• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Dual Mono PSU with shared earth..

how to implement? I've been building an amp for a friend of mine. The Cleo V by triode Dick. It uses a dual mono PSU but i've used a common earth. (I'm having major HUMM problems)

When discussing that with another friend and forum member Mark25, he suggested that I change the phase on one channel because your transformers should have the same phase when you have a common earth. I guess he was right because the amp is a lot quiter...but now I'm curious...:
How do you guys implement such a scheme? 2 seperate earths or a common one...and if one earth...then should they be in or out of phase?

Regards,
Bas
 
How many lumps Sir? 1, 2 or 3

Bas,

If the dual power suplies and amps are on the same chassis, then follow the same rules as normal for a single PSU.
Determine the main frequency of the hum - 50Hz or 100Hz or sometimes a sharp buzz containing lots of harmonics, and report back;)

If the PS is remote, then the problem may be more complex.
 
Hallo John,

It's all on the same chassis. What are the normal rules?
My rules are simple :
If I build an amp simple there is one start earthing point all roads lead to it. ;)

I did the same with this amp..but apparently different rules apply? Or at least there are some extra considerations.. The plot thickens because there is a phono amp with seperate supply in there also. I have made a seperate star earth for that and one wire from that star earth to the main one.

Regards,
Bas

[IMGDEAD]http://basenjes.de/photoalbum/altjo/slides/DSCN6333.JPG[/IMGDEAD]
 

EC8010

Ex-Moderator
2003-01-18 7:57 am
Near London. UK
Bas Horneman said:
You mean rebuild the amp? :cannotbe:

'Fraid so. You have coupled your mains transformers straight into your output transformers. You could turn either the output transformers or the mains transformers. Turning the mains transformers would be better because you have pointed their hum at your delicate audio circuitry.

You also appear to have AC wiring running down the left hand side that then feeds a rectifier and capacitor, but passes near to the inputs. Very bad. Move that rectifier/capacitor and regulator up to the noisy end of the chassis and feed clean DC past the inputs.
 

EC8010

Ex-Moderator
2003-01-18 7:57 am
Near London. UK
Ah ha! I had completely the wrong end of the stick. Now I understand what's going on. The labels make all the difference...

Each of the mains transformers is coupling hum directly into its associated choke. Rotating the mains transformers is the best solution as they are presently directing hum at the audio circuitry. Looks like rotating the phono stage mains transformer could be tricky. Check the orientation of the second choke to make sure it isn't picking up hum from the first, or from the mains transformer.

Making a single chassis phono stage and power supply is always tricky - that's why so many people prefer to use a separate chassis for the power supply.
 
EC8010 said:
If changing the mains phase of one of the mains transformers helped, then that suggests that the hum is due to the magnetic field generated by those transformers. It won't change the phase of the ripple.

I believe the phase of the ripple will change. But, the type of rectification used will determine if the effect is observable, or not.
 

EC8010

Ex-Moderator
2003-01-18 7:57 am
Near London. UK
No, the phase of the ripple won't change. Think about it; by inverting the polarity of the input to the mains transformer, you invert the polarity of the AC reaching the rectifiers. But all that means is that at any given instant, different rectifiers are switched on compared to the original connection. The phase/polarity of the ripple waveform is determined purely by the rectification. If the rectifiers are configured to produce a positive supply, then the ripple sawtooth will have a steep positive-going edge as the reservoir capacitor charges and a shallow negative-going trailing edge as the reservoir discharges into the load. For a negative supply, the steep edge will be negative-going and the shallow trailing edge will be positive-going.