Positional motorboating on amp channel—help?

[srkbear]

I own an iFi Pro iCAN Signature amplifier coupled with a Topping D90se DAC. I have the two connected via good quality, balanced XLR cables. I noticed recently that if I stack the two with the amp on top, I’m hearing a low-grade motorboating oscillation on the right channel when the amp is in solid state mode, and the noise curiously transfers to the left channel when I switch to the tube circuit.

Strangely, when I move the amp forward about 3 inches so it is overhanging the DAC, the noise ceases. I’ve reproduced this exact same behavior on multiple attempts and I can only get a quiet sound when the amp is not sitting directly on top of the DAC. Also, raising the amp up on a riser does not resolve the noise (unless it is positioned three inches forward on the DAC so they’re not evenly stacked).

Can anyone offer some possible explanations for this please? I would consider a bad filter cap if it weren’t for the fact that it switches channels and disappears with amp placement. I tried removing the Bluetooth antenna on the DAC with no improvement. Help needed!

 

[Blumlein 88]

Patient: Doctor it hurts when I raise my arm like this.
Doctor: Don't raise your arm like that.

So don't stack your components that way that causes the problem. Some kind of RF/EMI problem most likely. You could try putting a grounded plate of metal between the two and it might work. Easiest solution is don't position them the way that causes motorboating. Most likely neither component is broken.

 

[srkbear]

Patient: Doctor it hurts when I raise my arm like this.
Doctor: Don't raise your arm like that.

So don't stack your components that way that causes the problem. Some kind of RF/EMI problem most likely. You could try putting a grounded plate of metal between the two and it might work. Easiest solution is don't position them the way that causes motorboating. Most likely neither component is broken.

Thanks for your kind response—I am indeed a doctor so I got a chuckle at the Occam’s Razor reference.

The problem is I don’t have any other option in my set up due to space limitations. The only thing I haven’t tried is turning off the Bluetooth radio on my DAC, which I don’t use anyway. What do you think would be the likely source of EMI in this case just out of curiosity? I’m not a a complete novice about amplifier schematics, but I’m far from a pro unfortunately…

 

[Blumlein 88]

You'd have to do a process of elimination to determine which is the problem. My guess would be the DAC is the source of the interference and the amp is amping up some interference it picks up. Doesn't matter you just can't use it that way without changing something.

Just suggestions on guesswork here. Does it go away if you reverse position of the two bottom pieces? Put the amp on bottom. You might wish to add taller rubber feet to the DAC so the amps gets a little ventilation if this works.

It looks like you nearly have room to put the DAC to the right beside the amp. If you get things on the edge does that fit?

Or maybe put the DAC on the right front corner of the shelf to get it in a position of non-interference.

 

[jasonhanjk]

Ensure casing are grounded properly.

 

[srkbear]

You'd have to do a process of elimination to determine which is the problem. My guess would be the DAC is the source of the interference and the amp is amping up some interference it picks up. Doesn't matter you just can't use it that way without changing something.

Just suggestions on guesswork here. Does it go away if you reverse position of the two bottom pieces? Put the amp on bottom. You might wish to add taller rubber feet to the DAC so the amps gets a little ventilation if this works.

It looks like you nearly have room to put the DAC to the right beside the amp. If you get things on the edge does that fit?

Or maybe put the DAC on the right front corner of the shelf to get it in a position of non-interference.

I’ll try those things, thanks. It’s odd that it’s only audible on one channel, and that it switches channels with different amplifier stage settings. It persists on the right when in solid state mode with the tubes turned off, then shifts to the left channel with the tube stage engaged. Very odd. And what’s more odd is that it only occurs with my headphones plugged into the XLR jack—when I’m plugged into the 4.4 pentaconn jack it‘s dead silent. Must be some odd wiring configuration in the amp.

 

[srkbear]

You'd have to do a process of elimination to determine which is the problem. My guess would be the DAC is the source of the interference and the amp is amping up some interference it picks up. Doesn't matter you just can't use it that way without changing something.

Just suggestions on guesswork here. Does it go away if you reverse position of the two bottom pieces? Put the amp on bottom. You might wish to add taller rubber feet to the DAC so the amps gets a little ventilation if this works.

It looks like you nearly have room to put the DAC to the right beside the amp. If you get things on the edge does that fit?

Or maybe put the DAC on the right front corner of the shelf to get it in a position of non-interference.

Go figure, I disassembled the whole setup, reseated all the power supplies, dusted things off around the power strip, then reassembled everything back together. No noise, dead quiet.

Gremlins? Borrowers? Something shifted around microscopically when I shook the chassis a bit? We’ll never know. Thanks anyway for your kind input…

 

[DonH56]

Probably a bad (loose or oxidized) ground connection somewhere.

My suggestion would have been to get something to use as spacers (footers) to move the top unit further away from (above) the bottom.

 

[srkbear]

Probably a bad (loose or oxidized) ground connection somewhere.

My suggestion would have been to get something to use as spacers (footers) to move the top unit further away from (above) the bottom.

When it was occurring I tried elevating the amp on a translucent, durable plastic riser, putting a good two inches between the two devices. Noise still persisted. Given that it resolved with disassembly and reseating all the connections, I can only guess that there must have been a loose cable somewhere. Who knows.

My understanding about motorboating is that it is low frequency interference most often caused by RFI, faulty filter caps or voltage fluctuations from a poorly-wired power supply. Since the sound resolved without any hardware mods, I’m left to assume that it was RFI of some sort being picked up at one of my connectors somewhere—I’ll likely never find out the root cause, but I learned something new in the process!

 

[srkbear]

Go figure, I disassembled the whole setup, reseated all the power supplies, dusted things off around the power strip, then reassembled everything back together. No noise, dead quiet.

Gremlins? Borrowers? Something shifted around microscopically when I shook the chassis a bit? We’ll never know. Thanks anyway for your kind input…

@Blumlein 88 and @DonH56, I spoke to soon—the motorboating came back. But I have found another diagnostic clue—when I touch both my amp and DAC simultaneously, the sound goes away. Take my hands off, it comes back.

Surely this must represent some sort of grounding issue? Any suggestions on how to resolve please?

 

[mhardy6647]

It is as @Blumlein 88 says -- most likely. Induced "hash" from one component to another, which is solved by distance and/or reorientation between components.
Don't get me started about the prevalence of RF crud in today's digital/switchmode/class D world! It's called progress.

I also feel compelled to note that @Blumlein 88's doctor joke was made famous (with a visual motif) by the iconic comedian Henny Youngman (who to my knowledge held no doctoral degrees, except perhaps honorary ones) -- although it probably dates back to the dawn of written history (along with take my wife... please).

EDIT:

@Blumlein 88 and @DonH56, I spoke to soon—the motorboating came back. But I have found another diagnostic clue—when I touch both my amp and DAC simultaneously, the sound goes away. Take my hands off, it comes back.

Surely this must represent some sort of grounding issue? Any suggestions on how to resolve please?

Yes it may -- start lifting grounds and/or tying things together.
If you don't have a bag of clipleads, get yourself one!

 

[DonH56]

I wonder if there is a bad cable someplace. Rearranging things fixed it, so there might be a bad internal connection on one of the cables. It could ask be a bad jack on one of the components; a bad solder joint can be vexing. Without touching the amp, and with the volume turned low, try gently pushing on the cables and connectors and see if one changes the sound (better or worse). If you find one, replace the cable and repeat. If it persists, may be internal to the component, requiring a repair. Broken solder joints on jacks are not all that uncommon and an easy fix for a tech.

HTH - Don

 

[Blumlein 88]

@Blumlein 88 and @DonH56, I spoke to soon—the motorboating came back. But I have found another diagnostic clue—when I touch both my amp and DAC simultaneously, the sound goes away. Take my hands off, it comes back.

Surely this must represent some sort of grounding issue? Any suggestions on how to resolve please?

Don't really have anything to add to what the others have said in terms of finding the problem. If it is not a cable, and connecting the two device grounds with a jumper fixes it, then connect them. I don't know of any problem it would cause. You could put a 10,000 ohm resistor or even a small little cap in the middle of the connection and it probably would still work. Your body is like a high impedance cap coupled connection. It must be enough to drain off some stray voltage or some such.

Did the motorboating stay in the same channel? Swapping cables to see if it swaps channels is worth doing. Or using a multimeter to check connections on each end of the cabling to see if you have a bad connection.

 

[srkbear]

Don't really have anything to add to what the others have said in terms of finding the problem. If it is not a cable, and connecting the two device grounds with a jumper fixes it, then connect them. I don't know of any problem it would cause. You could put a 10,000 ohm resistor or even a small little cap in the middle of the connection and it probably would still work. Your body is like a high impedance cap coupled connection. It must be enough to drain off some stray voltage or some such.

Did the motorboating stay in the same channel? Swapping cables to see if it swaps channels is worth doing. Or using a multimeter to check connections on each end of the cabling to see if you have a bad connection.

@DonH56, @Blumlein 88, @mhardy6647, thanks again so much for offering your insights. I hadn’t seen the clip leads before and I’m going to try jumping the amp and DAC together (once I figure out where to do so). The noise is definitely motorboating, and as I mentioned before it is prominent in the right channel only when the amp is in solid state mode, then it switches to the left channel (a bit quieter) when I engage the tube stages—God only knows what the hell is going on.

I grabbed my multimeter and touched the chassis of the amp, along with sleeve of both the XLR headphone output as well as the sleeve of the XLR input on the back—in both cases it read a very tiny voltage, so I’m wondering about a faulty or loose ground in the amp. When I open the chassis there is a ground contact on one of the housing screws and I wonder if it isn’t a robust connection, but now I’m getting way out of my wheelhouse.

I’m not sure why the XLR cables themselves don’t close the loop, given that they’re connected to both units—and the weird thing is that I don’t even have to fully contact the two units with my hand to eradicate the noise—just getting my hand in the vicinity resolves it, and it only works when I make contact on the right side of the amp/DAC—I can grab the left all day and the sound persists. If that sounds like I’m nuts you may be right.

If I do try these clip leads to contact the two components, if someone could advise the best location for me to make these contacts on the two units that would be terrific! Right now I’m improvising by leaning a tiny metal ruler against the side panels of both and that’s working, but the damn thing keeps tipping over…

Why the hell did this start happening out of the blue when I’ve had these two units sitting on top of each other for over a year and have never so much as moved them since, other than to swap out the tubes (let’s not go there, I learned my lesson already)? I hate not knowing why things happen—it tweaks my OCD in a scorching way

 

[DonH56]

Why the hell did this start happening out of the blue when I’ve had these two units sitting on top of each other for over a year and have never so much as moved them since, other than to swap out the tubes (let’s not go there, I learned my lesson already)? I hate not knowing why things happen—it tweaks my OCD in a scorching way

Connections loosen (lose "springy-ness") oxidize over time, vibrations and thermal cycling (on/off cycles) cause materials to flex, etc. Cables hanging rom the unit can stress the internal connection of the jack(s) and open a bad solder joint. I am more and more suspecting a latent defect (cold solder joint) in one of the components, but check the cables first as they are cheap and easy to replace.

 

[Blumlein 88]

Okay, looking inside it appears the base of the tubes in the iCan are directly over the DAC chip in the Topping. That may be why when you move the amp forward the sound goes away. Why would it start up now? I don't know, some ground has been lost, maybe one of those caps surrounding the DAC is starting to lose capacity. Or maybe the tubes. Tubes will sometimes pick up more noise as they age (though I think that is a long shot). You might even try swapping the tubes one side to the other. Here are pics of why I think you are picking up some RFI from the DAC.

The square chip inside the 4 gold capacitors is the DAC. It almost lines right up with the base of the tubes. The tubes or the base may be picking up RFI even when you aren't using them. You would think if the bottom of the iCan is metal and grounded it would shield it. Can you touch the multimeter leads to top and front face, top and back face, and see if you get something close to zero ohms. Maybe some of the casing isn't grounded well. Looks like the casing is one piece around top, bottom and sides.

 

[Blumlein 88]

A kludgy solution I've used with phono stages is to put aluminum foil on some posterboard, and connect that to the third pin ground. You end up with a grounded plane which can shield or drain away RFI. If it is permanent then find a slim piece of metal, like you find in electronic project boxes and connect it to the 3rd pin safety ground. A safe way to do that is buy a replacement plug for extension cords, and only connect a wire to the 3rd pin ground. Plug it into a 3 pin electrical socket and you have ground to work with. If you aren't absolutely certain which is the safety ground don't do this.

Meanwhile you can tape some foil to a piece of stiff posterboard and clip those jumper leads to it and try touching the other end to one of the exposed RCA outer ground sockets to see if that stops the noise. I'm pretty certain since the metal ruler is working this will too. If it works slipped between the two devices you can devise a way to put something between them ground connected that will be out of sight.

 

[Blumlein 88]

Another kludgy thing to try. Stacks some coins, quarters, nickels or pennies between both components on that right side until it touches both components and see if that connection kills the noise.

If this works another kludgy out of sight temporary solution: get a small metal spring that you can lightly compress between the components and that will do, it will stay put, and you won't see it. Springs at a big box hardware store like this are a not much money.

 

[srkbear]

Okay, looking inside it appears the base of the tubes in the iCan are directly over the DAC chip in the Topping. That may be why when you move the amp forward the sound goes away. Why would it start up now? I don't know, some ground has been lost, maybe one of those caps surrounding the DAC is starting to lose capacity. Or maybe the tubes. Tubes will sometimes pick up more noise as they age (though I think that is a long shot). You might even try swapping the tubes one side to the other. Here are pics of why I think you are picking up some RFI from the DAC.

The square chip inside the 4 gold capacitors is the DAC. It almost lines right up with the base of the tubes. The tubes or the base may be picking up RFI even when you aren't using them. You would think if the bottom of the iCan is metal and grounded it would shield it. Can you touch the multimeter leads to top and front face, top and back face, and see if you get something close to zero ohms. Maybe some of the casing isn't grounded well. Looks like the casing is one piece around top, bottom and sides.

View attachment 216682

View attachment 216683

OK, I am truly indebted to you for going to these lengths to troubleshoot this little ol’ problem of mine—I’m truly not worthy, and thank you!

 

[srkbear]

Another kludgy thing to try. Stacks some coins, quarters, nickels or pennies between both components on that right side until it touches both components and see if that connection kills the noise.

If this works another kludgy out of sight temporary solution: get a small metal spring that you can lightly compress between the components and that will do, it will stay put, and you won't see it. Springs at a big box hardware store like this are a not much money.

Infuriatingly enough the damn problem seems to crop up at some times then mysteriously vanish—however when it recurred this last time I tried the quarters and it seemed to attenuate considerably. Then I went to the garage and got some pure copper washers, and when I stacked a few of those on the right hand side the noise vanished completely. Maybe something about the nickel content of the quarters, or the oxides on their surfaces?

Regarding the influence of the tubes, I verified that when in solid state mode, the tube circuit is powered down and bypassed—that’s when the noise isolates to the right channel. When the tube stage is engaged and the little bastards light up (augmented by a row of LED lamps surrounding them by the way), the noise jumps to the left channel. So I don’t think the tubes are likely contributing to the problem in and of themselves.

Whatever, your idea worked. My sincerest gratitude.