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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Passive Preamp: Arduino based, remote control, Relay R2R, input selection
Passive Preamp: Arduino based, remote control, Relay R2R, input selection
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Old 14th June 2015, 09:44 PM   #11
maxw is offline maxw  United Kingdom
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Passive Preamp: Arduino based, remote control, Relay R2R, input selection
And here's a pic of the some of the components mounted on to the machined front panel.
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Old 20th June 2015, 10:43 AM   #12
harwoodspark is offline harwoodspark  England
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I have to say that just looks so much better than a box with a knob sticking out the front. Very nice.
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Old 20th June 2015, 02:20 PM   #13
Nisbeth is offline Nisbeth  Denmark
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Passive Preamp: Arduino based, remote control, Relay R2R, input selection
Looks superb!

/U.
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Old 22nd June 2015, 08:45 PM   #14
maxw is offline maxw  United Kingdom
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Passive Preamp: Arduino based, remote control, Relay R2R, input selection
Quote:
Originally Posted by linuxworks View Post
btw, I really do not suggest going passive. each time I've done that I've regretted it. for relays, you end up with a pretty high-z at the output once all the stages are passed thru and unless your next stage is about an inch away, cable's length, you are degrading the signal and will likely have ground issues and hum. I find its good to have some buffer right after the relay atten, as close as possible. after that, you are now low-z and can run your cables like any other preamp's output.
Yeah I know all this and agree. Also relay attenuators usually 'click' at certain points too. Passive preamps are still very popular though. My reasons for making this preamp were just for fun really.

Quote:
Originally Posted by linuxworks View Post
finally, its very important that the digital ground and analog grounds are connected. even though they are logically quite separate, I have seen hum happen when they are not connected.
I don't really have this problem. There is some small hum but no more than the Khozmo one I have.
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Old 22nd June 2015, 08:50 PM   #15
maxw is offline maxw  United Kingdom
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Passive Preamp: Arduino based, remote control, Relay R2R, input selection
I decided to just use USB power for this preamp because:
- A modern USB mobile phone charger is very efficient and about the same size as a mains plug.
- It's much easier not having to worry about safety earth
- It's cheaper

I used a normal Samsung USB charger and have configured the Preamp to turn off the lights after 2 minutes. All the relays are latching so there is no need to have them powered unless changing an input or the volume level. This gives the following power consumption...
Lights on: 2.7W
Lights off: 0.9W

With 0.9W consumption I didn't really think it necessary to have a power switch. At my current rate in Germany this costs only 2 euro per year if no 24/7.
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Old 22nd June 2015, 09:03 PM   #16
maxw is offline maxw  United Kingdom
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Passive Preamp: Arduino based, remote control, Relay R2R, input selection
I finished the Arduino, here are the features:
  • Remote control using an Apple remote
  • Remote control of: Volume, mute, input selection.
  • Adafruit NeoPixel colour to indicate volume level (red = loud, blue = quiet)
  • Encoder to change volume
  • Button to change input (push the encoder)
  • Different increments for remote and encoder
  • Sleeps after 2 mins (just powers down the NeoPixel)


Arduino code and connection diagram are attached.
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Old 22nd June 2015, 09:06 PM   #17
maxw is offline maxw  United Kingdom
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Passive Preamp: Arduino based, remote control, Relay R2R, input selection
And complete

Click the image to open in full size.
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Old 25th June 2015, 05:09 PM   #18
Nisbeth is offline Nisbeth  Denmark
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Passive Preamp: Arduino based, remote control, Relay R2R, input selection
Once again, very nice

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Old 26th June 2015, 12:04 PM   #19
maxw is offline maxw  United Kingdom
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Passive Preamp: Arduino based, remote control, Relay R2R, input selection
Thanks
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Old 26th June 2015, 12:30 PM   #20
thimios is online now thimios  Greece
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Very nice ,congratulation!
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