Help me , JHL 1969 class A amplifier hummms

[Johnsykes]

I bought this assembled modules on eBay , they only hummm through the speakers , I think it's a grounding problem but I don't know how to ground them. Is it a problem that both modules share the same dissipator? I have 4 fans on the chassis to prevent heating.

1pair A6 HD1969 Pure Class A Power Amplifier Board Power Enhanced Version | eBay

 

[ubergeeknz]

Do they work? Aside from the hum?

 

[Johnsykes]

I think so , didn't blow up or smoke but what comes out of the speakers is a loud hummmm only

 

[ubergeeknz]

How have you wired them up?

Could be they just don't work, often the transistors in these are fake

 

[Johnsykes]

Just 3 connections, 30v a.c. Speakers and signal input

 

[Johnsykes]

Schematic

 

[Johnsykes]

Maybe I need to adjust the Quiescent current to the 30v a.c. I'm using, still I think there should be a connection from ground to the chassis

 

[ubergeeknz]

Yes ground should be connected to chassis, usually at the inputs.

But you need to set the quiescent current and bias.

 

[Johnsykes]

i will connect the input ground to chassis and see what it does , thanks

 

[Johnsykes]

Thank you Ubergeeknz for all your help , it's working fine , just had to connect input ground to chassis , my first amp build I'm still a newbie

 

[ubergeeknz]

Great stuff [emoji106]

 

[Johnsykes]

Sounds really good