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Old 4th December 2010, 08:05 PM   #1
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Default Headbanger Grounds Trouble

hey guys
i built myself a Headbanger Headphone amplifier for the second time, and i have oscillations.i am just very sure its the grounding.the article makes the grounding very difficult to understand as there are tit-bits here and there in the article.the only thing i understand is input grounds wont be connected to output grounds. if i dont connect input ground to output grounds, i dont get sound.if i do, its sound + oscillations. please just help me figure out the grounding scheme here, i am attaching the schematic, linking the tutorial.maybe edit the schematic in paint to demonstrate connections.am clueless, please do help.

please note i get sound + oscillations when i connect all the grounds in the schematic.

tutorial: HeadBanger Headphone Amp Construction Kit

please help

thanx a lot.
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Old 4th December 2010, 08:59 PM   #2
godfrey is offline godfrey  South Africa
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Each channel of the headbanger is almost exactly the same as the other amp you built, except for the parts circled in red. Those new parts should'nt make it oscillate, though. The 10uF capacitor from pin 7 to earth is to reduce hum if you're using a mains power supply. The other capacitor and resistor give the amp some extra gain, but also make distortion a bit worse.

The layout in that tutorial you linked to is a mess anyway, so why not just build it the same way you did the other one?

The most important thing is probably the capacitor you added last time that fixed the oscillation.
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Old 5th December 2010, 05:44 AM   #3
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But i have already built the amp.i dont want to assemble it once again.takes a lot of tym.plus, i want to finish what i started.any info about the grounding u might have to help me complete it?jus guide what ground wire goes where.
Thanx.
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Old 5th December 2010, 07:40 AM   #4
Bonsai is offline Bonsai  Taiwan
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Can you post up a photo of the inside of your headphone amp.
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Old 5th December 2010, 09:11 AM   #5
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yup, sure bonsai
uploaded (though i guess the images wont help much)
also, i am getting good sound from the left and right channels when separately run.(as in left channel ground disconnected, right channel grounds connected, input inro right channel, and i get cool sound on right channel). only when i have to run them together is there a problem.

please note "Grounding is the only problem here" (i dont know what to do with the grounds in this particular circuit).when right channel grounds and right channel grounds are connected together, there is oscillation. as in the schematic with the red circles.

please help me guys.

also, godfrey, please note the 470microfarad cap and the 0.1microfarad cap in the battery circuit.i am surely not missing the 0.1microfarad cap this time.
Attached Images
File Type: jpg Image295.jpg (121.7 KB, 80 views)
File Type: jpg Image298.jpg (176.5 KB, 72 views)
File Type: jpg Image301.jpg (153.0 KB, 66 views)
File Type: gif schem.gif (12.9 KB, 35 views)
File Type: gif original schematic.gif (8.4 KB, 31 views)

Last edited by noobman92; 5th December 2010 at 09:15 AM.
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Old 5th December 2010, 04:27 PM   #6
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The optional resistor can reduce hum, if you still have some after using separate leads to the starpoint.
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Old 5th December 2010, 04:28 PM   #7
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thankx guys. its working.....the trouble was with the placement of the ground wires (astonishing; atleast for me)
thanx everyone.
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Old 6th December 2010, 12:07 PM   #8
AndrewT is offline AndrewT  Scotland
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Everyone's problem is that we call everything "Ground".

Most of these wires/connection are the return of a Flow and Return Pair.
They should be run as a pair from the Source to the Receiver.

The power supply to your 386 is a pair, +ve Flow and 0V return. Run these as a pair.
The speaker feed is also a pair. Speaker Flow and Return as a pair from amp to terminals. But here we have our first exception. Do not take the Speaker Return onto the PCB, unless the PCB has the Main Central Audio Ground on board. Multi-channel amplifiers usually have the amps on different PCBs. These must have a separate Main Central Ground and Speaker Return goes here after it arrives at (but not connected) the PCB.

Then consider which returns need to be referenced to a common reference voltage. Use a main Central Audio Ground for this common voltage reference.
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