RMI-FC100, a single stage audio power amplifier - Page 122

zdr · 11th January 2012, 10:32 AM

I am just enjoying the build - I would not count on myself as an amp reviewer (unless there is really dramatic change in sound)

zdr · 17th January 2012, 09:59 PM

Well, I am done now. I just have one little problem - how do I stop those little hairs on the back of my neck from standing up while this baby is playing?

I am done with amps now, I might build one day another just like this one. I just need to solve some minor hum issues, and it's getting a bit hot with Re=0.1 on those small sinks, so I might go for 0.22.

I am using BF862 in the front. Right channel pair is matched on Idss only at 0.01mA, and offset is at 0.4mV. The other channel is a bit loose at 1.4mV.

zdr · 17th January 2012, 10:21 PM

Photo:

zdr · 21st January 2012, 09:32 PM

I had a strange occurence today. I had to increase all Res to 0.15ohm since my sinks were not up to the task. When I reassembled the amp, I got trafo hum from both channels - and excessive buzzing noise from the output stage toroid itself. I disconnected output stages of both channels and noise went away. I connected one channel back, still no noise. I put back the second channel - again no noise! Any ideas what happened?

Macleod · 23rd January 2012, 07:54 AM

And what happen is you plug in first the faulty amplifier?

Is the DC level at the output of the amplifier 0V?

Toroid may buzz when a DC current flew through their windings. Depending on the way you designed the power supply (one diode bridge or two diode bridges?), different consumption on + and - rail main lead to DC current.

Check DC condition with no signal and compare Left and right channels.

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11th January 2012, 10:32 AM	#1211
zdr diyAudio Member Join Date: Nov 2005 Location: Brussels	I am just enjoying the build - I would not count on myself as an amp reviewer (unless there is really dramatic change in sound)

21st January 2012, 09:32 PM	#1214
zdr diyAudio Member Join Date: Nov 2005 Location: Brussels	I had a strange occurence today. I had to increase all Res to 0.15ohm since my sinks were not up to the task. When I reassembled the amp, I got trafo hum from both channels - and excessive buzzing noise from the output stage toroid itself. I disconnected output stages of both channels and noise went away. I connected one channel back, still no noise. I put back the second channel - again no noise! Any ideas what happened?

23rd January 2012, 07:54 AM	#1215
Macleod diyAudio Member Join Date: Dec 2008 Location: Toulouse, south of France	And what happen is you plug in first the faulty amplifier? Is the DC level at the output of the amplifier 0V? Toroid may buzz when a DC current flew through their windings. Depending on the way you designed the power supply (one diode bridge or two diode bridges?), different consumption on + and - rail main lead to DC current. Check DC condition with no signal and compare Left and right channels.

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