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Annoying bass "pulse" w/ subwoofer and transducers

13454 Views 18 Replies 9 Participants Last post by  sanjoseskater
I've been happily enjoying my budget-enthusiast HT for quite a while now: 6 Paradigm Atoms, 1 CC-170, 1 PDR-10; Yammy HTR-5660 AVR; and 4 Aura Pro shakers powered by a Radioshack PA amp. Trouble is, several months ago both the subwoofer and the shakers started exhibiting an annoying problem. Each time an audio signal begins or changes (e.g., I power up/down the currently active source, I change a channel on the cable box, I skip a chapter on the DVD, etc.), I hear a fairly loud, abrupt "pulse" sound coming from the subwoofer and shakers. It sounds similar to tapping the end of a 1/4" plug that's currently plugged into a powered-on guitar amp. It's a low-frequency pulse, and it's not a nice sound. I'm worried that it might be damaging the subwoofer.

No particular event I'm aware of occurred that would explain this. It was all working fine, and then suddenly one day, *pulse*. Previously I received advice to power on the subwoofer after all my other components were on, and power it off prior to powering anything else off. That actually helped a bit, as the pulse sound was very diminished for the first minute or two of operation. But the pulse returned in full force fairly quickly -- after I changed the cable channel 10 times in a row, for example.

Can anyone help me diagnose what could be going wrong? The only (perhaps) unusual thing I'm doing is in routing the LFE from the receiver to the woofer/shakers. I have a y-adapter coming out of my receiver's LFE pre-out; one goes to the subwoofer, the other goes to *another* y-adapter that feeds the L/R inputs on the amp used for my shakers. I have 2 shakers per channel on the amp.
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I forgot one thing: I always had a gut feeling that this was a power-related issue -- i.e., some sort of surge was entering the power line and manifesting itself in the subwoofer as the sound I describe. But one time I unplugged the sub from the power supply, changed the cable channel, and was surprised to hear the pulse persisted even with the sub unplugged! Of course, the sub was still plugged into the LFE output of the AVR, and this made me wonder if my AVR itself is sending this obnoxious signal through the LFE output. Just thought I'd add that in case it helps someone in formulating a response to my problem.
This thread is old, but still relevant. Problem's still there. Maybe someone reading this will have an idea this time around. :D
FWIW, maybe do a full process of elimination run to see if you can find/isolate the weak link?

I'd start with disconnecting everything off your LFE to see if it pulses without anything connected.

Then add just the sub without the shakers

Then add just the shakers without the sub

at least then you have a better guess at what combination is causing the pulse?
I would be most suspicious of the receiver. Does it auto-detect the surround mode? If so, does it have an option to defeat the auto-detect?

Also, does putting the receiver on mute before changing channels, etc. eliminate the pulse?

I would agree with Tweak in that this sounds more like an amp/preamp/receiver type problem. What you describe sounds a bit like a capacitor that is discharging into an input. Something is possibly changing a dc bias and when you switch channels, that change results in a thump as the voltage on that particular pin in the circuit goes back to normal. Some other things to check besides Mute mentioned above is whether it is sensitive to volume control setting. Does it happen when you are in a stereo direct mode or only in one of the surround modes?

Thanks for the responses, guys. You gave me a couple new ideas that might help isolate the problem. I'm 90% sure it's a problem with my AVR, because it happens regardless of the input source. I didn't think to switch modes on the AVR to see if it's limited to surround modes. I'll check that out this weekend.
Ok, I just spent a bit of time trying to debug the problem. I found a few interesting things. The "thump" seems to occur when the input signal is switched to or from a digital stream. Some examples include:

- changing the cable channel from an analog station to a digital station, or vice versa

- changing the channel from a digital to another digital station (there is roughly a 1 second delay while the cable box switches the channel, during which the "Digital" indicator on my AVR will turn off, then turn on again when the signal is recognized as digital)

- hitting MUTE/UNMUTE at any time

- powering on or off the AVR, or any active input source while the AVR is in a digital mode

- In a DVD menu screen, the thump will occur when the (usually short) menu theme reaches the end of its loop and begins again

I've verified that it's only occurring on the LFE/Subwoofer-out channel. With that channel disconnected, there is no thump. With just the subwoofer connected, the thump is there. With just the transducers connected, the thump is there. I tried a couple different sets of cables to make sure the cable wasn't the problem.

So, it definitely sounds like the AVR is the culprit. The digital indicator might be a bit of a red herring -- I think all of the instances when the AVR displays "Digital" correspond to instances in which the subwoofer-out is getting a signal. Doyle, your suggestion about the capacitor makes some sense. Could this potentially be as simple as replacing a faulty capacitor? If so, I'm tempted to approach this from a DIY mindset.

I (but especially my wife) would much rather have this AVR repaired than have to spring for a new one at this point. But obviously that depends on the repair cost. I remember bringing my old Sherwood AVR (pre 5.1) in for repair because of a problem where the unit would just shut off after 15 seconds or so. The estimated repair bill was almost $200. The cost of a brand new unit was about $150. :D
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This is a difficult decision. Normally the AVR should mute while the digital stream is being acquired and then there should be a "soft entry" back into the signal. The fact that it thumps when you press the mute button indicates to me there is a problem. It could be a bad component like a cap or it could be one of the ICs that is causing the problem. Unfortunately, tracking it down is not a simple deal.

I did a quick Google search for HTR-5660 popping problem and got 3 hits. Two were dead but here is the other.

Unfortunately I don't think it is much help. I tend to think they were on the wrong track. To determine whether to have it repaired, I think you have to know for sure that this problem was not inherrent to the receiver and that it just started happening. I also don't think it is an inexpensive problem as a tech could spend a lot of time looking for this. Unless you can find a flat fee repair, this may be an expensive undertaking. I had a similiar problem with a B&K preamp. The popping drove me crazy and I pretty much knew it was a problem in the surround decoder. The repair price was just too high and so I bought a new Pioneer receiver and have been happy ever since. Still not sure what to do with that B&K.

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Doyle, thanks for your reply. I appreciate your advice.

Reading your post, I realized I never searched with "pop" as a search term. I was inspired to do a bit more searching, and I came across several problems that sounded identical to mine -- on Yammy and other receivers. Unfortunately nobody ever got it resolved apparently.

One person suggested to send the LFE to the main L/R speakers, and use the AVR's L/R pre-outs to drive the subwoofer. I think I will give that a try. I know my Monitor 7's can't handle the LFE stuff, but I hope that this won't result in any damage done to those speakers. Any thoughts on that? I know it's not an ideal solution, but it might be a reasonable stop-gap solution, possibly preferable to the obnoxious thump I'm getting these days.

I'll put out feelers to local repair shops to get an idea what sort of repair cost I might be looking at. Although, I'm sure the answer will be "bring it in, and we'll take a look."
Ok, I tried routing the LFE through the MAIN L/R speakers, and using the L/R pre-outs to drive my sub. That worked. No more popping sound. Coincidentally, I also realized that I've been sending the LFE to the mains (and sub-out) all along. :rolleyes: So I'm at least happy to have a reprieve from the popping for now. Still, I'd prefer to run my system in a different configuration than this, so I'll continue to investigate my options. Doyle, I suspect you're right that it likely won't be an inexpensive repair.
Sorry I missed your posts, I was away a couple days. The other thing I begin to wonder is whether you have DC on your LFE output. Is there any chance you have a voltmeter you can connect to the LFE output and then do some channel switching and see what happens. A DC level shift can cause a pretty big thump in a subwoofer and that may be relatively easy to fix with a Capacitor and some resistors. Here is my thinking. The LFE output likely has an output impedance around 100 ohms while the input to most powered subs is going to be between 20K ohms and 50 k ohms. So, if there is some shifting DC on that output, the input of the sub is going to follow that DC shift and try to reproduce it in the speaker. Possibly putting something like a 1 k ohm resistor across that LFE output would dissipate that DC and prevent the shift from occuring. Check it first with the voltmeter to see if there is DC there right before you change channels and then watch it when you do change channels. This is far easier with an Oscilloscope but most people don't have access to that type of equipment.

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Thanks Doyle. I'll borrow a voltmeter and see if I can find out anything interesting.
I just got off the phone with a technician from a Yamaha service center. I was basically trying to get a feel for whether it would be worth repairing my AVR, considering I could buy a refurbished one for $150.

After a little Q&A, the technician seemed reasonably convinced that there was a defective transistor in the muting circuitry. He looked at a schematic while we were on the phone, and said that there were 2 possible transistors that could be bad. Since the problem is isolated to the subwoofer pre-out, he felt it would be pretty trivial to identify the faulty transistor and replace it.

His estimate? $110 (an hour for labor, $10 for the part). So now I need to decide whether I want to spend $110, or put $110 towards my next AVR upgrade. Tough call!

I'm kinda surprised to see this similar problem previously happened to my system. I am using Krell showcase pre-pro for sometime and lately added Buttkicker +wireless kit and was using the balanced output from the pre-pro. In the initial 3 days it was functioning nicely, then I noticed some low frequency sound coming out from the subwoofer (connected through RCA preout) and vibration from the buttkicker LFE at the same time. Though I'd experienced it only 3 times in a week even during normal playback of nonspecific softwares in DVD, It was annoying.

Then I tried to switch from a common wall plug to a dedicated power source along with my system for the wireless sending unit which was connected via balanced preout .. And the problem was gone since the latest 2 weeks till now. ( about 10 days period )

I'm still monitoring this disturbance and hope this helps

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Hi guys.

You can't believe how long I've been searching the net for someone else having the EXACT problem i've been having for almost a year with my sub('s).

I have a Pioneer Elite VSX 47-TX Receiver and have a B&W C6 Sub. I started having the same problem a year ago when I would hear a faint "bump" when a light switch on the same circuit would turn off and on. Over time it became louder and more frequent, then about 6 mos ago it starting doing it like mad with ANY electrical interruptions on the circuit, such as powering on/off other equipment, changing the channel on the dvr or selecting a different input source.

I did track down it was from the LFE line out, but, figured it was my sub that must have taken a surge somehow so just turned my sub off and did without it for a few months waiting for some renovations to be completed since I was planning on upgrading my speaks anyway. I purchased a new Paradigm sub the other day, moved all into my new room and low and behold, yep, same thump. Upset to say the least.

I believe my receiver is still under warranty at 1 1/2 years old, but, now I have to take it to an authorized repair dealer and have them check it out. At least now I know I'm not crazy since I've talked to many people and none seem to have any sort of rational answer for me. Thanks for the insight. Now I have something to work with when I take it in. I love the receiver and got it for a great price of $1600 so I'm sure it will be worth repairing (otherwise my wife will shoot me and you'll never hear from me again)

Thanks and have a good one,

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I can share my experience as well on this topic. It is a real "bump" and it started about 6 months ago. I have a Pioneer Elite VSX-26TX connected to a Polk PW150 Subwoofer. Regardless of what command selected on the AVR, the result was an unexpected pop from the subwoofer, especially the mute command. I am attempting to isolate the fault as to AVR or Subwoofer. I was going do some further research for Pioneer AVR issues. Good luck to you as well.
here is what's happening...the AVR is sending a dc transient across the LFE output when the signal changes, and the sub amps do not have any DC decoupling caps in place. It's an easy fix costing about 10.00....all you need to do is the place a High Pass filter with a corner frequency of about 5hz between the AVR and the Subs...on the LFE low level line. This will keep the transients from reaching the subs....

I made one for decoupling my adcom from my pioneer 1014 a while back...mine happens to be a 2 channel, a mono is that much more simple.


You can google for any of the thousand HPF calculators. You will have to account for the input impedance when calculating for the cap....

The ideas discussed in this thread will do the same thing...a rumble filter is nothing more than a really low HPF

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I have a Pioneer 1015TX and I get the thump with my HTD Level III sub.

I have the sub power connected to a power conditioner with a remote switched outlet. When the 1015 is powered down, the power conditioner shuts of the switched outlets which has the sub connected to it. When I turn off the reciever the sub makes a loud THUMP!

Is there something wrong with my setup or is this an expected phenomenea? I have made other setups like this before with a Pioneer amp and a Cerwin sub and don't have this problem. Is there anything else that could be causing this besides the DC transient discussed already?
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