Contest: Linear Power Amp in a mint tin (class Aa, class AB, or class B) - Page 14 - diyAudio
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Old 29th November 2012, 11:22 AM   #131
bigwill is offline bigwill  United Kingdom
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Quote:
Originally Posted by littlerick View Post
Almost got the board together... just got to wangle my 2 input caps into a spot and i'll be ready to plug it in and test it.... Oh yes and I gotta find a heatsink that will fit, do the job and leave space for input, output and a volume pot!

Not sure if it will fit in a tin, but i'll be happy if it works.. Maybe if i just tap the caps down a bit with a hammer and twist the chip with a screwdriver it just squeeze in.
Good going I'm going the way over the weekend, so I wont be able to make my boards until early next week.

My transformer arrived this morning, as well as a bridge rectifier and capacitors. I've always needed a +/- supply so this was a good excuse to build one. The transformer will happily fit in a PC power supply case. I have plenty of old ones!

I added a small value capacitor across the input of the amplifier - this improves its behaviour dramatically, now it's not having to dear with unreasonably fast rise times on the square waves from my sig gen. My earths are definitely getting dirtied up by the lash up wiring, but this will go away when I build it and earth it like a proper amplifier.
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Old 29th November 2012, 05:08 PM   #132
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Well i'm surprised... It worked first time... I Have it in a watch tin at the moment... bit bigger than a mint/bakki tin but wanted to see it in A tin...

Its not a great sound, but that could be a number of things... crappy test speakers or it could be my power supply... 240 - 12v torroid at 3.5 Amp... got it running through a makeshift rectifier made up with 4 1n4001's and a 100uf cap. Giving me about 18v DC.

I have put RCA inputs and just got wires hanging for power and speaker output, but I might change to small jackplugs if it goes in a bakki tin.

Then I can start working on the making it pretty bit!
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Old 29th November 2012, 05:41 PM   #133
bigwill is offline bigwill  United Kingdom
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Nice one! Be sure to post pics.
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Old 29th November 2012, 06:02 PM   #134
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Quote:
Originally Posted by bigwill View Post
I added a small value capacitor across the input of the amplifier - this improves its behavior dramatically, now it's not having to deal with unreasonably fast rise times on the square waves from my sig gen.
Partners to this cap could include picofareds capacitor parallel with the feedback resistor (for linearity), Vas compensations of different types (for pretty square wave), and output RC (for fine tuning) as well.
Quote:
Originally Posted by littlerick
Almost got the board together... just got to wangle my 2 input caps into a spot and i'll be ready to plug it in and test it.... Oh yes and I gotta find a heatsink that will fit, do the job and leave space for input, output and a volume pot! Not sure if it will fit in a tin. . .
If you post some photos, perhaps someone will offer a helpful response on how to fit the amp into the enclosure. When posting photos, click the button marked "go advanced" and then scroll down to the button marked "Manage Attachments" and then you can post your photos.

A heat spreader bar in the tin can be used in thermal management. This can be made with aluminum bar stock from the hardware store (or aluminum scrap) and white thermal paste from the computer store.

The warmed air that goes up and out of the output vents at near the top, creates a miniscule vacuum force when it leaves and this is why cool air will rush into the bottom intake vents if the tin has some rubber feet giving clearance for the intake vents to work. It maybe be nice to have air intake vents near capacitors, to cool them, as long as a finger couldn't get onto the pins. Decorous ventilation is appreciated.

The input load on the schematic can be either potentiometer or resistors. Volume control is appreciated, but not required.

In the "simple elegance" approach popular with chip amplifiers, you can size your output caps to suit your speakers. For 8 ohm speakers the range is approximately 800u for miniature compact speakers with 4" woofers, to 4400u for full size speakers with 8" woofers, and your schematic shows the average size between those two examples. Those are all just estimates. A real speaker can react noticeably well to having chosen the right size cap for it.

Be sure to use non-shorting connection for speaker jacks. What works well is RCA's, binding posts, and retail looking plastic spring clip speaker jacks, because they don't short when you plug in the speaker.

However, because of violent explosion, 1/8" and 1/4" jacks won't do for either speaker or power connectors. I found this out already.
Quote:
Originally Posted by littlerick
. . . got it running through a makeshift rectifier made up with 4 1n4001's and a 100uf cap.
Kudos for getting it up and running so fast!
Before judging the sound, you might want at least a minimal power supply with something like 1n5405 or larger size diode bridge rectifier followed by a parallel pair of 2200u caps (4400u or more works fine for single rail), capacitance at the power supply.
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Last edited by danielwritesbac; 29th November 2012 at 06:11 PM.
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Old 1st December 2012, 12:55 PM   #135
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My car chip happened to need a volume pot for lower distortion. I'll probably give that pot a slight automation in the form of a low parts count "overdo reducer," so now awaiting the mailbox for some germanium parts to arrive for a fun experiment. Unfortunately, the car chip has a locked gain setting, so the prospect is hit or miss because I can't fine tune the gain. There may be barely enough for 9 watts. I don't know yet. Personally, because I'm host, I'm not intending to win. But, I would like a fun and useful project.
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Old 2nd December 2012, 10:03 AM   #136
bigwill is offline bigwill  United Kingdom
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Just a quick bump to say I haven't disappeared or given up - I'm just away for a few days running some errands.
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Old 9th December 2012, 07:43 AM   #137
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Hi again.. lost my net for a while... is this still going... will try for picture later... Something called christmas keeps getting in the way of getting stuff done.
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Old 11th December 2012, 12:58 AM   #138
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Yes, we're still on. Some people are waiting for parts, some are busy with Christmas activities.

I need some input on an appropriate closing date, since I don't have an idea on that. Just like phase linear, we shouldn't go either too slow or too fast.

At this time, I do have news of one Blameless style discrete amp, one truck chip, and one car chip, all of which are looking good so far.

Another possible way to get low bias is to play a game of limbo (how low can you go) by under-volting a more powerful chip amp, and setting the gain lower to both match up with the smaller scale amp as well as reduce some of the "naf" consequences of lower bias.

And, of course New Class A equipped with auto bias and Class G power supply (makes AaG) is a possible way to get a fairly high power Class A into a mint tin. However, the newest high-efficiency linear tech is currently pushing phone antennas instead of speakers, efficient fet outputs have been hard to find and the amp designers are busy with Christmas activities.
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Old 24th December 2012, 11:51 PM   #139
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Default DMOSfets and Lateral Fets found!

Power MOSFET - Wikipedia, the free encyclopedia
Searching for lateral fets results in mostly obsolete devices because both the language and the packaging are obsolete. Today, these are called power mosfet and for an additional set of inconveniences, the model numbers are all changed, the tabs are cut off, and sometimes the center pin is also cut off. Nevertheless, they do still exist, they're plentiful, they're efficient and they're inexpensive. At low voltages, such as this thread, the power mosfet is extremely efficient. With Class AB, we could perhaps reach 20 watts per channel (max?), or even more with Class AaG.
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Old 26th December 2012, 10:06 AM   #140
bigwill is offline bigwill  United Kingdom
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Caught up with Christmas at the moment - I've also been off the site for a few of days as diyAudio is being reported as an 'attack site' by firefox. I've now given in and ignored the warning for now.
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