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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 8th July 2018, 04:46 AM   #531
daansan is offline daansan
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Quote:
Originally Posted by tomchr View Post
You should see 230 V from pin 1 to pin 4 on the output connector. If the relay clicks and you don't see 230 V there, you probably have a measurement error.

I've noticed that some terminal blocks have the screws floating, so if you measure by touching the head of the screws, you'll see 0 V.

Have you tried connecting a known good load, such as an incandescent lightbulb to the output of the ISS (pin 1, 4)?

Tom
Ill measure pin 1 and 4 today and will also try connecting a light bulb.

The 4 pin output connector reads:
Pin 1: ac
Pin 2 and 3: 0
Pin 4: ac

So i was under the impression i should be able to find 230v on pins 1&2 and 3&4, so i guess that is incorrect?

As i have 4 SMPSs to connect, do all 4 have to go to pin 1 and 4?

Thanks
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Old 8th July 2018, 03:59 PM   #532
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by daansan View Post
The 4 pin output connector reads:
Pin 1: ac
Pin 2 and 3: 0
Pin 4: ac
That's exactly what you want in a 230 V system.

Quote:
Originally Posted by daansan View Post
So i was under the impression i should be able to find 230v on pins 1&2 and 3&4, so i guess that is incorrect?
For 230 V operation, you'll find the AC mains on pins 1 and 4. For 120 V operation, you'll find the mains at pins 1-2 and 3-4. Recall, the 4-pin output connector is intended for connecting to a power transformer with two primary windings which need to be in parallel for 120 V operation and in series for 230 V operation.

Quote:
Originally Posted by daansan View Post
As i have 4 SMPSs to connect, do all 4 have to go to pin 1 and 4?
Correct. That will work on all mains voltages.

Sounds like I should expand the documentation a bit regarding how to connect the board. Thanks for mentioning this.

Tom
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Modulus-686: 240W/8Ω @ <0.00025% THD. Modulus-86: 40W/8Ω @ 0.000054% THD. DG300B & Other Tube Circuits.
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Old 8th July 2018, 08:26 PM   #533
daansan is offline daansan
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Tom,

Hope you dont mind me asking a few more questions.

Do you know of any decent in-chassis power strips/deviders that provide a decent solution to split the ac mains coming from the iss into 4 different ac leads for my smpss?

I can think of many solutions, like:
- daisy chaining the smpss and connecting the last one to the iss
- using wago 222 devices
- using barrier strip with jumper wire

But none of those sound like decent to me. I almost thought i would need to create a small pcb with some faston connectors for this, but i cannot imagine no good solution exists for this purpose. However i cannot find it.

Also, i seem to be really unable to attach the megafit connectors to my speakerwire. It was a longshot as the speakerwire was too thick (5.3 mm2), but even with soldering on the crimp terminal it would not go in to the connector, got stuck at the last mm or so.

So now i am thinking of the following:
- mod686 to guardian686: using molex precrimped leads
- guardian686 to my terminals: use my speaker cable attached to the terminal on the guardian686

It is a bit of a bummer to not be able to use my kinber 8tc between the mod686 and guardian 686 but the megafit connectors seem unforgiving.

The iss works by the way, perfect!
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Old 8th July 2018, 10:02 PM   #534
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by daansan View Post
Do you know of any decent in-chassis power strips/deviders that provide a decent solution to split the ac mains coming from the iss into 4 different ac leads for my smpss?
The Mean Well SMPSes use JST connectors. You can get the matching female housings and pre-crimped leads at Digikey. Just google the part number mentioned in the Mean Well data sheet. I'd go that route. If you can get all four wires into the terminal blocks on the ISS, that's probably the best way to go. Alternatively, a barrier block or "euro terminals" (Mouser P/N 571-1776296-4 for example) would work. I'm not a fan of the Wago devices.
You can also daisy chain the supplies in groups of two and put two wires into the terminal blocks of the ISS.

Quote:
Originally Posted by daansan View Post
But none of those sound like decent to me. I almost thought i would need to create a small pcb with some faston connectors for this, but i cannot imagine no good solution exists for this purpose.
That seems overkill. I'm also not a fan of faston/QC connectors. They're great if you have the right tools and never need to disconnect them. For DIY stuff I much prefer connectors with a lower insertion/removal force. If I was to make a PCB, I'd stick with the JST connectors and use pre-crimped leads.

Quote:
Originally Posted by daansan View Post
So now i am thinking of the following:
- mod686 to guardian686: using molex precrimped leads
- guardian686 to my terminals: use my speaker cable attached to the terminal on the guardian686
Sounds good to me.

Quote:
Originally Posted by daansan View Post
It is a bit of a bummer to not be able to use my kinber 8tc between the mod686 and guardian 686 but the megafit connectors seem unforgiving.
Even if you could make it fit, you'd have had issues with the bending radius on the heavy gauge cable. For the 15-20 cm of wire inside the chassis, there's really no reason to use a super heavy gauge wire. The AWG12 or AWG16 pre-crimped MegaFit leads are fine.

Quote:
Originally Posted by daansan View Post
The iss works by the way, perfect!
Awesome!

Tom
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Modulus-686: 240W/8Ω @ <0.00025% THD. Modulus-86: 40W/8Ω @ 0.000054% THD. DG300B & Other Tube Circuits.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 12th July 2018, 10:27 PM   #535
Mark Johnson is offline Mark Johnson  United States
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Modulus-686: 380W (4&#937;); 220W (8&#937;) Balanced Composite Power Amp with extremely low THD
Tom, congratulations on your Power-686. Also congratulations on your change of heart about providing CRC snubbers for the transformer secondaries.

I think you and your customers will quickly discover that there is not a huge amount of unit-to-unit variability in transformer secondary leakage inductance, even though this is not a measured specification on the transformer datasheet. Thus all customers who optimize a CRC snubber for Antek transformer # ABCDE, will get almost identical results (on their Cheapomodo tester).

So, if you feel like it, you can maintain a two column list which shows customer-measured optimum snubbers. Column1 is transformer make+model, Column2 is optimum snubber for that transformer. It might save people a couple hours of lab work. More importantly, it might allow builders to order CRC components even before their transformer is delivered, secure in the knowledge that another Power-686 customer has determined the optimum component values. Call it a transformer database for that up-to-date feeling.

If you're interested in viewing the before-and-after-snubbing performance, I've discovered that a battery powered, handheld oscilloscope is just the perfect tool for the job. Look at the God-awful kludge Bob Cordell had to perform (Figure 16.10 in his book) to get something halfway useful with a conventional grounded scope. Whereas with a battery powered scope, the entire instrument is floating, independent of "ground", and you can perform differential measurements with ease. So the waveform you actually want to see (across the two AC inputs to the bridge rectifier) is easily probed even though neither of the two nodes is "ground". Word to the wise: get a scope whose bandwidth is at least 10 MHz, not because you need this high bandwidth to see snubbers in action (you don't), but instead because you need very high performance scope triggering. They don't build great triggering circuitry in low bandwidth handheld scopes.

Couple years ago I published an article in Linear Audio volume 10 (here is a link) whose Appendix contains a circuit analysis of transformer + CRC snubber behavior using Laplace Transforms and such. It derives a rule of thumb for CRC capacitor selection, as a function of the desired damping factor zeta (zeta=0.5/Q).

BTW I still have a small number of fully assembled & tested RingNot power supply boards, which include discrete diodes and CRC snubbers. It's function compatible to the Power-86 (little brother of Power-686), both are designed to drive two LM3886 chipamp boards. $50 for the stuffed, soldered, and tested board, which compares favorably to the price of bare PCBs for chipamp PSUs.

~
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Old 13th July 2018, 01:11 AM   #536
tomchr is offline tomchr  Canada
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I haven't had a change of heart, actually. I still don't see any need for snubbers beyond the simple capacitor, which works with all transformers. But I do realize that some builders do see a need for fancier snubbers. I chose to add the two footprints necessary and optimize the routing so that I could cater to those builders as well.

You are correct that the CRC snubber will need to be optimized for the specific transformer and secondary wiring. Thus, I leave the optimization of the CRC snubber as an exercise for the advanced builders.

Tom
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Modulus-686: 240W/8Ω @ <0.00025% THD. Modulus-86: 40W/8Ω @ 0.000054% THD. DG300B & Other Tube Circuits.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 13th July 2018, 08:31 PM   #537
tomchr is offline tomchr  Canada
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The Guardian-686 is taking shape.

Tom
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File Type: png Screen Shot 2018-07-13 at 2.29.18 PM.png (67.6 KB, 209 views)
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Modulus-686: 240W/8Ω @ <0.00025% THD. Modulus-86: 40W/8Ω @ 0.000054% THD. DG300B & Other Tube Circuits.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 15th July 2018, 08:33 AM   #538
TioFrancotirador is offline TioFrancotirador  Poland
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Tom,
I have mod86. Willing to get mod286, but cannot wait that long , so I want to get mod686. The only concern I have is heat dissipation and power consumption.
For my daily normal use the heatsinks of my mod86 are warm.
Assuming I will replace mod86 with mod686 and keep same listening conditions (use same speakers, same listening levels) then, should I also expected the total heat generated from mod686 to be the same as from mod86? (heat will be balanced across 6 lm3886(mod686) instead of cumulated on one lm3886(mod86))?
Should I also assume that the power consumption for same listening conditions will be also the same (or almost the same), so that I can resue trafo (300VA) and caps 2x22000uF from my mod86 build?

Last edited by TioFrancotirador; 15th July 2018 at 08:49 AM.
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Old 15th July 2018, 09:25 PM   #539
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by TioFrancotirador View Post
I want to get mod686. The only concern I have is heat dissipation and power consumption.
For my daily normal use the heatsinks of my mod86 are warm.
Assuming I will replace mod86 with mod686 and keep same listening conditions (use same speakers, same listening levels) then, should I also expected the total heat generated from mod686 to be the same as from mod86? (heat will be balanced across 6 lm3886(mod686) instead of cumulated on one lm3886(mod86))?
You'll get six times the idle dissipation, so on 30 V rails, you'll get ~18-20 W instead of 3ish W per channel. If you leave your MOD86 amp on at idle (no music) for a few hours and the heat sinks are more than 2-3 C warmer than the room, I'd get larger heat sinks for the MOD686.

Quote:
Originally Posted by TioFrancotirador View Post
Should I also assume that the power consumption for same listening conditions will be also the same (or almost the same), so that I can resue trafo (300VA) and caps 2x22000uF from my mod86 build?
I'm assuming 2x22 VAC @ 300 VA here. That's a wee bit underpowered if you intend to run the amp to clipping. If you're not changing your listening level by much, the 300 VA and 2x22000 uF will probably be OK.

Tom
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Modulus-686: 240W/8Ω @ <0.00025% THD. Modulus-86: 40W/8Ω @ 0.000054% THD. DG300B & Other Tube Circuits.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 15th July 2018, 09:27 PM   #540
tomchr is offline tomchr  Canada
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The Guardian-686 is now up for pre-order: Guardian-686 (PRE-ORDER)

The boards are in production and should be ready by the end of July.

Tom
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Modulus-686: 240W/8Ω @ <0.00025% THD. Modulus-86: 40W/8Ω @ 0.000054% THD. DG300B & Other Tube Circuits.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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