My version of GC, a LM3886 based

Dino-Indo

Member
2007-01-19 6:18 am
Oops...
Forgot the attachment!! Sorry...
 

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Dino-Indo

Member
2007-01-19 6:18 am
PCB view...

Simple PCB layout, several Riken RM resistors , one 0.7uH inductor paralleled with 10R 1 Watt resistor (at bottom side of PCB), Nichicon Gold 47uF, Nippon Chemicon 100uF...

LM3886 supply pins (at the bottom side) decoupled to ground with 3300pF Wima FKS and ground pin connected to central grounding with 22K Resistor... reducing the DC offset from 30mV to approx. 4mV....
 

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Dino-Indo

Member
2007-01-19 6:18 am
Hi Puffin,

Thanks for your respond..
Enclosed please find the schematic....

The PCB was purchased (together with the components, toroids, etc) in a kit form from a local electronic supplier in Jakarta, Indonesia (Mr. Alex MNP at www.langsungjadi.com).

I put the inductor as per schematic, parallel with R7...

Problem is... now I'm hearing very small hum...
:xeye: (shouldn't be isn't it ?)


Regards,
 

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Dino-Indo

Member
2007-01-19 6:18 am
Dear All...

After browsing so many threads in this site, I finally found a way out to solve the humming problem... A separate ground for power and signal (sounds silly eh? :rolleyes: ... one of those DIY Greenhorn mistakes I presume...)

I also applied grounding circuit as suggested in Elliot Sound Project' website on grounding a power supply for amp...

So, afterward...humming is VERY SMALL and only on right channel.. only can be heard when gain knob at full volume...

Now.. everything ROCKS!! ...

I really glad to be the member of this forum....

God Bless You All....

:D
 

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ttan98

Member
2006-04-04 11:24 am
Melb
Dino-Indo said:
Dear All...

After browsing so many threads in this site, I finally found a way out to solve the humming problem... A separate ground for power and signal (sounds silly eh? :rolleyes: ... one of those DIY Greenhorn mistakes I presume...)

I also applied grounding circuit as suggested in Elliot Sound Project' website on grounding a power supply for amp...

So, afterward...humming is VERY SMALL and only on right channel.. only can be heard when gain knob at full volume...

Now.. everything ROCKS!! ...

I really glad to be the member of this forum....

God Bless You All....

:D


If your chasis is metal sheilded you must not separate the main earth with signal gnd, it is dangerous.

main earth can be connected to signal gnd via a 10 ohm resistor that will reduce gnd loop and elevate danger.
 

Dino-Indo

Member
2007-01-19 6:18 am
Hi Ttan98 & Andrew T

Thanks for your advise...

FYI, the electricity socket from state supply to most housing in Indonesia is having 2 prongs only ... not 3 prongs as in many other country (which one of it is for earth grounding...)...

As to the signal groundings to the chassis, I have attached 22K resistor (please refer to my previous picture).... hopefully it is a safe measure...

Best regards,
:)
 
hi dino, we have the same source getting the kit:D . i have the same problem as yours, n i think i'll try your method.
anyway i have several question, before you fix the problem:
1. did you try to connect the amp with any source?
2. did you use input caps?

when i connect my amp with an mp3 player as a source(cheap one:D ), all of that noise is gone, no hum or low frequencies noise. without a source connected, i can hear that noise from the speaker.
i also try to take out the input caps, an the noise become smaller.
one more think, when i check the DC voltage on the output, its only -0.3mv. is this normal?
thx
 

Dino-Indo

Member
2007-01-19 6:18 am
Hi Johny!

I did not use input cap and yes, I did tried out to connect the amp, either directly to the CDPlayer or to my Non OS DAC, both produced very small hiss ... (just recently). I would assume that this might be relate to different impedance issue between the amp and the source...

I did rearrange the grounding cables and use thicker (I think it's a 18 AWG cable) cable for the PS grounding.
- 0.3mV DC output? I assume it should be OK...

FYI ... I also install additional smoothing caps on the PSU, as now I got 6 x 4700uF caps per power rail (total PSU capacitance now 28200 uF x 2... I hope it is not overkill hahahaha...) and I also changed the bridge rectifier with 4 SF4007 sinterglass avalance diodes... the result?? Awesome!!

Jawdropping bass.. its gets punchier and deep... also I noticed mid range and high improved... clearer...
:D:D
 

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