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Old 24th March 2010, 12:30 PM   #1
sulenta is offline sulenta  Australia
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Unhappy gainclone distortion problem "help"

Hi i've just build a gainclone amp 3876(altronics australia kit) and i hooked up in a chasiss with tube buffer(x10d clone from e bay),and i have a problem i started it up and on a about half way of a pot start distorting badly(squeeking noise).
I've done a ground star,as i've seen it in books and on the net,help please !
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Old 24th March 2010, 03:21 PM   #2
sulenta is offline sulenta  Australia
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well i separeted all of components and i test just the amp boards and they seem to start distorting(metal sounding,squeiki sound with no power) so problem is not in tube buffer.
but i test those boards and they seemed to be ok,the only thing that is changed since testing is power supply
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Old 24th March 2010, 09:10 PM   #3
johnr66 is offline johnr66  United States
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Quote:
Originally Posted by sulenta View Post
well i separeted all of components and i test just the amp boards and they seem to start distorting(metal sounding,squeiki sound with no power) so problem is not in tube buffer.
but i test those boards and they seemed to be ok,the only thing that is changed since testing is power supply
Sounds like oscillation. Possible too high of impedance on the input? To help you, schematics are needed and pictures of your rig. Oscilloscope is often a mystery solver.
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Old 25th March 2010, 05:45 AM   #4
ratza is offline ratza  Romania
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Quote:
Originally Posted by sulenta View Post
the only thing that is changed since testing is power supply
What do you use now? Are the chips hot if you let them idle for a few minutes?
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Old 21st April 2010, 03:15 PM   #5
sulenta is offline sulenta  Australia
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yes they get really hot
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Old 21st April 2010, 04:00 PM   #6
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Quote:
Originally Posted by sulenta View Post
but i test those boards and they seemed to be ok,the only thing that is changed since testing is power supply
1. Probably that low power of a power supply unit. What supply voltage without a signal and at distortions? How much falls under load?

2. Try to disconnect one channel - probably that Grounds of the right and left channel among themselves are incorrectly connected
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Old 21st April 2010, 04:45 PM   #7
sulenta is offline sulenta  Australia
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must be something with the power supply,cause i've tried amps before and they were working just fine but since i put them in this amp with this power supply started playing up.
i dont think is a ground cause is connected to the "star".
Must be something with a bypassing caps in a supply or with snubbers on diodes !?
I dont have a drawing to show you guys,thanks anyway for trying to help me !
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Old 21st April 2010, 04:48 PM   #8
sulenta is offline sulenta  Australia
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Well is not transformer definetly cause i wounded myself(thats what i do for living),transformer can easily supply 5 amp per rail,without any increase in temp.
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Old 21st April 2010, 05:05 PM   #9
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Originally Posted by sulenta View Post
about half way of a pot start distorting badly(squeeking noise).
It is a bit difficult to guess how that corresponds to the output power, because we don't know how efficient your speakers are, how loud your source is and what pot you got. Is it already much louder than a normal conversation when it starts to distort?

Quote:
Originally Posted by sulenta View Post
Must be something with a bypassing caps in a supply
Polarity?
Could there be a short (solder sputter, touching wires) at the amplifier output?
Do you have the RF filters installed, especially the combination of RC snubber from output to ground and L||C from output to speaker?
Did you keep the wiring to the input separate from the wiring to the speaker and from the PSU? If you wind transformers, you know what inductive coupling means.

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I dont have a drawing
How did you build it without a drawing?
You could also post photos.
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Old 21st April 2010, 10:01 PM   #10
wazzy is offline wazzy  Zimbabwe
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that sound is the protection working, a picture of both sides of the board would be very useful, there is hope, use safety resistors before you test with full power, keeps the smoke in the ic's...
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