Intrest Check : Pretty Simple Digital Preamp / Volume Control

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I'm currently using a PGA2310 homebrew preamp and controlling it through a Microchip microcontroller. I'm very happy with it, since I'm one of those people who are constantly fretting about whether the vol control is still balanced, and this keeps it stable at all volume settings. I'd really like to be able to add IR remote control to it, though, where do you get info on how to do that?? I searched through the internet a while back but couldn't find an easy way to to do that (at least not with regular "universal" remotes).

BTW, rather than rotary encoders, I'm using the ADCs on the microcontroller to read DC voltages off a couple of cheap linear-taper pots, and using that reading to determine where to set gain and balance for the two channels. That makes for very inexpensive knob operation and works really well. It feels and acts to the user as if it were a regular volume pot and a balance pot, except that the channel to channel tracking is accurate (and of course the signal never goes through a pot). I didn't like the idea of having the micro running all the time and possibly making noise so I have it sleeping normally, but waking up when either knob setting changes. The DC pot voltages run to a couple of comparators that wake the micro on changes.

Anyway, one thing sorely lacking is remote control. Any pointers on how to attack that would be appreciated.
 
bwaslo said:
I'm currently using a PGA2310 homebrew preamp and controlling it through a Microchip microcontroller. I'm very happy with it, since I'm one of those people who are constantly fretting about whether the vol control is still balanced, and this keeps it stable at all volume settings. I'd really like to be able to add IR remote control to it, though, where do you get info on how to do that?? I searched through the internet a while back but couldn't find an easy way to to do that (at least not with regular "universal" remotes).

BTW, rather than rotary encoders, I'm using the ADCs on the microcontroller to read DC voltages off a couple of cheap linear-taper pots, and using that reading to determine where to set gain and balance for the two channels. That makes for very inexpensive knob operation and works really well. It feels and acts to the user as if it were a regular volume pot and a balance pot, except that the channel to channel tracking is accurate (and of course the signal never goes through a pot). I didn't like the idea of having the micro running all the time and possibly making noise so I have it sleeping normally, but waking up when either knob setting changes. The DC pot voltages run to a couple of comparators that wake the micro on changes.

Anyway, one thing sorely lacking is remote control. Any pointers on how to attack that would be appreciated.

bwaslo,

Thankyou for your comment, i have looked into ADC's and using a pot instead of a rotary encoder, but i have decided i do not want to re write the firmware i have allready found to use on my board, i agree that it feels a lot nicer to the touch but its somthing i would never get round to. I agree, the micro should be sleeping when not in use, this is part of the reason why i decided not to use extras like a lcd display etc.

About the remote control, i have also searched pretty much the whole internet for pointers on how to do this remote control efficiantly. I have came up with two quite good resources and source codes for decoding philips remote controls, one of them using a PGA2310 itself.

1. http://avr-mcu.dxp.pl/rc5+remote+control+infrared+assembly.html

2. www.latke.net/blog/punkengineer/archive/000049.html

I hope this helps, as i am also pretty confused on how to start on this, (im a php programmer :( ).
 
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bwaslo said:
I'm currently using a PGA2310 homebrew preamp and controlling it through a Microchip microcontroller. I'm very happy with it, since I'm one of those people who are constantly fretting about whether the vol control is still balanced, and this keeps it stable at all volume settings. I'd really like to be able to add IR remote control to it, though, where do you get info on how to do that?? I searched through the internet a while back but couldn't find an easy way to to do that (at least not with regular "universal" remotes).

BTW, rather than rotary encoders, I'm using the ADCs on the microcontroller to read DC voltages off a couple of cheap linear-taper pots, and using that reading to determine where to set gain and balance for the two channels. That makes for very inexpensive knob operation and works really well. It feels and acts to the user as if it were a regular volume pot and a balance pot, except that the channel to channel tracking is accurate (and of course the signal never goes through a pot). I didn't like the idea of having the micro running all the time and possibly making noise so I have it sleeping normally, but waking up when either knob setting changes. The DC pot voltages run to a couple of comparators that wake the micro on changes.

Anyway, one thing sorely lacking is remote control. Any pointers on how to attack that would be appreciated.


Bill,

Contact me through the forum, I may be able to help you.

Jan Didden
 
rhysh said:
Ok everyone, here is the deal.

I can either do this, with a LCD and a remote (no rotary)
OR
Do this with the rotary encoder, no LCD and no remote.

What do you think?

Nevermind, i have decided to keep the simplicity of this project, simple! Having a remote only controlled preamp doesnt really fit the bill, for hi-fi.
 
Right choice imo. Keeps things cheaper too :)

Just checking, one of these attenuators when powered up will apply the same attenuation as it had when powered down last? As far as I know rotary encoders turn indefinately and I don't know if there is a memory on board anywhere (in the micro?).
 
Rhysh

You are going to hate me for proposing a new design ;) but hear me out:

Instead of using 2 off THS4131's to convert SE outputs to balanced,
why not use 2off PGA2320's daisy-chained, one for left, one for right.

This way you get balanced or SE in, balanced or SE out and a simpler PCB.

i.e. you don't have to worry about THS4131's & their PS because you can omit them completely (unless you want them there for gain)

As for encoder vs remote dillema, I agree I would also go for the encoder option.

I am wondering whether you can get shaft type, top adjustment encoders so that the PCB can sit directly behind a panel with the knob mounted directly on the encoder shaft

- does that make sense?
 
As for those who think SMD components are tricky to solder, there's a neat little you can do to make life easier:

When you are designing the PCB you can use extended pads or allow enough track behind the sides of the SMD component so that you always solder the sides of it to the pad or track

if you are etching your own pcb that's very easy to do, you can just solder the part to the copper tracks if wide enough

this way you can use even the smallest 0603 resistors with no problems - very easy :D
 

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Dr.EM said:
Right choice imo. Keeps things cheaper too :)

Just checking, one of these attenuators when powered up will apply the same attenuation as it had when powered down last? As far as I know rotary encoders turn indefinately and I don't know if there is a memory on board anywhere (in the micro?).

Yes, the microcontroller stores the last volume level applied on powerdown, and restores this level on powerup.
 
chatziva said:
Rhysh

You are going to hate me for proposing a new design ;) but hear me out:

Instead of using 2 off THS4131's to convert SE outputs to balanced,
why not use 2off PGA2320's daisy-chained, one for left, one for right.

This way you get balanced or SE in, balanced or SE out and a simpler PCB.

i.e. you don't have to worry about THS4131's & their PS because you can omit them completely (unless you want them there for gain)

As for encoder vs remote dillema, I agree I would also go for the encoder option.

I am wondering whether you can get shaft type, top adjustment encoders so that the PCB can sit directly behind a panel with the knob mounted directly on the encoder shaft

- does that make sense?

chatziva,

If you think about your proposal again, this will not actually shrink pcb size at all, but instead will loose functionality.

Each channel has 1/2 a opa2134 for the buffer stage, and there are two buffer stages per channel. This equals out as one opamp per channel, if i was going to use daisy chained PGA's i would then need 4 opa2134's. This will just fill up the space of the THS4131's.

If i was to go this route, there is no way to get balanced output from a single ended input, that i can see, as the balanced line drivers wont be on the board layout. The only real advantage of this design that i can see, is the ability to use single balanced inputs.

Sorry if i am misunderstanding you, you may be proposing somthing completly diffrent.

The reason i dont really want balanced inputs on a single board, is becuase i have no balanced sources. This is why i am going to leave the option for the board to be stacked (using 2 boards) for a balanced input. All you would need on the second board, would be the PGA, resistors and the opa2134's. All power and digital control would be routed thru a 2 x 5 pin header.

I have not really looked at the variation in rotary encoders, but i think i would rather leave the encoder off the pcb, so people can choose which encoder they want to use.

Rhys
 
An externally hosted image should be here but it was not working when we last tested it.


Here is the latest draft layout i have came up with, it is not complete, just to give a basic idea on what it will look like. In this new design, you cannot see by the picture, but there is just a single trace per power rail, instead of power being routed all over the pcb, this should keep noise down a lot. Also, decoupling caps have been added to all opamps.

All the output opamps are now all along the top as you can see, with balanced and single ended outputs all available.
 
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