Commercial Gainclone kit- building instructions

[AndrewT]

I agree with Ud, remove chassis and layout the modules in a string, Mains at one end, then through the stages, to the input RCA at the other end.
Couple up and power up.
Is hum or buzz heard and/or measured.
Connect as a stereo pair. Test again, measuring the hum or buzz.

Remove the source leaving the RCAs unterminated.
Does the noise measure worse?

Now that you know what the system can achieve, start casing it up.

 

[pmchoong]

pmchoong, please make sure of these things:
1: As with the other gentleman your rcas should be insulated from the chassis. (its okay that they touch but it can cause ground loops which will buzz)
2: Do you have signal going to signal or do you have signal and ground switched around on your RCA plugs?
3: this buzzing can be caused by bad solder joints and if you made your own RCA cable there could be bad joints there or you could have bad joints in your input RCA jacks on your chassis.
4: solder joints could be bad at signal input to amp boards.

....That covers bad solder joints I guess. .... Wiggle the wires, touch the volume pot, touch the heatsink. Does the hum/buzz change when you do this?

Uriah

1) I have removed the rca from the chassis
2) Signal wire going to signal and grd wire going to ground
3) will check
4) will check

Thanks. Yes...wiggle the wires (that connects the rca and the board) and the buzz gets real loud....depending on how gentle or rough you wiggle them.
Will check again on solder.

 

[pmchoong]

do i need to connect the 'chg' from main board to the chassis? Did this and resolder the joints, now the buzz is less but when connect to preamp, the output from source (my radio for testing) is very faint.

 

[pmchoong]

"With dual mono version though, you will run a ground wire from CHG (chassis ground hook up point on each amp board) to chassis." post 168 from peter

 

[pmchoong]

connected the cg
hg to the chassis...resoldered joints....still buzz when connect to preamp. sound from radio is very faint.

 

[pmchoong]

now when i wiggle the rca wires....the buzz remains at same loudness. the buzzing sound is much lower now...but constant....sound from the radio is at background...can be heard when turn preamp volume to maximum.

 

[Peter Daniel]

Are you using dual mono or stereo setup? Do you have buzz with only a single channel connected to PS?

 

[pmchoong]

i am using dual mono....buzz in both mono

 

[Peter Daniel]

Is there buzzing when signal connected to one channel only (the other channel completely disconnected)?

 

[pmchoong]

ehhh....i use the same transformer to test each individually

 

[pmchoong]

this is how i hook up everything......at present i am using one transformer to test both mono block channel.....the other transformer is still wip

 

[pmchoong]

should i resolder the chip again?

 

[Peter Daniel]

If the buzzing can be detected with both channels connected separately, it's probably something else than bad soldering. It's quite unusual to get a hum with a single mono channel, unless the buzzing comes from your source?

 

[pmchoong]

dc offset at 14.5mv with volume down but when volume turn up to 9 o'clock....dc offset is at 7.9mv....and when turn all the way up, dc offset at 300mv!

 

[Peter Daniel]

Without input coupling cap it's normal for offset to change up to 80mV or so.
300mV high could indicate that your source produces some offset as well.

 

[pmchoong]

it change to 7.9 (7 point 9)mv....not 79mv

 

[pmchoong]

.... It's quite unusual to get a hum with a single mono channel, unless the buzzing comes from your source?

Stupid me....i forgot to turn the preamp source selector to tuner.....sorry everybody.....i feel very bad making you guys putting on your thinking cap to discover something i did stupid......now i got sound coming out from the speaker except the buzzing sound still exist...errrrrg...how the heck can i get rid of this buzz sound..it is very low and audible on close up......on both mono....same issue....how come? When i switch off the preamp, i still can hear this buzz from the speaker

 

[Peter Daniel]

If your source is tuner it's quitepossible buzzing comes from it. Do you get hum with volume all way down?

 

[pmchoong]

sounds good except for the buzzz...is it the transformer?

 

[pmchoong]

If your source is tuner it's quitepossible buzzing comes from it. Do you get hum with volume all way down?

yes....even if i turn off the preamp