another buzzing 3875 GC...

hello,

it's my first post on this forum... the GC is my first diy amplifier.
I searched and found great infos about GC... but I'm lost with so much solutions for humming ou buzzing GC...

my 3875 is a stereo briangt kit; offset is below 13mV and 4 mv but it still remains a very light buzz ...

maybe a picture is better than words...

thanks for any answer and sorry for my poor english....
http://home.tele2.fr/robicam/gainclone.JPG
 
Bonne nuit,

I keep saying that those boards have a design fault, they are not properly designed to use with a single PSU/rectifier board for two channels.:rolleyes:

I suggest that you join PG+ and PG- on the rectifier board (make it the star ground), place it on a central position between the two channels and use as short as possible wires to be amplifier boards.
THICK wires for PSU, specially (very important) the ground.
Space is limited, though... the rectifiers will be too close from the RCA plugs.:xeye:
 
thanks carlos,

I ve modified the ground wiring ( join pg+/- on the amplifier and rectifier )

it looks like this now.... I ve used 1 and 1,5mm Cu wire....
but there is still a buzzzz.... the same as before: not worse, but not better....:xeye:
http://home.tele2.fr/robicam/gainclone2.JPG

I m working on a separate PSU in a 2nd box with one of your schematics..will that solve this buzzing problem ?

is it possible to use the second rectifier pcb with just one transformer ? ( i ve got the rev 3 with 2 rectifiers pcb )

thx
;)
 
Cameo, try disconnecting the wire from the earth on the ac receptacle and the power supply ground. Since your case is not electrically conductive, it is not really needed.

Also, I'm not sure but it looks like the signal cables are shielded. Is there a center wire, surround by some soft plastic like material, and then braided copper wires covering that? If so, you can use one cable to connect each channel to the amp pcb. Connect the center wire at each end of the cable to the signal inputs and twist the braided stuff together and connect that to signal ground on the PCB. For now, do NOT connect the braided wires on the other side (RCA socket side). Try powering it up, and see if the hum is gone, if not, try connecting the braided wires to the ground tab on the rca socket.

You can also try using a thicker wire to connect the ground between the amps and the power supply.

To answer your question, I dont think using a second rectifier pcb with just one transformer is going to help.
 
carlosfm said:
I keep saying that those boards have a design fault, they are not properly designed to use with a single PSU/rectifier board for two channels.:rolleyes:
The main problem is the documention of the product. If Brian all by himslef did stand for all support he would rather soon fix the documentation.

The problem is a typical connection for stereo in a clear schematic with recommendations for suitable wire dimensions and also very clear pictures.

Most troubles with Peter Daniel/BrianGT Gainclones are grounding issues and especially in stereo amps.

No offence Peter but since your product is "serious" it needs also a serious documention and this is especially important since many (most?) of your customers are newbeginners.

I don't agree with Carlos, your design is pretty OK and also the pcb's.
 
cameo

from the pic... seems the chasis ground (green wires) not connected to chasis?
try to connect these wire together....
I had buzing problem b4... when implementing monoblock with BGT3886 (2 chasis)....nothing I did ever solved the problem until I steroed it ... one PSU, one chasis, ground joined together and connected to chasis... no more buz
 
Hi, Carlos;

I'm confused -- are you saying that the BrianGT "Stereo Kit" (Two 3886 + 1 PS board) is likely to be problematic? There seem to be several in Brian's gallery using this configuration.

If so, can you shed light on *why*? I would think that with only one PSU, there is less likely to be a ground loop between PSUs. :)

I am planning on ordering one of those kits in the next day or two, and would like to know if I'd be significantly better off going dual PSUs, and basically run dual monoblock off one transformer (I have a 400VA toroid coming). My chief goal with this project is to build a good, solid amplifier with very little noise, good frequency response, that is very hard to clip. And do it on a small budget (time AND money). Eventually, I also want to be able to bridge the stereo amp into a louder mono amp (where noise is less important).

My back of the napkin calculations suggest that each board is capable of handling around 300W of power continuously (assuming the diodes are heat-sunk). So is there another reason? Snubber circuit not designed for the two amps' impedance? Given that the Pd of each chip is about 40W and they will put out around 60W of sound power, that leaves about 100W of headroom in a stereo setup.

Looking forward to your comments.

Oh, one more thing, when you spec'd out the PS boards -- did you intend for the diodes to be heat sunk?

Wes
 
wes-ninja250 said:
Hi, Carlos;

I'm confused -- are you saying that the BrianGT "Stereo Kit" (Two 3886 + 1 PS board) is likely to be problematic? There seem to be several in Brian's gallery using this configuration.

If so, can you shed light on *why*? I would think that with only one PSU, there is less likely to be a ground loop between PSUs. :)

You can make a perfectly silent stereo amp with one PSU, I didn't say you can't.
But separating the ground on the rectifier board and on each amplifier board is not optimal.
I wanted to make it on the snubberized PSU of Brian's LM3886 kit, but he didn't implement it because he had the LM3886 boards done and he wanted to keep the same approach.

I did discuss this grounding issues several times, you can search the forum.
You will find pictures and my suggestions on how to make the grounding arrangement with these boards.

wes-ninja250 said:
Oh, one more thing, when you spec'd out the PS boards -- did you intend for the diodes to be heat sunk?

The MUR860 diodes are fine for a two channels/chips, even without heatsinks.
They will only get slightly warm at LOUD levels, listening to some types of music.
Like Ben Harper. :D
You could use small clip-on heatsinks on the diodes, if you can find them. I can't.:xeye:
On some commercial gear I see them, but I can't get them here, on the usual places.
On one of my (regulated) PSUs I used MBR16100 diodes, heatsinked. They don't even warm up.
 
carlosfm said:
You could use small clip-on heatsinks on the diodes, if you can find them. I can't.:xeye:

Digikey part number HS198-ND (there are tons of these. This particular one is cheap and available (though I guess not in portugal -- sorry Carlos))

[IMGDEAD]http://rocky.digikey.com/WebLib/Aavid/Web%20Photos/574502B00000.jpg[/IMGDEAD]