| Dxvideo |
Hi all,
I plan to make a digital preamp/volume control circuit for my LM3886 GC...
I know a lot of DIYer works on PGA2310 like precision devices. But i already have a TDA7309 chip from ST..
It looks like not bad. It has
109dB SNR
%0.01 THD
Handling 2Vrms signal input.
0 to -92dB control range with 1 dB steps....
I plan to write some codes on 8051 platform to control via IR and encoder. Then add a quality op-amp (like LM4562) with 3vv gain before it. What do you say about it? Do you think it works fine? Or anybody use that IC before? I dont want to spend more times if its a rubbish!
Thanks a lot in advance..
http://www.st.com/stonline/books/ascii/docs/1560.htm |
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| youyoung21147 |
Don't know how it sounds, though I'd say 0,02% of THD is absolutely enormeous for a line-level circuit !
Have a look at Maxim IC's digital pots, they have discrete resistor steps and much better specs.
IMHO the best attenuator is to have no attenuator. If you use the PC as soundcard, just use the computer's volume control, it's very efficient ! |
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| Gordy |
The specifications seem fine. (The THD figure may not be the best, but is acceptable).
Note that the maximum supply is 10.5V and hence 9V regulators would be advisable.
The data sheet notes a maximum input of 2V, so do not put an amplifier before the chip, as it is likely to over-drive the input. Use either 1) a straight feed via the capacitors as noted in the data sheet, or 2) use a buffer before the capacitors / chip (i.e. a stage with a gain of x1). If you need additional amplification it can go after the chip. |
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| Dxvideo |
| quote: | Originally posted by youyoung21147
Have a look at Maxim IC's digital pots, they have discrete resistor steps and much better specs.
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I can buy a PGA2310 also... I guess its better than Maxim ICs.. But as i said i have already have one of this. Anyway..
| quote: | [
The data sheet notes a maximum input of 2V, so do not put an amplifier before the chip, as it is likely to over-drive the input. Use either 1) a straight feed via the capacitors as noted in the data sheet, or 2) use a buffer before the capacitors / chip (i.e. a stage with a gain of x1). If you need additional amplification it can go after the chip. |
If i put an op-amp after this chip, and when attennuation is @ -92dB what happens? May i have total muting? |
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| Gordy |
From a nominal input level, an attenuation of -92 dB is a very, very low level. You would have to try it to be sure.
Remember that your LM3886 has an in-built mute function at pin 8. If your amps and preamplifier are in the same box, then using the mute function of the LM3886 is worth consideration. |
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| Dxvideo |
Hmm.. I must consider that. However my mute pin is connected to Vee via a 20K on board. It wil be quite hard. But as you say i must try it.
Thank you |
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