Hi fellow members. While waiting on some parts, I am about to try to find the hum from my speakers when playing the FH9HVX amp with my preamp. I can power on the amp without the preamp and it is dead silent. I turn on the preamp and I have a mild buzz from the speakers.
Please see the pic of my setup. All the PE's, HS, IEC, shown as dotted lines are connected to the star ground (dirty gnd).
One of the things I have noticed looking at xrk971 drawings is that only the + or Out from the amp is connected to the In spades and Out spades of the SSR. None of the Gnd spades on the SSR are used. The Gnd on the spkr binding posts are connected back to the All Cees 0V post.
My diagram has all of the spades occupied on the SSR and connected to the spkr binding posts.
Could this be the source of the hum?. If I disconnect the gnd from the amp to the SSR In and remove the gnd from the SSR out and connect it to the 0V on the All Cee's, will it hurt anything.
Please see the pic of my setup. All the PE's, HS, IEC, shown as dotted lines are connected to the star ground (dirty gnd).
One of the things I have noticed looking at xrk971 drawings is that only the + or Out from the amp is connected to the In spades and Out spades of the SSR. None of the Gnd spades on the SSR are used. The Gnd on the spkr binding posts are connected back to the All Cees 0V post.
My diagram has all of the spades occupied on the SSR and connected to the spkr binding posts.
Could this be the source of the hum?. If I disconnect the gnd from the amp to the SSR In and remove the gnd from the SSR out and connect it to the 0V on the All Cee's, will it hurt anything.
Sounds like a ground loop between your preamp and the FH9, which can be hard to track down. I had the same issue when I built mine. It has been a year and a half since my build, so my memory may not be crystal clear. 🙂
In my case, I attributed it to the use of a non-shielded Antek transformer (I think I used the same one as in the diagram), because I did not have any hum at all from my class-A First Watt F7 look-alike, which did use a shielded version.
Upon further tinkering, I was able to solve the issue by adding a ground-lift circuit to my preamp, which had previously had the signal grounds floating (i.e. not connected to chassis or earth). This consisted of a simple thermistor and a capacitor in parallel. Since this solved the issue, I did not bother replacing the Antek in my FH9.
BTW - my preamp is a DIY project, so your mileage will obviously vary. It is hard to see in the picture, but the thermistor and cap are circled in red. This preamp has an Arduino-controlled stepped attenuator and input selector, as well as a Pass crossover circuit.
Preamp interior:
My FH9:
In my case, I attributed it to the use of a non-shielded Antek transformer (I think I used the same one as in the diagram), because I did not have any hum at all from my class-A First Watt F7 look-alike, which did use a shielded version.
Upon further tinkering, I was able to solve the issue by adding a ground-lift circuit to my preamp, which had previously had the signal grounds floating (i.e. not connected to chassis or earth). This consisted of a simple thermistor and a capacitor in parallel. Since this solved the issue, I did not bother replacing the Antek in my FH9.
BTW - my preamp is a DIY project, so your mileage will obviously vary. It is hard to see in the picture, but the thermistor and cap are circled in red. This preamp has an Arduino-controlled stepped attenuator and input selector, as well as a Pass crossover circuit.
Preamp interior:
My FH9:
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wtnh, thanks for your experience with your system. I am using the preamp portion of an iDecco integrated amp as my pre amp. I doubt that I have the experience to open it up and start to experiment with ground lifts... etc, on a commercial product. I will have to figure out other ways, or just live with the minor hum.
Going back over some old posts - looks like you have been fighting the hum issue for a while. 🙁
It might all boil down t how you implemented your star ground and the use of GLBs. I recall that the FH9 boards already have mounting holes for thermistors, but I have had good luck isolating the star ground from the chassis and using an external thermistor GLB between the star and chassis. I used a nylon spacer with a nylon shoulder washer on the underside which isolates the PS and amp board grounds. The thermistor bridges that to the chassis. Here is an example of what I am talking about:
It might all boil down t how you implemented your star ground and the use of GLBs. I recall that the FH9 boards already have mounting holes for thermistors, but I have had good luck isolating the star ground from the chassis and using an external thermistor GLB between the star and chassis. I used a nylon spacer with a nylon shoulder washer on the underside which isolates the PS and amp board grounds. The thermistor bridges that to the chassis. Here is an example of what I am talking about:
Hi Myles,
Sorry for your troubles with ground loop hum. Thanks for the diagram. Very helpful. You can try the following:
1. connect speaker GND directly from banana to All Cee’s. It may or may not help.
2. makes sure RCA jack is isolated from chassis with plastic shoulder washer.
3. Add 10ohm resistor in series from RCA to amp input on ground wire.
4. Isolate star hub with ground lift using NTC like Wtnh has shown (clever idea with plastic shoulder washer).
5. if you have a smartphone with a 3.5mm stereo out adapter or other battery powered DAC, connect a 3.5mm make stereo jack to dual RCAs and see if hum goes away. If it does, the problem may be the source has a ground loop to earth ground. Or there is a ground loop with a USB cable etc. much harder to debug with this. Only try diffferent sources and see if there is one that works.
I suspect number 3 and 4 from the list above are probably going to solve the problem assuming 2 is not the problem.
Thanks for your patience.
Sorry for your troubles with ground loop hum. Thanks for the diagram. Very helpful. You can try the following:
1. connect speaker GND directly from banana to All Cee’s. It may or may not help.
2. makes sure RCA jack is isolated from chassis with plastic shoulder washer.
3. Add 10ohm resistor in series from RCA to amp input on ground wire.
4. Isolate star hub with ground lift using NTC like Wtnh has shown (clever idea with plastic shoulder washer).
5. if you have a smartphone with a 3.5mm stereo out adapter or other battery powered DAC, connect a 3.5mm make stereo jack to dual RCAs and see if hum goes away. If it does, the problem may be the source has a ground loop to earth ground. Or there is a ground loop with a USB cable etc. much harder to debug with this. Only try diffferent sources and see if there is one that works.
I suspect number 3 and 4 from the list above are probably going to solve the problem assuming 2 is not the problem.
Thanks for your patience.
Thanks guys, I will try the easy ones first and graduate down the list. May take a while, but I will answer back.
I think the first thing I will do is reduce the size of my grounding bolt, so I can find some suitable shoulder washers and nylon standoffs. I can then reduce the size of my crimp connectors also. This is in anticipation of using the ground lift.
I think the first thing I will do is reduce the size of my grounding bolt, so I can find some suitable shoulder washers and nylon standoffs. I can then reduce the size of my crimp connectors also. This is in anticipation of using the ground lift.
I disconnected the gnd from the amp to the SSR and from the SSR to the spkr binding post. I connected the gnd from the spkr bindiong post to the 0V of the All Cee's psu. Did not get rid of the hum.
I checked the RCA inputs and the shoulder washers. All looks good., but still hum.
I inserted the 3.5mm plug into my iphone and plugged the RCA cables into the input jacks. No hum, dead silence.
Just to be sure I used the 3.5mm /rca cables and my chrome book operating on battery. No hum, dead silence.
Question's:
1. Should I try the 10 ohm resistor in series from rca gnd to amp input gnd or just go for the gnd lift on the star hub ?.
2. I am thinking of leaving the HS gnds and the IEC mains ground as they are attached to the big ground bolt, and installing another central ground to handle the 4 PE grounds from the All Cee's and the amp boards for the gnd lift and thermistor as outlined by wtnh . Any problems with this strategy ?.
Thanks for the help,
I checked the RCA inputs and the shoulder washers. All looks good., but still hum.
I inserted the 3.5mm plug into my iphone and plugged the RCA cables into the input jacks. No hum, dead silence.
Just to be sure I used the 3.5mm /rca cables and my chrome book operating on battery. No hum, dead silence.
Question's:
1. Should I try the 10 ohm resistor in series from rca gnd to amp input gnd or just go for the gnd lift on the star hub ?.
2. I am thinking of leaving the HS gnds and the IEC mains ground as they are attached to the big ground bolt, and installing another central ground to handle the 4 PE grounds from the All Cee's and the amp boards for the gnd lift and thermistor as outlined by wtnh . Any problems with this strategy ?.
Thanks for the help,
Hi Myles,
The fact that your phone and chromebook do not have hum seems to indicate that your other audio source, is unfortunately, the source of the hum (possibly because it is plugged into mains and earth ground). If the FH9HVX is quiet with the phone, it means that it inherently has no ground loop and the ground wiring topology is sound. I am not sure anything you do to the amp will fix your source of hum from the other device. Do you have other amps that play nice with it (no hum)?
It doesn't hurt to try to add the 10ohm in series from RCA ground to input ground and ground lift the star hub. WTNH's suggestions can also be tried. Just do one thing at a time.
Good luck!
The fact that your phone and chromebook do not have hum seems to indicate that your other audio source, is unfortunately, the source of the hum (possibly because it is plugged into mains and earth ground). If the FH9HVX is quiet with the phone, it means that it inherently has no ground loop and the ground wiring topology is sound. I am not sure anything you do to the amp will fix your source of hum from the other device. Do you have other amps that play nice with it (no hum)?
It doesn't hurt to try to add the 10ohm in series from RCA ground to input ground and ground lift the star hub. WTNH's suggestions can also be tried. Just do one thing at a time.
Good luck!
This can be really tough to track down but keep at it. For a really good overview of grounding in general, here is an article by Rod Elliot on his website. It may help with your understanding of the problem, FWIW: https://sound-au.com/earthing.htm
Also, search this forum for ground loops - you'll see lots of hints.
Also, search this forum for ground loops - you'll see lots of hints.
You need a ground loop breaker between the star gnd to earth gnd. Anti parallel diode, thermistor are both good options. Also might want 10ohm ground lift from the rca IN to the main ground.
The psu and amp boards already have integrated ground lift NTC's, so Myles is covered there.
Thanks for all the help from everyone so far. I was thinking about the ground issue, so I took some measurements as to how far away I had to be to not notice any hum. With my old ears, I noticed mild hum as I approached about 1 ft. away from the speaker. Even at the speaker it is not so bad, so I might leave it for awhile. I now know what to do if I want to experiment further.
Could be the preamp itself then. Internal hum or its picking up emi from the outside due to weak shielding. For latter try moving the preamp away from its current location. If the hum changes its chassis shielding issue
I have some 10 ohm 5W resistors. Is that a bit excessive for this process. I also have some 1W and 1/4W, but they are slated for the Nirvana. Will use them if necessary rather than the 5W ones. Recommendations please.
Thanks,
Thanks,
Try adding 10ohm (1/4w) between RCA jack ring and ground pin of amp PCB audio in for each channel.
Absolutely X, I plan to cut the wire and solder in the resistor. That way I save my existing crimp on the jack ring. I need to de-solder my Molex connector on the pcb audio in and replace it with a JST type. The wire jumped the crimp in molex connection (lousy crimp I guess), and I do not have any more Molex crimp terminals. I have lots of JST type, so should work out fine. Hope this resistor will help, if not, I will proceed with the ground lift process.
While waiting for parts for the FH9 and doing other summer work in the mountains, I have begun some serious work on the the enclosure and layout for the Xmas amp. Will post some updates in awhile in the Xmas amp thread.
By the way, the new case for the AN looks fantastic, and nice job making it all fit.
While waiting for parts for the FH9 and doing other summer work in the mountains, I have begun some serious work on the the enclosure and layout for the Xmas amp. Will post some updates in awhile in the Xmas amp thread.
By the way, the new case for the AN looks fantastic, and nice job making it all fit.
Tried the 10 ohm resistor in series between RCA jack ring and ground pin of amp PCB input on one channel. No change in the hum, still minor and noticeable within 1 ft. I will do the same to the other channel just to be consistent, and if no change, I will have to think on whether to employ a ground lift as in above post's.
Here is also a very good source of info for wiring an amplifier and all the different kinds of issues you can run into.
Thanks for all the help so far. I think I will go forward with the the ground lift on the star hub as outlined by wtnh in post #1084. My plan according to my connection diagram in post #1081 is:
1. Connect the PE wires from the 2 PSU & 2 amp boards to a ground lift hub.
2. Disconnect the ground wire from both heatsinks, as the heatsinks are attached to the chassis and should not need grounding. This will leave just the mains ground attached to the chassis ground.
3. Connect a thermistor between the ground lift and the chassis ground.
If this all makes sense, I will proceed. Let me know your thoughts.
MM
1. Connect the PE wires from the 2 PSU & 2 amp boards to a ground lift hub.
2. Disconnect the ground wire from both heatsinks, as the heatsinks are attached to the chassis and should not need grounding. This will leave just the mains ground attached to the chassis ground.
3. Connect a thermistor between the ground lift and the chassis ground.
If this all makes sense, I will proceed. Let me know your thoughts.
MM