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Old 6th January 2004, 12:03 AM   #1
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Default Preamp design

Hi guys im after a nice simple design for a preamp to got with the apox volume control setup.

Any ideas ?
just needs to be clean - no balance or tone controls.

Also if possible a pcb be avaliable


I'm open to more complex ideas - but would prefer simple. ie not discrete ( woud be nice but pcb design etc is not my forte )
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Old 6th January 2004, 02:37 AM   #2
tg3 is offline tg3  United States
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The High Quality Preamp from Elliott Sound Products seems to fit your criteria, and you can buy the PCB.

Click the image to open in full size.
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Old 6th January 2004, 02:57 AM   #3
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I looked at that one - but wasn't sure how to bypass the balance .

Buying from these guys would be great cause they are just up the road from my place
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Old 6th January 2004, 03:13 AM   #4
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Omit VR2. No balance control.
But note well Rod's comment about the effect of the pot on sound quality.
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Old 6th January 2004, 05:17 AM   #5
sonnya is offline sonnya  Denmark
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Default Re: Preamp design

Quote:
Originally posted by FBLEAGH
Hi guys im after a nice simple design for a preamp to got with the apox volume control setup.

Any ideas ?
just needs to be clean - no balance or tone controls.

Also if possible a pcb be avaliable


I'm open to more complex ideas - but would prefer simple. ie not discrete ( woud be nice but pcb design etc is not my forte )
Next monday i will upload a complete schematic on my homepage for a simple preamp....

But at the moment the attenuator and output can be found in a PDF file
here ..

Feel free to use it.
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Old 6th January 2004, 04:43 PM   #6
sobazz is offline sobazz  Denmark
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Nice!

Which microcontroller will you be using for the pot? Or can you connect a rotary encoder directly to that potentiometer chip?

I'm trying to get started with programming og PIC's, but it's certainly not easy, when my only programming experience is with PHP...

But I'm wondering - what would it require to do a balanced version of your pot-circuit? I'd need two pots, but how would I connect them to the PIC/rotary encoder?
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Old 6th January 2004, 08:14 PM   #7
sonnya is offline sonnya  Denmark
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Hi , actually i have a circuit diagram for the balanced too....

I will use ATmega8515 or ATmega16/32. depends on my memory needs. And they are programmed in "C"

More to come...
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Old 6th January 2004, 11:19 PM   #8
sobazz is offline sobazz  Denmark
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Great, I'm looking forward to seeing it...
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Old 7th January 2004, 07:20 AM   #9
sonnya is offline sonnya  Denmark
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The Balanced version is here : mirandp2-1.pdf

As you can see the two XWM8816 is connected in parralel on the SPI bus (MUTE,CS1,SDI,SCLK) if you want to control them individual you need to seperate CS1. You still use the same SPI interface. Only chip select is separated.
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Old 7th January 2004, 08:08 AM   #10
sobazz is offline sobazz  Denmark
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Great. I'll dig into this whenever I get around to making a PIC burner.

Have you thought about biasing the opamps into class A? With AD8620/AD8610 the improvement is minimal if existing at all, but with OPA627 there should be a noticable improvement.

Btw - how many microcontrollers do you end up using for the whole preamp?
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