Pops heard when audio source is changed

[sredmyer]

I hope some of the more technical here might be able to help with this.

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First let me explain my setup:

I use the HK AVR 7300 in my home theater, which is a 5.1 setup. I also use the HK to drive a second zone. The second zone is only used occasionally and is a music (2 channel) setup only. The 5.1 system includes the HK AVR7300, 2 Adcom GFA-555s (running bridged as mono blocks), a DVD/CD player, an HTPC (used to serve mp3s only), a DirecTV receiver, and a 50" plasma display. All source devices are connected to HK 7300 via digital audio (either optical or coaxial) and component video (YPbPr). The HK 7300 is then connected to the display via component video (YPbPr). The HK 7300 is used to directly drive the center and surround channels. The front main L/R channels are driven by the Adcoms (1 Adcom for each channel), which are connected, to the pre-amp outputs of the HK 7300. A powered subwoofer is also connecter to the sub/LFE output of the HK 7300. The sub is a Klipsch RSW-12, which uses a 650watt rms BASH amp.

Now the problems:

Since initially connecting this system I have had a loud pop from my main speakers whenever the system switches audio sources (i.e. from CD to SAT. TV) or whenever the system switches audio modes (i.e. from Dolby Digital to Logic7). I had always just assumed this popping was a normal thing due to DC transients created by the switching and although I did not like it, it did not seem to be causing any real problems. This system has been in place and being used for about a year now. During this time I had a problem with my Klipsch subwoofer in which it (the sub) blew out its amplifier, which caused the driver to also get fried. The driver was replaced and the amp rebuilt. Then after a few weeks the sub's amp was blown again. It is this blowing of the sub's amp that has caused me to start wondering if the DC spikes causing the pop that I hear might actually be a problem. I began researching the issue and learned from other HK owners that the popping was not normal. Other users with a similar setup have told me they do not experience the popping. In an attempt to further understand (and find a solution for) the problem I contacted HK tech support and explained the problem to them. They informed me that the 7300 has an auto-muting feature, which mutes the audio (by dumping it to ground through a "muting transistor") whenever the audio stream is broken (such as when source or mode are changed). They further stated that since the signal was being "dumped" to ground through a transistor there might be some residual voltage remaining in the capacitors and this residual voltage would create a DC spike at the output as soon as the mute was disabled allowing signal to flow to the amp.

Some tests I have done to identify the problem:

1) A simple test to verify what HK tech said about muting. I checked this by muting the system (using the mute button) then un-mute it. What I found was that the system pops going into mute but not when coming out of mute. This behavior is completely repeatable. Now given the explanation from HK this results confuses me, I would expect the exact opposite.

2) Tried to measure the DC spike voltage at the RCA connector using a VOM. I found no voltage spikes here. Note this is likely because the meter used (a digital one) was to slow to see the spike.

3) I have connected the speakers up directly to the HK (using its internal amps). In this configuration there are no pops.

4) I have tried using a different preamp (a Carver C1) this configuration did not exhibit the popping problem.

Based on these tests I think I can just about definitely say the problem is with the HK.

Some of the things I have tried to fix this are:

1) Per a suggestion from a tech at HK I installed a 10kohm resistor between the two conductors of the each of the RCA interconnects between the HK and the external amps. This just caused a loud scary buzz.

3) Tried grounding the chassis' of all the equipment (both Adcoms and the HK) with a simple ground wire connected to all of the cases. This produced a slight hum but did not fix the popping.

Finally I called HK tech support again and explained all the above, their response was that it was a ground problem. More specifically there is a potential difference between the ground references of the Adcoms when compared to the HK. They said that there is really no fix for this. Although they did say that I might connect a .01uf or .001uf capacitor to the HK's output and this would likely stop the popping but it would also likely degrade the sound quality.

So after all of this explanation I am hoping that some of the more technical folks here can chime in with opinions as to:

1) The cause of the popping

2) Possible solutions

3) If the capacitor is indeed a solution that will work with minimal impact on sound quality...how should the capacitor be installed?

Thanks for your help.

[mark1101]

Some of the gurus here will study your post and help you out.

I have the same problem but ONLY when I select my PC sound card as the source. I have the sound card output plugged into my preamp. My entire stereo system other than the PC is all plugged into a single circuit and has a single ground point. I lifted all the components ground with cheater plugs, except for one component (preamp). My PC is on another circuit and uses a long run of RCA cable (20 ft.) to get to the preamp. I always thought it was either the grounding difference or the long run cable. But the popping issue is only minor in my case and I never bothered to figure it out.

Have you tried making sure you have only a single ground point? If you have cable TV plugged into your system, try disconnecting it.

[sredmyer]

Some of the gurus here will study your post and help you out.

I have the same problem but ONLY when I select my PC sound card as the source. I have the sound card output plugged into my preamp. My entire stereo system other than the PC is all plugged into a single circuit and has a single ground point. I lifted all the components ground with cheater plugs, except for one component (preamp). My PC is on another circuit and uses a long run of RCA cable (20 ft.) to get to the preamp. I always thought it was either the grounding difference or the long run cable. But the popping issue is only minor in my case and I never bothered to figure it out.

Have you tried making sure you have only a single ground point? If you have cable TV plugged into your system, try disconnecting it.

Thanks for the response. I know you are right about the local gurus...I have availed myself of some of the expertise here before regarding my subwoofer. These guys are very helpful.

For me the problem happens on all sources. The only common point is that it happens when the audio signal is muted by the HK. It does not matter weather that muting is done manually (by pressing the mute button) or auto-magically by the HK due to a break in the audio stream resulting from source mode changes.

As for grounding, I do not think that can be an issue. All of the components are plugged into the same powerstrip. The Adcoms have their original cords/plugs and are only two conductor. The Adcoms are connected to the switched outlet on the HK AVR thru a SSR. The power for the SSR is sourced via the same outlet strip as all other components. This outlet strip is then pluged into a non-dedicated (some misc. lighting is also on this circuit) 20 amp outlet. This arangement allows me to leave the power switches on the Adcoms in the on position and have them turned on and off whenever the HK is turned on/off

[mark1101]

I'm still a little suspicious that components in your system are chassis grounded to one another through the connections between components and then make at least a second connection to your electrical ground. For instance, in my system I ground the preamp and pass that ground to the other components via RCA jacks between the components and the preamp. All other connections to ground are lifted. Thus, one ground.

In your system you mention a TV and dish setup. I am also not sure how ground is passed through HDMI or other types of digital cables. But I suspect it is. I'm guessing.....but I think you have a grounding issue. Let's wait for the gurus.

Have you tried disconnecting portions of the system to see if individual components like the TV make it go away?

Edit: I just reread your original post. You mention component video cables to the TV. Those are RCa jacks and bring the TV ground into the receiver. Is the TV on a cheater plug or 2 prong plug....and the dish reciever as well? See...this is what I am referring to.

[sredmyer]

I'm still a little suspicious that components in your system are chassis grounded to one another through the connections between components and then make at least a second connection to your electrical ground. For instance, in my system I ground the preamp and pass that ground to the other components via RCA jacks between the components and the preamp. All other connections to ground are lifted. Thus, one ground.

In your system you mention a TV and dish setup. I am also not sure how ground is passed through HDMI or other types of digital cables. But I suspect it is. I'm guessing.....but I think you have a grounding issue. Let's wait for the gurus.

Have you tried disconnecting portions of the system to see if individual components like the TV make it go away?

Edit: I just reread your original post. You mention component video cables to the TV. Those are RCa jacks and bring the TV ground into the receiver. Is the TV on a cheater plug or 2 prong plug....and the dish reciever as well? See...this is what I am referring to.

Yes the TV and the DirecTV receiver are connected to the AVR via RCA component video cables. I do see what you mean about the possible grounding issue (I do not fully understand it though). I am not sure about the plugs on these devices (weather they are 2 prong or 3) but they are plugged into the same power strip as the AVR. Wouldn't that mean that their ground is the same as that of the AVR? Regardless I will try disconnecting devices this evening when I get home to see if that helps.

[mark1101]

What you are trying to avoid is multiple paths to ground. What I would do in your case is ground the AV recevier. It probably has a 3 prong plug. Then make sure that ANYTHING connected within the entire system is on a cheater or 2 prong plug. Components connected together with RCA cables will be grounded (safe) via the connection to the receiver (and hence its connection to ground). Digitally connected cables....I'm not sure...so let others help with this point (digital cables and if they provide ground). But give it a temporary try and I bet it helps the situation. I'm suspicious of the dish system and the TV. Many have issues when these (and CATV) enter the equation. Try temporarily disconnecting all connections from the TV and dish receiver to the audio system...including the component jacks.

[sredmyer]

What you are trying to avoid is multiple paths to ground. What I would do in your case is ground the AV recevier. It probably has a 3 prong plug. Then make sure that ANYTHING connected within the entire system is on a cheater or 2 prong plug. Components connected together with RCA cables will be grounded (safe) via the connection to the receiver (and hence its connection to ground). Digitally connected cables....I'm not sure...so let others help with this point (digital cables and if they provide ground). But give it a temporary try and I bet it helps the situation. I'm suspicious of the dish system and the TV. Many have issues when these (and CATV) enter the equation. Try temporarily disconnecting all connections from the TV and dish receiver to the audio system...including the component jacks.

Ok I understand...I will do what you suggest (using the cheater plugs where needed). If this works you will be the bomb...such a simple solution to a problem which I have been fighting for a few months now.

[DrWho]

Just a quick little test...

Unplug the powerstrip from the
wall. Then unplug every other electrical device on the same circuit
breaker (usually multiple wall outlets share a breaker). So basically,
completely isolate the system and then plug the HK and the Adcom
directly into the wall. You will want to disconnect everything from the
HK as well. Not sure if the description is enough, but you want the HK
plugged into the wall. No inputs. Just one set of cables going between
it and the Adcom. Then with the Adcom you want it plugged into the same
wall outlet and the signal cables coming from the HK. Leave only the
main speakers plugged in. If the pop does not go away with this
configuration, then try different signal cables between the HK and
Adcom. If you can't get it to go away, then no fancy connection of the
other equipment is going to help - basically your HK is at fault.

Just a few more questions:

1. Does the pop happen in both speakers?
2. What happens if you plug them into the other preouts? (specifically the subwoofer output).
3. How loud is the pop?
4. Does it go away on the LR preouts if you set the mains to small?
5. What was the gain set at on the subwoofer?

To be honest, I highly doubt this problem caused your subwoofer
amp to blow up. They have all sorts of protection circuitry and
filtering inside to protect against failure. A sharp transient like
this would require a huge amplitude to cause damage (heat is ultimately
what causes the damage and I don't see how heat is going to build up
that quickly). It sounds to me like Klipsch fixed the broken parts, but
not the one broken part that caused it to break in the first place. At
least that's the most optimistic review. If your other preamp doesn't
cause problems, then perhaps replacing the HK might be in order...but
I'd hate to recommend such an expensive solution to a wierd problem.

[Arky]

I think you guys are all over it with the video sources likely the problem. Isn't it reccommended that amps be plugged directly into the wall outlet?

[sredmyer]

What you are trying to avoid is multiple paths to ground. What I would do in your case is ground the AV recevier. It probably has a 3 prong plug. Then make sure that ANYTHING connected within the entire system is on a cheater or 2 prong plug. Components connected together with RCA cables will be grounded (safe) via the connection to the receiver (and hence its connection to ground). Digitally connected cables....I'm not sure...so let others help with this point (digital cables and if they provide ground). But give it a temporary try and I bet it helps the situation. I'm suspicious of the dish system and the TV. Many have issues when these (and CATV) enter the equation. Try temporarily disconnecting all connections from the TV and dish receiver to the audio system...including the component jacks.

Ok all devices are plugged in using only 2 prongs (cheater applied where needed)...still get the pop

Disconnected all signal conections (other than optical) except those for the preamp outputs to the Adcom...still get the pop

So does this mean it is not the ground thing?

[sredmyer]

Does the pop happen in both speakers?

yes

What happens if you plug them into the other preouts? (specifically the subwoofer output).

Will try it and let you know

How loud is the pop?

I think it is fairly loud and system volume has no impact on how loud the pop is

Does it go away on the LR preouts if you set the mains to small?

Will try it and let you know

What was the gain set at on the subwoofer?

About 1/2

To be honest, I highly doubt this problem caused your subwoofer amp to blow up. They have all sorts of protection circuitry and filtering inside to protect against failure. A sharp transient like this would require a huge amplitude to cause damage (heat is ultimately what causes the damage and I don't see how heat is going to build up that quickly). It sounds to me like Klipsch fixed the broken parts, but not the one broken part that caused it to break in the first place. At least that's the most optimistic review. If your other preamp doesn't cause problems, then perhaps replacing the HK might be in order...but I'd hate to recommend such an expensive solution to a wierd problem.

I agree, the guys at Klipsch (Steve Phillips) have convinced me that the pops were not the cause of the subwoofer problem. I also agree that the HK is the likely culprit but when I talk to the tech support there they say it is the either a ground issue (which prior to the helpful insight I've gained here I did not understand) or it is a problem with the Adcoms. I do not understand that one either as they are just amps...they do not create anything...just amplify what they are given (including DC spikes)

[sredmyer]

What happens if you plug them into the other preouts? (specifically the subwoofer output).

Will try it and let you know

Cant tell can not get any output from subwoofer out??? very curious this is likely the part of the sub issue but I do not think this has anything to do with the popping??? Does it?

Does it go away on the LR preouts if you set the mains to small?

Will try it and let you know

Nope still pops

[mark1101]

What happens if you narrow your system down to just the HK AV receiver, and 2 speakers. Nothing else.....and you switch between FM radio stations? If it still pops and there is only the HK in the system.....guess what?

[sredmyer]

What happens if you narrow your system down to just the HK AV receiver, and 2 speakers. Nothing else.....and you switch between FM radio stations? If it still pops and there is only the HK in the system.....guess what?

Tried that (see the original post)...No pop when speakers connected directly to HK's internal amplifiers regardless of source or mode switching or muting.

I think the issue here is that the HK uses some form of capacitance coupling internaly between it's preamp and its own internal amps. However I think this is not done on the preamp output circuit therefore when the mute is engaged a DC shift or transient or whatever is created on the outputs. Since there are no filtering caps in the HK and the Adcoms are direct coupled (again no filtering caps) this DC spike is simply amplified on out to the speakers. This problem is exacerbated by the fact that in the current configuration I have 600 watts available to each of the RF7s. That high power when coupled with the RF-7s high efficency makes what might otherwise be a slight pop a much louder and annoying (possibly damaging) one. This jives with what the HK tech told me...but it just seems backward to me. It seems to me that the spike (if in fact created by the muting) should occur when the mute is disengaged not the other way round.

[DrWho]

What happens if you plug them into the other preouts?

(specifically the subwoofer output).

Will try it and let you

know

Cant tell can not get any output from subwoofer out??? very

curious this is likely the part of the sub issue but I do not think

this has anything to do with the popping??? Does it?

1. So it didn't pop with the subwoofer preout? You must have been in

   a mode where the subwoofer wasn't active and therefore always muted.

2. Does it pop with the surround pre outs or the center preout? I would try all of them.

Does it go away on the LR preouts if you set the mains

to small?

Will try it and let you know

Nope still

pops

This means the popping is not coming from upstream

(since any DC would be filtered out). So the issue is going to be

somewhere after the DACs and before the analog preouts. Really, you

just have the output of the DAC going straight into the amplifier and

straight into the preouts. There will be a preamp of some sort along

with the muting circuit.

I just can't fathom any way for there to

be a pop without a ground loop hum being present. It's almost as if

some inductance is putting a voltage on the ground of the HK when the

mute switch is engaged. Perhaps something in the muting relay? I really

think it's something shorted inside the HK.

Not to discredit the

HK engineers, but claiming something is a grounding problem is just

another way of saying "I don't know" - grounding problems do happen,

but they're vague enough in nature that it's easy to send someone on a

long rabbit chase. If you've unplugged all of your electronics (both

from the wall and from the reciever), then you have verified that it's

not a grounding issue with any of the other equipment. It could still be a grounding difference between the HK and the Adcom, but why isn't there a ground loop hum?

Do you

have any other amplifiers that you can test with? Perhaps your local

dealer that you purchased the HK from wouldn't mind letting you

experiment with something? Or another forum member in the area? If you

can show that it happens with more than one amplifier, then you can

pretty much tell the HK tech support guys that it's a problem inside

the receiver. For your sake, I would hope that there is more than a 1

year warranty (even though the problem was occurring a long time ago).

Short

of tearing the receiver apart and measuring some things on the inside,

I don't think there's much you can do. But if the popping doesn't

happen on all of the preouts (make sure you switch in and out of modes

that use the surrounds), then it just goes to show that something is

wrong with the LR preouts. However, it doesn't make sense that a

failure rears its head in two different chanels at the same time...

For

what it's worth, putting a cap on the output is the same thing as a

high-pass filter - the idea is that DC is 0Hz and will get knocked out

by the filter. It's a valid approach and shouldn't cost you that much -

and I can't imagine it hurting the signal quality at all? I've read

that most electronics tend to use 5Hz filters all the time anyway...

Another

alternative would be to install a 1:1 transformer between the HK and

the Adcom. I think this is a better approach, but it's also going to be

more expensive. DC signals can't travel through transformers and the

frequency response isn't going to be affected at all. You just need to

make sure you find something with the proper winding and quality metal

to not introduce any nonlinear effects - I imagine this would be rather

easy at the line level.

Or you can implement a circuit like this:

http://www.prosoundweb.com/install/spotlight/cardioid/poponoff.shtml

The

DC offset from phantom power is going to be no different than your

situation. The circuit would just need to be modified to apply to your

unbalanced situation.

Anyways, I'm no expert so take it all with a grain of salt. All the circuits we learn about in class assume linear normal behavior (like wires with no resistance). Most of the problems like this tend to be the result of things not following ideal behavior (if it is indeed part of the HK design and not a failure). But as an end-user of the product, you shouldn't have to be troubleshooting at the circuit level.

[sredmyer]

So it didn't pop with the subwoofer preout? You must have been in a mode where the subwoofer wasn't active and therefore always muted.

No...the subwoofer channel should have been playing...As I say I believe (now) that there is definitly a problem with the subwoofer preout. This subwoofer preout problem is likely the cause of all the problems with the RSW-12 I have been having. And although this subwoofer preout does point to a definite problem with the HK I am not sure that it is in anyway associated with the popping problem.

Does it pop with the surround pre outs or the center preout? I would try all of them.

I still need to try connecting Adcoms to other channels (other than mains and subwoofer). This is a bit more difficult (due to it requiring moving of quite a bit of heavy equipment) and therefore I have not yet tried it.

Do you have any other amplifiers that you can test with? Perhaps your local dealer that you purchased the HK from wouldn't mind letting you experiment with something? Or another forum member in the area? If you can show that it happens with more than one amplifier, then you can pretty much tell the HK tech support guys that it's a problem inside the receiver. For your sake, I would hope that there is more than a 1 year warranty (even though the problem was occurring a long time ago).

I have a friend who is bringing by a couple of Carver cubes (M400a) amps to test with but I do not know if those amps are direct coupled or not. If they are not they will not likely exhibit the popping but that will not mean that the HK is ok. The HK is still under warranty (they have a 2 year warranty).

Or you can implement a circuit like this:

http://www.prosoundweb.com/install/spotlight/cardioid/poponoff.shtml

The DC offset from phantom power is going to be no different than your situation. The circuit would just need to be modified to apply to your unbalanced situation.

Would this circuit eliminate the thump I get on power up? I think this thump (different than the popping we are discussing) at power up is due largely to the fact that all devices (HK and both Adcoms) are being powered up simultaneously. The in-rush current draw of all the caps in these amp charging and all of the massive transfomers stabilizing is quite significant. I get a mini brown-out when I power this system up.

Well I appreciate all of the help here but now with this certain problem (no output on subwoofer channel) I will be taking the HK to the warranty service center. I would have done this earlier but the HK techs were working hard to convince me there was no problem with the HK. I still worry that, while they will surely fix the subwoofer channel, they may not do anything about the popping issue (claiming that it is not a problem with the HK). Of course the other issue with taking the HK in for repairs is that the closest service center is in Cincinatti (bout 1.5 hours away) and I am sure I will have to leave the unit. The latter would be the most inconvenient since I use the HK for audio as well as video switching...without some serious re-wiring I will have no audio or video while it is gone.

[JJkizak]

In the great kingdom of multiple Hi-DEF, Stereo, 7.1, 5.1, amplifiers, pre-amplifiers, tuners, turntables, computers, dvd players all hooked up together and plugged into several outlets I have had only one problem with grounding and it was traced (by me) to my Samsung T165 HDTV tuner. The power supply was either a poor design or defective and I had to feed it with an isolater plug, and then it didn't work quite right but it was ok for a year then it popped it's cork. ($799.00) Installed an LG 3510A HDTV tuner and had no problems at all. My suggestion is to isolate your units one at a time to find out what is the cause and then eliminate that unit. It will more than likely have a solid state power supply. My system has antennas, tuners, 4 computers, 3 dvd players, 3 component distribution units, LCD HDTV's, old CD players, external hard drives, networks switches, routers, equalizers, expander/companders, two Denon receivers, 4 printers, 2 S-VHS VCR's, Mini-DV VCR, BETA-SP VCR, cassete player, 8-track player, D-VHS VCR, 2 scanners, 5 monitors, turntable, Xerox copier all hooked together ground wise and 4 different 120VAC outlets. I can turn any combination on/off without any pops with system set at full volume.

PS---You have to make up your mind to correct the problem. You can't pretend. If the HK is the cause get rid of it and get something else. In the words of Genral Patton, "You have to kick butt to get the job done." Oh well, I just made that up.

JJK

[sredmyer]

Ok now I am completely lost. I bit the bullet today and made the drive to the warranty center it turned out to be in Greenville, OH not Cincy which ment it was a 3 hour one way trip not 1.5. I left my 7300 and they sent me home with a 635 as a loaner. Guess what...THIS DAMN THING POPS TOO!!!! So as i say I am completely confused.

[DrWho]

me too...

Sounds like Adcom and HK don't play well with each other. Do you know anyone with the same combination?

[sredmyer]

me too...

Sounds like Adcom and HK don't play well with each other. Do you know anyone with the same combination?

No I don't.

Can you give me some more info on installing the capcitors between the HK and the Adcoms like the HK techs suggested. How should they be installed? How does one calculate the correct size and type of capacitor?