Neet to make a + 0 - 12dB software controllable line level amp. - diyAudio
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Old 18th April 2005, 12:11 AM   #1
bans25 is offline bans25  United States
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Default Neet to make a + 0 - 12dB software controllable line level amp.

HI all,

I am new to playing in the audio / video world so forgive me if I ask dumb questions! .

Currently interfacing to a TI AIC23 ( http://focus.ti.com/lit/ds/symlink/tlv320aic23b.pdf ) audio codec that has unbalanced consumer line level inputs and outputs.

What I need to do is make a PCB that will convert these 1Vrms I/O's to interface with (unbalanced) Professional line levels (+4dbu).

So I will need to PAD the input to the codec ( +4dbu Professional line level ----> -10dbv Consumer line level) right? 12db pad?
I am thinking of using the DS1808 for the attenuation.


Now I need to amplify the output of the codec (-10 dbv Consumer line level ----> +4dbu Professional line level) 12db amp.
Any ideas on whats good to use for a 12dB line level amp?

Here is the catch, I would like to be able to still also interface my AIC23 to consumer equipment or professional equipment and select the pad/amp via software control. So the DS1808 works out well for that, but I am having trouble figuring out what to use for a Software controllable 0-12dB amp!

Does anyone know of any ICs that may help me out to do this? maybe some digitally controlled pots?

I need to fit this circuitry on a 3" x 3" board to fit in the box.

Any suggestions are greatly appreciated

thanks

-Bill
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Old 18th April 2005, 12:58 AM   #2
bans25 is offline bans25  United States
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Im now thinking a simple OPA627 for the line level amp...

Whats a good way to be able to control the gain via SW?

Is it posible to be able to select from a gain of 1, or 4?

Will the op amp operate at a gain of 1? or is there always a gain greater that 1?

thanks
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Old 18th April 2005, 01:40 AM   #3
paulb is offline paulb  Canada
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A relay would be the simplest. Small double pole reed relay should do it. Have it switch in different resistor values to choose your gain.
Yes you can have an opamp with a gain of 1.
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Old 18th April 2005, 08:32 AM   #4
Rambi is offline Rambi  Netherlands
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Quote:
Originally posted by paulb
A relay would be the simplest. Small double pole reed relay should do it. Have it switch in different resistor values to choose your gain.
Yes you can have an opamp with a gain of 1.
Not all opamps are unity gain stable (OPA627 is). If you use an opamp other than the OPA627 don't forget to check the specs to see if it is unity gain stable!

Good luck,

Remco
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Old 18th April 2005, 08:18 PM   #5
jaycee is offline jaycee  United Kingdom
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WM1886 will allow you to control the gain of an opamp via SPI.. you could hook this up to a Microchip PIC which could be programmed as an SPI<->RS232 interface or whatever you need
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Old 19th April 2005, 06:02 PM   #6
Rambi is offline Rambi  Netherlands
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Quote:
Originally posted by jaycee
WM1886 will allow you to control the gain of an opamp via SPI.. you could hook this up to a Microchip PIC which could be programmed as an SPI<->RS232 interface or whatever you need
Probably you mean WM8816?
Other chip is MAS9116 which is similar (?), at least according to this page.

I haven't tried these personally. I did try PGA2310 + PIC as a volume control; but I wasn't impressed by the sound quality (dull, flat, and lifeless are words that come to mind).
Difference is that the PGA2310 has an opamp built in (so I might try a WM or MAS with a discrete opamp some day, to see/hear if that sounds better).

To be honest: People have reported good results with a PGA2310, so personal preferences possibly play a role here
(and the effects of using a breadboard for testing)

Remco
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Old 19th April 2005, 07:09 PM   #7
jaycee is offline jaycee  United Kingdom
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Whoops, yes I meant the 8816.
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Old 20th April 2005, 01:06 AM   #8
bans25 is offline bans25  United States
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HHmm.. for the output gain, I think I could use the Head phone outputs (which have volume adjust) and then used a fixed gain opamp right?
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Old 20th April 2005, 06:31 PM   #9
Rambi is offline Rambi  Netherlands
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Quote:
Originally posted by bans25
HHmm.. for the output gain, I think I could use the Head phone outputs (which have volume adjust) and then used a fixed gain opamp right?

You're right.
That makes it much easier: simple resistor divider at the input and fixed gain opamp at the output.
I guess I should read the sheets first before commenting
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