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Old 8th May 2014, 04:24 PM   #2731
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Quote:
Originally Posted by bcmbob View Post
Very interesting. Looks like a tiny space for the RCAs and posts. Just did a quick look at the LM1875 data sheet. Any info on why you chose that one, and if/how it compares to the 3886?
I found a low-profile banana socket that fits comfortably (it's not a binding post, so it's not a perfect solution, but acceptable). I think there are some EBay sources for small binding posts also, will check later.

The initial design I came up with was the LM1875, because I had an acceptable simulation model for it, and also because of (perceived) area limitations in the board. Subsequently, I found I could fit a pair of LM3886s without increasing the board area! So both designs exist - MiniRef 1875, which has been championed by PreSapian in Seoul (with extensive experimentation and additions), and MiniRef 3886, which I have been playing with off-and-on (and which took a while to stabilize).

The broad differences are (LM1875 vs. LM3886):
1) Lower power vs. higher power (more compact heatsink vs. larger heatsink)
2) Easier to stabilize vs. a bit more finicky to stabilize
3) Smoother, darker, more "tubey" sonics vs. edgier, micro-detailed, "solid-state" sonics (this is probably subjective and arguable).

I have auditioned both, but not very scientifically and not strictly A-B - which I'll do eventually. It's still Apples vs. Oranges, because the two builds differ in a lot of details, while sharing a common topology.
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Old 8th May 2014, 07:50 PM   #2732
bcmbob is offline bcmbob  United States
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Thanks, Please keep us up to date on your progress.

Quote:
Originally Posted by linuxguru View Post
....
3) Smoother, darker, more "tubey" sonics vs. edgier, micro-detailed, "solid-state" sonics (this is probably subjective and arguable).......
Lots of comments on that "signature". I come down on the side believing the edege can be beneficial - but it's tightly related to both the source and the speakers in a given system. As posted earlier, I'm basing my XO mods on that theory. Time will tell.

The new board looks like a very attractive layout. There is also a new Pass amp (Amp Camp Amp) that uses AC adapters successfully. Did you do any comparisons between power supplies?
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Old 9th May 2014, 05:14 PM   #2733
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Quote:
Originally Posted by bcmbob View Post
The new board looks like a very attractive layout. There is also a new Pass amp (Amp Camp Amp) that uses AC adapters successfully. Did you do any comparisons between power supplies?
Hi Bob - I'll continue the discussion at the MiniRef thread, to avoid cluttering the photo thread:

MiniRef Schematic and PCB layout
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Old 9th May 2014, 07:42 PM   #2734
bcmbob is offline bcmbob  United States
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Good idea - Just subscribed to that thread.
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Old 11th May 2014, 05:41 AM   #2735
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Figured I might as well throw some pics up on this thread for posterity's sake. Here's my second Peter Daniels LM4780 paralleled build. Dual torriods int he bottom with the rectifier bridges. Wiring could be neater up top for certain but she sounds good and the noise floor is somewhere in the basement.

The cheap ebay preamp in the right of the first picture needs some work, there's a vicious ground loop that I need to chase down..

Currently powering some celestion bookshelfs but hopefully it will soon be relegated shortly to powering a nice 10" sub to go with some fostex full ranger metrenomes that will be powered by a LM3875 build that will take some design inspiration from Daniel's Pateks.
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Old 11th May 2014, 07:54 AM   #2736
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Quote:
Originally Posted by vapemaster View Post
Figured I might as well throw some pics up on this thread for posterity's sake. Here's my second Peter Daniels LM4780 paralleled build. Dual torriods int he bottom with the rectifier bridges. Wiring could be neater up top for certain but she sounds good and the noise floor is somewhere in the basement.

The cheap ebay preamp in the right of the first picture needs some work, there's a vicious ground loop that I need to chase down..

Currently powering some celestion bookshelfs but hopefully it will soon be relegated shortly to powering a nice 10" sub to go with some fostex full ranger metrenomes that will be powered by a LM3875 build that will take some design inspiration from Daniel's Pateks.
Heavy metal!
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Old 14th May 2014, 03:05 PM   #2737
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realy nice heatsinks , will you put 3875 in same box?
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Old 14th May 2014, 04:04 PM   #2738
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Haha seriously mhouston, the thing weighs a good bit..


Toni: The heatsink is from Heatsink USA, don't know if they do international shipping but they make a very quality and affordable option for custom lengths with a variety of different widths and fin profiles. I ordered one to match the top box's opening and cut out the sold side to mate the two together.

even with that giant heatsink (10"x8") it still gets warm (~50 deg C) when playing music loudly which is well within the safe operating temp for the chips but about as warm as I want it to get, no doubt things will get toastier when it's pushing a big subwoofer, I think i'm going to stick with 8ohms for that...

I think I am going to build a separate enclosure for the lm3875 build, maybe a separate power supply enclosure style. I've got some ideas, i'll throw up pics when that happens!
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Old 14th May 2014, 07:53 PM   #2739
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Quote:
Originally Posted by vapemaster View Post
Haha seriously mhouston, the thing weighs a good bit..


Toni: The heatsink is from Heatsink USA, don't know if they do international shipping but they make a very quality and affordable option for custom lengths with a variety of different widths and fin profiles. I ordered one to match the top box's opening and cut out the sold side to mate the two together.

even with that giant heatsink (10"x8") it still gets warm (~50 deg C) when playing music loudly which is well within the safe operating temp for the chips but about as warm as I want it to get, no doubt things will get toastier when it's pushing a big subwoofer, I think i'm going to stick with 8ohms for that...

I think I am going to build a separate enclosure for the lm3875 build, maybe a separate power supply enclosure style. I've got some ideas, i'll throw up pics when that happens!
nice work and nice ideas thats great, thanks for information on heatsinks couse i dont realy trust chinease ebay stuff for heatsinks ,i used to remove them from old equipment, now i hope they ship worldwide .

edit: what are dimensions of top maybe you could find realy big quiet fan and put it on top and then 4 ohms no problem how many volts psu??

Last edited by tonitonitoni; 14th May 2014 at 07:58 PM.
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Old 22nd May 2014, 11:36 AM   #2740
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Default P2P Lm3875

Point to point Lm3875.
Twin 18v 120va Trannies (one per rail)
40,000uf PSU (20,000 per rail)
Snubbered rectifiers,
Alps pot.
Large heavy heatsink.
Total weight is 8Kg

Most stuff had lying around.

Minimal woodwork. Ends made form 'bamboo' chopping boards!
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