Humm in a gainclone by a newbie

[spacemen12]

Hi,

I've built my first gainclone (first electronic project as well) a few month ago. It made from a kit of audiosector withl dual mono power supply.

It works fine: it amplify the sound and plays the music! But when there is no sound getting in (like no track playing on the cd) there is noise in the sepaker. This noise is not strong but its audible.

This noise didn't get out after the burn-in period.

The noise is like the sound of giant speaker in a show when there is no music playing or when you crank up the volume of a guitar amplifier without a gitar plug in.

The noise don't vary in intensity when I change the volume (turn the volume pot on the preamp)

I use a cambridge 540A as a preamp (through the preamp output) and a cambridge 540c as a cd player.

I ran some tests, here the results (I'm not able to interpret them alone).

1. When the only thing plug in my "power bar" (AC) is the amp, and the speaker are connected to the amp, there is no noise.

2. When I connect 1rca wire to the input of the amp on configuration 1. (and the other end of the rca is not connected), then the noise come back.

3. When I touch with my finger on the unconnected side of the rca wire in 2. configuration:
a) the noise increase if I touch the hot (pin)
b) the noise reduce if I touch the ground (circle)


Here are some picture of my gainclone
http://geocities.com/spacemen12/gainclone/

If I'm not clear, tell me.

Thanks

 

[elementx]

can you post a closeup pic of both the ps and the amp boxes? in the mean time check all your grounds.

 

[budwiser]

I had a similar problem. Mine was caused because the wires to my rca jacks where switched.

 

[spacemen12]

I had a similar problem. Mine was caused because the wires to my rca jacks where switched.

Hi,
I will post picture latter on, I don't have digital camera, so it may take a little bit of time.

For the rca, I've pluged the IN in the hot of the rca (pin) and the sg in the ground (circle).

I've tried some stuff with the ground, without succes:
1. ground both channel on a same point in the amp chassis
2. Remove all the ground in the amp chassis

It's not doing anything.

Thanks

 

[Nordic]

Just check what happens if you move the amp further from the PSU. Also make use of shielded or twisted pair cables. Make sure sockets are isulated from the case... Something I find good too is to use a much thinner wire from the input ground to the starground than any of the other wires... or you could add a small resistor.
So seperate the grounds 1 for power and speaker and one for inputs then form a weaker connection between the 2 grounds....


0v rail -----Power groundstar--SGS---- input signal ground
Speaker -- ----

 

[spacemen12]

Hi,
Thanks nordic. which pair should be twisted? Now only "sound wire" are twisted, not the psu wired.

Thanks

 

[Nordic]

Twist them all, here is a whole thread dedicated to the topic.

 

[gmphadte]

Does only the RCA wire give u that noise,
Check by connecting/disconnecting just the wire.
If it is the case, u have to use 2+shield cable and make a new RCA to RCA where the shield is not used for the ground connection. Connect shield only to the GC

Gajanan Phadte