RMI-FC100, a single stage audio power amplifier - Page 122 - diyAudio
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Old 11th January 2012, 10:32 AM   #1211
zdr is offline zdr  Belgium
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I am just enjoying the build - I would not count on myself as an amp reviewer (unless there is really dramatic change in sound)
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Old 17th January 2012, 09:59 PM   #1212
zdr is offline zdr  Belgium
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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.
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Old 17th January 2012, 10:21 PM   #1213
zdr is offline zdr  Belgium
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Old 21st January 2012, 09:32 PM   #1214
zdr is offline zdr  Belgium
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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?
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Old 23rd January 2012, 07:54 AM   #1215
Macleod is offline Macleod  France
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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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Old 1st July 2012, 06:06 AM   #1216
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I don't suppose there are any PCB for amp and PSU still available?

Thanks
Do
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Old 3rd July 2012, 04:10 PM   #1217
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Hi,
may I ask, if I can use 39VAC secondary transformer (39VAC without load, perhaps it's 37VAC transformer) for Fronted PSU with 39V zener diode and TO-220 VERT 7.5 TR heatsinks? If yes, what other components shall I change for 42VDC output?
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Old 25th October 2012, 09:03 AM   #1218
atupi is offline atupi  Romania
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Hello, a 150VA toroid 2x30V per channel (power) would be good to use ?
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Old 25th October 2012, 09:45 AM   #1219
AndrewT is offline AndrewT  Scotland
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30+30Vac would be good to use with 8ohms speaker.
150VA would power one channel.
But, be careful, some devices dissipate a lot more power when the higher voltage transformer is used. You really do need to check every component for current flow to ensure the circuit will still work as designed and then check every component for maximum power dissipation to ensure they are all within a sensible operating temperature.
If you cannot do this your self, then you should not be changing the transformer from the designer's specification !!!!!!!!!!!!
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Old 25th October 2012, 07:57 PM   #1220
alex mm is offline alex mm  Romania
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zdr if not to late " It is very important that the bolt through the center of the toroid not be allowed to
create a shorted turn by having both ends of it conductively tied to the chassis. One end of the bolt should float."
Regards Alex.
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