My version of GC, a LM3886 based

[Dino-Indo]

Hi All,

Just wanna share my version of Gainclone using LM3886..

 

[Dino-Indo]

Oops...
Forgot the attachment!! Sorry...

 

[Dino-Indo]

Another view..

Bought in a kit mode… Toroid is 300VA, using 18V supply from it with Carlos FM’s snubber circuit design on the PS PCB (thanks for sharing Carlos!!)

 

[Dino-Indo]

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....

 

[Dino-Indo]

Another pic

 

[Dino-Indo]

Last pic..

Input Buffer BU-2 from Audio-GD…

Really improves the sound performance

Overall... really satisfied with this new toy...

 

[Puffin]

The pictures are difficult to follow. Did you have your own PCB's made ? if so show us the schematic. I have not used an inductor. where have you put it ?

 

[Dino-Indo]

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...
(shouldn't be isn't it ?)


Regards,

 

[Puffin]

The one thing that is different to the circuit I used is the use of the inductor. Do you know why it is there ? I understand that inductors pick up RFI.

 

[peranders]

The output inductor is for isolating the amp against capactive load but also to block RFI picked up from the speaker cable.

 

[Puffin]

Peranders. Is it just Class D where inductors attract RFI ? They say that when modding Class D amps you should shield the inductors (copper) and ground it ?

 

[AndrewT]

The Thiele network on the output does two jobs.
1.) it provides a defined load at high frequency.
2.) it attenuates back emf/RFI that tries to enter the feedback route.

 

[Dino-Indo]

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? ... 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....

 

[ttan98]

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? ... 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....

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.

 

[AndrewT]

don't confuse the Safety Earth with the Audio Ground, Power Ground, Signal Ground etc.

 

[Dino-Indo]

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,

 

[gainphile]

Bagus

 

[Dino-Indo]

Hi Gainphile...

Terima kasih...Thank you.. Arigato...

Actually, one of the posted thread mentioned in my previous reply was yours... Hehehe...

Again... Many thanks

 

[johny]

hi dino, we have the same source getting the kit . 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 ), 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]

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...