SERIAL TONE KILLER - II Le Retour

Reprise du projet - nearly one year later !

I was somewhat fed up by the too numerous issues, and having other things to do...





For those who are still interested in ... More adventures and pics tomorrow !

A+!

 

Exactly, Ricochet : you got it = noise, or more precisely hum due to magnetic induction. And it's still the issue that I have to cure...

I used a toroidal transformer because - among its significant lightweight - I read everywhere that they provided much less 50Hz magnetic radiation than the classic EI transformers but I'm experiencing that this is not true at all !

I will probably have to displace the reverb unit, because with already shortened cable, the improvement is good, but I want silence : I am hum allergic...

Well, I use the (excellent) Spring preset only, so...

I made some displacement test to judge the hum attenuation :



I draw the conclusion that it was the wires... So I shortened the IN / OUT connections to the reverb. Neat improvement, indeed... But not perfect !



That's why I think that a displacement may be mandatory... It's not what I would, but...

A+!

 

Thanks dafreeze !

Well, The Great Hum Song isn't my preference at all - I much prefer That Great Gretsch Sound - without hum !

Yes, Ricochet : these are the screen serial resistors of the 6L6GC power tubes (1K/5W) - usually 470R on Fenders and 1K on Marshalls. This allow me to install 6L6 or EL34.

Today I made a power transformer displacement tests - quite conclusive :



An EI type transformer of the same power may finally radiate less hum , or at least an orientated one , moreover I can find one giving 2 plate voltages allowing HI power - FIXED bias / LO power - CATHODE bias.

But the drawback is the weight increase : +3kg ! I tried to design this amp to be lightweight... I'm somewhat puzzled...

Wait and See...

A+!

 

Latest news for today...

Thanks to a tech-minded member on another forum, I placed the toroidal transformer with its axe horizontal (90° rotation) :



And It eradicated the hum in the reverb circuit ! As simple as stupid as that...

That said, the toroidal transformer is nonetheless a widespread magnetic hum generator : don't expect to approach the amp at less than 2 meters with a single-coil pickups guitar in overdrive mode, and in a chosen precise position, at moderate overdrive and gentle volume.

I just imagine playing loud with a hi drive level with a strat ...

Tentatively, I'll install the transformer on a bracket in order to go further in the building / setting of the amp, and make other tests to see if an EI transformer would be worth to install.

Despite that, I can say that the short sound test I mad this evening were very promising, both in clean and overdriven mode... It's encouraging, finally !

Wait and See, then.

A+!

 

Thanks for the suggestion, but this grounded shielding is already in the cab since its construction, making a Faraday cage, you guess it, wabash slim...



But this has no efficiency against magnetic field hum radiations. To be truly efficient, the chassis and the upper shielding would have been made from µ metal, an absolute pain to work and costing an eye !

A+!