lb in a motorcycles forum but in a plastic bits hardware store they say its 3–4 in-lbs (0.34–0.45 N·m). Go figure.

 

[Salas]

The fuse saved the situation I believe. You did not also notice any hint of magic smoke or funny smell, right?