This configuration is quiet.
The only connections to chassis are the screws.
All other connectors and jacks are isolated from chassis.
Also run all wires as close to chassis as possible.
The only connections to chassis are the screws.
All other connectors and jacks are isolated from chassis.
Also run all wires as close to chassis as possible.
This particular PCB design turns the ground plane into a "radiator" -- in the sense of being a antenna like receptor of of hum. Folks have addressed the issue by separating the power supplies from the signal boards with separate chassis and an umbilical.
Me, I use old Heath and Eico test equipment boxes for several RIAA amplifiers and don't have the issue.
Wayne shows a ground loop breaker in the power supply schematic -- this is helpful as well.
Good DIYAUDIO article on grounding and shielding: Audio Component Grounding and Interconnection - diyAudio
There's no question at all that the Pearl 2 is only quiet when the transformer is ~1m from the PCB.
I always tell people building it to make the raw PSU in an ugly box (or one that at least doesn't match the RIAA) so they are not tempted to stack them on on top of another.
If you run it like this, it will have some hum. 🙂
I always tell people building it to make the raw PSU in an ugly box (or one that at least doesn't match the RIAA) so they are not tempted to stack them on on top of another.
If you run it like this, it will have some hum. 🙂
A wise man once advised me to put the external power supplies on the floor,
both to give some physical isolation, and to save on shelf space.
I was moving stuff around the other day and my cheap and cheerful MM phono stage
started humming loudly. Turned out it was its proximity to the TT's external
power supply...
I'm now in the process of procuring an ugly non-matching box. 🙂
both to give some physical isolation, and to save on shelf space.
I was moving stuff around the other day and my cheap and cheerful MM phono stage
started humming loudly. Turned out it was its proximity to the TT's external
power supply...
I'm now in the process of procuring an ugly non-matching box. 🙂
Thanks... I knew the mistakes I made but didn't have time till now to start revisiting them. Here are some of my mistakes in order or seriousness.
1. I first tried with transformer in the box, once I took it out hum was almost completely gone. The bridge that I used also generated more noise. Didn't get around to using Quasimodo to estimate the E-core shielded transformer parameters for snubbers yet. Also didn't use the recommended CRCRC filter, had an old veroboard that I used.
2. I used metal standoffs, which was also grounded board to chassis on multiple points. Being an RF Engineer that's standard practice but that doesn't scale down to 5~6km wavelength (50~60Hz).
3. The RCA have thin insulators between chassis and the RCA ground, bought something with the Canon plate with RCA.
4. I used a Belden foil+braid shielded twisted pair, small diameter cable. In hind sight it has too much capacitance that also reduce the treble, but when I had flying leads no hum duh. Going to swap to mic cables or twisted-pair from LAN cable
5. Going to also put a decoupling cap between Ground and R14 and change Q2. First part I used semi died, sort of work but I can see DC swings with no signal (even grounded input) and fairly high distortion when I injected external signal to Q4 gate , RIAA disconnected. Improve quite a bit when I replace with new part, but I'm hesitant if the new replace part is still 100% good. Going to swap to Fairchild/OnSemi FQP3P20.
One interesting thing observation,problem that someone else mentioned I thought I was the only having was the hum comes only when I plug in both channel to my pre-amp. If I use L or R hum is not there. Probably related the many possible ground loop path.
Alex
1. I first tried with transformer in the box, once I took it out hum was almost completely gone. The bridge that I used also generated more noise. Didn't get around to using Quasimodo to estimate the E-core shielded transformer parameters for snubbers yet. Also didn't use the recommended CRCRC filter, had an old veroboard that I used.
2. I used metal standoffs, which was also grounded board to chassis on multiple points. Being an RF Engineer that's standard practice but that doesn't scale down to 5~6km wavelength (50~60Hz).
3. The RCA have thin insulators between chassis and the RCA ground, bought something with the Canon plate with RCA.
4. I used a Belden foil+braid shielded twisted pair, small diameter cable. In hind sight it has too much capacitance that also reduce the treble, but when I had flying leads no hum duh. Going to swap to mic cables or twisted-pair from LAN cable
5. Going to also put a decoupling cap between Ground and R14 and change Q2. First part I used semi died, sort of work but I can see DC swings with no signal (even grounded input) and fairly high distortion when I injected external signal to Q4 gate , RIAA disconnected. Improve quite a bit when I replace with new part, but I'm hesitant if the new replace part is still 100% good. Going to swap to Fairchild/OnSemi FQP3P20.
One interesting thing observation,problem that someone else mentioned I thought I was the only having was the hum comes only when I plug in both channel to my pre-amp. If I use L or R hum is not there. Probably related the many possible ground loop path.
Alex
My mistake was I ordered a shielded transformer with center tap, so I'm unable to implement Wayne configuration. Although I did find a patent that claims to address this, I did use this config in my F6.
BTW Q3 is connected as a common base amplifier.
Rout= rO || RC.
So what you measure is pretty close since Rc is R9, 499 ohm.
BTW Q3 is connected as a common base amplifier.
Rout= rO || RC.
So what you measure is pretty close since Rc is R9, 499 ohm.
Anyone have a source for this adhesive backed mu-metal state side?
I found non adhesive, they recommended double sided carpet tape for attachment. The self adhesive product looks way handy by comparison.
Russellc
Here's where I found mine:
Mumetal, Nikel Permalloy, Magnetic shielding foil, Mu-metal 0.1T-a, 30x100cm | eBay
Mumetal, Nikel Permalloy, Magnetic shielding foil, Mu-metal 0.1T-a, 30x100cm | eBay
Sorry, late to the low output party, which resistors am I changing to 300 ohm? Have my eye on that low output Hana unit, some have told me a step up transformer is a better option, resistors are a lot less expensive.
Thanks, Russellc
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That would be R14 from 1k to 300R.
I was looking at the 2 Hana low output units as well and I believe they are 0.5mV.
Dealers I've talked to have are very positive on the Hana.
I was looking at the 2 Hana low output units as well and I believe they are 0.5mV.
Dealers I've talked to have are very positive on the Hana.
It seems a well received choice for 750. My current MC is higher output, 2.5 I believe, plenty of gain there.
Russellc
Russellc
New Pearl2 added to the fold.
A little late to the game but happy to have it up and running...
Used the DIYAudio PSU and Slimline cases.
Loving it all the way...
I was lucky in that I had no major issues after reading this and the original thread carefully. Fired up right away with all main voltages in range.
Did have to figure out the orientation of the LED connections in the PSU...🙄
I do have a humm when I turn things way up, but not noticable during play.
Will investigate and resolve later.
Thanks to Wayne and Nelson for the great design, 6L6 for the Pearl2 and PSU threads and Berd for his BOM.
Thanks to all others for sharing their experiences.
I have included pictures, but any suggestions/recommendations for improvement are appreciated.... thx
Rega RP6/Exact2>Pearl2>BAT vk50se>Parasound JC1>ProAC d38...
A little late to the game but happy to have it up and running...
Used the DIYAudio PSU and Slimline cases.
Loving it all the way...
I was lucky in that I had no major issues after reading this and the original thread carefully. Fired up right away with all main voltages in range.
Did have to figure out the orientation of the LED connections in the PSU...🙄
I do have a humm when I turn things way up, but not noticable during play.
Will investigate and resolve later.
Thanks to Wayne and Nelson for the great design, 6L6 for the Pearl2 and PSU threads and Berd for his BOM.
Thanks to all others for sharing their experiences.
I have included pictures, but any suggestions/recommendations for improvement are appreciated.... thx
Rega RP6/Exact2>Pearl2>BAT vk50se>Parasound JC1>ProAC d38...
Attachments
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Get the phonostage away from the other components and see if the hum goes away. Just lift it up.
I think we should have an "ugliest" Pearl 2 power supply contest. I have a serious candidate in an old Dynaco Pat 5 chassis.There's no question at all that the Pearl 2 is only quiet when the transformer is ~1m from the PCB.
I always tell people building it to make the raw PSU in an ugly box (or one that at least doesn't match the RIAA) so they are not tempted to stack them on on top of another.
If you run it like this, it will have some hum. 🙂
Russellc
Once back from holiday. It has no face plate. I do have an aluminum piece of correct size that would be a little more presentable, but it sits off to the side on the floor, out of sight....unless lights off and you can see blue speckles on wall from leds shining through topside ventholes...