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Sep 23 2013

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Rectifier noise antenna – big or small ?

Rectifier antenna – big or small ?

Relating to the amount of nasty, high frequency noise bouncing around within the insides of your amplifier chassis, please choose one:
a). A huge quantity of the above, please, or:
b). I’d rather have that minimized, or at best get rid of it at all !

Last time, I made some insinuations regarding some really nasty, ultra-high current peaks, that range in the tens or possibly more Amperes,
that are running around in circles between your secondary transformer winding and the rectifier bridge and the first electrolytic capacitor of your filter.
The spikes have a fill factor of probably 3% or in those whereabouts, meaning that for 97% of the time, your amplifier is essentially being run from the
load stored within the filter capacitors, and as for the 3% of the time, of the full sinus cycle,
when the actual “sinus” from the transformer winding is higher in terms of instantaneous voltage value, during this 3% period, we observe a
*** MEGA super HUGE *** current spike, that needs to instantaneously “fill-up” the load of the capacitor by an amount,
that was depleted during the past 97% of time, when we were draining it.  We also said that those spikes are nasty, because they tend to have a very
steep trailing edge, which translates in to lots of high order harmonics. It essentially translates to lots of high frequency noise.

High frequency sounds like radio frequency … does it not ?
So, here we come to the concept of the rectifier loop antenna, as I shall call it for shorts.

Returning to the question as in the very beginning – lets assume that you wish to minimize the amount of high frequency radio noise
polluting the insides of your amplifier.  What should you reasonably do ?   My hint is:

Get rid of the transmitting antenna.

A multiple Amperes worth of current heavy, spike rich, high frequency noise transmitting antenna.

Two pictures shall say say more than a thousand words. So please have a look at these and compare:

Rectifier antena 1
{{ Fig. 1: Rectifier Antenna 1 – The bad option }}

Rectifier antena 2
{{ Fig. 2: Rectifier Antenna 2 – The better option }}

As can be seen, the first picture depicts some ad-hoc routed cabling between the transformer secondary winding and the bridge rectifier.
The big amount of the orange colored space is the cross section of your transmitter antenna, the one that sends vast amounts of rubbish into the insides of your amplifier.

On the second picture, you see that the cables going from the secondary winding of the transformer to the bridge rectifier, are arranged in a tight twisted pair.
The area between the two wires is essentially none, as they are practically touching each other, by their insulations.   But, there is more to this arrangement, than
just the reduced surface area of the orange colored, rubbish transmitting antenna.  The two wires constitute a dipole of sorts, that “transmits” in a direction that is orthogonal to the plane as defined by the two wires. BUT, but, but …. we just said that the two wires are TWISTED !!!
This means, that this “dipole” is also twisted. The denser the twist = the better.
Why is this so ?
Simple.
Each half turn of the wires implies that the dipole is now standing “back to front”.   This essentially means that at this particular spot, whatever leftovers of rubbish it is transmitting, it is transmitting that rubbish in ANTI-PHASE.   So, what I am saying is this:   You have a tight twist, so you have closely spaced transmitting dipoles, and the close proximity of the In-phase and the anti-phase planes, … essentially results that the transmitted rubbish is essentially “nulled out”.   Two signals, transmitted in antiphase, from (almost) the same location, tend to annihilate each other.

My recommendation:  Take those leads going from your transformer, and make them into twisted pairs ….  Like this:

Rectifier - my twisted pairs
{{ Fig. 3: Rectifier – my twisted pairs 1 }}

I would even say more:  If you have a “double floor” or some other means to “route” such pre-rectifier, AC driven leads, not only should you execute them as tight twisted pairs, but more – try routing them under that double metal floor, or in the corners of the metal chassis, or at least directly adjacent to the metal surfaces of your chassis.
This way, you shall enjoy the additional “screening-effect” that is delivered by those metal parts of the chassis, which shall further dampen the bad influences of such noisy lines.

I did it. And I am a happy user of a very silent amplifier. Those photographs of mine represent the work-in-progress, whilst I was constructing my OTL amplifier.  \

Rectifier - my twisted pairs 2
{{ Fig. 4: Rectifier – my twisted pairs 2 }}

We see a 1400 Watts, 15 kg, toroid transformer, that is supplying 17 various voltages for the amplifier unit.  All AC cabling is routed as tightly twisted pairs of cables, routed UNDER that double aluminum floor.  A few of those thinner twisted pair strands, not yet “routed” – can be seen laying on the table – waiting for their turn to be threaded under and beneath the double floor of the chassis.

Best Regards,

zjj_wwa

P.S.  Last but not least, I would just like to mention, that I have some aliases to my hiend-audio.com site.  Any of the following links as below shall bring you to these pages: http://capacitorless.com 
http://currentdriven.com  http://diy-hi-fi.com http://diy-hi-fi.com.pl  http://diy-hi-fi.eu  http://diy-hi-fi.pl  http://hi-fi-diy.com  http://hi-fi-diy.com.pl  http://hi-fi-diy.eu  http://hi-fi-diy.pl  http://hiend-audio.com.pl  http://hiend-audio.eu  http://hiend-audio.pl  http://hiend-system.com  http://hiend-systems.com  http://hiendsystem.com  http://hiendsystems.com  http://highend-system.com
http://highend-systems.com  http://otlaudio.com  http://straightwiregain.com  http://transformerless.com  http://zjjaudio.com 

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