Amplifier Projects

Elekit PS-3239

A small amp kit using the TEA2025B chip. Looks pretty much like the design in the datasheet.

The screw terminals wasn't included in the kit but it felt like a good idea adding them. Lesson learned from my CMoy that is basically soldered into its Altoid box never to be moved. Nice with some extra flexibility.

Completed board

Put together as a small and cheap and battery operable stereo system. I got a pair of Fostex full range speakers to use for this purpose. These are good quality drivers so should be able to keep them if I build better amps in the future.

BOM:

Total: 12000 JPY (mainly for the speakers)

Testing

Worked well. Unless you're throwing a party or is in a big room it's powerful enough with these speakers. Audio quality it seem to sound best at about 1/3 of max volume with a 9V battery. Data below on the TEA2025B chip supports that.

Mounted in Altoid tin

With the screw terminals on the board the final assembly was a breeze.

Power supply

The 12V wall wart I got didnt work well. I'm not sure about it's specs. I verified it's isolated but might be unregulated and maybe a switcher. Anyway it makes the amp hum. Will try and make some measurements on it later.

Result was a lot better with a single 9V battery.

TEA2025B

From data sheet:

The TEA2025B/D is a monolithic integrated circuit intended for use as dual or bridge power audio amplifier portable radio cassette players.

So not exactly a Hi-Fi amp perhaps.

The power output is a function of speaker impedans and input voltage. In 8 ohm 9V give a maximum of 1.4W and 12V give 2.4W.

In 8 ohm the THD (Total Harmonic Distortion) take a big jump above 0.4W in output power.

Stepped Attenuator

A stepped stereo attenuator in a separate enclosure. So you don't have to put a high quality volume control pot in every single amplifier build.

Inside Stepped Attenuator

BOM:

T-Class 2x15W

Decided I needed a small amplifier on my desk/workbench for listening to music while working, testing DACs and speaker builds. The amplifier chip used is the Tripath TA2024.

The enclosure is a bit on the big side but it's nice not to be cramped and I expect to reuse the enclosure for other modules when this one gets dated.

Mounted in enclosure

Here shown with a Airport Express as a source and the stepped attenuator.

T-class + stepped attenuator + Airport Express

BOM:

LM1875 based 25W mono blocks with balanced input

For the livingroom. Using two K50 PCB kits.

Similar build:

http://www.frontiernet.net/~jff/lm1875/25W_Stereo_Amp_using_LM1875.html

LM1875

http://www.ti.com/product/LM1875

Powersupply

The amps need a dual power supply (+/- 25V).

2x 60VA 35V center tapped secondary.

IEC connector with switch and fuse holder. Grounded chassi.

Balanced tube preamp/buffer amplifier


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