Classroom amp recommendations?

xron · 30th December 2010, 07:29 PM

I've recently set up an audio/video system for a meeting/training room at work, but ran into problems with the in-ceiling stereo amplifier. The problem is the loud buzz when nothing is plugged into the end of the 25' input cable. As soon as an MP3 player or laptop is plugged in it's dead silent and sounds great. The amp I tried is a Lepai TA2020.

In a Lepai amp thread I was told I need an amp with balanced inputs or a balanced to unbalanced converter (thanks MWN). All I'm finding through google and Ebay for balanced amps are headphone amps and $2000+ overkill amps. I was hoping someone could let me know what to search for or recommend a suitable 15-20 watt amp that can drive four 8 Ohm speakers. My budget is $200 max, but I'm perfectly willing to spend less :-)

theAnonymous1 · 30th December 2010, 07:54 PM

Your problem really has nothing to do with balanced vs unbalanced inputs.

The problem is that when you disconnect the audio source from the amp the inputs are left floating with a long wire still attached that acts like a big antenna, injecting noise into the amplifier.

Budgie · 30th December 2010, 08:06 PM

A simple solution is to build a small box with a switch to mute the lines when the device is going to be unplugged.

xron · 30th December 2010, 08:30 PM

In a different video conference room we have similar setup, but with a different amp and a longer input cable. It's dead quiet. I don't know the amp make or model # (not working this week), but while googling for balanced/unbalanced amps I ran across the Extron MPS-152. From memory, the amp looks like our VC system amp, and the Extron website says it has balanced and unbalanced inputs. I know a quiet setup is possible, I just don't know how...

30th December 2010, 07:29 PM	#1
xron diyAudio Member Join Date: Nov 2010	Classroom amp recommendations? I've recently set up an audio/video system for a meeting/training room at work, but ran into problems with the in-ceiling stereo amplifier. The problem is the loud buzz when nothing is plugged into the end of the 25' input cable. As soon as an MP3 player or laptop is plugged in it's dead silent and sounds great. The amp I tried is a Lepai TA2020. In a Lepai amp thread I was told I need an amp with balanced inputs or a balanced to unbalanced converter (thanks MWN). All I'm finding through google and Ebay for balanced amps are headphone amps and $2000+ overkill amps. I was hoping someone could let me know what to search for or recommend a suitable 15-20 watt amp that can drive four 8 Ohm speakers. My budget is $200 max, but I'm perfectly willing to spend less :-)

30th December 2010, 07:54 PM	#2
theAnonymous1 diyAudio Member Join Date: Feb 2004 Location: Anonymityville	Your problem really has nothing to do with balanced vs unbalanced inputs. The problem is that when you disconnect the audio source from the amp the inputs are left floating with a long wire still attached that acts like a big antenna, injecting noise into the amplifier. __________________ "If you don't like funerals don't kick sand in Ninja's face." - Ninja

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30th December 2010, 08:06 PM	#3
Budgie diyAudio Member Join Date: Jan 2003 Location: Paymoretaxin, Oregon	A simple solution is to build a small box with a switch to mute the lines when the device is going to be unplugged.

30th December 2010, 08:30 PM	#4
xron diyAudio Member Join Date: Nov 2010	In a different video conference room we have similar setup, but with a different amp and a longer input cable. It's dead quiet. I don't know the amp make or model # (not working this week), but while googling for balanced/unbalanced amps I ran across the Extron MPS-152. From memory, the amp looks like our VC system amp, and the Extron website says it has balanced and unbalanced inputs. I know a quiet setup is possible, I just don't know how...

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