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Class D Switching Power Amplifiers and Power D/A conversion

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Old 17th May 2018, 04:41 PM   #591
matt_garman is offline matt_garman  United States
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Fasten seat belts.  TDA8932 pessimistic review.
Looks good!

Quote:
Originally Posted by abraxalito View Post
Any Kicad users know how to get the TDA8932 to show up in the 3D rendering? At present I'm calling up the SOICW-28 pin 3D model but nothing is showing.
If you look at the 3d images of my boards (above), you'll see mine are also missing the 3d model for the tda8932 IC. I haven't tried messing with it, though, I just chalked it up to a beta issue that will be worked out (I'm using the nightly builds). For me, the 3d models also aren't working (or are missing) for the screw terminals.

But anyway - I recommend doing a raytrace render for screenshot purposes. That's what gives that "photo realistic" look. It is time-consuming (a couple minutes or so on my fairly modern PC), but worth it IMO for pretty screenshots.

Edit: what regulator are you using for pin8? Is that a tl431 I see?

Last edited by matt_garman; 17th May 2018 at 04:47 PM. Reason: add question
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Old 17th May 2018, 06:49 PM   #592
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If nothing else this little bugger learned me how to build a linear voltage regulator. It is very sensitive for input ripple from an SMPSs. Now it sounds good.
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Old 18th May 2018, 02:03 AM   #593
abraxalito is online now abraxalito  United Kingdom
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Quote:
Originally Posted by matt_garman View Post
If you look at the 3d images of my boards (above), you'll see mine are also missing the 3d model for the tda8932 IC.
Do you mean the pics in post #572? Perhaps my eyes are playing tricks on me but I'm definitely seeing an IC in those. Seeing you'd got one was what made me think there's a solution to this somewhere, but perhaps its because you have a more up to date version of Kicad than me?

Quote:
But anyway - I recommend doing a raytrace render for screenshot purposes. That's what gives that "photo realistic" look. It is time-consuming (a couple minutes or so on my fairly modern PC), but worth it IMO for pretty screenshots.
Thanks for the tip, I shall look into that.

Quote:
Edit: what regulator are you using for pin8? Is that a tl431 I see?
Yes, using a TL431 to generate a stable reference voltage (about 14V) then (based on my experience with lingDAC's PSU) filtering that output rather heavily (two series RCs) to remove noise before sending the filtered output into a CFP as pass transistor.
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Old 18th May 2018, 02:58 AM   #594
matt_garman is offline matt_garman  United States
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Fasten seat belts.  TDA8932 pessimistic review.
Quote:
Originally Posted by abraxalito View Post
Do you mean the pics in post #572? Perhaps my eyes are playing tricks on me but I'm definitely seeing an IC in those. Seeing you'd got one was what made me think there's a solution to this somewhere, but perhaps its because you have a more up to date version of Kicad than me?
D'oh, I guess I did have a 3d image. I'm already working on a revision, and have since lost the 3d model.

Which version of KiCad are you using?

I'm using v5 beta (i.e. nightly builds). I'm also using the new libraries and footprints (pulled from GitHub).

The old v4 had an SOJ-32 footprint in the SMD_Packages library. This was an exact match for the TDA8932 footprint. Looks like that footprint has not been ported to the new footprints/libraries yet, see this post on the KiCad Forums.

I attached my little library of a few random things, but it also includes the SOJ-32 footprint from the old v4 libs.

I found a 3d model in the new libs that is a close match: Package_SO.3dshapes/TSOP-II-32_21.0x10.2mm_P1.27mm.wrl. You have to rotate it an scale it a bit (see screenshot), but it's close enough IMO.
Attached Images
File Type: jpg SOJ-32_3d_model.jpg (91.9 KB, 464 views)
Attached Files
File Type: zip lib-workpc.zip (9.2 KB, 3 views)
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Old 19th May 2018, 04:32 PM   #595
matt_garman is offline matt_garman  United States
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Fasten seat belts.  TDA8932 pessimistic review.
Stereo test is working great! I ran them for over an hour on the basement speakers, no issues. That gave me the confidence to try them on my office speakers. They sound pretty good to me - good enough that I think they deserve an actual case.

The only caveat so far is a bit of hiss with my ear close to the tweeter. It wasn't noticeable at all on the low-sensitivity basement speakers, but my office speakers are more sensitive (87dB). It's not noticeable at normal listening distances. I don't think I've had any amp that didn't exhibit this behavior to some degree, though. But there is something satisfying about a completely silent background (if you have to ask, "is it turned on?" I consider that a good thing!)

I'm definitely glad I implemented the gain reduction. In my office (10x11) with the 87dB speakers, they have plenty of volume with more headroom than I'll ever need. And that's with only 13.8v supply.

With regards to heat, so far there isn't any. I know this chip got hot on the tiny cheap boards with 24v (or more) supply. But with 4R speakers and 13.8v supply, the chips and inductors are tepid - that is, just a bit above room temp, but warm would be too strong of a word. (Temps measured with the always-accurate, infinitely-precise touch-my-finger-to-it technique. )

I'm using balanced inputs. But the amps play with the cold signal shorted to ground (with an expected reduction in volume). So these should work with single-ended inputs.

As mentioned above, pin31/OSCIO is not connected to anything. I'm running both amps as master, no sync between them. I can't hear any obvious aberrations, which is consistent with my experience with TI TPA31xx amps.

I did realize the silkscreen on the input side is mislabeled. It reads SLAVE|GND|SLP|GND|MUT|GND|POS|GND|NEG, but it should be: SLP|GND|MUT|GND|SLAVE|GND|POS|GND|NEG. (In other words, the signal inputs are correct, just the slave, mute, and sleep pins are messed up.)

Now that I know the design is working, I'm working on a revision that makes room for the "deliciously overkill" VER2923 inductors. I also expose pin31/OSCIO on the input terminal block, and make the slave setting a jumper. I used 1206-sized components where tight spacing wasn't necessary, just to make assembly a bit easier. And the terminals for DC power and speaker outputs got a bump in size (from 3.5mm pitch to 5.08mm pitch). A rendered image is attached.

So anyway - I have several spare boards, the offer stands - if anybody wants some, PM me, they are free if you pay shipping (or stop by if you're in the Chicago area!).
Attached Images
File Type: jpg stereo_test_20180519.jpg (178.8 KB, 447 views)
File Type: jpg tda8932_btl_ds_ref_raytrace-20180518_edit.jpg (304.1 KB, 435 views)
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Old 20th May 2018, 02:15 PM   #596
abraxalito is online now abraxalito  United Kingdom
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Quote:
Originally Posted by matt_garman View Post
Which version of KiCad are you using?
Still on the original one I downloaded, 4.0.7.

Quote:
The old v4 had an SOJ-32 footprint in the SMD_Packages library. This was an exact match for the TDA8932 footprint.
Thanks, I found that and it worked very nicely with 0.5X scale on Y and 0.6X on X, together with a 90o Z rotation. Then a 0.05" offset to get the correct position.

I played with different rendering options, couldn't see a ray tracing one so is that also a feature that's not present in 4.0.7 or have I just missed it?
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Old 20th May 2018, 04:45 PM   #597
matt_garman is offline matt_garman  United States
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Fasten seat belts.  TDA8932 pessimistic review.
Quote:
Originally Posted by abraxalito View Post
Still on the original one I downloaded, 4.0.7.
...
I played with different rendering options, couldn't see a ray tracing one so is that also a feature that's not present in 4.0.7 or have I just missed it?
Ah, I did a quick web search, it appears the raytrace feature was added to the nightly builds (i.e. v5 beta). I've been using the nightly builds for so long now it's hard to remember the differences between v5 and v4.


Quote:
Originally Posted by matt_garman View Post
The only caveat so far is a bit of hiss with my ear close to the tweeter. It wasn't noticeable at all on the low-sensitivity basement speakers, but my office speakers are more sensitive (87dB). It's not noticeable at normal listening distances.
So, after spending more time with this, the hiss is a bit louder than I'd like. It's generally not noticeable. But on quiet passages of some recordings (particularly older classical works), it becomes one of those things that once heard can't be "un-heard". But on more modern/"cleaner" recordings, it's really only noticeable on quiet passages with my ear a few inches from the tweeter. Thus, observation #1: it's at least somewhat recording-dependent.

Another thing I noticed is that it's dead-quiet when no music is playing. To me that says the noise is not from the amp itself, but from the source component. So observation #2: it's likely coming from the upstream device.

As I wrote that, I had a "duh" moment: why not try with a different DAC? Previously I had been using my tda1387 balanced out RPI HAT DAC. I swapped out that DAC with my Allo Boss (another RPI HAT DAC, though single-ended). No hiss!

It even passed the "Bolero" test. Ravel's Bolero is a great song to do testing on, since it starts out so quiet, and very slowly builds in volume (it's basically an extended quiet passage, conveniently right at the start of the track). It allows me to crank the volume to neighbors-call-the-cops levels, but without without actually souring relations with my neighbor.

In short: good news for this tda8932 design, bad news for my tda1387 DAC.

Even despite the hiss, I was wanting to say that this amp really seemed to have a "polished glass"-like detail to it. Now that the hiss is gone, I definitely feel that's the case. To my mediocre ears, it manages to be detailed but smooth at the same time. (Although, I'm missing the "organic character" of the tda1387 DAC, as the Allo Boss feels a bit analytical in comparison.)
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Old 17th June 2018, 11:53 PM   #598
matt_garman is offline matt_garman  United States
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Fasten seat belts.  TDA8932 pessimistic review.
Default The Pessimist v1.1.0

OK, after a day of work (pretty much eight hours of labor), I have my revision 1.1.0 boards built, put into a case, and playing sweet, sweet music!

Several people have emailed me about getting boards. I was holding off until this revision was validated. I will respond to you in the next day or two. If anyone else is interested in some "naked" PCBs, please let me know. Boards are free, you pay only shipping. I have both v1.0 (see previous posts) and v1.1 boards. There are some minor bugs with the v1.0 boards (listed above), but they are much cheaper to build. I've thus far only tested that the v1.1 boards play music, so there could be undiscovered bugs. But they are much more expensive to build, mostly due to the big Coilcraft VER2923 inductors.

The power supply is an Antek AS-1215 transformer (15V/100VA) paired with a Sigma11 PSU set to 14V output. The Sigma11 was recycled from a previous project. Case is from the diyAudio store, the Galaxy 2U, 230mm x 280mm.

Here's some "amp porn" for those of you who are into it (I know I am).
Attached Images
File Type: jpg pair_boards_overhead.jpg (564.8 KB, 344 views)
File Type: jpg pair_boards_overhead_front.jpg (542.0 KB, 333 views)
File Type: jpg board_detail_birdseye.jpg (573.9 KB, 124 views)
File Type: jpg in_case_all_birdseye.jpg (595.1 KB, 159 views)
File Type: jpg in_case_all_angle_view_1.jpg (610.2 KB, 151 views)
File Type: jpg in_case_all_angle_view_2.jpg (668.2 KB, 136 views)
File Type: jpg case_rear_panel.jpg (525.8 KB, 118 views)
File Type: jpg case_closed_3-4_view.jpg (392.0 KB, 102 views)
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Old 18th June 2018, 10:02 PM   #599
danielwritesbac is offline danielwritesbac  United States
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That looks wonderful!

I had a thought: If there were vent holes in the bottom of the enclosure, located directly underneath all 3 boards, then cool air would voluntarily blow against the bottom sides of the boards.
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Old 19th June 2018, 04:56 PM   #600
matt_garman is offline matt_garman  United States
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Fasten seat belts.  TDA8932 pessimistic review.
Default v1.1.0 Board Info

See post #585 above for v1.0.1 files (schematic, gerbers, KiCad, BOM). A quick recap of known bugs/issues with this version:
  • pin31/OSCIO is not connected to anything. If you want to sync two amps, you'll have to manually solder directly to the chip pin. (Note: I'm running both amps as master, no sync between them. I can't hear any obvious aberrations, which is consistent with my experience with TI TPA31xx amps. YMMV.)
  • The silkscreen on the input side is mislabeled. It reads SLAVE|GND|SLP|GND|MUT|GND|POS|GND|NEG, but it should be: SLP|GND|MUT|GND|SLAVE|GND|POS|GND|NEG. (In other words, the signal inputs are correct, just the slave, mute, and sleep pins are messed up.)
Also, I originally suggested Coilcraft RFS1113 inductors, but I actually changed to RFS1412: they fit the footprint perfectly (13mm diameter, 7mm lead spacing), have a bit better specs, and aren't much more expensive.

---------------

Now I'll switch gears and talk about the newer revision, v1.1.0. This is a minor update to the previous version. See post #598 above for pictures of my completed amp build using this board. Changes from previous version:
  • Use of Coilcraft VER2923 inductors. These are big and expensive, but should alleviate worries of inductor-limited performance.
  • The previous version used strictly 805-sized SMD components; this revision uses a mix of 805 and 1206. I tried to use 1206 when it wasn't necessary to get super close to the tda8932 chip.
  • Fixes input label silkscreen.
  • Slave setting is now a jumper.
  • Pin31/OSCIO is now exposed on the input terminals.
  • Use bigger (5mm pitch) terminals for speaker output and DC power in.
  • Slightly bigger board, bigger top-layer ground pour (should help with thermals).
  • Could be new, yet-undiscovered bugs.

Note1: the attached BOM file is a zip archive that contains two CSV files (one for each PCB revision), and a single ODS file that has both BOMs on separate sheets. Make sure you're looking at the right sheet! I also have Mouser projects saved for these BOMs, PM me and I can send you the link.

Note2: I'm using the KiCad nightly builds (aka v5.0 beta). You'll need a similarly new version and the latest (non-legacy) libraries and footprints to use these files.

---------------

Lastly, a word on the output filter. Class-D amplifiers (such as the tda8932, TI tpa311x), as switching amplifiers, generate noise on the output signal. This noise is well above the audio band, so in theory your speakers should filter the noise. However, having this high-frequency noise on your speaker wires can cause EMI to nearby devices. So most designs call for an RLC filter to remove this noise. The "R" is your speaker; the LC are typically on the board itself.

I recommend reading this primer on class-D output filters: EE Times: Understanding output filters for Class-D amplifiers, John Widder and Yun Tao Zhao, STMicroelectronics, Jan 9, 2008. This topic has been discussed many times here on diyAudio. Here is one short but sweet thread: Some rambling calculation on TPA3116/8 filters. Lastly, this website has useful online RLC calculators.

My design is based on the datasheet reference schematic, Fig 39, page 40. The output filter components are "Llc" and "Clc" in that schematic. On my boards (both revisions), these components are L1, L2, C8, C12. Also in the datasheet, Table 14 on page 24 gives L and C values for common speaker impedances. I included this table on the PCB silkscreen.
Attached Images
File Type: jpg tda8932_btl_ds_ref_v1.1.0_bare_board_bottom.jpg (481.9 KB, 91 views)
File Type: jpg tda8932_btl_ds_ref_v1.1.0_bare_board_top.jpg (551.3 KB, 98 views)
Attached Files
File Type: zip tda8932_btl_ds_ref_v1.1.0_gerber.zip (85.5 KB, 13 views)
File Type: zip tda8932_btl_ds_ref_v1.1.0_kicad.zip (126.0 KB, 13 views)
File Type: zip tda8932_btl_ds_ref_v1.x_BOM.zip (19.4 KB, 21 views)
File Type: pdf tda8932_btl_ds_ref_v1.1.0_schem.pdf (67.5 KB, 35 views)
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