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Modulus-686: 380W (4Ω); 220W (8Ω) Balanced Composite Power Amp with extremely low THD
Modulus-686: 380W (4Ω); 220W (8Ω) Balanced Composite Power Amp with extremely low THD
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Old 19th May 2019, 04:54 AM   #1091
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by Mark Johnson View Post
That particular transformer, and I suspect, all instances of that same part number transformer from Antek, has got plenty of loss at the secondary resonant frequency. [...] But as-is, it seems to be plenty damped all by itself.
That could be. Thankfully, one of the transformers in my arsenal wasn't one of the self-damped ones. It's a 2x35 VAC, 530 VA toroid. Quite good quality. It came from RS Components some 20+ years ago. P/N: 177-945.

I hooked it up to a Power-86 and tried the three snubber combinations:
  1. NO snubber
  2. CRC: 10 nF || 10 Ω + 150 nF (Mark's)
  3. RC: 10 Ω + 100 nF (Rod's)

Results:
  1. Some ringing without snubber. The ringing dies pretty quickly. I'm not overly concerned by it, but also don't see any harm in removing the ringing.
  2. CRC snubber: Dampens out the ringing nicely. Lowers the flyback amplitude dramatically. I could reduce R if I wanted a tighter response, but it looks good as-is.
  3. RC snubber: Same as for CRC snubber.

My method takes place in situ, with the mains impedance reflected by the transformer, requires only an RC highpass filter (1 kΩ, 10 nF) and an oscilloscope, and requires only two snubber components.

You're right that the components are only 20 cents each, so it's not a lot of money. Still, using three components where two will do the job just as well is just not my cup of tea. Each to their own.

You're certainly free to keep arguing. I'll keep reading. At this point, though, I think I have enough data that I should focus on getting it onto my website (Snubber page) and into the design documentation for the Power-86 and Power-686. :micdrop:

Tom
Attached Images
File Type: png PWR86_RS_NOsnubber_Annotated.png (28.5 KB, 203 views)
File Type: png PWR86_RS_10nF_10R150nF_Annotated.png (27.3 KB, 202 views)
File Type: png PWR86_RS_10R100nF_Annotated.png (44.2 KB, 202 views)
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Modulus-86, 186, 286, 286 Kit, & 686: 40-240W (8Ω) at <-120dB THD. HP-1: 3W/20Ω, -130dB THD, 128dB DNR.
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Last edited by tomchr; 19th May 2019 at 04:58 AM.
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Old 19th May 2019, 05:59 AM   #1092
SyncTronX is offline SyncTronX  United States
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I have a solution, I've included the logo that MJ can use on his avatar While he might tPiss people off, he means well, I think. Just like the image of the guy I posted here. Why don't we just call him DIY dad and be done with it.

Cheers,
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Old 19th May 2019, 07:21 AM   #1093
tomchr is offline tomchr  Canada
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This time with corrected image text.

As far as the discussion goes: I agree wholeheartedly with BrianL's comments from earlier. That said, it was insightful for me to take a second look at snubbers. I now have more than enough scope shots to put a good page together on the topic. Life is good.

Tom
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File Type: png PWR86_RS_NOsnubber_Annotated.png (43.8 KB, 200 views)
File Type: png PWR86_RS_10nF_10R150nF_Annotated.png (27.3 KB, 28 views)
File Type: png PWR86_RS_10R100nF_Annotated.png (43.5 KB, 31 views)
__________________
Modulus-86, 186, 286, 286 Kit, & 686: 40-240W (8Ω) at <-120dB THD. HP-1: 3W/20Ω, -130dB THD, 128dB DNR.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right

Last edited by tomchr; 19th May 2019 at 07:25 AM.
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Old 19th May 2019, 01:34 PM   #1094
Mark Johnson is online now Mark Johnson  United States
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Modulus-686: 380W (4&#937;); 220W (8&#937;) Balanced Composite Power Amp with extremely low THD
Hi Tom, I'm actually agreeing with you, not arguing.

Your data from the Antek AN5225 transformer shows
Some (Transformer + Rectifier) Combinations Don't Ring At All; they don't need a snubber
I believe you conclude that: no ringing means no need for a snubber. I completely agree.

Also congratulations for measuring another transformer to see whether it also has the property above. Many, many do not. In particular, we don't yet know whether a 500VA transformer made by Toroidy instead of Antek, exhibits enough self-damping to not need a snubber. I've never measured a Toroidy myself, but I have measured toroidal transformers by Triad, Avel-Lindberg, and Antek. They all rang differently in my testing, FWIW.

Since diyAudio members just love the shiny stainless steel Faraday cages that Toroidy installs over their transformers, it's only a matter of time until somebody pairs a Toroidy with your PSU and asks, snubber or no snubber? I understand that European DIYers pay huge shipping fees when buying from Antek, but much lower shipping fees when buying from Toroidy (in Poland). So it's natural and expected that European buyers of your PSU, probably will buy a Toroidy transformer too.

In situations where the transformer+rectifier does in fact ring, it can be damped with a 2-element snubber (1R+1C) or with a 3-element snubber (1R+2C). One way to size these components is to build the complete PSU, attach a high wattage dummy load, connect the snubber-under-test, turn on the mains power, and measure with an oscilloscope. Which is the approach you took, and it was successful.

Another way is to use a battery powered test jig like the one shown below ("Cheapomodo"), to stimulate the transformer in isolation: connected to nothing else. The complete PSU need not be assembled yet, mains power is not applied, high wattage dummy loads are not required. This even works for 2-element snubbers (1R+1C) although it requires you to know the zero bias capacitance of your rectifier diodes. QM Figure 14 (pages 12-13) shows how.

Don't let the length of this message distract from my main theme, which is: congratulations.

Mark Johnson

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File Type: jpg vero_cheapo_modo.JPG (300.1 KB, 67 views)

Last edited by Mark Johnson; 19th May 2019 at 01:39 PM.
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Old 22nd May 2019, 01:12 PM   #1095
TioFrancotirador is offline TioFrancotirador  Poland
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Tom,

I thought it might be good idea for you to consider following SMPS supplier for 686 builds.
HDPLEX 400W AC-DC Internal Adapter with PFC

I had couple of items from them. They are very robust, reliable and compact designs. One of the things things HDPLEX specializes in are low noise SMPS for Audio PC. I thought you may want consider them to build 28V or 36V version as alternative to connex and meanwell. Just a thought ...

Last edited by TioFrancotirador; 22nd May 2019 at 01:17 PM.
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Old 23rd May 2019, 04:39 AM   #1096
tomchr is offline tomchr  Canada
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Interesting power supply. It seems optimized for use in PCs, though. One could toss them an email to enquire about audio supplies...

I find it interesting that the supply comes with an IEC320-C8 harness (shaver plug) in addition to the more commonly used IEC320-C14 (D shaped connector). There's no mention of the isolation level between primary and secondary. I'd definitely ask about that should I contact them.

Tom
__________________
Modulus-86, 186, 286, 286 Kit, & 686: 40-240W (8Ω) at <-120dB THD. HP-1: 3W/20Ω, -130dB THD, 128dB DNR.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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