Serial Tone Killer

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lhwarp
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Re: Serial Tone Killer

Post by lhwarp » Wed Aug 14, 2019 10:32 am

carron wrote:
Wed Aug 14, 2019 10:09 am
Great detective work!

Yes, aluminum is not the best, and mumetal is expensive. Perhaps you can try to cover some of the aluminum enclosures in copper tape to see if that helps. Though two types of metal together are a recipe for corrotion.

In principle a toroidal transformer should minimize the leakage of magnetic flux, so I would have thought it should have minimizde hum relative to a classic transformer design.

It is true that the radiation has a "more" omnidirectional structure than a classic transformer, where it is even more concentrated in one direction. Nevertheless the radiation of a toroidal transformer is not perfectly omnidirectional. It should be larger along the axis perpendicular to the toroid "circle", because the inner side of the coil and farther side are at different distances to the center and the effect does not perfectly cancel out, and the effect sums from every direction along the center symmetry axis. Perhaps there is something just directly below that transformer, along that axis that is acting as an antenna and picking that noise. Have you tried turning the Toroid 90 degrees on its side, to see if anything changes?

Reducing hum is a difficult art for any expert designing circuits, and I am no expert by any stretch of the imagination.

Again, amazing build.
Thanks @carron for your external analysis ! 8) ;)

Yes, like you, I was prone to think that toroidal transformer would be better in terms of magnetic hum field, combined to a welcome known significant gain in weight... It's not the case here, at least... :(

Consecutively to your fine thoughts 8) , I now consider the central screw of the toroidal transformer : wouldn't it be a "good magnetic hum field spreading accessory" ? ??? It's made of steel - hence magnetic, so replacing it with a brass one is maybe a test to do.

And yes, good idea : I will try to turn the toroid transformer at 90° also. ;)

Thanks again for your suggestions ! :)

-lhwarp

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lhwarp
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Re: Serial Tone Killer

Post by lhwarp » Wed Aug 14, 2019 11:31 am

Yes, @carron : you had a good idea ! 8) 8) 8)

So I turned 90° the toroidal transformer and the hum in the reverb circuit is eradicated... ;)

Image

you have been a good advisor - thanks ! :)

-lhwarp

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lhwarp
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Re: Serial Tone Killer

Post by lhwarp » Sun Aug 18, 2019 7:25 am

Finally, and tentatively, I put the toroidal transformer surelevated from circa 20 mm : it's enough to attenuate the induced hum to negligible :

Image
Image

But that transformer "sprinkles" generously his hum around so that single coil pickup guitars picks it almost at an equal level to their output in overdriven mode at a distance of circa 2 meters... which is not acceptable :wtf: ! It's even critical in clean mode at circa 1m... >:(

However, this toroidal transformer has a shielding ribbon around its core, supposed to decrease the hum radiations ???

Image

So I made a comparison with my venerable (restored/improved)) 1980 Boogie MKIIA :

Image

No picture : way much less hum in any mode for the Boogie - and his original EI transformer. 8)

Verdict : next step - exit the toroidal, despite his good performances in weight and supply... :fp:

So it is a tentatively situation which allow me to finish the development and construction of the circuits.

-lhwarp

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somanytoys
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Re: Serial Tone Killer

Post by somanytoys » Sun Aug 18, 2019 8:55 am

That’s a bummer.

Wish that could have worked out for you, that’s a great idea, and less weight is always nice.

But now you can move forward, at least. Looking good!
-David

It's a boost booster, to boost your boost - it makes your tone much muchier.

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lhwarp
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Re: Serial Tone Killer

Post by lhwarp » Mon Aug 19, 2019 4:46 am

somanytoys wrote:
Sun Aug 18, 2019 8:55 am
That’s a bummer.

Wish that could have worked out for you, that’s a great idea, and less weight is always nice.

But now you can move forward, at least. Looking good!
Thanks @somanytoys ! ;)

Yes, true ! The intention was good, but the result is not... So I'll have to return to an EI conventional (low loss) transformer, and the amp wil take 2 more kg... Compensator Bonus : I'll be able to add a HI Fixed bias / LO Cathode bias feature, thanks to a half plate voltage tap on the EL Xfo.

The current weight of the amp is 24.3kg :

Image

Not so bad for an amp that is full tubes, gives 100W output and embodies an EVM12L speaker which is 8.9kg just by itself... It will reach 26-27kg. :mellow:

For the moment, I'm working on the tone corrector values and pots for better efficiency range and spreadness of adjustment, and also a high pass filtering for the overdrive stage to cut some infrabass muddiness.

Wait and See !

-lhwarp

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carron
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Re: Serial Tone Killer

Post by carron » Wed Aug 21, 2019 5:58 pm

Glad I was not completely full of Sh__t...

Anyway, you seem to have a handle on your noise source, and have identified, and mapped how the transformer is producing the hum. That is great detective work!.

Good luck with the traditional transformer, which mounted with a good orientation of its core should work out just fine.

I will be following this thread.

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lhwarp
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Re: Serial Tone Killer

Post by lhwarp » Thu Aug 22, 2019 12:53 pm

carron wrote:
Wed Aug 21, 2019 5:58 pm
Glad I was not completely full of Sh__t...

Anyway, you seem to have a handle on your noise source, and have identified, and mapped how the transformer is producing the hum. That is great detective work!.

Good luck with the traditional transformer, which mounted with a good orientation of its core should work out just fine.

I will be following this thread.
Yes, @carron !

Thanks again for your simple (but forgotten :-[ ) suggestion... ;)

I made some experimentations with an EI transformer of similar power to search what would be the best orientation - sorry, the comments are in French, but below are the main explanations... ;)

The best results have been obtained with the transformer orentated like in the 2nd picture : the main magnetic radiation direction is not looking where the guitar and the guitarist is, conversely to the 1st picture.

The 3rd picture shows the comparison of magnetic influence between Toroidal and EI. In this figure, the best result in term of radiated hum was obtained by the EI, but I thought that the gap would have been wuch great...

In fact, listening to the tone of the hum - more "bassy / hummy" for the EI, more "edgy / buzzy" for the Toroidal - I guess that the EI radiates a more "magnetic than electric" disturbing field, and conversely for the Toroidal. This comes probably from the shielded coils (by the covers) on the EI Xfo.

Image

So this led me to go for another test : shielding the laminations of the EI transformer...

At left, a U cover made from 3mm thick lead foil : absolutely NO efficiency !
At right, a simple screen of 2mm thick aluminium interposed between the Xfo and the guitar (at distance) to cut the main radiation direction : attenuation of the hum !

I strongly would have bet for the contrary ! :wacko: :wacko: :wacko:

Image

In the meantime, I discovered and bought on eBay shielding covers of suitable dimensions for my Toroidal transformer, made from annealed iron (not steel, which would be less efficient), along with Mumétal ribbon... So I'll made some shielding test on the Toroidal Xfo : who knows ? :blush:

In waiting, I'm building the footswitch...

Wait and See ! ;)

-lhwarp

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lhwarp
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Re: Serial Tone Killer

Post by lhwarp » Fri Aug 23, 2019 12:31 pm

Footswitch built - the sign plate has to be designed and engraved. Note the 2 sockets offering the possibility to connect the FSW cord to the box at the right or at the left, depending on stage placement... ;)

Image

It controls : Overdrive, Booster, Reverb, FXLoop. Unlike the power transformer issues, this FSW works perfectly at the first time and silently ! 8)

The amp is also able of powering the FXs of the loop, supposing you put them on the top of the amp itself :

Image

-lhwarp

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somanytoys
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Re: Serial Tone Killer

Post by somanytoys » Fri Aug 23, 2019 12:48 pm

All superb, very forward-thinking ideas, and great implementation and build quality.

Does it do the dishes?
-David

It's a boost booster, to boost your boost - it makes your tone much muchier.

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lhwarp
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Re: Serial Tone Killer

Post by lhwarp » Fri Aug 23, 2019 1:49 pm

somanytoys wrote:
Fri Aug 23, 2019 12:48 pm
All superb, very forward-thinking ideas, and great implementation and build quality.

Does it do the dishes?
Thanks somanytoys ! ;)

Does it do the dishes? = Fait-il la vaisselle? ??? :wacko:

Ah, sorry, its confusing... :-[ Please note that it is a guitar amplifier - I omitted to mention it... ;D

I would prefer it hum dead-silent ! :squint:

-lhwarp
Last edited by lhwarp on Fri Aug 23, 2019 11:24 pm, edited 1 time in total.

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somanytoys
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Re: Serial Tone Killer

Post by somanytoys » Fri Aug 23, 2019 2:03 pm

I just meant that it does almost everything else...

Hopefully you’ll get it silent. Some amps are a little noisier than others, you may just have to live with a little bit of hum.
-David

It's a boost booster, to boost your boost - it makes your tone much muchier.

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lhwarp
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Re: Serial Tone Killer

Post by lhwarp » Fri Aug 23, 2019 11:52 pm

somanytoys wrote:
Fri Aug 23, 2019 2:03 pm
I just meant that it does almost everything else...

Hopefully you’ll get it silent. Some amps are a little noisier than others, you may just have to live with a little bit of hum.
Thanks @somanytoys ! ;)

I hope you will be right ! :)

I'll take the time to make some samples of the different tones of the Serial Tone Killer - once that ugly radiating hum problem will be muzzled :squint:

Wait and See !

-lhwarp

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lhwarp
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Re: Serial Tone Killer

Post by lhwarp » Sun Sep 15, 2019 10:35 am

Some new in the hum radiation war...

I added an additional 3mm alu baseplate to screen the radiations of the toroidal on the EHX reverb and FX facility :

Image

No more hum radiation in the amp circuits, now, but...

I also received my toroidal Xfo cap (reputedly made from iron, not steel), and installed it, with a 3mm alu baseplate to close it at best, and still on a shim to remove it from direct contact with the chassis :

Image

The goal was to tame, to "encase" the omnidirectional hum spread of the toroidal Xfo, which is picked by guitar pickups. Guess what ? No effect, as if there was no cover... :wtf: :bored:

Of course, I tried to find some in aluminium, but it doesn't exists. And moreover making one in 3mm thick is not possible because the extra-thickness won't enter the amp chassis allowed surface...

OK. I think that this time "the trial is done". Exit toroidal transformers, welcome EI transformers. :whistle:

Wait and See...

-lhwarp

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lhwarp
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Re: Serial Tone Killer

Post by lhwarp » Fri Nov 01, 2019 2:24 pm

OK - some delay due to emergency amp repairs and building another amp (the FB CUSTOM), sorry... :-[

But the story is still on ! ;) :)

-tbln

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