shielded wires in 5E3?

[kbobb]

Hi folks,
Building my 5E3 kit and am wondering if it is common practice to use shielded cable for the input jacks, control leads and preamp grid connection?
My instructions recommend using shielded cable for a quieter amp but the local amp guru said try it with cloth wire first.
I would like to build it just once and get the best(quietest ) result the first time.
Any input is appreciated.
Thanks

[HTH]

I wouldn't consider it necessary in a 5E3, it's not exactly a high-gain shread machine. Use the cloth wire and be done with it, worked for Fender all these years.

[Robert M. Martinelli]

I would like to build it just once and get the best(quietest ) result the first time.

Well' if you'd like to build it once and get the best ( quietest ) results, using shielded cables IMHO can help you get there, HTH is right when he says old Fenders like the 5E3 are not hi-gain machines, on the other hand, I have worked on many Fender amps, and I found hum to be a little too much on some of them ( at least to my ears ); also, shielded cable is more forgiving if you make some layout mistakes ( e.g. laying signal wires over, or close to, a "noisy" area of the amp ).

Anyway, be aware that the final result you' ll get will also depend on many other factors,( e.g. the filaments' supply and wiring, the transformers position and orientation and so on.... ).

In the end, it depends on what your goal is : If you like the idea of a vintage-correct 5E3 with all the pros and cons of the original, stick to cloth wire, if you want the great sound of a 5E3 but with lower hum/noise stick to shielded wire, but be also aware you' ll have to pay attention to a number of things...

Hope this helps

Best regards

Bob

[Bruce / Mission Amps]

Hi folks,
Building my 5E3 kit and am wondering if it is common practice to use shielded cable for the input jacks, control leads and preamp grid connection?
My instructions recommend using shielded cable for a quieter amp but the local amp guru said try it with cloth wire first.
I would like to build it just once and get the best(quietest ) result the first time.
Any input is appreciated.
Thanks

NO it is not common to use shielded cable.
The only place that really makes a very slight difference is the wire from the volume controls to grid #2 of the 12AX7.

[dai h.]

if you want the great sound of a 5E3 but with lower hum/noise stick to shielded wire

regular shielded wire can't help with hum since it provides electrostatic (capacitive) shielding not magnetic (i.e. doesn't work against frequencies that low). Should help with "buzz" (the higher harmonics of hum). Layout and grounding would be some of the aspects to pay attention to for low noise. Don't forget the gtr. end too since noise can come through that way. Also, with the amp if you have some slack with a wire, moving it can help (farther away from the noise source) and laying it down close to the chassis can provide a bit of shielding effect and a bit more isolation through slight increase in capacitive coupling.

[Robert M. Martinelli]

regular shielded wire can't help with hum since it provides electrostatic (capacitive) shielding not magnetic (i.e. doesn't work against frequencies that low). Should help with "buzz" (the higher harmonics of hum). Layout and grounding would be some of the aspects to pay attention to for low noise. Don't forget the gtr. end too since noise can come through that way. Also, with the amp if you have some slack with a wire, moving it can help (farther away from the noise source) and laying it down close to the chassis can provide a bit of shielding effect and a bit more isolation through slight increase in capacitive coupling.

AFAIK shielded cable acts much like a Faraday cage, provided the shield is kept at zero potential ( e.g. connecting the shield to GND only on one side to avoid ground loops due to differences in ground potential at the two ends ), I can witness it still works at 50 Hz, and I have experienced it indeed keeps the sensitive stages of an amp from picking up hum and noise - time ago I rewired my Vox V15 substituting the original stiff wire with shielded wire and it made a huge difference ( before that the amp was humming even if the heaters' wires were factory twisted all along their way ). I was then able to completely cancel hum by adding a hum balance pot which killed what little residual hum I had. The only noise I currently get out of that amp is thermal noise from the valves and resistors, barely audible with the amp fully cranked.

Having said this, I believe nothing can take the place of a good layout and good grounding practices, and nothing on earth will keep a badly laid-out/badly grounded amp from humming/buzzing.

[dai h.]

if electrostatic shielding was the only type of shield necessary to prevent low frequency noise, why do transformers such as say mic input transformers come with magnetic (often both electrostatic and -magnetic shielding) shielding? Wouldn't they just need some copper if that was true? I understand that electromagnetic shielding such as mumetal shielding is more expensive. Why would they spend more if it wasn't necessary?

[Robert M. Martinelli]

if electrostatic shielding was the only type of shield necessary to prevent low frequency noise, why do transformers such as say mic input transformers come with magnetic (often both electrostatic and -magnetic shielding) shielding?

Hi dai h,
probably my written English is not so good ( I' m neither English nor American as you might have already guessed ) and sometimes I tend to be rather wordy, if so I beg your pardon...I' ll try to better explain my point of view...

Well, I never said shielded wire was the "one-and-only" cure, I just wanted to point out that it helps - and it surely does, together with a good layout, correct transformers orientation, proper grounding practices - to keep hum and noise down; I can' t even imagine the way some modern very-very-very-high-gain tube amps would hum and buzz without all of the above precautions.

Noise has many faces, hum, hiss, buzz, noise induced by external electromagnetic sources, ( think lamps, dimmers, several kind of appliances as TV sets etc ), thermal noise. In all of the above cases ( with the exception of thermal noise ) "electro" and "magnetic" shielding together can be very useful.

As to the mic input transformers, mics are a rather low noise source, being LO-Z, LO-L devices, and mic transformers are designed to take a differential signal with respect to GND, ( balanced ) so whatever "common-mode" noise likely to enter tends to be canceled because it enters the two conductors at the same time with opposite phases, resulting in a hum-bucking design, much alike a push-pull stage OT or an RS422-485 data transmission line. This of course in a perfect world, something our world is very far from being, so, since perfect symmetry is impossible to achieve, some hum or disturbance is likely to pass through, and that's why we always find electromagnetic shielding in every well-designed-and-built equipment. Careful designers always prepare for the worst case.

I' m leaving thermal noise out as it is not the subject of the post, and as it would need to be dealt with separately.

My .0001 ( Euro ) cent

Take care

Bob

[dai h.]

AFAIK shielded cable acts much like a Faraday cage, provided the shield is kept at zero potential ... I can witness it still works at 50 Hz

to my knowledge this is not correct and it's the only issue I have. I think I pretty much agree with the other stuff.