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Old 7th November 2011, 01:41 PM   #21
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Thanks Andrew

Cheers Einric and go for it, If you have any questions just PM me.
I will post a few more photo's in the next few days for inspiration and may even have the beast running by the end of the week.

Can you give any subjective impressions/comparisons on how hours sounds, I have never heard any of the LM series.
Maybe I should have started with one kit and built my way up... lol

Dean
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Old 7th November 2011, 03:10 PM   #22
Einric is offline Einric  United States
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My LM4780 & Speakers
I tried the LM without "Snubber" and Big uF first.
I liked it very much. It sounds better than my 120W Class H.
I have a feeling that in Stereo mode the LM4780 lacks drive for low sensitivity speakers that have dual 5.25", single 8" or larger drivers.
When I built the TriTrix MTM TL kit from Parts Express they lacked bass without some sort of boost when run by the LM4780 in stereo.
Once I hooked it up to my Class H the bass came back.
I then went through and added the "Snubber" & 10000uF.
After that I have not been driving large speakers just my home made 4" 2-Way bookshelves.
They are approx. 86db sensitivity and this amp in stereo mode will drive them off my laptop until they nearly explode.
Under more reasonable drive condition the amp sounds more wonderful than I could ever imagine.
I can't wait until I parallel the chips and re test the drive capability with my TriTrix.
I am driving my single chip in stereo with dual 24v secondaries @ 240va.
I figured that when in stereo @ 8ohm or 4ohm in parallel mode.
I am running the amp on a line conditioner so I don't really have to worry about line level fluctuation.
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Last edited by Einric; 7th November 2011 at 03:21 PM.
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Old 7th November 2011, 11:54 PM   #23
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Nice work Einric, I must say I have a bit a bit of workbench jealousy after looking at your photo. It looks like a bit of geek heaven going on there.

After some advice from Andrew I decided to go for the parallel config, hoping that the amp could be used in as many situations as possible (tolerant of load and flexible with connections).

The transformer stack was the only way I could fit 3x400VA Antek units in a standard size chassis, but she is a heavy bugger.

The top, bottom and front plates are 5mm thick hand cut alloy. I did these the hard way with a 1mm blade on a 4" grinder. I don't recommend this at all. An alloy blade on a 10" drop saw is much easier but I didn't find this until cutting the 3mm back plate. Even with the 5mm alloy it just glides through like butter.

I also had allot of trouble tapping m3 holes in this alloy. Its 4000 series and very easy to cross thread the holes with fine threads found on m3 bolts.
M4 is much easier and would really be my minimum in the future.

The LM4780 wont fit anything larger than an m3 in the cutout on the chip die, so as you can see I used a clamping plate and m4 bolts. The other advantage here is that hopefully the bar acts as a further heat spreader for the chip. Apparently the 4780 package cant dissipate enough heat when run full power (it probably wont be used that hard anyway), so this might help.

Getting the last terminal strips today which should complete the wiring.

Dean
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Old 8th November 2011, 12:34 AM   #24
Einric is offline Einric  United States
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When I complete my 7 or 8 channel version of the Parallel LM4780 I was looking at mounting the 1500uf's on the bottom of the pcb for easier mounting to the heatsink.
I used M4-40 just fine on my chip in the picture, i used the washer head ones from a computer fastener kit.
I was also looking to use Computer Memory heatsinks on the print side of the LM4780 to help facilitate even more cooling.
I could then attach a spreader or just use it as the clamp to hold the LM's in place.
I would recommend using a little thermal paste on the topside of your chips to help maximize dissipation (everything helps).
I too am using Antek transformers (AS-2224), since I am on 60hz power the manufacturer states the transformers will provide approximately 20% more power (bonus for me).
I really like the way you stacked your transformers.
I will probably look at doing something similar with three 400VA's to run 6 channels and two separate 200VA's to run the main L&R.
I eventually would like to get a preamp that supports front height channels and I could have 5.1+Front Heights with my 8 channels.
My inputs were wired with RG-142 coax cable, it's a dual silver plated copper shield (99%) with a 20 awg silver plate copper center conductor.
I have no hum that I can hear even at max volume.
When I needed jumpers I just gutted some 142 and had great silver plated copper jumpers.
This coax is very common in my profession so it was readily available at a reasonable cost.
That is my workbench at work, it's an L shape of about 20 feet.
I was listening to the speakers and my 4780 while I made the post.
I am a Two-Way and Microwave Radio tech so I need a lot of space to work sometimes.
I have another chassis that I will put my dual mono LM4780 into that is a recycled 24vdc site power inverter.
It had a built in EMI/RFI input and I figured that would make a nice addition.
This will be a temporary solution until after Christmas and I can convince the wife to let me spend another $300 on 4780 kits and chassis parts.

Last edited by Einric; 8th November 2011 at 12:47 AM.
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Old 8th November 2011, 01:55 AM   #25
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I am not sure if it obvious in the picture but I have put a 1mm rubber spacer then a 3mm alloy plate between each transformer.

Alloy/rubber/traffo/rubber/alloy/rubber/traffo/rubber/alloy/rubber/traffo/rubber/alloy.

Hopefully this provides some mechanical/electrical shielding between each traffo.

I have used Keratherm pads from ZouPhang on both sides of the chips.

I have found it best to order gear and then tell my wife, sneaky but effective

Dean
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Old 8th November 2011, 02:43 AM   #26
Einric is offline Einric  United States
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I think that maybe having an iron/steel alloy between the toroids would add an additional layer of shielding.
Did you pick up the AS4222 transformers?
They have the purple drain wire on a Mylar shield between the primaries & secondaries.
I would be interested in hearing the difference between the two transformers, if there is any.
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Old 8th November 2011, 04:15 AM   #27
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Yeah, the alloy plates will hopefully add shielding between transformers.

I did get the AS4222's mainly because they were out of stock of the normal ones and because these only cost a few bucks extra. I am still thinking of running a alloy plate the full length and height down each side of the transformers but it may not be necessary.

Dean
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Old 8th November 2011, 01:25 PM   #28
Einric is offline Einric  United States
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I doubt it would be necessary but if you decide to go that way you might want to look into a perforated metal screen like you find around some switching supplies.
It would help let any heat that builds up get away from the trafo's.
Just remember to ground the screen if it's not in direct contact with chassis ground.
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Old 9th November 2011, 12:28 AM   #29
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Never thought of grounding the shield but its a good idea, even with a perforated plate the heat would still be stuck in a tunnel so I may just leave it shielded.

Cheers Einric

Dean
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Old 11th November 2011, 01:32 PM   #30
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Einric,

What are you using the 6 channels for? To drive separate drivers on the speaker or to drive separate speakers?
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