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Old 7th June 2013, 05:22 PM   #1
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Default Poor Man's Sonos Class D

I'm trying to build my own Multizone audio system based off of iTunes Airplay as the backbone. I'm thinking of embedding a RaspberryPi, with USB Wifi card and USB sound card along with a Class D amp board into some bookshelf speakers for each zone. A Raspberry Pi running AirPi and a USB sound card and a set of bookshelf speakers (AirPi – AirPlay audio with Raspberry | trouch.com) seems to have been shown to work. The issue I'm having is with the amp. I'm thinking of using this board TA2020 MKII Bluetooth Tripath amplifier 2X 25 Watts 12V fully finished | eBay

My main concern is that I want everything controlled from the iPhone so I don't want to have to go turn on the power to the amp if I want a zone on. I don't want to just leave the amp on all the time because there will be some very low level humm that will drive me crazy. So I think I need an line level sensing relay to turn off the amplifier, or that part of the circuit, when there is no input. I'm thinking of using Radio Design Labs ST-ACR2. At a $99 that would be the most expensive component! Does anyone have any ideas on how to accomplish this cheaper?

I was also looking at the Leipai amp as it has a "sleep pin" which I thought might be useful for muting the amp and avoiding hum when the amp is not receiving a signal, but I have not heard from anyone in that forum about any ideas on how to do that.
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Old 8th June 2013, 11:32 AM   #2
oli1122 is offline oli1122  United Kingdom
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Location: Kent, UK
Quote:
Originally Posted by JustinCA View Post
I'm trying to build my own Multizone audio system based off of iTunes Airplay as the backbone. I'm thinking of embedding a RaspberryPi, with USB Wifi card and USB sound card along with a Class D amp board into some bookshelf speakers for each zone. A Raspberry Pi running AirPi and a USB sound card and a set of bookshelf speakers (AirPi – AirPlay audio with Raspberry | trouch.com) seems to have been shown to work. The issue I'm having is with the amp. I'm thinking of using this board TA2020 MKII Bluetooth Tripath amplifier 2X 25 Watts 12V fully finished | eBay

My main concern is that I want everything controlled from the iPhone so I don't want to have to go turn on the power to the amp if I want a zone on. I don't want to just leave the amp on all the time because there will be some very low level humm that will drive me crazy. So I think I need an line level sensing relay to turn off the amplifier, or that part of the circuit, when there is no input. I'm thinking of using Radio Design Labs ST-ACR2. At a $99 that would be the most expensive component! Does anyone have any ideas on how to accomplish this cheaper?

I was also looking at the Leipai amp as it has a "sleep pin" which I thought might be useful for muting the amp and avoiding hum when the amp is not receiving a signal, but I have not heard from anyone in that forum about any ideas on how to do that.
Sound like a nice project, very interesting and a nice idea to use the Raspberry Pi. I would recommend one of the SMSL amps or even a Lepai 2020 (may need modding) Both can be found for around £25 or even cheaper in the US $20.

Personally I would look at getting a Lepai and modding that. You could just use the outputs on the Pi to control a relay (replaceing the on/off switch) and modify the code for the AirPi so that when no device is conncted it would power off the amp.

Anyway good luck I hope I helped, and be sure to keep posting updates.
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Old 8th June 2013, 09:06 PM   #3
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STOP!!! Do NOT even begin to think about anything with the "Lepai" brand on it!

Go with SMSL, 41Hz AMP6, Topping, Indeed or similar high quality properly built amp using genuine high grade components.
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Old 10th June 2013, 06:03 PM   #4
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Thanks for the encouragement. I just ordered an ACR1 from ebay for a nice price ($13 shipped), but it only has a 5 second delay. I'm guessing I can swap out a capacitor or something in the circuit to extend that.
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