F5 hums only after my iTouch is connected - diyAudio
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Old 14th November 2009, 05:09 PM   #1
NV&H is offline NV&H  United States
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Default F5 hums only after my iTouch is connected

With no input source connected, my F5 is as silent as the grave. As soon as I attach my iTouch, I get alot of noise. It doesn't seem to matter if the iPhone backlight is on or off. The iTouch doesn't seem affect other amps in this way...or perhaps other amps don't affect iTouches in this way. Not sure which.

Is there something about the F5 that can explain this? Could the very high bandwidth emf from the F5 be getting picked up by the iTouch?

No, I don't want to do serious listening with this arrangement, but until I get a Wadia and a D/A converter, it's all I've got.
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Old 14th November 2009, 05:16 PM   #2
tinitus is offline tinitus  Europe
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Be careful that you dont burn your F5
Its said to possibly be sensitive to such noisy things connected, driving it into oscillation
Which you may not even hear clearly, but only result in overheating

Yes, I did build some nice hefty AB amps to a friends
But one channel burned suddenly
And he did say that it happened when he connected his sons Ipod or similar
Im was told that if such amp rely on zobel on output to be stable it can become critical
A zobel can also burn, and the ball rolls
Well, F5 doens need zobel
But I would be very careful about which kind of sources to connect

Last edited by tinitus; 14th November 2009 at 05:21 PM.
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Old 14th November 2009, 05:16 PM   #3
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Either the iTouch is making the amp oscillate or it is emitting
noise which is affecting the amp. You can try a number of
things, including higher value input resistor than 1 Kohm,
or perhaps some small capacitance across the 100 ohm
feedback resistors.

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Old 16th November 2009, 11:20 PM   #4
alazira is offline alazira  United States
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Is the cord you use to attach the iTouch shielded? This amp is very sensitive to non-shielded connectors.
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