TDA 2822 compatibility
Dec 1, 2007 at 3:50 PM Post #4 of 17

balou

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okay... the sources on the net i found always showed a 16-pin amp.
do you have any datasheet with the pinout?
but I don't think there's much to do. the datasheet of the 16-pin version showed that it's a chip which requires huge electrolytics, indicating that it's a rather cheap and low quality dc-coupled amp. you could try a resistor at the output of both channels, this might lower the hiss.

but in the end, building another amp (cmoy, pimeta, etc.) might be the only option to overcome sonical shortcomings
 
Dec 1, 2007 at 4:32 PM Post #6 of 17

NelsonVandal

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You have to do some hardwiring. Everything's possible. Tell us what amp this is and show us some pictures. If you're going to use it as a headphone amp, maybe all you have to do is lower the gain to get lower noise, if noise is your only problem and not bad SQ in general.
 
Dec 1, 2007 at 4:45 PM Post #7 of 17

zer061zer0

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its a simple kitset and i dun have camera with me now. SQ, there is nothing u can say at that price point. I just got it up yesterday and the hiss is terrible. when nothing is playing there is this background his going on.

The kitset also mentioned that it can drive 8 ohms at 1w, thats abt all the info i have. its more like a school project sort of kitset, for the fun of it i even bought a small speaker driver to see if it works.
 
Dec 2, 2007 at 10:18 AM Post #8 of 17

NelsonVandal

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Do you have a link to the schematic? What are the resistor values? Try to lower the gain. You don't need more than a gain of 2 - 4 in a headphone amp.
 
Dec 2, 2007 at 5:45 PM Post #10 of 17

balou

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doesn't look moddable. first it hasn't got any external feedback loop, so no gain adjustments are possible. and the 8-pin version is also dc coupled (the 470uF electrolytics at the output).

have you got this amp on a etched board, or on a protoboard? you can surely reuse the jacks and the pot, maybe with some creative air-wiring you could transform the board into a cmoy. but I think ordering some protoboard, an opamp and some resistors would be better than modding this circuit which is quite far away from a standard opamp amplifier

btw, I'm completely dumbfounded by C1 and C2. What do these caps do? shouldn't the "-" pin somehow be referenced to ground?
 
Dec 2, 2007 at 7:09 PM Post #11 of 17

NelsonVandal

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Look at this, here it's used like a common opamp.
1 W Home Stereo Amplifier Constructional Project
It's explained how you alter the gain. A gain of 11 is way too much. The S/N ratio is claimed to be >80 dB wich isn't good but not a disaster either.

If the noise really bothers you, and lowering the gain doesn't help, you can add some resistors in series with the output. I think 100 Ohms will be fine. This will alter the tonality though depending on your phones impedance curve.
 
Dec 7, 2007 at 8:00 PM Post #14 of 17

zer061zer0

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not sure if anyone can help me with the hiss problem though, and also if the opamps can be directly replace with the more common ones like opa2134, lm 4562 etc.

here are some pics of the amp
The first build, cased up in a hammond box
100_4434.jpg


The uncased one with a volume pot wired in
100_4442.jpg


100_4441.jpg
 
Dec 7, 2007 at 9:16 PM Post #15 of 17

NelsonVandal

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I don't understand the circuit. Is it the "test circuit 1"? I see 9 caps and 2 resistors on your board but 7 caps and 4 resistors in the schematic, or are the grey cubes resistors. Is this amp amplifying the signal? Is the noise the same independent of the volume? What pot do you use, and where in the schematic is it?

If you want to use LM4562 or some other high quality opamp, it's better to build a new amp, like a CMOY on a stripboard. If you want something better, I'll recommend Mini3. You can use the board and populate it with the opamps of your choice if you don't find the AD8397 attractive, but AD8397 is very low noise. Mini3 as a whole is very quiet.
 

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