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Class D Switching Power Amplifiers and Power D/A conversion

TI TPA3255EVM
TI TPA3255EVM
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Old 28th June 2018, 08:16 AM   #791
abraxalito is offline abraxalito  United Kingdom
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Quote:
Originally Posted by linuxfan View Post
Thanks irribeo. But I don't know how to interpret this information - adding a cap multiplier to a Connex is a good idea?
What he's saying is if you're worried about capacitance on the output of your switcher you'd better be more worried by a direct connection to your EVM than going via a cap multiplier. Conclusion - a capx is the solution to your problem.

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Since I have a cap multiplier already on hand, maybe I will just try it. My only measure of success will be if I hear a better or worse sound.
Can't beat experiment
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Old 28th June 2018, 09:11 AM   #792
linuxfan is offline linuxfan  Australia
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Thanks.
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Old 28th June 2018, 12:18 PM   #793
mboxler is offline mboxler  United States
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Quote:
Originally Posted by 2wice View Post
Thanks, I've changed it back to default 2XBTL to see if all is OK.
I'll swop around and take some pics.
Instead of re-soldering J24 and J25 tabs if it would be possible to replace with a high current switches???

I would think going back and forth between BTL and SE would be a pain.
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Old 28th June 2018, 12:19 PM   #794
2wice is online now 2wice  South Africa
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Bit of a pain yes, but less painful than no music at all.
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Old 28th June 2018, 12:51 PM   #795
mboxler is offline mboxler  United States
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Old 28th June 2018, 01:04 PM   #796
doctormord is offline doctormord  Germany
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Using 2.1 BTL + 2 SE needs 3 input signals from your DAC. If you get same signal on both SE channels, then you missed pulling the jumper that connects both opamps for C+D.
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Old 28th June 2018, 05:21 PM   #797
DPH is offline DPH  United States
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^ specifically speaking, that is the "diff" input setting on C+D (J19), which sends each respective RCA input to that amplifier channel. If that's set to SE, then you'd have the inverted (C) and twice inverted (D) input from the C-channel input jack being sent to the amps.
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Old 28th June 2018, 05:57 PM   #798
doctormord is offline doctormord  Germany
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Bit confusing.
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Old 2nd July 2018, 03:10 AM   #799
psemeraro is offline psemeraro  United States
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Finally wired up the TPA3255EVM today, using the lab supply (30v/5A x 2) in series mode. With the module in 2 channel mode quick measurements show that DC offset at speaker terminals tracks the power supply voltage. Lowest offset of 0mv +/- a few tenths of a milli-volt were at at 48.7 volts supply. Current draw at idle and low volume seems to be about .2 amps at 48.7 volts supply. Always check your offset at the speaker terminals but the module seems to be optimized for a 48 volt supply.

The lab power supply is linear (large toroid) and regulated and always sounds good on amplifiers dues to low specified noise and ripple. As a further step I'm passing the output through a 50uh choke with 10,000uf Sikorel pre choke and 100uf of film caps post choke, and there's STILL an audible improvement using another film cap right at the board where the power connects. This board is fairly responsive to how quickly it receives current, with a notably clearer sound, and deeper soundstage with film caps right at the power terminals.

First impressions are that the amp sounds really good. I don't like that there are two stages of coupling caps in the input path and suspect that bypassing them with Clarity MR or similar will open up the sound even more.
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Old 5th July 2018, 01:50 PM   #800
rhing is offline rhing  United States
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Quote:
Originally Posted by sharpi31 View Post
I have the TPA3255EVM board and have been following this thread with interest. Iím pretty set on removing C17, C28, C55 & C63 and connecting two Lundahl LL1521 input transformers (like LL1540 but with a small step up). All opamps out the circuit, and no coupling caps. I did similar mods with a couple of TPA3116 boards and preferred the change. Hoping to find an hour or two over the next week or so to get it done
sharpi31,

Have you had a chance to wire the Lundahl input transformers directly to the TPA3255 inputs (bypassing the SMD electrolytic input caps and TI NE5532 op amps)?

Changing subjects, DizRotus lent me his Pono Player portable digital audio player, and I used his 3.5mm TRS-to-RCA balanced cables to directly connect the player in balanced output mode to the amp's differential inputs (jumpers switched from SE to DIF). The sound quality was very impressive and easily bested the combination of my Audio Research LS7 tube line stage with either my Sony ES DVD/SACD/CD player or the Pono Player in single-ended output mode. I still found my turntable feeding the Audio Research PH5 tube phono stage and LS7 line stage to be the best sounding source, but the gap between the Pono Player playing high res digital and my vinyl playback system was not that great.

The late Charles Hansen of Ayre Acoustics designed the Pono Player's playback circuitry and he really favored balanced circuits. The rich tone, articulation and huge soundstage that comes from the diminutive Pono Player feeding the TPA3255EVM's differential inputs really highlights what high-end performance is possible with the TPA3255.
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