My first class A amplifier

[meanman1964]

The third board is the soft-start of the toroid.
I gonna try with connecting all 3 wires to one point on the board.I keep you informed.

 

[R-K Rønningstad]

Hi! Nice amp you built there. The chassis looks like a lot of work went into this amp. So let's make sure it also sounds that way.

The first thing to do is to make twisted pairs out of all the wires which carry AC, which means

twist the wires from the switch going to the transformer
twist the wires from the transformer going to the rectifiers
twist the wires from the rectifiers going to the boards
twist the wires from the boards to the outputs

and so on. This prevents wires from picking up any noise (from the transformer for example) and looks neat.

Correct. I would like to mention that if you do NOT twist your wires they end up in a loop. And a loop acts as a (loop) antenna, picking up noise, and possibly transmitting noise.
I am glad Rodeodave listed these "twists".
Also, in cases where you do not use shielded cable from the input RCA sockets, make sure you twist the signal and ground here as well.
I hope you will get to fix the problem!

Rolv-Karsten

PS. Nice cabinet!

 

[meanman1964]

Update;at this moment I'm rewiring the amp,hopely loosing the hum this way.Keep you posted.

 

[Rodeodave]

Good luck.

 

[meanman1964]

The iron core inductors could be a problem. If the circuit draws too much current, the core will saturate and the inductor will let the ripples pass unfiltered. This will result in a 100Hz hum (50Hz rectified is double the frequency) appearing at the output.
Solution: Replace the iron-core inductors with big, bulky air-core inductors. You can use the ones used in crossovers or even a spool of wire. I'm using 0.5kg of 1.25mm wire per channel in my Zen lite. Just make sure the inductor can handle the current.

About the inductor I've a air-core of 1,5mH and 1.40mm wire may I use this instead of the iron-core inductor for testing

 

[Rodeodave]

Yes, I'd say that inductor should do fine. A solid wire with 1.4mm in diameter can handle a lot of current, so no worries here. The spool should get warm, but not too hot to touch.

 

[meanman1964]

I did twist the wires and connect ground to one point but the problem remains but not as loud as before.The next thing is replaycing the inductor.

 

[Rodeodave]

Sounds good.

Just curious, what is your setup? Like what source do you use (CD, LP,PC,...), preamp and so on. All powered from the same outlet?

 

[meanman1964]

That's my second question when I want to test if there's any hum left do I have to connect as in my case a cd player?

 

[Rodeodave]

Okay,

At first I would short the inputs to ground (shorted RCA plug). This way you make sure that there is no input signal (0V).

Take a look here: http://www.diyaudio.com/forums/showthread.php?threadid=62849.

 

[meanman1964]

Twist wires,star-ground and bigger air-inductor still having the hum.
Now I'm gonna dismantle my amp and build it on the table channel by channel.

 

[meanman1964]

Amp rebuild on the table,made star-point with powersupply-ground,output-ground and input ground hearing hum.
Disconnect the input-ground and connect it to the original place a little hum like you're hearing a little transformer humming.

 

[meanman1964]

Is a inductor of 1,5mH enough or should it be 2mH?

 

[meanman1964]

Transformer proximity and grounding. You'll have to play with
it to see what makes it better.

Hi Nelson,
Did you follow the topic?
I keep having a hum it's not loud but in my mind very annoying.Can I get my amp completly death silent or is that something that I've to live with?
When I connect 2 extra caps the sound lowers is it possible that I've to replace the psu caps?
Greetz
Patrick

 

[JC Fardo]

Patrick

Where do you hear the hum from? From your speakers or direct from the trafo?
Is your trafo VA enough for class A operation?

Hope this helps

 

[meanman1964]

Patrick

Where do you hear the hum from? From your speakers or direct from the trafo?
Is your trafo VA enough for class A operation?

Hope this helps

The is coming from the speakers.I twist the wires made a grounding point.My trafo is 2x30VAC/500VA.I think I've to look at the PSU because when I move the wires the humming is louder or lesser loud.
I'm planning to build the PSU in a seperate housing.

 

[meanman1964]

Amp rewired,twisted cable,new coils and heatsink for the rectifiers.I'm planning to build the PSU extern.

 

[Rodeodave]

The external PSU is a great idea.
Move the switch, the fuses and the rectifiers to that separate box as well. You could also have some capacitors for additional filtering in that box. This would make something like a CCLC filter. That additional capacitance would also compensate for the 1.5mh instead of the 2mH, but don't be too worried about it. To connect the two boxes you could use XLRs (rated 50V and 16A).

See also the "Top ten ways to a better Aleph?" thread for more ideas.

http://www.diyaudio.com/forums/showthread.php?threadid=12923


Good to see you're still motivated. A dead silent amp is definitely something achievable!


P.S. Sorry to bother you, but for the desired effect you'd need to twist the wires real tight. I usually use a vice and a power drill to twist wires.

 

[meanman1964]

About the twisting I know you're right but I was a bit laisy.
I make new ones long enough and after twisting give them the right lenght.Why should I put the rectifiers together with the rest of the PSU?What do you think about using an extra inductor of 1mH/1.40mm with the seperate PSU?

Patrick

 

[Rodeodave]

Why should I put the rectifiers together with the rest of the PSU?

The wires from/to to the rectifiers carry AC. Of course the wires from the rectifiers to the boards have less ripple-voltage left (before the choke that is), but still, they are running close to the inputs' wires which may pick up noise this way.
And if you want to add some extra caps in the external PSU the rectifier-bridges would have to be there anyway.