Will,
I can only speak to my experiments. My FE RC is still on a board (wood), so I was playing around with how the rather unusual (at least to me) grounding scheme of the MyRef works. When I run a jumper wire from PGND to safety ground is when I pick up some hum and lose a little sound quality. The same thing happens when I run a jumper around R11, the 1 ohm resistor between the audio ground and PGND.
I have also seen some hum when I had a contact issue at the Molex input. At that time, the connector was connected to signal, but not to the ground side of the input. That caused hum.
I'm no expert, but it appears that MyRefs, at least most FEs, float in the sense that they are grounded through the input return (shield) to the source. When set up this way, the safety ground isn't connected to PGND and current from the PGND side flows through R11 to the audio ground.
You might try checking the path from audio ground on the FE board, back through the Molex, all the way to the music source.
Good luck. These things are sometimes hard to find.
Jac
I can only speak to my experiments. My FE RC is still on a board (wood), so I was playing around with how the rather unusual (at least to me) grounding scheme of the MyRef works. When I run a jumper wire from PGND to safety ground is when I pick up some hum and lose a little sound quality. The same thing happens when I run a jumper around R11, the 1 ohm resistor between the audio ground and PGND.
I have also seen some hum when I had a contact issue at the Molex input. At that time, the connector was connected to signal, but not to the ground side of the input. That caused hum.
I'm no expert, but it appears that MyRefs, at least most FEs, float in the sense that they are grounded through the input return (shield) to the source. When set up this way, the safety ground isn't connected to PGND and current from the PGND side flows through R11 to the audio ground.
You might try checking the path from audio ground on the FE board, back through the Molex, all the way to the music source.
Good luck. These things are sometimes hard to find.
Jac
Thanks Jac, I am suspicious of the input ground connection at the board too. It is the only molex I used and it does not seem to be very tight. Tommorow I will solder the connection and remove the wire from pgnd to safety earth. It still seems strange to me that if these were the cause they would be fixed by the earth to pgnd connection. I will see.
Yes, probably at the molex input connector.
I use them but they're a bit flimsy.
Also some cold joint of the 1 Ohm resistor or similar.
IMHO every shield MUST be connected, everytime, or it will act as an antenna disturbing signal.
My R-Cores shield has always been connected to safety earth.
Mmh... the input ground connection seems suspicious... also prone to pickup noise, maybe.
As Jac already wrote, the amp sound better with PGND unconnected.
That tab is there 'just if'
The original My_Ref was floating, original My_Evo was grounded, My_Evo Rev A floating.
But, usually, each build was unique.
Will, that is great work. Very clean and visually appealing. I'm so glad you took your time to keep the quality of the build equal to the quality of the sound produced by the FEs. Like Jac, I'm trailing behind you as I'm still on plywood.
My only suggestion would be to consider getting as many signal wires as close to the chassis as possible. It looks like you may be attempting to do that with the proximity of top cover but I'm not sure. I'd try to get as many of those signal wires to pass under the PCB and lay on the bottom plate to lessen the chance of that antenna effect. Your attention to that artistic wiring is so impressive though that those changes should only be considered if you get any further hum problem.
Super impressive work and I'm anxious to hear about your auditions in the coming days and weeks.
P.S. If you are/were a machinist by trade as it appears, that makes four in the MyRef family that I'm aware of. Nice metal work!
My only suggestion would be to consider getting as many signal wires as close to the chassis as possible. It looks like you may be attempting to do that with the proximity of top cover but I'm not sure. I'd try to get as many of those signal wires to pass under the PCB and lay on the bottom plate to lessen the chance of that antenna effect. Your attention to that artistic wiring is so impressive though that those changes should only be considered if you get any further hum problem.
Super impressive work and I'm anxious to hear about your auditions in the coming days and weeks.
P.S. If you are/were a machinist by trade as it appears, that makes four in the MyRef family that I'm aware of. Nice metal work!
On the subject of board connectors, no connector with wires soldered to the board is likely the best approach, but sometimes you just need a connector.
I did some looking around at the options and will be trying the connector shown in the links below. It is a little more expensive than the one in the BOM and slightly bigger.
I have them in my hands and they solve some of the problems of the BOM connector. The housings are a satisfying fit and latch with authority. The pins are the same design as the BOM connector, but the female contacts have spring contact surfaces that squeeze both side of the pin. They will still have flaws compared to soldering, but I think they will turn out to be more reliable than those in the BOM.
70543-0001 Molex | Mouser
50-57-9402 Molex | Mouser
16-02-1125 Molex | Mouser
I'm sure there are lots of other good choices. This is just the one that I picked.
Jac
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Happy easter to all.
After hunting for some eggs and making a preliminary breakfast out of chocolate I was able to sneak off and do a little soldering. I made a solid connection of the input ground and removed the pgnd connection. Hum is still present, darn. I do have another idea though and will try to get to it sometime today. I wont take much time to test. I am now suspicious of the body of the k71-4s. I tested them with my DMM and didn't find continuity, but still I am running out of ideas. Onward.
Bob, thank you. I am not a machinist just a hobbyist. I have done a lot of work with steel in the past, but I really like working with aluminum. Aluminum works muck like wood, which is nice. It does not require endless grinding and thicker pieces are easily cut using a jigsaw. Plus it is attractive in its raw form. More to come
After hunting for some eggs and making a preliminary breakfast out of chocolate I was able to sneak off and do a little soldering. I made a solid connection of the input ground and removed the pgnd connection. Hum is still present, darn. I do have another idea though and will try to get to it sometime today. I wont take much time to test. I am now suspicious of the body of the k71-4s. I tested them with my DMM and didn't find continuity, but still I am running out of ideas. Onward.
Bob, thank you. I am not a machinist just a hobbyist. I have done a lot of work with steel in the past, but I really like working with aluminum. Aluminum works muck like wood, which is nice. It does not require endless grinding and thicker pieces are easily cut using a jigsaw. Plus it is attractive in its raw form. More to come
They seem a good choice, I will try them too.
Take your time and you'll find the cause... consider also a different routing of input cabling, as already noted line input on top of AC power it's not optimal.
BTW I forgot one thing... your cabinet simply ROCKS!
Will,
I'm not sure how you are controlling volume at this point. At this moment, I am using my Squeezebox as a digital volume control and outputing digital to my DAC. I run analog from there to the FE. In that past, I have used a volume pot between the DAC and the FE.
Just for a reference, I measured from the audio ground on the board at the ground end of R13 -- to the cable shield as it comes out of the DAC. I get 0.28 ohms on the left and 0.37 on the right. This runs through the molex, my output wires, the RCA jack, and the RCA cable.
Just for fun, I measured my pot set up which has longer wires. 0.76 ohms and 0.57 ohms respectively.
If yours are similarly low, then I think you can rule out high resistance on the ground path. Good luck, again.
Jac
I'm not sure how you are controlling volume at this point. At this moment, I am using my Squeezebox as a digital volume control and outputing digital to my DAC. I run analog from there to the FE. In that past, I have used a volume pot between the DAC and the FE.
Just for a reference, I measured from the audio ground on the board at the ground end of R13 -- to the cable shield as it comes out of the DAC. I get 0.28 ohms on the left and 0.37 on the right. This runs through the molex, my output wires, the RCA jack, and the RCA cable.
Just for fun, I measured my pot set up which has longer wires. 0.76 ohms and 0.57 ohms respectively.
If yours are similarly low, then I think you can rule out high resistance on the ground path. Good luck, again.
Jac
Jac, I am using a Yamaha integrated amp pre section as volume control for testing. I will measure my cables later. I tried disconnecting the transformers ground shield on the off chance they were causing a loop, but to no avail. However your post got me thinking that I have not turned on the amp with source cables disconnected. When I did the hum was significantly louder. I don't know if this indicates anything but anyways onward.
Thanks for all the ideas guys!
Thanks for all the ideas guys!
When unconnected some hum is always present with all version of My_Ref, connecting PGND that hum goes lower.
So your experience is perfectly normal.
Did you tried to short input?
Also, you can rule out routing problems connecting to boards input some 'floating' cables and RCAs.
Okay so even crudely separating the k71s from their mounts has eliminated 99% of the hum! There is a small amount of noise with my ear to the tweeter that does not increase with volume adjust. I also do not have the ground shield connected for the traffos. I will re-connect those and properly shield the the k71s and see where I am at.
Thanks again guys!
Thanks again guys!
Good. It looks like you've got it. I've spent a lot of time playing K71s, but as you have guessed, I never had them in contact with ground. I am surprised that a cap casing would be a path to ground, but it sure is possible, probably with any metal can cap. I learn something new everyday. Thanks.
At least it is an easy fix.
Jac
At least it is an easy fix.
Jac
Very good!
You can use teflon tape to insulate K71s.
If I remember correctly Suburra suggested it as a must for those caps.
Jac, this surprised me too because I did check for continuity from the cap to chassis with my DMM and did not get a positive. Who knew.
Dario I have been contemplating ways to mechanically disconnect these from the chassis. I will keep the teflon in mind. I will be browsing the nylon fastener section of the hardware store tommorow to see if there are worthy options.
Also to note I would say the hum is all gone, the noise that is still present (which I may add is minuscule, and only audible with my ear to the tweater) is a slight hiss, which may be attributed to the eccentric wiring inside the enclosure or the retired rcas on the outside. One of these was replaced because of a slight noise issue some time ago iirc.
After I do some patching I will organize my wiring and see where Im at. Thanks again guys
Dario I have been contemplating ways to mechanically disconnect these from the chassis. I will keep the teflon in mind. I will be browsing the nylon fastener section of the hardware store tommorow to see if there are worthy options.
Also to note I would say the hum is all gone, the noise that is still present (which I may add is minuscule, and only audible with my ear to the tweater) is a slight hiss, which may be attributed to the eccentric wiring inside the enclosure or the retired rcas on the outside. One of these was replaced because of a slight noise issue some time ago iirc.
After I do some patching I will organize my wiring and see where Im at. Thanks again guys
If I remember correctly Suburra suggested it as a must for those caps.
I'll keep it in mind- it was my choice from the bom until I get tru copper
Hey Will, good detective work. FWIW - Just want to add that my power up is often DAC > FEs > Power center > Computer > JRiver Media Center. The DAC is fed by S/PDIF over BNC. There is an audible hiss from the tweeters until the Windows audio driver activates - then silence. Not sure if using a direct feed from a pre makes a difference. Turning the FEs off first also prevents pops/thumps to the speakers.
If the speaker protection relay drops out on loss of AC, then the speakers cannot pop, nor burp, nor react to any other switch off, if the whole system is switched off together. Even if mains power fails during a storm.
That is what the speaker relay should do. It should drop out within a few tens of milliseconds of losing AC.
That is what the speaker relay should do. It should drop out within a few tens of milliseconds of losing AC.
That hiss is related to the mini2496, which lacks muting circuitry, nothing to do with pres or the FEs...
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