Noise with Computers, USB DACs, and Powerline Ethernet Kits

[ideal.hat]

Can this mod be installed on an Eros v1 and Mainline as well?

[Deke609]

Can this mod be installed on an Eros v1 and Mainline as well?

I don't see issues doing this with any of our products.  I do also plan to test whether a UF4007 can throw a 20A breaker and survive, as this could also be a suitable part to use.

[ideal.hat]

Thanks, I seems to have missed that info.

[Paul Birkeland]

Are you feeding your Eros with a signal from a computer?  If not, then I would not install this in a phono preamp.

[Jsin]

Yes, the 1N5408 would work well.

Hey there! Just picked up some of the above diodes, but the leads seem mighty thick - and double thick once twisted - wondering whether ill be able to attach to the ground etc effectively. So, my question: do the STTH2R06 diodes have skinnier leads?

[Paul Birkeland]

Yes, they would have skinnier leads.

[SeaCaptain]

I'd love to try this mod, but the only diodes I've got on hand are 1N4001, which are rated to 1A.

It's been quite a while since I built my crack, but can you confirm for this beginner that I should find a different set of diodes to use?

[Paul Birkeland]

The peak current capability of the 1N4001 is 30A, which is more than enough to get the job done.

[baseonmars]

Hi - would 1N5408 work here? Rated at 3A and 1000V? the datasheet says it's a rectifier diode. I'm not sure if that's a problem in this application?

[Paul Birkeland]

The peak/surge current is 125A, so no problems there.

[jivex5k]

A little more specifically, if you have a small AC voltage, say 100mV, the diodes present a pretty large impedance and this is what's broken.  If you have more than about 0.7V of anything AC or DC, then the diodes will start to short that out.

Forgive my ignorance, but am I understanding this correctly?
It sounds like this will prevent voltage under 0.7V from passing through the diode bridge.

I presume the noise coming from a nearby PC/USB DAC is somehow linked to small changes in voltage sent through the power cable, and somehow this small resistance will prevent these changes from translating into the audio signal.

[Paul Birkeland]

It's not exactly a resistance, it's more of an open circuit below a certain threshold.

[Crackling]

I had severe noise problems with two different Crack amplifiers that I had acquired no matter what DAC I used as long as the main source was my computer's USB port. Tried ALL my USB ports including a powered and unpowered USB hub too. Regardless, the noise was very much available and loud especially when I started playing a video game on my PC or did anything that put my GPU to work. Used at least 6 or 7 different models and brands of DAC. Then I found out the same happened with other tube amplifiers too (DV and woo) so it was definitely my system. Tried a myriad of USB noise reduction gizmo from iFi. Tried all sorts of fancy power cords both for my Crack and my PC to no avail. Some of these would reduce the noise a little bit or change its nature somewhat but it was still there and in full force! Ultimately did the resistor mod suggested here and just like magic, all the noise disappeared... But I couldn't find a similarly simple solution for other tube amps, so continued my troubleshooting steps until I came across this magical USB isolator after having read about it on various forums:
https://hifimediy.com/product/hifime-high-speed-usb-isolator/. The noise is now completely eliminated with all my tune amps. I have tried it with an Topping E30 and SMSL SU-8 v2, Khadas Tone Board, and a few other DACs I can't even remember in combination with my two non-Crack tube amps and no noise whatsoever... Now I've been tempted to remove the resistors from my Crack to test it with this to see if the noise will be gone, but don't feel adventurous enough.......yet.

Sorry for the super long post, but it was driving me crazy trying to eliminate the weird noise problem I was having, so I figured I'd share some of what I went through and what ultimately worked for me in case it can also help someone else out.

[Deke609]

For the purpose of this mod, you can think of a diode as erecting a barrier that is approx. 700 mV tall: @700 mV and below, no current flows, but everything above 700 mV passes over the barrier. (The "height" of the barrier, called the diode's "forward voltage" -- the minimum voltage required to turn the diode "on" and permit voltage and current to pass, varies a bit by type of diode). This applies to a "forward biased" diode - i.e., one where the anode is more positively charged than the cathode (banded end).  Because the mod uses two "reverse paralleled" diodes, there is a forward-biased diode in each direction: to earth ground and from earth ground -- so it blocks sub-700 mV currents in both directions.

In reality, the "barrier" is sloped and some small amount of current makes it through when the applied voltage is less than 700 mV.  See attached graph, and specifically the region to the right of the X,Y origin.

cheers, Derek

[Crackling]

One thing I have noticed after doing the diode mod is that my tubes, especially the power tube, doesn't get as brightly lit as before or as compared to when I use the same power tube in another tube amp. As you can tell from my posts, I severely lack technical knowledge in this area, but is this a general side effect of this mod?