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Class D Switching Power Amplifiers and Power D/A conversion

My 1st Class-D Amp -TPA3255 with PFFB
My 1st Class-D Amp -TPA3255 with PFFB
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Old 25th February 2017, 12:43 PM   #1
JohnnyInBris is offline JohnnyInBris  Australia
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Default My 1st Class-D Amp -TPA3255 with PFFB

I hadn't looked at Class-D for a couple of decades and I was surprised at the performance levels now being achieved. This prompted me to have a go at building my own. After much reading I decided on the TPA3255 with post filter feedback in stereo BTL configuration.

The power supply is a 400W 48V LED supply out of china turned down to 45V. I chose this one because it has a thermostatically controlled fan which doesn't kick in at normal listening levels. The minimal heatsink gets warm to the touch at ear shattering levels from my Klipsch floor standers.

I'm still looking for a suitable enclosure but in the meantime I've breadboarded it on some acrylic.

The inputs are balanced but my DAC isn't so I'm using balanced to unbalanced cables.

The chokes I wound myself using 15 turns of 2 x 1mm stands on sendust cores. with AL=51nH/T. These barely get warm.

I'm still waiting on some 48V to 15V DC-DC modules so in the mean time I've fitted a 7815 with a couple of 100R/1W droppers.

How does it sound? Well I don't have golden ears but it's on par with a tube hybrid that I have except that the bass seems tighter and it has a very neutral and uncoloured sound. Despite the single power supply, imaging is also very good. And it is so quiet.

Gerbers for the PCB are available if anybody wants them. How did I load this board? rather crudely! I apply solder to all the SMT pads using my iron and then dip each component in rework flux before reflowing them into place using a hot air tool.
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Old 25th February 2017, 03:23 PM   #2
theAnonymous1 is offline theAnonymous1  United States
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Nice work!

I think it's recommended to ground the negative input right on the board for single-ended use. If you're not having any noise issues doing it the way you are now, then I guess it doesn't matter though.
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Old 25th February 2017, 09:59 PM   #3
impuls60 is offline impuls60  Norway
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Wow! I want to try out this chip so bad!! A couple of years ago I started on a huge amp build for 2x tpa5630 cards only to find the sound quality lacking in those. So I never bothered to finish it. So now I am waiting for the 3255 to go mainstream, so I can finish my dream amp. I don't understand why this chip hasn't generated more of a buzz on this forum! Everyone that has built one says it sounds really good, and getting a usable 48V psu doesn't cost that much either. I've built and bought several tpa3116 amps but this is the next big thing!! Let'ss jump on the 3255 wagon instead
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Old 26th February 2017, 11:16 AM   #4
mikey_audiogeek is offline mikey_audiogeek  New Zealand
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Kudos!
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Old 26th February 2017, 06:47 PM   #5
matt_garman is offline matt_garman  United States
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My 1st Class-D Amp -TPA3255 with PFFB
+1 to all the positive comments. That looks great, thank you for posting!

Random question - looks like your PCB has space for a big capacitor (next to the heatsink), but it's not there. I assume that was left off intentionally?
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Old 26th February 2017, 09:03 PM   #6
JohnnyInBris is offline JohnnyInBris  Australia
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Yes there is provision for a larger bulk cap. I added that in case there was issues with the power supply due to high power low frequency signals but looks like it's not needed.
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Old 26th February 2017, 10:00 PM   #7
doctormord is offline doctormord  Germany
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May you do a "THD vs. Amplitude" measurement for the output but in SE manner?

Like
Channel-A <-> GND
Channel-B <-> GND
Channel-A - Channel-B

Where Channel-A + Channel-B are one BTL output.
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Old 26th February 2017, 11:02 PM   #8
JohnnyInBris is offline JohnnyInBris  Australia
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Yes, I am planning to do some THD measurements. My oscilloscope doesn't have the resolution needed but I will soon be getting a USB audio interface with the following spec for line input:

Dynamic Range 106 dB (A-weighted)
Frequency Response 20 Hz to 20 kHz, 0.1 dB
THD+N <0.003% (minimum gain, -1dBFS input with 22 Hz/22 kHz bandpass filter)
Maximum Input Level+22 dBu
Gain Range 50 dB
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Old 6th March 2017, 10:48 AM   #9
mantabernd is offline mantabernd  Germany
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Nice work!
I also collected some experiences with TPA3255 in PFF configuration.

I posted my info here: http://www.diyaudio.com/forums/class...ication-6.html

Now I wanted to ask you... Do you have problems with your PFF snubber (1uF + 3.0 Ohms) when there is no load connected?

In my design this snubber dissipates a lot of power and sometimes even dies if amp
clips without load. I need to replace the R then... But I'm actually using 1.33uF + 3.3 Ohms so corner frequency is a bit lower in my design.

Did you try this?

Thanks and regards
Bernhard
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Old 6th March 2017, 10:01 PM   #10
JohnnyInBris is offline JohnnyInBris  Australia
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I haven't seen any issues with the snubber but I'll have a closer look next week as I'm currently away on business.
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