TDA2822 Amplifier
5 Zone Alarm
TDA2822 Amplifier
Circuit : Rodney Byne, UK
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This is a modified input circuit for the TDA2822M 1 Watt stereo amplifier. This input circuit eliminates the standing 2V DC voltage across the volume control, which would eventually make a carbon based potentiometer go noisy.

TDA2822 Input Circuit

However, I have first hand experience that over long periods of years use, the manufacturer's legacy circuit used around the input area is a wrecker of volume control pot tracks. This is worthy of explanation, as the cause could be commonly found in other examples of IC audio amps.

After home-building such an amp for the purpose of connecting to the LS outputs of my laptop and tablet to enhance music quality (which is great from bookshelf speakers mounted on the wall by the way), I tended to leave the amp permanently powered for convenience.

To date, I am on my third stereo dual control pot, as the tracks had become extremely noisy and so were unusable. A track on the second pot was even o/c at the bottom end. This annoyance merited further investigation and admittedly should have been done much earlier when first discovered. It appears that at IC audio input pins 7 & 6, derived from the chip's internal transistor network, there are standing voltages of +2v dc directly connected to each pot wiper in the traditional circuit. To mitigate this intrusion, I have added a re-designed input circuit and attached this to view for your interest and reference. The two 33 ohm loading resistors simulate a pair of stereo headphones plugged in the pc LS socket. Left and right channels have fixed loading resistors for the +2v dc mentioned. Each +2v dc is blocked by electrolytic caps to protect the pots. Note the polarities. The two 3k9 resistors act as audio current feeds rather than audio voltage feeds, to stop shrieking instability at high inputs. The two 33k resistors limit maximum audio output level.

Hopefully my third dual pot will remain in pristine condition. I trust the above comments might be helpful to your readers and constructors, to not fall into the same cycles of puzzlement as myself.

Please Note
Maplin no longer sell this useful item as a discrete component device. It is now only sold included in a Kitronik kit, code A52RJ at the base price £7.99 of three available kits. The Kitronik 2 x 1w o/p amp kits, now include a newer version chip called NJM2073D made by JRC, to replace the obsolete TDA2822.

Webmaster Note
I have found some online sources of the TDA2822 at Bowood Electronics and ESR Electronics links below:

Bowood Electronics

ESR Electronics

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