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.
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 ?
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 ?
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?.
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?.
mskeete said:
any web pages to help me with that ?
i really know nothing about those 🙂
the problem with vca is that they change the feedback while changing gain - thats bad for audio 🙂
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...
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...
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
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
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.
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.
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
http://www.sprut.de/electronic/pic/projekte/brenner5/br5_sch.gif
link also on my page
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