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Old 23rd September 2021, 03:03 AM   #241
Dibya is offline Dibya
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60% efficiency on class A holy smokes
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Old 23rd September 2021, 04:39 AM   #242
xrk971 is offline xrk971  United States
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FFT measurements of SuSyLu...

And the measured harmonic profile looks great at 8Vrms or 8w even (THD of 0.015%):
SuSyLu Where Are You?-susylu-fft-8-0vms-10ohms-jpg

At the reference 2.83vrms, the THD is 0.0037% vs 0.01% for the single LuFo:
SuSyLu Where Are You?-susylu-fft-2-83vms-10ohms-jpg

At 20Vrms, the profile is starting to switch over to third order dominant:
SuSyLu Where Are You?-susylu-fft-20-0vms-10ohms-jpg

I suspect that the dominant second harmonic is due to imperfect matching of the actives between the two sides.
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Last edited by xrk971; 23rd September 2021 at 04:41 AM.
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Old 24th September 2021, 02:40 PM   #243
xrk971 is offline xrk971  United States
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Starting to button up the SuSyLu amp into a real chassis. I really hate chassis work. It takes forever.

A couple of mistakes worthy of Homer Simpson along the way. The soft start board was mounted about 2mm too high because I thought top panel rested on top of the back edge but was in fact flush with it.

In squeezing everything together I think the power trafo is simply too close to the amp. So dealing either with a ground loop or just EMI pick up. But it was 5am when I got to this stage so could not chase it down yet. This may immediately say that the only PSU that can work in a tight chassis like this is a SMPS.

Nice Viborg solid copper binding posts on the back and TRS jack for balanced input. I wanted to install Neutrik XLR but my step drill doesn’t go big enough:
-2ac7187e-84fd-44a4-86c9-d2a0ee7ef983-jpeg

Installing the balanced inductor and SLB pass transistor onto the floorboard which is now a heatsink for about 18w of dissipation from the SLB:
-693ed7b3-c3f0-4fa1-9e08-cbcd8c3e6121-jpeg

Here is the inside of the rear panel all connected with 16ga silicone insulation wire for the mains hookup and speaker cables. Ground wire is nice industrial green/yellow appliance grade wire. SFP soft start board is mounted oh so nicely, but 2mm too high. Although 2mm lower and it would interfere with the binding post nut:
-6b34a4e1-bc03-43b4-b750-84038aa931b4-jpeg

All assembled - the main power trafo is mounted on the floor towards the rear lying flat. The SLB sits on top of it for now. It’s tight. I wish I removed the big output coupled caps (labeled DC coupled) but they would have required a hot air pencil and pulling off the heatsink and I thought maybe leaving them in place let’s me test each leg in SE mode if I remove the jumper. In hindsight, should have removed it:
-7ead53b5-b2a2-4bc1-b478-87d563f0f9ef-jpeg

View from to with rear panel:
-1271922c-0b47-4235-a778-a8f142f03644-jpeg

Front panel but VU meter is not connected yet:
-bff807ce-8487-4f6a-96f6-b649df8e312c-jpeg

A couple of observations on this build, first thing is that it is massively heavy. I can barely move it and it’s a monoblock. There is no way this could have been done in stereo and be a device that can be transported by one person without rigging or dolly/hand truck. The other thing is that the quality of this CNC chassis is superb. Everything fits together nicely, perfectly aligned (I would say all screws fit within 0.1mm tolerance) and ALL screws for assembly or disassembly are accessible from the outside! I should have taken a photo of the assembly when I lowered the floor plate complete with inductor and trafo down onto the 4 assembled walls. Finally, the build is tight. I still need to put the VU meter board and a RTR SSR speaker protection board in there somewhere.
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Old 24th September 2021, 03:25 PM   #244
dBel84 is offline dBel84  United States
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That is looking phenomenal - congrats . A finished product worthy of the effort put into the design and testing. ..dB
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Old 24th September 2021, 03:51 PM   #245
Vunce is online now Vunce  United States
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Fantastic progress X!
Hopefully you don’t suffer too much today from sleep deprivation, recovery time isn’t what it used to be
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Old 24th September 2021, 05:44 PM   #246
xrk971 is offline xrk971  United States
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Well, not quite finished. I need to chase down a ground loop. I may be missing an NTC between chassis and mains earth ground. That was there on the plank amp but not here because I thought the NTC on the SLB was enough. I do note that the LuFo boards themselves don’t have NTC ground loop breakers (which is usually the norm on all JPS64 amp layouts). I’ll try taking the amp apart again and play with grounding. Luckily only 10 externally accessible M4 socket cap screws take all the walls apart and 6 Philips head screws from the bottom drops the floor panel.
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Old 24th September 2021, 11:59 PM   #247
xrk971 is offline xrk971  United States
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Jhofland made these cute little TRS jack helper boards for me. I hate soldering wires directly to pins on these jacks. They always break from wire strain.

Properly crimped Molex KK connectors are always better for reliability and longevity vs flying leads.

-7fad27c4-eb26-44e3-a0b4-789efce61567-jpeg
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Old 26th September 2021, 03:00 PM   #248
xrk971 is offline xrk971  United States
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Swapped positions of the trafo and inductor 180deg by flipping the floor plate around to see if noise would go down. It helped a little but not enough.

Click the image to open in full size.

Click the image to open in full size.

The next step is to take the linear toroidal trafo outside. Maybe a third chassis for the PSU is what is needed.
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Old 26th September 2021, 03:04 PM   #249
Dibya is offline Dibya
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Hi X,


How much VA is that toroidal trafo? It looks Huge
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Old 26th September 2021, 04:00 PM   #250
Vunce is online now Vunce  United States
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It's only 400va, this gives perspective about how narrow the space is between heatsinks.
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