I agree that cooling slots are probably unnecessary. I bought the Pearl 3 chassis from Modushop so that's how it came. I'm pondering using a metal screen accross them, but the question I asked about grounding applies there as well. I think I know the answer (ya gotta ground it), but wanted to ask anyway so I can bring up the thinking to the hive of minds and get a little razzing in the process 😉
If you add metal, and don’t ground it, nothing happens.
Is closing up the phonostage that tight worth it? Maybe? Try it for sure and report back… if it’s beneficial we’d love to know..
The biggest consistent improvement with noise control I get with any and all phonostages is the addition of a clamp-on ferrite on the tonearm leads. Makes an enormous difference with the ingress of broadcast radio and many other RF -producing widgets like cellphones and some switching PSU.
Is closing up the phonostage that tight worth it? Maybe? Try it for sure and report back… if it’s beneficial we’d love to know..
The biggest consistent improvement with noise control I get with any and all phonostages is the addition of a clamp-on ferrite on the tonearm leads. Makes an enormous difference with the ingress of broadcast radio and many other RF -producing widgets like cellphones and some switching PSU.
Thanks Jim! Good suggestion!
I am just super interested in understanding both how noise enters into the circuit as well as the ground loop issue. The Pearl 3 has exposed me to these concepts due to its extremely sensitive nature and I'm enjoying pondering how to attack every possible angle on reducing interference. Grounding any sort of Faraday shield makes sense. I thought putting a washer in the home made 3D printed blanking plate might, ....just might, help, but also had strong doubts, hence the post.
We can all learn from my dumb ideas. Occasionally I might have a good one.
I am just super interested in understanding both how noise enters into the circuit as well as the ground loop issue. The Pearl 3 has exposed me to these concepts due to its extremely sensitive nature and I'm enjoying pondering how to attack every possible angle on reducing interference. Grounding any sort of Faraday shield makes sense. I thought putting a washer in the home made 3D printed blanking plate might, ....just might, help, but also had strong doubts, hence the post.
We can all learn from my dumb ideas. Occasionally I might have a good one.
Hmmm, my microwave oven operates at 2 GHz and its "chassis" which keeps the microwaves inside from leaking outside, is perforated by 3mm holes. Those holes allow me to see through the front glass door + electromagnetic screen. I suspect this means we can conclude that if I had a second chassis perforated by 10X bigger holes { 30mm (1.2 inch) }, it would be an effective electromagnetic screen/shield for 10X lower frequency (200 MHz) radiation. Since audio is concerned with much lower frequency electromagnetic noise than 200 MHz, I don't think cooling slots are anything to worry about.
Well I tend to agree with you Mark. I've seen the effects of an aircraft microwave vs home microwave on VHF radio through testing. It can have an impact.
Anyway, if the slots actually have no impact due to size then that's fine. Most of my questions are due to my lack of understanding so thank you for sharing your knowledge.
I do know that taking the top plate off likely does have an impact though based on my experience troubleshooting. A massive difference in ground hum with chassis top on vs off from my experience.
Edit: I'll stop asking nonrelevant inquisitive questions. Don't want to distract from the intent of the thread. Apologies.
Anyway, if the slots actually have no impact due to size then that's fine. Most of my questions are due to my lack of understanding so thank you for sharing your knowledge.
I do know that taking the top plate off likely does have an impact though based on my experience troubleshooting. A massive difference in ground hum with chassis top on vs off from my experience.
Edit: I'll stop asking nonrelevant inquisitive questions. Don't want to distract from the intent of the thread. Apologies.
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Based on this then having the top of the chassis off won't have any effect on EMI in a frequency range near audio either. Top plate on chassis vs off sure seems to have a significant affect though for my Pearl 3. Just holding my open palm over the open chassis created a significant increase in noise. I'd like to understand what's happening to help avoid issues with future builds.
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Holding hands close to very sensitive circuits will introduce noise. Just try to put your finger on the oscilloscope probe and you will see 50/60 Hz noise. The body acts as an antenna and the hands radiates the noise to the circuit. That is quite normal. The tubes in a tube preamp can be quite sensitive and also jfet input preamps with very high gain.
@mhenschel
My solution is a bit different from others. I use the UDP3 PSU. I have the yellow/green wire all the way from UDP3 (connected to chassis in UDP3 and also in P3 chassis). The green devices are just the usual NTC's that makes the audio gnd to chassis ground lift. I just do what I have done in all my other DIY amps which are very quiet and P3 also. I was thinking about isolating the grounding post from chassis so only chassis connection was the "star-screw" but works fine as is. No hum / noise.
Holding hands..........sensitive circuits........yes yes......
My solution is a bit different from others. I use the UDP3 PSU. I have the yellow/green wire all the way from UDP3 (connected to chassis in UDP3 and also in P3 chassis). The green devices are just the usual NTC's that makes the audio gnd to chassis ground lift. I just do what I have done in all my other DIY amps which are very quiet and P3 also. I was thinking about isolating the grounding post from chassis so only chassis connection was the "star-screw" but works fine as is. No hum / noise.
Holding hands..........sensitive circuits........yes yes......
I think you have other problems in your build.
Claiming noise because of the airgaps in the lid, is like saying, that a Faraday cage doesn´t work, because it´s
perforated on all sides. Suggest you fix the P-3 and don´t create imaginary problems.
All written with the best intensions
That very well could be the case. So chassis top has to be on. Holes in chassis totally irrelevant. Copy all.
I'll investigate further when back in MN.
To be clear, I didn't claim noise was coming through slots. I asked if covering holes/slots would provide benefit, and if so, would the "cover" need to be grounded. Sounds like it's a waste of energy and time, so easy to skip the idea all together.
Edit: Also, thank you to everyone who had chimed in on the ground hum and noise issues I experienced. This is all new territory for me and I'm trying to understand what's going on from a physics perspective as much as just resolving the issue. I feel if you can understand the "why/how" behind why something does, or does not, work then that's real valuable knowledge gained. So again, thank you for sharing your knowledge.
I'll investigate further when back in MN.
To be clear, I didn't claim noise was coming through slots. I asked if covering holes/slots would provide benefit, and if so, would the "cover" need to be grounded. Sounds like it's a waste of energy and time, so easy to skip the idea all together.
Edit: Also, thank you to everyone who had chimed in on the ground hum and noise issues I experienced. This is all new territory for me and I'm trying to understand what's going on from a physics perspective as much as just resolving the issue. I feel if you can understand the "why/how" behind why something does, or does not, work then that's real valuable knowledge gained. So again, thank you for sharing your knowledge.
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Further to Mark's comments, I run a perforated top plate made of stainless steel and painted black on my Spectral DMC-12, but grounded in one location to the rest of the chassis enclosure. It originally came with a solid steel lid, but after hours of use, it accumulated enough heat inside the enclosure to give me concern about the effect on the 30-year-old MOSFETS. The entire lid is perforated, perhaps about 40% of the total area; there are a bucketload of 2mm-diameter holes in the lid.
There is no added audible noise, and I tested it with my QuantAsylum Q403 and measured no additional noise in any part of the frequency range tested. Lid off? Another matter.
My three Pearl 3 are not as sensitive as some are indicating. They are all sensitive to any transformers in use for other audio gear, and to close proximity to the preamp being used (whichever of the 5 that are nearby), but as long as I keep it about 2-3' away, there is no added noise.
The thing that does add mains hum is if I plug the Pearl 3 power supply into a different outlet, or different power conditioner/surge protector (SurgeX sx-2120) than is supplying the preamp. The further away I plug in the Pearl 3 power supply, the more audible hum. This suggests it is sensitive to ground loops. This is also true of almost any of my various phono preamps, and certainly true of my amps on the other side of the room when used with preamps one outlet away. I have to use the same outlet to supply any given system.
Another source of hum resulted from me having ground wires running from each phono preamp to my turntable relay switching box - again, a ground loop problem that was easily solved.
There is no added audible noise, and I tested it with my QuantAsylum Q403 and measured no additional noise in any part of the frequency range tested. Lid off? Another matter.
My three Pearl 3 are not as sensitive as some are indicating. They are all sensitive to any transformers in use for other audio gear, and to close proximity to the preamp being used (whichever of the 5 that are nearby), but as long as I keep it about 2-3' away, there is no added noise.
The thing that does add mains hum is if I plug the Pearl 3 power supply into a different outlet, or different power conditioner/surge protector (SurgeX sx-2120) than is supplying the preamp. The further away I plug in the Pearl 3 power supply, the more audible hum. This suggests it is sensitive to ground loops. This is also true of almost any of my various phono preamps, and certainly true of my amps on the other side of the room when used with preamps one outlet away. I have to use the same outlet to supply any given system.
Another source of hum resulted from me having ground wires running from each phono preamp to my turntable relay switching box - again, a ground loop problem that was easily solved.
Attached to ground, it's shield, just a small localized one. Attached to anywhere else in circuit, it's an antenna which can receive or transmit or do neither, depending on the circuit. You've already made them, so I'd just make a hole in the plastic, put a screw, nut and solder terminal connected to the washer and ground them. Then you will be slightly more shielded than before.