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PostPosted: March 25th, 2023, 1:39 pm 
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Yea, no noise at full volume and no difference between min and full volume and that is using an input connected to my DAC (so shorted input would be even better if that is possible). There is certainly no real need to add more shielding.



SoundMods wrote:
TubeDriver wrote:
I have wondered whether it would be worth it to fabricate a shied between my preamp PT and the board? I don't have any noise issues that I can detect (preamp is virtually as quiet as a passive) but the location of the PT seems less that ideal. A copper sheet, cut out to fit and form an internal wall between PT and board, bolted in and grounded? Worth it or just destroying the resale vale of an Ayre preamp?

Like Rosco said -- ". . . if it ain't broke - don't fix it."

So -- the way find out if its "broke" -- short out a pair of inputs to isolate the pre-amp from the outside world -- switch to those inputs and run the pre-amp up to full volume. Does it know the words or is their hum?

No hum? It ain't broke.


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PostPosted: March 25th, 2023, 1:40 pm 
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TubeDriver wrote:
Does that trump the 3rd rule of audiophilia: nothing is good enough, make it more better!


Roscoe Primrose wrote:
The first rule of engineering: If it ain't broke, don’t fix it……


HELL NO!! Some manufacturers either don't do enough to make their products perform better -- or don't know how -- or have that NIH syndrome.

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PostPosted: March 25th, 2023, 1:43 pm 
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[quote="TubeDriver"]Yea, no noise at full volume and no difference between min and full volume and that is using an input connected to my DAC (so shorted input would be even better if that is possible). There is certainly no real need to add more shielding.

When the DAC is not on (or in a lot cases not producing music) the output is shunted to ground.

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PostPosted: March 25th, 2023, 2:21 pm 
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SoundMods wrote:
A copper sheet, cut out to fit and form an internal wall between PT and board, bolted in and grounded?

If you decide to try shielding, you may want to use a conductive mesh instead of solid sheet material. You don't want to make a sweat box around the transformer, and mesh looks solid to most RF (except very short wavelengths.)

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PostPosted: March 25th, 2023, 3:35 pm 
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If the transformer is radiating any energy it will most likely be at line frequency, not RF. Solid or mesh copper is good for RF but not very effective for low frequency shielding. Either steel or preferably Mumetal or other high permeability metals are better for low frequencies. Without a doubt, if it fits into your aesthetic requirements, separating the transformer from sensitive circuitry is still the best option.


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PostPosted: March 25th, 2023, 3:46 pm 
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tomp wrote:
If the transformer is radiating any energy it will most likely be at line frequency, not RF. Solid or mesh copper is good for RF but not very effective for low frequency shielding. Either steel or preferably Mumetal or other high permeability metals are better for low frequencies. Without a doubt, if it fits into your aesthetic requirements, separating the transformer from sensitive circuitry is still the best option.


Tom is 100% correct! Just saying.

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PostPosted: March 25th, 2023, 7:19 pm 
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Actually, Ayer using an EI transformer is a good thing. Toroidal transformers, although great for low magnetic field, is high bandwidth and HF noise will pass thru to the power supply. An EI transformer is more effective in filtering that out.

David


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PostPosted: March 25th, 2023, 9:19 pm 
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Joined: June 4th, 2013, 2:39 pm
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So I mounted it under the chassis. One channel is dead quiet, the other channel has slight hum. I pulled it and moved it 6 inches from the chassis. Then both channels hum. ;-) Go figure. I'll try the can on top when it arrives. If that doesn't solve it I'll switch to an EI tranny.

BTW, this is now a 6SN7 Aikido for my lawyer/musician friend in Florida. He has a pair of the Heyboer/Peerless Williamson amps, which he likes a lot and wants to keep. Currently he's using a Schiit Ferya S, which isn't bad at all. He likes the zip and tight bass (he's a bass player among other instruments) but we both think it lacks bloom. I intentionally made this Aikido a bit zipper than mine to match the tighter sound he likes. We'll see how it goes.


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PostPosted: March 26th, 2023, 10:45 am 
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David McGown wrote:
Actually, Ayer using an EI transformer is a good thing. Toroidal transformers, although great for low magnetic field, is high bandwidth and HF noise will pass thru to the power supply. An EI transformer is more effective in filtering that out.

David


Actually EI transformers pass RFL/EMI hence the need for isolation versions with a shield between windings.


Attachments:
Isolation_Transformer.jpg
Isolation_Transformer.jpg [ 31.7 KiB | Viewed 34417 times ]

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PostPosted: March 26th, 2023, 11:13 am 
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Walt,

What I was suggesting was the HF bandwidth of an EI power transformer is limited, and therefore can act as a filter for noise on the lines. For instance, EI core isolation transformers are much more effective than cheaper toroidal isolation transformers in filtering lines noise. Smaller toroidal transformers can have bandwidths up to 100kHz, Richard Sears successfully used an off-the-shelf Talema power transformer as a full audio bandwidth output transformer in a small PP amplifier. Try doing that with a 60Hz EI power transformer. What is best probably depends on circuit susceptibility to EM fields vs. lines noise, i.e., the specific application.

David


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