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Class D Switching Power Amplifiers and Power D/A conversion

Ideas/advice TPA3255 project
Ideas/advice TPA3255 project
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Old 24th March 2020, 08:49 AM   #11
ElliJ is offline ElliJ
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Not sure when I will get the case for my amp with this Coronavirus crisis. I got hold of some hookup wire and re-wired the amp. I’m still not please with the potentiometer, there are some very good smd type ones out there but at least mine sound ok. I was struggling to solder to the RCA sockets and speaker terminals even with new lead solder, I need some practice.

Can I insert pictures from my phone on this forum?
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Old 24th March 2020, 09:33 AM   #12
Turbowatch2 is online now Turbowatch2  Germany
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The potīs connections are pictured at the shops page. It is no "Pot", but a switched resistor with 21 positions. If you have wired it as shown (in=3, out=2, ground=1) it might be normal to have some minor signal in the last switching position. Maybe check again?

It is a good idea to ground such a potīs case if it is not screwed to a grounded metal case. This way you prevent it from humming when you touch it.
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Old 24th March 2020, 10:06 AM   #13
ElliJ is offline ElliJ
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I have wired it correctly, checked yesterday when I re-wired the amp. I don’t have a case but I mounted everything to a length of aluminium bent up at each end, it is like a case without sides and top. There is no humming coming from the amp when touched or during use. The amp is very sensitive and I only have one source clean enough to play my music. I have ordered an iBasso DX160 to use as source. I could have got a DAC instead but the DX160 will do so much more as it can stream, store, be a usb DAC and it is portable.
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Old 26th March 2020, 07:58 PM   #14
ElliJ is offline ElliJ
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My iBasso DX160 arrived today �� It sounds awesome, the detail, clarity and its really clean with no distortion. Both streaming through the DAP and when in USB DAC mode it sounds perfect. I can’t wait to get my 48v smps, but I am impressed with what 24v can do. I only have a pair of Mordaunt Short Aviano 1 speakers so they won’t take that much more power. I found out the wire I used was 2T (I think) spec which has a high tin content used on aircraft, not pure copper or silver so that will upset all the audiophiles out there. When I get a better switched resistor or pot I might stick some copper wire in there. My soldering is not the greatest yet so I might get some help from a pro for the next re-wire. I should post some pics (if I can work out how). I’m working my way through the Amazon Music new music playlist atm so I will get back to that.
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Old 26th March 2020, 08:18 PM   #15
ElliJ is offline ElliJ
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I hope this image uploads. The aluminium that I have mounted everything in represents the case I am waiting for and measures 145x200x82mm. I don’t like the gland for the power lead and will work out something else for the proper case. I did not install the power switch or the additional panel mounted fuse in this build. I plan to put a wooden front on the proper case, something like Zebrano with some laser etching.
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Old 27th March 2020, 03:23 AM   #16
e_fortier is offline e_fortier  Canada
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Ideas/advice TPA3255 project
Suggestion; Reroute your black/yellow wires connected from your volume to the amplifier input, they are passing right above AC mains and are not shielded. You have a better chance of having a less noisy amp if these black/yellow are moved away from mains. Just moved them on the other side of your power supply.

BR
Eric
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Old 27th March 2020, 05:56 AM   #17
Rick PA Stadel is offline Rick PA Stadel  United States
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Or, cannibalize an old stereo cable with RCA's -- you probably have one lying around somewhere, forgotten about when one of the connectors became intermittent -- makes excellent shielded interconnect.

As long as you have the input connectors on the opposite end from the volume control, then another nearly chassis-length run back to the amp inputs, it really should be shielded. Even if you didn't have a switching power supply in the same box, shielded would be considered 'standard practice'.

As to your 'soldering skill' -- how big is your iron? Those are some honking-serious output jacks and they'll take a lot of heat. A better bet would be a 100 Watt gun. Otherwise, there's only one place you can solder a stranded 16 gauge tinned-copper wire to it: Right at the end of the hole where the brass is thinnest. Make a sharp hook in the wire, hook it in that hole, and put a slight bit of tension on it with a paperweight or hand tool. Then make firm contact with the iron on that spot to transfer heat before feeding in the solder.

It may not be 'your skill' at all.

Cheers
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Old 27th March 2020, 06:55 AM   #18
ElliJ is offline ElliJ
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All suggestions have been noted. I think the yellow and black wires are a tiny bit too short to be routed the other way round the power supply but I will try. Is shielded wire with the braided wire on the outside and doesn’t the shielding need to be grounded to work? All the cable runs are very short, I think that helps to stop interference. When I move the amp to its proper case I can change the routing slightly and will need to re-wire the speaker terminals ( solder where the metal is thinnest (great tip thanks )). I haven’t noticed any interference but will try to route those wires differently. Thanks for the advice Fortier and Rick.
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