Music auto fader device: M.A.F.?

4 answers	Answer it!

Jun 4, 2010. 6:51 AM

steveastrouk says:

Take a look at the Maxim data sheet, figure 6a and build a gain controlled amplifier. As an exercise, using a TTL is great. Steve

Jun 11, 2010. 4:00 PMProdigity (author) says:

Hey Steve, I've sent Maxim an email regarding the component and apparently it does not support negative voltages. Kinda bizarre because the datasheet mentions it can be used as a volume controller :S Oh well, I thank you for taking time to answer my question :) Greetings, Prodigity

Jun 11, 2010. 4:09 PM

steveastrouk says:

You've missed the point. You don't USE it the way you have been doing. You use it in a AC coupled gain controlled amp ! There is a perfect application circuit in the datasheet, in fact two, one as a variable resistor, the other as a potentiometer. A pot based design is likely to be more thermally stable. Steve

Jun 4, 2010. 6:26 AMProdigity (author) says:

I'm currently working on a project with a few people from my class.
We need to make a device which lowers the volume of a CD-player when someone starts talking into a microphone.

(ignore the dots)
...........................______
Microphone ->| .............| --Mic--> [Amplifier]
..........................|..M.A.F..|
CD-player --->|______| --CD--> [Amplifier]

We've split the device into several pieces so everyone could work on one piece.
My part is the actual audio dimmer;
I receive a HIGH digital signal (from another part in the M.A.F.) which tells me that the volume needs to go low for both CD audio channels.
As soon as the digital signal goes LOW, the volume of both audio channels needs to slowly rise back to full volume. (in 2 to 3 seconds)

My current setup is a digital potmeter over an opamp controlled by 2 555 timers to be able to adjust rising&dropping volume time.
The selection of which 555 timer is allowed to adjust the resistance of the dig. potmeter is arranged by a few TTL chips.

It actually nearly works except the digital potmeter(MAX5453) seems to display diode like behaviour when the signal goes below ground.

My question is: is there a chip that can replace the function of my entire part? or would you happen to know another solution?

Any ideas would be greatly appreciated.

p.s.
Adding DC offset to my signal is a possibilty but the MAX5453 has a very limited range in where it could work.