Annoying bass "pulse" w/ subwoofer and transducers

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.

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.
http://www.soundandvisionmag.com/ide...&topicID=33944

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.

..doyle

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.


..Doyle

margomaps,


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

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,

S.

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.

http://www.cyberfrogs.net/photo/inde..._032.jpg&id=31


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

http://www.avsforum.com/avs-vb/showthread.php?t=661135