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Old 22nd May 2014, 12:06 PM   #2741
bcmbob is offline bcmbob  United States
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Join Date: Dec 2009
Location: Bay City, Michigan
Very creative! I have a lot of LM3886 related stuff in the drawer and your build encourages a new adventure into P2P.

Bob M.
"Arrange Whatever Pieces Come Your Way."
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Old 28th May 2014, 01:33 AM   #2742
tonitonitoni is offline tonitonitoni  Croatia
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Location: Croatia
Default tda7265

simple small tda7265 25w *2 on one chip(with this small trafo maybe 10-15wpc)
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File Type: jpg 2014-05-24 20.10.25.jpg (302.5 KB, 2470 views)
File Type: jpg 2014-05-24 20.12.23.jpg (223.8 KB, 2373 views)
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Old 30th May 2014, 07:46 PM   #2743
onuhannes is offline onuhannes  Estonia
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Default 7293 plywood chipamp getting friends

psu almost done and a high bitrate flac player using raspberry in progress.
BurrBrown dac module still missing

Click the image to open in full size.
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Old 2nd June 2014, 11:01 AM   #2744
onuhannes is offline onuhannes  Estonia
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[QUOTE=onuhannes;3945608]psu almost done and a high bitrate flac player using raspberry in progress.
BurrBrown dac module still missing

Click the image to open in full size.
Click the image to open in full size.
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Old 14th June 2014, 07:32 PM   #2745
Nounours18200 is offline Nounours18200  France
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for onuhannes: where have you bought your 2 cabinets ? they seem to be made of wood ?

Thanks for your reply...
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Old 15th June 2014, 03:08 PM   #2746
Mihkus is offline Mihkus  Estonia
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Those bigger ones seem to have 4GD35 as woofers... But I have no idea what those tweeters are...
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Old 26th July 2014, 08:01 PM   #2747
Elvee is offline Elvee  Belgium
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Default Chip-Lab

Here is my latest baby: it is a lab amplifier, which means an equipment that will only occasionally reproduce audio, but will mainly serve as power driver for various experiments, 4-quadrants supplies, measurements, emulation of power systems, 400Hz or 60Hz generation, etc, etc.

Once you have tasted the convenience of such an amp, you inevitably become addicted: I have already built a huge number of them but I never have enough.

All the previous versions (except for a notable one) used discrete circuitry, at least for the power section.

This one is based on LM12's: they are stable, have good performance and include thermal protections impossible to achieve with discrete devices.
Here, the two power channels have an additional protection in the shape of a fast fuse (included in the FB loop). This affords one more protection layer, because such amps are sometimes included in complex setups, with supplies that can widely exceed that of the Opamp itself and require external protection.
The power channels are configurable as +10 and -10 gain blocks.

4 additional lower power channels are also included:
-two are high-accuracy, based on OPA27's, with one configurable for +1, +10 and +100 gains and the other as +10 or -10
-two are general-purpose, based on the NE5532: one as +1 and +10, the other as +10 or +100.

All the gain-setting resistors are either 0.1%, or have been hand-picked to 0.1% to ensure a good enough accuracy, essential for any lab gear.

The active circuits are complemented with variable attenuators based on high quality potentiometers.

All the coaxial outputs are protected by 50 ohm resistors, and the inputs have series 1K to 5K resistors..

The PSU uses a 200VA/2x22V toroidal and 2 32,000µF capacitors, plus two 20V regulators for the low-power channels: no rocket science, just plain and dependable electronics.

The whole thing is built as a class II device: no earth connection. In addition, the chassis is floating wrt. to the signal ground: this is essential for a test instrument, it gives a maximum of flexibility.

Since the mechanical design is centered on the principal elements, capacitors, heatsinks, transformer, etc, I had the opportunity to size it optimally: large enough to work comfortably, but as small as practical to fit into my already overcrowded lab.

Why use SMB connectors for most interconnects?
They have many advantages from my point of view: they are of the quick connect/disconnect variety, they mate reliably and give excellent contact, they have a controlled impedance, they use very little real-estate (the front panel has 16 of them, and it's far from cramped), and I can have them by the buckets (and the patch-cords too). All this means they are ideal for me.

I have made a tentative here: the heatsinks have a very good anodization, and I used it as an insulator for the LM12's. Risky? Maybe, but I made scratching and 500VDC tests, and they were all conclusive.
If it fails, it will result in a blown fuse, and I can always revert to the good (or not so good) insulation methods.
We will see....
Attached Images
File Type: jpg lab1.jpg (266.0 KB, 583 views)
File Type: jpg lab2.jpg (241.0 KB, 568 views)
File Type: jpg lab3.jpg (574.2 KB, 613 views)
File Type: jpg lab4.jpg (405.9 KB, 617 views)
File Type: jpg lab5.jpg (574.7 KB, 442 views)
. .Circlophone your life !!!! . .
♫♪ My little cheap Circlophoneİ ♫♪

Last edited by Elvee; 26th July 2014 at 08:06 PM.
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Old 27th July 2014, 12:03 AM   #2748
mhouston is offline mhouston  Australia
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Elvee, very nice work.
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Old 12th September 2014, 04:01 AM   #2749
Carlp is offline Carlp  United States
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Default First chip amp from a tube guy

Hi all,

Quite a few years back I purchased some LM3886 boards (two channels and a PS board) for next to nothing (maybe $3US) because they were CHEAP and I had some ebay bucks I wanted to use up. It's basically the chipamp.com circuit. I slowly pulled together parts from my bin (other than the 3886s, the PS tranny and the big caps) and built it over the summer.

The case was an old DVD/surround sound player that bit the dust and which I modded to work as a chassis for this. Wood is a scrap piece of pine I had around, stained red mahogany (a mistake - I should have left it natural or a more neutral color) and shellac'ed. I'm a card-carrying cheapskate who takes pride in spending as little as possible to get really good sounding music. But this chip-amp thing had me both intrigued and skeptical.

I have to say (against my better tube-loving judgement) that this silly little amp does a surprising job of reproducing music with decent soundstage, great clarity, tight and weighty bass. In short, most of the things I look for. There's a smoothness that it's missing compared to my DIY tube gear, and it seems slightly over-accentuated in certain frequencies (upper mids/vocals in particular). While my Marsh A200 is more balanced overall and probably a bit better with soundstage, the LM3886 has less grain to the sound than the Marsh and the vocals are really present.

For the chump change it took to build, this amp is impressive indeed. Hope the photos make it through.
Attached Images
File Type: jpg DSCN5547.jpg (915.9 KB, 469 views)
File Type: jpg DSCN5548.jpg (878.6 KB, 519 views)
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File Type: jpg DSCN5555.jpg (785.0 KB, 241 views)
File Type: jpg DSCN5556.jpg (860.3 KB, 312 views)
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Old 12th September 2014, 08:01 AM   #2750
jemraid is offline jemraid  United Kingdom
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Hello Carl,

Nice job that I agree that a better sound is obtained from using a 'proper' power supply with some large caps. I have two versions one like yours that sounds fat round and engaging and one with just the decoupling caps which sounds a bit austere and remote.

Anyone wanting a 'valve' like sound would be well advised to make something like this, I have friend with a 300B and we both admit that it's got the edge over the GC but we are only talking half a Gnats knacker.

Cheers - Jim
FH3 build using very simple tools and a point to point Gain Clone with largish power supply. http://www.jasread.com/fh3/index.html
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