[AnA1995]

I had just completed my amp. But, there are one major problem; the hum.

I am suspecting the power as the contributor to the humming noise. I had tried to use a external power supply and not using the internal one and the hum disappear.

I am using the unregulated power supply consist of only one Bridge diode, 2 x 10,000uf capacitors and a toriodal transformer. I read somewhere this single ended Sijosae's amp required regulated power supply. Anyone could confirm is a must to use regulated power supply? Thanks.

This is the amp's circuit....
http://www.headphoneamp.co.kr/bbs/zb...esc=asc&no=247

This is the layout... transformer too near to the circuit?


One more thing, may I know how to adjust the VR as below? I seem very difficult to get to the right voltages of 16-17v for both sides. Example, if one side manage to get 16-17v, the other side will be out again and vice versa.

 

[3amsleep]

you definetly need to add some type of regulation if you want to avoid hum. the transformer is a bit too close but i think it shouldn't be a problem. Anyways you could try with the toroid offboard just in case.

 

[Seaside]

Hey, great job. I hope you enjoy this great amp as much as I do with mine.

Check few things first.

- Regulated 24V DC power supply is highly recommended for hum-free sound.

- Q1 is pnp transiter. 2N3904 is not. Use pnp type such as 2N3906, PN2907 or BC550 instead.

- It is not easy to get 16-17V at both sides because part of the circuit tied together. Don't have to worry about them when you get above 13V at both sides.

 

[AnA1995]

Thanks Seaside for you kind advise. Yes, I am enjoying this amp when I powered it with external power without the hum.

Ok, I guess regulated power supply is a must for hum-free sound.

As for the Q1, I am using 2N2907. May I know what is the different and expected to see if we are not using a PNP?

So, as long as we get both side voltages above 13v and even if it is not equal it is consider all right? Please advise if possible. Thanks and appreciated.

Quote:

Originally Posted by Seaside /img/forum/go_quote.gif Hey, great job. I hope you enjoy this great amp as much as I do with mine. Check few things first. - Regulated 24V DC power supply is highly recommended for hum-free sound. - Q1 is pnp transiter. 2N3904 is not. Use pnp type such as 2N3906, PN2907 or BC550 instead. - It is not easy to get 16-17V at both sides because part of the circuit tied together. Don't have to worry about them when you get above 13V at both sides.

 

[AnA1995]

As regulated power supply is a must to have a hum-free amp. Anyone could advise and recommend a good regulated power supply for this amp? My chassic space seem a little limited now; so a small and good regulated power supply circuit will be prefered...

Maybe using LM338? Thanks.

 

[Seaside]

I happened to have 24V SMPS notebook style power supply, and it work well. I know SMPS is not desirable option for audio though, I don't mind it as long as it works well w/o problem.

Usual 19.5V notebook PS works too. You need to adjust trimmer to get 6.3V at the tube and your FET voltage will be somewhat lowered to 9V or so. That's ok as long as it sounds well. So check your amp with those PS and see it works. You always can build better PS later.

 

[digger945]

Have you tried removing the transformer from the chassis to see what effect it has?
I don't think all the regulation in the world will defeat the magnetic field of the toriod being that close to the signal.

 

[AnA1995]

Yes, just tried to take out the transformer from the chassis and the effect is the same. Hum still there.

Quote:

Originally Posted by digger945 /img/forum/go_quote.gif Have you tried removing the transformer from the chassis to see what effect it has? I don't think all the regulation in the world will defeat the magnetic field of the toriod being that close to the signal.

 

[FallenAngel]

It might be because your MOSFETs are air-wired.

 

[smeggy]

That was the first thing that popped into my head as well when I looked at the pic.

 

[Voodoochile]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif It might be because your MOSFETs are air-wired.

At the very least, could you re-route the one wired closest to the toroid so it's on the other side? Might be worth a shot in the interim. It looks as though those long leads are almost touching it right now.

 

[AnA1995]

Using the switch-mode power supply, the hum is not so obvious. It was only noticeable on the left side of the earphone.

As for the Mosfet, the one about to touch the trans is the right side. As the noise is on the left, I presume re-route may not be needed. Anyway, will try.

The mosfet I use is IRF 620 instead of the 610.

Touching the red capacitors will somehow change the humming noise. Sometime to the extend of stopping the hum. But, after a while, it comes back on again.

 

[fran]

This sounds more like a grounding issue than anything else.

How have you got the amp grounded?


Fran

EDIT: when you say you have just one diode - I take it you have a diode bridge like this:

 

[AnA1995]

Thanks fran, regarding the grounding, I hope I got it right. Anyway, how do you mean by amp grounded? So far, none of the "negative" connected to the chassis. Only the main power "green/yellow" connected to chassis. Please advise if possible. Thanks.

Yes, I have used one bridge rectifier.... not good enough?

Quote:

Originally Posted by fran /img/forum/go_quote.gif This sounds more like a grounding issue than anything else. How have you got the amp grounded? Fran EDIT: when you say you have just one diode - I take it you have a diode bridge like this:

 

[AnA1995]

Last night, I used the external switch mode power supply for this amp and it really really sounded nice. Sometime, the hum is totally gone. Anyway, this new amp has better sounding than my previous amp I got online. Very happy with the sound, but not the hum.

I also installed a regulated supply using the internal toroidal transformer and still encountered the same hum. Guess, regulated or unregulated is not the main reason for the noise problem; grounding is....

Maybe got to redo everything...