volume control

[Richard C]

I haven't investigated this but it might be worth considering some kind of optical coupling. Your pot could control the brightness of an led shining on a couple of ldr's the resistance of which controls the gain of a couple of op-amps.

 

[sss]

somebody else told me that already
it wount be linear though

 

[mskeete]

One way of controlloing the pga2311 is via a PIC microchip. A bit of a steep learning curve if you haven't programmed before but it can be quite fun once you get into it.

There are some bad IC's around that give VCA's a bad name but I thought that the THAT VCA's were quite good ?

 

[Richard C]

ahh yes, just spotted it, I should have read through properly.

It probably wouldn't be very linear and the only way to know for sure would be to build the hardware and take a few measurements. However, linearity is not a requirement for an audio attenuator (assuming that is its purpose), more important is that it gives a progressive and usable control range and that both channels are closely matched.

When you consider a standard passive attenuator consisting of a logarithmic pot of maybe 20k feeding a power-amp with an input impedance of 10k then this is also a far from ideal, it's behaviour is neither linear or logarithmic.

I would imagine that once the forward voltage of the led has been reached the light output relative to input current would follow a fairly gentle curve, and I doubt there would be any surprises from the ldr. My only concern is are ldr's too noisy?.

 

[sss]

One way of controlloing the pga2311 is via a PIC microchip. A bit of a steep learning curve if you haven't programmed before but it can be quite fun once you get into it

any web pages to help me with that ?
i really know nothing about those

There are some bad IC's around that give VCA's a bad name but I thought that the THAT VCA's were quite good ?

the problem with vca is that they change the feedback while changing gain - thats bad for audio

 

[till]

any web pages to help me with that ?

http://www.diyaudio.com/forums/showthread.php?postid=245342#post245342

 

[sss]

i wanna lern from scratch , thats not helping

 

[till]

but you can read and find links to the places for learning.

http://www.microchip.com/1010/index.htm

http://www.microchip.com/1010/suppdoc/design/start/index.htm

http://www.piclist.com/techref/piclist/index.htm

http://www.sprut.de/electronic/pic/index.htm

do you want to build a volume controll / preamp or do you want to learn programming microcontrollers?


if you say in your first posting exactly whats your aim its easy for people here to help. else...

 

[sss]

sorry for the confusion till
at first i wanted to find a way to control 2 channels with a single pot and couldnt find a way to do that .Then i looked at TIs website and saw the pga23xx chips , the specs are very good so i decided to use one of those , i got the pga2311 ,before buying it i thought its got up/down pins to control the volume as some of those digital volume controll chips do , then i realized .......i need a microcontroller

 

[till]

ok, so you would need a PIC16F628, a rotary encoder, and someone who has a programmer to flash the firmeware from my page into the PIC. For a simple solution.

If you want to make your own firmware, you need a programmer, some pic flash microcontrollers, and start to build simple circuits and programm things like flashing LEDs.

 

[sss]

can i program it from a pc port?

 

[till]

this information could also be found on my page - you need to buy or build a programmer. This device lives between PC port and the MC. I build this http://www.sprut.de/electronic/pic/brenner/#brenner5
http://www.sprut.de/electronic/pic/projekte/brenner5/br5_sch.gif

link also on my page

 

[sss]

thanx till
ii'll try to make it