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Old 8th January 2010, 04:59 PM   #81
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Caveat with a stereo build:
The 470uF capacitors will become paralleled.
Its because both amplifier boards are wired to one power supply.
This affects the audio.
The expected effect is slight decreased midrange clarity.
The fix:
You may wish to collect 220uF caps and 330uF caps to "test drive" at the amplifier board (instead of the listed 470uF caps).
Smaller caps here = louder and clearer midrange.
This will probably adapt the project to work well with a stereo build. In any case, this bit of information can help you control and adjust the midrange a bit.
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Old 8th January 2010, 05:02 PM   #82
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Quote:
Originally Posted by tommy_o View Post
. . . I plan on using the Avel 250VA 18V+18V toroidal transformer. . .
Its fine, but you could buy direct from a manufacturer if you like. Antek - AN-3218

Large transformers ring at a deeper pitch, and this is great news (it won't bug your midrange and it won't make boomy bass), except that one should expand the power supply on post #59 to use 10 of 2200uF caps (5 per each rail) in order to get full coverage of the bandwidth outputted from such large transformers.

These big size parts just happen to support big size pitches, so you'll have excellent bass. Its unnecessary overkill for sure. But, since it works so well, that's one less thing to worry about.

For reference:
Transformers are much like woofers, wheras power supplies are much like crossovers. There's more to it than that, but I think its a useful observation.

Last edited by danielwritesbac; 8th January 2010 at 05:27 PM.
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Old 12th January 2010, 05:23 PM   #83
tommy_o is offline tommy_o  United States
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Anyone have thoughts on building a wooden enclosure or photos of successful builds? I was thinking MDF top, bottom, and sides with the front and rear panels being aluminum. The top can attach with 4 screws entering vertically at all corners and attaching to hurricane nuts set in the bottom panel. The front and rear panels can mount to aluminum angle attached to the T/B/L/R panels. Service can be performed with the top removed and all other panels attached permanently.

A primed and painted finish on the MDF should look nice enough and the aluminum panels would provide easy tooling for attaching volume pot, selector switch and power switch if chosen.

Any thoughts? Or photos that may influence design?
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Old 15th January 2010, 01:44 PM   #84
AndrewT is offline AndrewT  Scotland
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Think about how you can let the heat out.
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Old 15th January 2010, 10:44 PM   #85
tommy_o is offline tommy_o  United States
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Quote:
Originally Posted by AndrewT View Post
Think about how you can let the heat out.
Heat dissipation and vertical height of enclosure are my two primary concerns. I believe the height of the transformer plus 2 panels of 0.5" MDF would be, well, ugly -- about 5" tall. Unfortunately I'm having a hard time finding photos of completed LM1875 amps (I'm still new to the forum and can't figure out searching the 'Completed Gainclone' thread). With these two factors in mind, I believe the best solution would be to heatsink into thick aluminum or brass panels on the left or right, similar in style to many of the LM3875 amps.

But I don't know how to tell if this will be enough protection for the chips. If using aluminum stock as a heatsink works with the LM1875 then, I can use Peter Daniel's guide to build an all aluminum chassis.
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Old 6th November 2012, 12:26 AM   #86
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Sorry for the late response.

To get the height requirements reduced you can use a Pair of 18+18vac Toroid transformers and Dual Mono. That's just exactly like two monoblocs inside one enclosure. Toroid transformers aren't very tall. 25w*2=50va so there's the minimum transformer per each chip.
With Antec transformers, use the 18v 100va (because they measure va with secondaries parallel--see the transformer datasheet) per each chip. For EI core, use 2a 36vct (18,0,18 center tap of two ampers) per each chip.

It would be good to provide a vent above the heatsink and a vent below the heatsink.

With a bit of creativity, the wooden amplifier enclosure can be 2" tall. If that's too tall, let me know, and we'll make it shorter somehow.

Anything made of aluminum can be used for a heatsink, if it is thick enough for heat spreader and big enough to transfer heat out of the heatsink and into the air. For example, Mark Houston used an aluminum pan.
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Old 9th December 2012, 08:06 PM   #87
lausar is offline lausar  United States
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Default Iv'e been looking...

Quote:
Originally Posted by m0b1liz3 View Post
I wanted to build a chipamp as small as physically possible for my desktop studio monitor speakers. Has anyone found a suitable SMPS that can be used with this chip amp (1 smps to power both channels)?
Meanwell makes some 24V units but not with dual 24V outputs. I'm leaning towards these units.
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Old 10th December 2012, 10:45 PM   #88
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Here's an article by Nick Whetstone on split rail SMPS power:
SMPS for the Gainclone chip amp

A pair of 24v rails would be just fine, but it would be nice if at least one of them had a multi-turn trimmer for fine tuning the voltage identical for both rails.
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Old 11th December 2012, 03:39 AM   #89
lausar is offline lausar  United States
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Quote:
Originally Posted by danielwritesbac View Post
Here's an article by Nick Whetstone on split rail SMPS power:
SMPS for the Gainclone chip amp

A pair of 24v rails would be just fine, but it would be nice if at least one of them had a multi-turn trimmer for fine tuning the voltage identical for both rails.
The Meanwell units are adjustable.
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Old 11th December 2012, 06:16 AM   #90
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Quote:
Originally Posted by lausar View Post
The Meanwell units are adjustable.
I think that I've seen those. It should be fairly easy to replace the single turn trimmer (looks like a dial) with a multi-turn trimmer (looks like a little box with a little screw on it), same for both rails. Then you can precision adjust the rails to identical voltage.

Any mixed/direct coupled amplifiers (amplifies DC by the gain factor) could have a rather bad accident if one power supply powers up before the other in a split rail SMPS scheme (really gigantic offset voltage results). Actually, we should probably consider a reliable center tap transformer and ordinary (or CRC) linear power supply for the amplifier on this thread.


P.S.
My TDA729X projects will easily tolerate SMPS.
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Last edited by danielwritesbac; 11th December 2012 at 06:27 AM.
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