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Old 4th August 2002, 08:54 PM   #1
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Default remote volume control digital? analog?

I am trying to design a "integrated" amplifer right now, not exactly integrated, It's going to have 3 chassis, one for a psu and the controls, another for the monoblocks, sort of like the Mark levinson "clean box" "dirty box" not just an outboard power supply.

The theory behind this is that if the audio is just exposed to nice clean dc, and the channels are seperate, it will sound reely good.

This however presents a very big problem for me, how do i have the psu unit operate the volume controls, now keep in mind i dont want any microprocessors to be in the chassis with the audio box.

I know i could use a motorized attenuator or pottmeter, but i would much rather get a more precise digital one (think Ti PGA 2310 or similar)

Could i have the 2310 attenuate a wave form, then rectify and filter it a bunch, then send that over to the amplifer chassis? I would want this DC to power a pre amp, What would changing the voltages supplied to a gain device have an effect on? I know it'd lower the output, but by how much, and would this degrade the sound a lot? Would there have to be some sort of active biasing?

any ideas would be greatly appreciated?
I need to worry about switching sources to.....


thanks,
ben
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Old 4th August 2002, 10:28 PM   #2
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If you used a PGA2310, it would have to be in the amplifier chassis, in the audio path. The micropocessor could be in another chassis - you could opto-couple the 3 control lines if you were worried.... And there would only be activity on these lines when the volume is being changed...

In my experience, there aren't that many VCAs (voltage controlled amplifers) out there. Especially if you are fussy about the audio specs and performance.

You could use a motorised pot. Simple, excellent sound quality, simple (ie clean) audio path. Easy to control. You'd have to rethink your scheme, as you need to run the audio signals through this pot... You couldn't have a pot in each monoblock, as they wouldn't stay in synch...

You could have a look at my website for some info about preamp volume controls....
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Old 4th August 2002, 11:04 PM   #3
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mhennessy,

your preamp is very nice. you mentioned opto-couple, i'm kinda confused, is the chip only switched on when it's receiving information?

From your website i got the impression that the programming is very difficult, without the menu system would there be any need for programming? i only want very basic functions, volume, mute and input switching.

thanks,
ben
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Old 4th August 2002, 11:34 PM   #4
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Using opto-couplers is a really good way of transferring the digital control signals (clock, data and /CS) to the PGA2310 in the amplifier chassis. It maintains electrical isolation between the analogue and digital circuitry, which makes life nice and easy and avoids a whole load of interferrence and ground-loop problems...

You'd mount the 3 optocouplers in the amplifier chassis - the transistors in the optocouplers are connected to the PGA2310. The LED's in the optocouplers are connected to a connector of some sort, which goes back to the controller chassis. Nice and simple.

For an example of this, check out http://www.die-klaassens.de/Audio_un...reamp_l10.html

The PGA2310 is powered continuously (of course!), but you only need to send it signals when you power up or change volume...

Yes, ignoring the menu's, the programming is quite simple. Addressing the PGA2310's is very easy indeed. Decoding remote control and front panel switches is a bit harder... But, I managed it, and I'd never programmed a PIC until last year!

Finally, something I forgot last time, for controlling input select relays, check the UCN5821 that I used. It is also serially controlled, so just another 3 control lines required...
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Old 5th August 2002, 12:09 AM   #5
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I cant seem to find any information on the UCN5821, who manufactures it?

i seem to be toying with the idea of making the display circuts. Would you be willing to share you code? My dad has an ic programer and i think i can figure it out. How much code did you have to write? Any good sites out there for help on doing this?

thanks,
ben
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Old 5th August 2002, 12:25 AM   #6
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Old 5th August 2002, 12:27 AM   #7
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Hi,

Actually, a co-worker ans I are starting to design a kit to allow one to add a display/key input/remote to any project.

What features are you looking for?

Best Regards,

Dale
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Old 5th August 2002, 12:52 AM   #8
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i was planning on the bare minimum, volume, souce switching and mute.

But if you're already designing one to use with any project, i think balance, input naming, presets being able to remember volumes for specific inputs (balance would be nice to) would all be reely cool

Also please put an option in to dim/turn off the display, there's nothing quite like listeing to music in the complete dark and wondering were the speakers are.

Would you offer preprogrammed chips? My design would need 2 seperate volume controls (pga2310) how hard would this be to add?

this would save me much heart ache if you have the controls already pre designed. How much longer do you think till there finished? i'd be reely interested in seeing the schematics you make.

Also what is the price goal for this circut? 100? 200?

thanks,
ben
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Old 5th August 2002, 01:49 PM   #9
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Don't worry about putting the uP in the same box as the attenuator chip. If you use the right uP, you can put it to sleep when it is not in use and it won't make any digital noise at all. Look at the PIC uC part. Sleep mode even stops the clock.

MR
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