Post by Owen Y on Jul 20, 2020 20:26:42 GMT 12
Most would agree with you I expect, from an aesthetic proportion POV (bottom 1/5) but... I say go for the practical solution (top) & turn the 'problem' to advantage somehow, eg... - LED in the middle (if the power switch is non-illuminated) or... - choose a nicely figured/grained pc of fascia wood panel (do I recall correctly that it's wood/ply?) & let the eye be distracted by the wood-grain/colour
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Post by colinf on Jul 21, 2020 6:30:35 GMT 12
The pot shaft would be 6mm wouldn’t it? So you can drill a 6mm (slightly bigger to allow rotation of the shaft without friction but not loose) in-between the heatsink fins. I like the 1/5 layout better.
AMR-iFi R&D
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Post by sadface on Jul 21, 2020 7:59:40 GMT 12
Would you have any concerns about heat coupling into the volume pot via the shaft?
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Post by colinf on Jul 21, 2020 22:19:54 GMT 12
Not really, the heatsink shouldn’t get extremely hot with the LM chips. If heat is a problem consider using a small, quiet fan with a thermal switch. What does kitty think?
AMR-iFi R&D
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Post by Owen Y on Jul 21, 2020 22:46:12 GMT 12
Or possibly a plastic extension shaft (vs metal)?
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Post by colinf on Jul 21, 2020 22:47:15 GMT 12
Plastic expands when it gets warm so might create friction when the heatsink is warm.
AMR-iFi R&D
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Post by Owen Y on Jul 22, 2020 12:07:12 GMT 12
I think I've seen some people use a heat-shrink coupling (vs metal sleeve & grubscrews), but I've not tried that. Likely the 'feel' of the vol control would be a little different. (I have once slipped some heat-shrink over an extension shaft, where I was concerned about proximity to nearby conducting electrics )
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Post by sadface on Jul 22, 2020 20:54:01 GMT 12
G'day Guys,
Thanks for the suggestions.
I will stare at this for a bit longer and figure out how much difficulty I want to deal with.
Easy mode without a hole in the heatsink or Hard mode with a hole in the heatsink....
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Post by sadface on Jul 23, 2020 21:04:08 GMT 12
Hard mode it is.
I will drill a 13mm hole so that there is plenty of clearance.
The tricky bit is going to be removing material around the fins, I will try simply doing it with the drill but I suspect the fin will move too much and I might have to resort to some kind of cutting tool.
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Post by colinf on Jul 23, 2020 23:17:21 GMT 12
Why such a big hole?
AMR-iFi R&D
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Post by sadface on Jul 24, 2020 9:26:12 GMT 12
Clearance, room for error and to prevent thermal coupling.
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Post by Owen Y on Jul 24, 2020 9:43:15 GMT 12
Form follows Function, I say (in this case).... Go the easy mode
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Post by sadface on Jul 24, 2020 18:18:20 GMT 12
I couldn't drill the hole out to 13mm as I couldn't fit the heatsink under the drill press with a 13mm bit due to the length of the drill bit.
I had to settle for 11.5mm.
I was able to get into the fin of the heatsink by bending the next fin over out of the way and grasping it with some pliers. I was then able to peel it back like opening a can of corned beef with the little key thingy.
It rough looking but it will allow me to go with the 1/5 spacing.
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Post by sadface on Jul 27, 2020 18:17:16 GMT 12
G'day Chaps,
I had time for a lot of engineering work over the weekend.
I built some brackets.
1 out of perspex to go in between the main PSU and the preamp PSU to account for the different hole spacings of the 2 boards.
1 of of 1.5mm steel salvaged from another amp chassis. This one is to house the power tx. This was to get around one of the feet screws fouling with the bottom of the tx and also allows easier wiring.
I also had time to mount the IEC socket and drill mount holes for all of the pcbs, rca sockets and speaker jacks.
Unfortunately, I forgot to drill a hole for a fuse holder.
I also seemed to have serious miscalculated the hole centres for the volume pot assembly. The L bracket that holds the volume pot itself has ended up a few mm to the left of the hole centre in the heatsink The hole in the steel front panel has ended up something like 10mm to the right of the hole centre in the heatsink.
Not sure how this happened but I will have to move both. Not the end of the world but slightly annoying....
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Post by Owen Y on Jul 27, 2020 19:58:11 GMT 12
Beginning to look like an amp
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Post by sadface on Jul 29, 2020 21:05:23 GMT 12
The power tx has ferrite beads on the secondaries which I am not used to.
Would it be beneficial to twist (braid since it's 3 wires) the wires like normal or will this interfere with the operation of the ferrite beads?
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Post by colinf on Jul 29, 2020 23:57:33 GMT 12
Braiding would look nice. The radiated field is lower with twisting the wires together (or braiding them). But as long as they’re away from the preamp and signal wiring you should be fine. The orientation of the transformer will have a larger effect. With a toroidal you want it to be mounted horizontally from signal wiring.
AMR-iFi R&D
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Post by sadface on Aug 2, 2020 22:35:41 GMT 12
G'day Guys,
I made a fair bit of progress.
I finally got the mains wiring drafted so that I could test the power supplies.
It turns out the my power transformer is 30-0-30 instead of 25 - 0 - 25 like I thought. This has required a bit of adjustment as I thought I would have +/-35vdc rails but it is actually +/- 40.5vdc.
I decided it shouldn't be the end of the world as the max voltage of the LM3886 is +/-42vdc so I am close but not over the limit. Presumably the voltage will sag a bit under high loads anyway.
This did require me to order new dropping resistors for the relay driver in the speaker protection.
I also used a step drill bit to take the hole in the heatsink out a bit further for clearance that was required due to poor mathematics and measuring.
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Post by sadface on Aug 3, 2020 21:11:29 GMT 12
G'day Guys,
Progress continues.
Here's the enlarged hole in the heatsink. I do love step drill holes...
I started on the wood working over the weekend.
I learned that my Ryobi 18v circular saw does not have the guts to handle 28mm brown wood ply. Nonetheless I managed to get a nice rectangle almost perfect in dimensions...
I've chiseled out the majority of the material from the rear side to make a 'socket' to slide over the front panel of the steel chassis.
I learned the hard way to be very careful chiseling near the edges.... Here's last nights repair job gluing the plys back together on one side. Unfortunately I still haven't learned to be gentle enough as I made the same mistake on the opposite side this afternoon.... I am out of glue so repair work will have to wait till I can visit bunnings.
There is a decent bit of material to remove at the top side of the socket.
A good 10mm but I will be being very slow and careful for that bit as the top side will be a bit more visible so I would prefer to not have it marred with glue.... There is still a mm or 2 to remove on the sides, I might also need to remove another mm from the depth of the socket but I will see once I get the socket edges fitting nice and tight.
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Post by colinf on Aug 4, 2020 6:35:22 GMT 12
I like how stepped drill bits conveniently give a de-burred hole. +/- 40v with no signal is ok for the 3886, the limit is +/- 47v. With a signal the limit drops to +/- 42v.
AMR-iFi R&D
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Post by sadface on Aug 15, 2020 23:18:55 GMT 12
G'day Guys,
Progress continues. I've spent many hours chiseling and sanding but the socket on the back is finally complete.
Next time I might invest in a wood router given how much time this has taken me.
I think I am on my 6th round of gluing the plys back together after I lifted one corner with a screw when testing the mount from the front panel to the bracket it attaches to.
The hole for the volume pot is nicely centered and ready to go hence the brass bushing in there.
Here's the bracket sitting nicely in its socket.
I've also finalised a bit more on the electronics side. I cannot use the ferrite bead on 15-0-15 secondary as it simply gets in the way and makes the wire run too short. The resistor finally arrived to stuff the relay boards.
All that remains now is to chisel out the socket for the power switch in the wooden front panel.
After that I can finally wire it up for the first round of testing.
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Post by sadface on Aug 16, 2020 15:17:14 GMT 12
G'day Guys,
I've reached a milestone today, I finally get to see what its going to look like!
The front panel is now done with cutting, chiseling and filing and is now affixed to the front panel bracket.
It is affixed by 4 wood screws from inside the chassis so that the front is nice and clean. I did toy with the idea of using some nice hex head M4 bolts straight through like my backup preamp but I am experimenting with a cleaner look this time.
Thoughts on the lack of bolts on the front?
The tolerances came out surprisingly good, there's no difference between the amount of edge at the sides. Both sides the wood protudes 6mm relative to the chassis behind. The top line is 1mm out with the left side being slightly higher, possibly misalignment on the bracket but probably more likely a slight difference in the thickness of the top 'lip' of the ply.
The front came out nice and flush with the chassis lid.
My fine woodworking skills are still not up to scratch though. The power switch socket is every so slightly off vertical but more important the wood got a bit gouged in an accident.
Once finished and stained I think the brown-wood is going to look lovely with the grey chassis. I should have time to sand and then slather on a fair bit of danish oil this afternoon, this evening I should have some time to get back onto the electrical side with the relay board and then wiring looming.
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Post by sadface on Aug 16, 2020 16:01:27 GMT 12
And then a wee set back.....
I dropped the work piece during sanding, luckily I have lots of chunks from the chiseling process that I can cut to size and slot into the gap.
Unfortunately I am out of glue and I can't just go down to Bunnings to buy some more... I should be able to do a click and collect tomorrow so I guess I'm done with wood working for the day and onto the electronics it is....
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Post by colinf on Aug 17, 2020 19:07:35 GMT 12
I like the smooth look without the bolts myself. Good it’s coming together, satisfying.
AMR-iFi R&D
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Post by Owen Y on Aug 17, 2020 20:44:09 GMT 12
Wood is forgiving, just slot in some ply/glue/filler. clamp it & then trim back & sand when dry. A wood-rasp is always a handy tool. For small cutting/grinding tasks, a powered dremel can be a handy tool for metal or wood. Routers are handy, but big & cumbersome sometimes, unless you're set up with ample workspace for safety. You can get wee battery-powered 'trim routers' - I'm not that familiar with what's available, but the Ryobi one I used briefly was lightweight & easy to handle, but you'd have to make-up guides and/or 'fences' to make it really useful.
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Post by sadface on Aug 17, 2020 21:39:33 GMT 12
Wood is forgiving, just slot in some ply/glue/filler. clamp it & then trim back & sand when dry. A wood-rasp is always a handy tool. For small cutting/grinding tasks, a powered dremel can be a handy tool for metal or wood. Routers are handy, but big & cumbersome sometimes, unless you're set up with ample workspace for safety. You can get wee battery-powered 'trim routers' - I'm not that familiar with what's available, but the Ryobi one I used briefly was lightweight & easy to handle, but you'd have to make-up guides and/or 'fences' to make it really useful. That's exactly what I've done. I've used some bits of chiseled out ply to refill the hole and some parafix superglue and clamps. I'm now on my 4th tube of the glue keeping the ply back together.
Here's how it looks currently with a bit of wet glue, there was a few small gaps to plug so it will need another night before I can get back to wood working.
A cheap Ozito dremel I purchased 5 years back has been one of the most versatile tools in my arsenal. A 40 grit sanding drum was quite good for material removal when taking the last 0.5mm inside the socket.
The need for guides and fences with a router is why I chose not to use one. Chisel and filing etc was a lot of work but with significantly less margin for serious error and ultimately quite satisfying for all of the work that had to go in.
I do generally take any chance I can to use power tools but its nice to pull out the hand tools every now and then. I probably should have remembered my wood rasp, it was probably a better tool for the job than the dremel.
Such is my enjoyment of power tools that I keep an 18v high power impact wrench and some impact sockets in my car in case I see a tyre that needs changing. Sadly I'm normally in the right hand lane on the motorway when I see somebody on the side of the road.
I will admit to almost never using a screw driver if I can use my impact driver instead. After years of use, I still giggle inside like a school girl while rattling in a bolt or a screw.....
I've also been known to use a brushless reciprocating saw for tree pruning.
Thanks for the vote Colin, I also prefer the no bolts look.
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Post by colinf on Sept 15, 2020 19:13:43 GMT 12
Hi Sadface, how you doing with the build, all ok?
AMR-iFi R&D
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Post by sadface on Sept 15, 2020 20:22:29 GMT 12
Hi Colin,
I managed to purchase a house in this crazy market recently.
I didn't manage to finish up before the move.
Since the move I haven't fully unpacked my lab yet to get back to work on the electronics. I can see the box with my soldering iron in it. But I can't get to it yet....
All things going to plan I will have time to setup a workshop in the basement on the weekend and re-start the finishing work on the front panel.
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Post by colinf on Sept 16, 2020 18:58:57 GMT 12
Well done getting a house in these unusual times! I know the feeling with boxes with your gear in them. It took me about 6 months to get things set up here, and still refining things even now.
AMR-iFi R&D
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Post by sadface on Sept 28, 2020 20:38:53 GMT 12
G'day Guys,
A wee progress report.
I haven't quite gotten my lab setup yet but I decided I had to get some work going on this project. I managed to find my pick set so I took some time on the weekend to clean up the underside of the various pcbs for this amp.
I've developed a process that seems to work really well.
First I use my pick set to scratch and scrape off the flux residue around the joins and the little gobs that sometimes splatter around. It seems to chip or flake off. Followed by brushing away the dust and flakes with a small wire brush. Followed by a good wipe down with some iso-prop and some cotton buds.
This seems to result in nice clean pcbs with no crud on them.
Hopefully by the end of the week I should have my lab setup enough sling around some solder. Not much actually needs doing now: 1) solder up the relay board 2) wire the bugger up 3) finish the front panel.
I haven't yet braved the basement enough setup a work bench to sand and stain the front panel but its not too far off.
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