Btw, soldered on some output snubber caps and resistors, and reworked some of the wire twisting, and all that hf stuff disappeared. Was not something I could hear pre se, just tiring to oisten to at high volumes. Hum remains unchained, even though i followed Bonsais recommendations to the point. Anyways, still more Bonsai tests to do, I am hoping next week will provide som time to do them.
And I am sorry I did not respond to that questions of yours in the previous post last week. I have NOT tried that in the amps current iteration. Reread your post earlier today, and I will get to it as soon as time allows. Konda excited about that test. But this is no cross channel loop. But still, might prove fruitful that test. It is possibly one of few tests I havent done.
I must add one of the most important parts of Bonsais test have not been adequately performed. The test involves putting the tranny out of chassis. Kinda hard with kids around the house =S
I must add one of the most important parts of Bonsais test have not been adequately performed. The test involves putting the tranny out of chassis. Kinda hard with kids around the house =S
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If you mean the Power supply board, its from Teabag. Not the smallest, but built like a tank. They are used in all my amps except my first build, F5 which used Peter Daniels amp and PS boards.
Russellc
Thanks, Russel. I checked it out. It had the same concept of gnd links. Since you guys manage to make the amp quiet with such PSUs, I guess the fault mot likely lies elsewhere (me). I mentioned following Bonsais test to the point, but maybe not. there is still much room for improvement wrt wire dressing, as well as reducing loop areas around both DC and AC wiring. Will get to it, following the example of your builds and Bonsais great tips. Time is just not on my side right now, but it is OK, I have fantastic sound right now, the best ever. Reached bias max with 230 watts dissipation in the 5U now, and must say the last bias increase to 1,28 amps per vertical pair really made my Fyne speakers sing.
Amazing.
The hum is irritating just cause I know it is there. No one else knows or are able to hear it. So I guess it is good enough, for now. But this is a power amp, supposed to be the easiest to get quiet of all builds. Despite low PSRR due to no feedback. So I put this down to my own skills, perhaps a bit influenced by the tranny. We will see.
Hope you guys are all right.
Cheers,
Andy
Amazing.
The hum is irritating just cause I know it is there. No one else knows or are able to hear it. So I guess it is good enough, for now. But this is a power amp, supposed to be the easiest to get quiet of all builds. Despite low PSRR due to no feedback. So I put this down to my own skills, perhaps a bit influenced by the tranny. We will see.
Hope you guys are all right.
Cheers,
Andy
Reposting since it got lost a few pages back. Here is the schematic of what i'm working with. I'm seeing LF motorboating on outputs (but music plays fine and isn't distorted). My amp is built with complementary stages in balanced config. bias + offest were set before FE R5 was bridged.
I have noticed that the motorboating happens when JUST the output stage boards are connected to PSU and the FE is disconnected (which I did to troubleshoot).
Does anyone see anything wrong with my schematic/wiring?
Thanks!
I have noticed that the motorboating happens when JUST the output stage boards are connected to PSU and the FE is disconnected (which I did to troubleshoot).
Does anyone see anything wrong with my schematic/wiring?
Thanks!
Attachments
pics attached!
R5 on the FE is connected on the bottom of the board (and covered with elec tape to protect it from shorts).
V+/- are also connected on bottom side of FE
Floating green wire from XLR Pin 1 is there for troubleshooting. I connected it and then grounded it to the chassis to troubleshoot (but it had no effect).
GND2.2 and GND3.3 on PSU are tied together on bottom side of the board
My schematic pic is on the last page (reached max uploads per post on this one!).
Wires are awkwardly routed and pushed to the sides for ease of taking pictures/camera angles.
I know the Trafo sitting underneath the PSU like that is less than ideal. This is the 3rd chassis layout i've tried, and they all exhibit the same motorboating behavior. I started with the trafo Vertically mounted with an L bracket. Then I moved the PSU and the trafo to a separate chassis and built a DC umbilical cable. Both of those layouts exhibited motorboating, so I moved everything back to a single chassis.
As mentioned, the putt putt putt motorboating pattern increases in speed (but not sound frequency) as voltage rises (both with Variac and benchtop PSU).
The motorboating also happens when the FE is disconnected from power (just the output stage boards connected).
I do not currently own an oscope but i'm willing to buy one if it will help with this. I've been wanting one for awhile anyway.
General questions: Should the DC V+/V- wires be tightly twisted like I have them? I have seen conflicting info about this online, so when in doubt, I twist. More than happy to untwist them though lol
Thanks in advance for your guidance!
R5 on the FE is connected on the bottom of the board (and covered with elec tape to protect it from shorts).
V+/- are also connected on bottom side of FE
Floating green wire from XLR Pin 1 is there for troubleshooting. I connected it and then grounded it to the chassis to troubleshoot (but it had no effect).
GND2.2 and GND3.3 on PSU are tied together on bottom side of the board
My schematic pic is on the last page (reached max uploads per post on this one!).
Wires are awkwardly routed and pushed to the sides for ease of taking pictures/camera angles.
I know the Trafo sitting underneath the PSU like that is less than ideal. This is the 3rd chassis layout i've tried, and they all exhibit the same motorboating behavior. I started with the trafo Vertically mounted with an L bracket. Then I moved the PSU and the trafo to a separate chassis and built a DC umbilical cable. Both of those layouts exhibited motorboating, so I moved everything back to a single chassis.
As mentioned, the putt putt putt motorboating pattern increases in speed (but not sound frequency) as voltage rises (both with Variac and benchtop PSU).
The motorboating also happens when the FE is disconnected from power (just the output stage boards connected).
I do not currently own an oscope but i'm willing to buy one if it will help with this. I've been wanting one for awhile anyway.
General questions: Should the DC V+/V- wires be tightly twisted like I have them? I have seen conflicting info about this online, so when in doubt, I twist. More than happy to untwist them though lol
Thanks in advance for your guidance!
Attachments
1: you have created a huge loop area in your PSU. Remove your ground links at the input end, and instead solder on the 4 ones at the output end of the PSU.
2: Disconnect ground between chassis and PSU. Does it still hum? If it does not, you have located your problem. If it still hums, reconnect.
3: Have you tried disconnecting one of your OS’es, one at a time? Does it still hum (fe disconnected)
4: put your FE returns twisted together in the SAME HOLE of euroblock.
5: put speaker returns in the block on opposite side.
6: check your chassis for ground loops. Turn amp off. Disconnect gnd link between chassis and PSU. Meausure resistance between input gnd and chassis, and psu gnd and chassis. Low resistance= likely gnd loop. Try to measure resistance between your output boards and chassis too.
7: replace the solid core gnd wires going into your euroblocks. They make bad contact.
8: Do NOT connect chassis gnd to the same euroblock as the FE returns.
9: Short inputs. Is there still hum? (Irrelevant if your FE is disconnected).
10: try to run the amp without the softstart. I know in at least one instance it had been the cause of hum due to error.
Do all your test with FE disconnected. When problem is solved, reconnect FE and hope for the best.
I have hum too, but not very much luckily. So I know it is frustrating. These are my best tips, but others while chime in with better ones i guess. ZM?
Good luck!
Andy
2: Disconnect ground between chassis and PSU. Does it still hum? If it does not, you have located your problem. If it still hums, reconnect.
3: Have you tried disconnecting one of your OS’es, one at a time? Does it still hum (fe disconnected)
4: put your FE returns twisted together in the SAME HOLE of euroblock.
5: put speaker returns in the block on opposite side.
6: check your chassis for ground loops. Turn amp off. Disconnect gnd link between chassis and PSU. Meausure resistance between input gnd and chassis, and psu gnd and chassis. Low resistance= likely gnd loop. Try to measure resistance between your output boards and chassis too.
7: replace the solid core gnd wires going into your euroblocks. They make bad contact.
8: Do NOT connect chassis gnd to the same euroblock as the FE returns.
9: Short inputs. Is there still hum? (Irrelevant if your FE is disconnected).
10: try to run the amp without the softstart. I know in at least one instance it had been the cause of hum due to error.
Do all your test with FE disconnected. When problem is solved, reconnect FE and hope for the best.
I have hum too, but not very much luckily. So I know it is frustrating. These are my best tips, but others while chime in with better ones i guess. ZM?
Good luck!
Andy
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Btw: Twisting is not the problem. You can try twisting your speaker returns together with speaker pos from OS, then fro OS with the dc wires to the PSU. But I do NOT think that is your main issue. Also, you have a large loop area since speaker wires are at opposite sides. Twist them together for as much of the way as possible, could help. But again, this is probably not your biggest problem.
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1: you have created a huge loop area in your PSU. Remove your ground links at the input end, and instead solder on the 4 ones at the output end of the PSU.
Nearly all the pics i've seen in this thread have the PSU tied together on both ends, including 6L6s in the guide. I've asked about this a few times but never got a direct answer. To me, it makes the most sense to only have them tied at the outputs, but there have been alot of people in this thread (which i've read cover-to-cover a few times) saying that you should tie them together in all locations for a good secure ground plane. I'm fine with clipping these if this is in fact a problem.
Also, the motorboating happens with a benchtop PSU, so i really don't think the PSU is the main problem.
2: Disconnect ground between chassis and PSU. Does it still hum? If it does not, you have located your problem. If it still hums, reconnect.
It is motorboating, not humming, but yes, I've tried every possible combination of things being grounded/not grounded and the motorboating persists.
3: Have you tried disconnecting one of your OS’es, one at a time? Does it still hum (fe disconnected)
This is a balanced BA3, so there are no speaker returns. Both speaker +/- are connected to L/R output stage respectively.
4: put your FE returns twisted together in the SAME HOLE of euroblock.
They are
5: put speaker returns in the block on opposite side.
N/A because this is a balanced amp
6: check your chassis for ground loops. Turn amp off. Disconnect gnd link between chassis and PSU. Meausure resistance between input gnd and chassis, and psu gnd and chassis. Low resistance= likely gnd loop. Try to measure resistance between your output boards and chassis too.
I will try this tonight after work and report back, but I think this is a problem with the OSes since the problem is the same with a benchtop PSU.
7: replace the solid core gnd wires going into your euroblocks. They make bad contact.
Will try this over the weekend when I have some time to solder things.
8: Do NOT connect chassis gnd to the same euroblock as the FE returns.
I've had the chassis ground connected to the ST_GND on the PSU before and the issue still persists. It's connected to the euroblocks in the photo out of laziness for pictures because I had to disassemble the amp a few times to get all those pictures. The problem doesn't go away regardless of where the chassis ground is connected to the PSU.
9: Short inputs. Is there still hum? (Irrelevant if your FE is disconnected).
Motorboating is there regardless of inputs shorted.
10: try to run the amp without the softstart. I know in at least one instance it had been the cause of hum due to error.
A little afraid to try this lol, but I effectively have done this by not-using the PSU and using a benchtop PSU. Problem still remains.
Do all your test with FE disconnected. When problem is solved, reconnect FE and hope for the best.
Motorboating is still there with FE disconnected. There is no way to really test this with just 1 OS connected since it's a balanced amp. I have tested it like this (even though it doesn't make sense). There is no motorboating with just 1 OS connected. But I suspect that is because the motorboating is being caused by some sort of coupling of the OSes. I don't know why this is happening though!
Btw: Twisting is not the problem. You can try twisting your speaker returns together with speaker pos from OS, then fro OS with the dc wires to the PSU. But I do NOT think that is your main issue. Also, you have a large loop area since speaker wires are at opposite sides. Twist them together for as much of the way as possible, could help. But again, this is probably not your biggest problem.
Thanks for this. I did have the speaker connections on the same end of the chassis before, I moved them to take these pictures because the wires were blocking visibility of the FE.
Should I be trying to twist the speaker connections even though this is a balanced amp and the OSes make up speaker +/-? I feel like that will result in longer wires needing to be used so that they can meet somewhere in the middle to be twisted together instead of going straight to the speaker posts.
Do you still have the motorboating sound when you ground the inputs and keep FE and OS powered?
Yes
From the top:
This is a balanced amp, so speaker + goes to one OS and speaker return goes to the other.
There is no hum, it's JUST motorboating.
Motorboating happens even with a benchtop PSU, and at all voltage levels above ~16VDC
Motorboating happens with both inputs shorted and FE disconnected.
I really think something is wrong with the OSes and they are coupling somehow. My benchtop PSU does NOT sound happy when it's powering both OSes. It hums like an SOB when it powers them, and does not exhibit this behavior with any other load.
Nearly all the pics i've seen in this thread have the PSU tied together on both ends, including 6L6s in the guide. I've asked about this a few times but never got a direct answer. To me, it makes the most sense to only have them tied at the outputs, but there have been alot of people in this thread (which i've read cover-to-cover a few times) saying that you should tie them together in all locations for a good secure ground plane. I'm fine with clipping these if this is in fact a problem.
Also, the motorboating happens with a benchtop PSU, so i really don't think the PSU is the main problem.
2: Disconnect ground between chassis and PSU. Does it still hum? If it does not, you have located your problem. If it still hums, reconnect.
It is motorboating, not humming, but yes, I've tried every possible combination of things being grounded/not grounded and the motorboating persists.
3: Have you tried disconnecting one of your OS’es, one at a time? Does it still hum (fe disconnected)
This is a balanced BA3, so there are no speaker returns. Both speaker +/- are connected to L/R output stage respectively.
4: put your FE returns twisted together in the SAME HOLE of euroblock.
They are
5: put speaker returns in the block on opposite side.
N/A because this is a balanced amp
6: check your chassis for ground loops. Turn amp off. Disconnect gnd link between chassis and PSU. Meausure resistance between input gnd and chassis, and psu gnd and chassis. Low resistance= likely gnd loop. Try to measure resistance between your output boards and chassis too.
I will try this tonight after work and report back, but I think this is a problem with the OSes since the problem is the same with a benchtop PSU.
7: replace the solid core gnd wires going into your euroblocks. They make bad contact.
Will try this over the weekend when I have some time to solder things.
8: Do NOT connect chassis gnd to the same euroblock as the FE returns.
I've had the chassis ground connected to the ST_GND on the PSU before and the issue still persists. It's connected to the euroblocks in the photo out of laziness for pictures because I had to disassemble the amp a few times to get all those pictures. The problem doesn't go away regardless of where the chassis ground is connected to the PSU.
9: Short inputs. Is there still hum? (Irrelevant if your FE is disconnected).
Motorboating is there regardless of inputs shorted.
10: try to run the amp without the softstart. I know in at least one instance it had been the cause of hum due to error.
A little afraid to try this lol, but I effectively have done this by not-using the PSU and using a benchtop PSU. Problem still remains.
Do all your test with FE disconnected. When problem is solved, reconnect FE and hope for the best.
Motorboating is still there with FE disconnected. There is no way to really test this with just 1 OS connected since it's a balanced amp. I have tested it like this (even though it doesn't make sense). There is no motorboating with just 1 OS connected. But I suspect that is because the motorboating is being caused by some sort of coupling of the OSes. I don't know why this is happening though!
Btw: Twisting is not the problem. You can try twisting your speaker returns together with speaker pos from OS, then fro OS with the dc wires to the PSU. But I do NOT think that is your main issue. Also, you have a large loop area since speaker wires are at opposite sides. Twist them together for as much of the way as possible, could help. But again, this is probably not your biggest problem.
Thanks for this. I did have the speaker connections on the same end of the chassis before, I moved them to take these pictures because the wires were blocking visibility of the FE.
Should I be trying to twist the speaker connections even though this is a balanced amp and the OSes make up speaker +/-? I feel like that will result in longer wires needing to be used so that they can meet somewhere in the middle to be twisted together instead of going straight to the speaker posts.
Do you still have the motorboating sound when you ground the inputs and keep FE and OS powered?
Yes
From the top:
This is a balanced amp, so speaker + goes to one OS and speaker return goes to the other.
There is no hum, it's JUST motorboating.
Motorboating happens even with a benchtop PSU, and at all voltage levels above ~16VDC
Motorboating happens with both inputs shorted and FE disconnected.
I really think something is wrong with the OSes and they are coupling somehow. My benchtop PSU does NOT sound happy when it's powering both OSes. It hums like an SOB when it powers them, and does not exhibit this behavior with any other load.
Regarding gnd links: Ask Bonsai. Use only the ones at the output end. Your first instinct was dead on. Using both or only the one on the input end increases loop area, and you want that as small as possible.
I do still have some belief in the test for a gnd loop, perhaps from OS. This will be an exciting one! Hope you keep us posted. Maybe my build too can benefit from what you find out. I have done almost all concievable tests, but still no closer to removing that hum.
Regards,
Andreas
I do still have some belief in the test for a gnd loop, perhaps from OS. This will be an exciting one! Hope you keep us posted. Maybe my build too can benefit from what you find out. I have done almost all concievable tests, but still no closer to removing that hum.
Regards,
Andreas
Dronevil,
Not that I really could help you, but I have the impression that if you could record this noise and show it, some would instantly know what‘s wrong... (just like posting fotos)...