Class A

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korcraft

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Joined 2017
#1
Hello all,

I'm new to speaker building. I'm about to build my first stereo bluetooth speaker using the ever popular Class D TDA7492p (I think that's correct). Little Chinese board, perfect for a first timer.

In the process of reading around and starting to understand the different classes of amplifiers, I decided to see if I could find anything similar to the amp mentioned above but in a class A. Anytime I do google searches for a stereo Class A amplifier, all the results are just explaining the different classes.

Are their any recommendations on a small Class A amp that isn't already in an enclosure and "complete" so to speak. Something similar to the class D mentioned above but Class A.

I realize class D will likely be all I really need, but I am very interested in trying out some different things, seeing the difference for myself and finding what I like to build.

Thanks for any info.
K
 
#2
It's much more expensive to build a class A amp. The power supplies and heatsinks are larger and thus more expensive. The closest to what you asked for may be the Pass Amp Camp Amp you may want to look at it and see how much larger the heatsinks are than would be used in your TDA7492 and keep in mind this is a small 6w amp by the time you get to a 50w amp your sinks and transformer have to be BIG, But just for scale look at this kit ( oh to get picky if it had been push pull that sink would have been good for a 10 to 12 watt amp but you should get the idea)

Amp Camp Amp Kit – diyAudio Store
 
#3
The JLH69 (John Linsley Hood) should be common enough to find as a kit. Its about as simple as a Class A amp can be and also a top performer.

Small and Class A don't go together I'm afraid. Even a modest 10 watt Class A will put out huge amounts of heat, as much as 30 watts for the above mentioned when its just sitting there powered up. A Class D amp might be dissipating well under 1 watt under the same conditions.
 
#4
That's going from one extreme to the other. The class D can run with small power supply and almost no heatsink. Equal power class A will need BIG heatsinks and power supply, so don't expect to use it in a portable boombox or anything similar.

You can get class A boards from places like Aliexpress, search under "JLH" for example such as https://www.aliexpress.com/item/1pc-JLH-1969-class-A-amplifier-Board-high-quality-PCB-Assembled-MOT-2N3055/32570249254.html?spm=2114.01010208.3.1.YNuWJR&ws_ab_test=searchweb0_0,searchweb201602_1_10065_10068_10000032_10000025_10000029_430_10000028_10060_10062_10056_10055_10054_10059_10099_10000022_10000012_10103_10102_10000015_10096_10000018_10000019_10052_10053_10107_10050_10106_10051_10000007_10084_10083_10080_10082_10081_10110_10111_10112_10113_10114_10115_10037_10032_10000041_10000044_10078_10079_10077_10000038_429_10073_10000035,searchweb201603_2,afswitch_2,single_sort_2_default&btsid=9fe3846f-e1fb-4e24-ae44-836324b99178

That's just the board, BTW, which is MUCH cheaper than the heatsink for it would be. (I also don't know if that board or others are any good, just something I saw -- rumors are that the output transistors used in a lot of these are fakes)
 
#5
Excellent! Thanks!

I knew that class A was far less efficient...I didn't make the obvious conclusion that of course less efficient>more heat...More heat> bigger heatsink...Thus the size of the thing would be much larger and likely need to be in a separate enclosure.

Of course now it seems obvious haha. I will still also check out that kit that was recommended, thanks for that. I would still love to build one even in a separate enclosure.

Any recommendations on high quality Class D amps? say...sub $50. I know the one I have is ok, but have heard of a bit of a noise floor with them, but again for the price it's great for a first build, but for future stuff when I start looking into more quality than price point.

Thanks again.
 
#10
I'd suggest a pair of IRS2092 boards like this one - https://www.aliexpress.com/item/Consumer-Electronics-Shop-Free-shipping-1pc-IRS2092-CLASS-D-Audio-Power-Amplifier-AMP-Kit-200W-MONO/32600161122.html?spm=2114.01010208.3.1.f0QN8C&ws_ab_test=searchweb0_0,searchweb201602_1_10066_10065_10068_10000032_10000025_10000029_430_10000028_10060_10062_10056_10055_10054_10059_10099_10000022_10000012_10103_10102_10000015_10096_10000018_10000019_10052_10053_10107_10050_10106_10051_10000007_10084_10083_10080_10082_10081_10110_10111_10112_10113_10114_10115_10000041_10000044_10078_10079_10000038_10073_429_10000035,searchweb201603_9,afswitch_3,single_sort_3_default&btsid=155fefea-420a-4137-b06e-daac09cbf4fd

If you care about dynamics you'll want to tweak the analog supply rails to the IRS chip, but apart from that you'll be good to go.
 
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