New Polk L800s Crackling/"Shrieking" with SDA

ryanmh1

After waiting entirely too long, I finally pulled the trigger on a set of L800s. The last pair in walnut that I could find. It took my awhile, I suppose, since I had just bought a full set of the LSiMs not that long before. I posted a review elsewhere of these things, and they're amazing. Enough said about that. But, now they've got an issue and I seem to have 250 pounds of speakers with broken SDA. They're so new I haven't even registered the warranty yet. Literally out of the box for about a week. I've searched the the forums and everywhere I can find for anyone who had a similar issue. Nothing. So, here goes the tl;dr: When the SDA cable is connected, they are crackling and, for lack of a better way to describe it, whistling or shrieking from both channels when the volume is turned up even a bit. Details follow.

The speakers are currently being powered by a Parasound HCA-3500, and a fairly rare vintage preamp which has all step attenuators. The "scratchiness" is not caused by the preamp so far as I can tell. I've swapped in another to confirm. But will swap in yet another new one tonight and amplifier to further confirm. But I don't think it is on the front end, and here's why:

[NOTE: I really need to go through this again tonight with a proper sequence and write it down, but here's what I recall.] The HCA-3500 is a dual mono design, right down the power switch. (And yes, it is a singled ended, common ground amplifier, so don't suggest that as the issue--it's not.) At first, I was listening and just heard some light crackling, like a bad volume pot. Never had that issue with this preamp, but who knows? So I wiggled the volume knob. Issue continued. Was it the amp? To isolate everything, I pulled the SDA cable, and shut down one channel. Issue stopped. Odd. So I switched amp channels. No scratching or shrieking. Neither channel was doing it when independently powered. Everything seemed to be fine. So I powered everything back up, connected the SDA, and left the room to let them play for a bit.

Then the song changed, and they were shrieking and crackling like crazy. I ran back into the room and shut it all down. It sounded almost like a cap going back in the electronics. Ran through the same thing again. Checked each channel independently, and it seemed okay. Powered it all back up, reconnected the cable yet again. Turned it up, and it was clearly even worse than before. The higher the volume, the worse it got, to where it sounded like shrieking coming from the speakers. Definitely not a scratchy pot. Sounded like feedback or something. But I'd checked each channel to try to isolate it, and everything was fine when isolated. So what else could it be?

Oh-oh. One last variable left. I pulled the SDA cable, and ran everything in stereo. Everything was fine. No scratching, no shrieking, and fine at any volume in stereo. I reconnected the cable and it all went to crap. And it sounds like it's both channels.

I have no schematic for the SDA circuit (and I doubt anyone outside of Polk does), so I'm not sure why, when SDA is connected it could cause shrieking in BOTH channels. Why would it work fine with SDA connected but only one speaker powered? (I need to double check this since it makes no sense to me.) I assumed that the SDA channels were independently driven off the other speaker, using the SDA cable to carry two "hots" and the using the "internal" neutral on each speaker. Are they not?

I have no idea where to start looking or what parts to ask Polk to send since it's somewhere in the SDA. I can't believe the drivers are bad, but who knows. And I've never heard anything in a crossover cause an issue like this, short of an inductor going bad and vibrating. I think that might be it, but why is it both channels? That is seems fine with one speaker and SDA connected, but problems with both speakers going with SDA connected is really weird.

It seems to me, though, that the issue is definitely with the SDA somewhere. The speakers are perfectly fine with SDA disconnected. Any ideas how to troubleshoot this? Hopefully Polk has crossovers available and they aren't too bad to get to, since I'm fairly sure it has to be something in one of them. The shrieking versus the crackle suggests its not just a bad connection internally But I'm open to suggestions.

Eventually, I'm going to have to call Polk tech support, but I don't know how helpful the guy used to dealing with soundbars will be unless they have someone specialized in their TOTL stuff.

SeleniumFalcon

Hello,
Welcome to Polk's forum, sorry you're having a problem. I've sent your post to Scott Orth, at Polk, who was the designer of the L800 and to Kim Jasper who is a product specialist. I'll post any replies as soon as I get them, we'll figure this out.

VR3

In full transparency I didn't read your whole post

My recommendation for troubleshooting speakers is to plug them up to an entirely different system.

If that isn't immediately possible, order you a cheap 50 dollar fosi integrated with Bluetooth.

This allows you to completely isolate the speakers from your system to be sure they are the issue. Speakers are pretty simple devices and the issue you are describing is not a common issue to experience

pitdogg2

Well did you try another amp ? You cannot rule out the amp by just saying "I know it's not the amp". There are some amps this new SDA is not friendly with. Try a different amp, if it does the same with the SDA cable then it most likely IS in the SDA part of the XO. Polk will send out new XO.

ryanmh1

Thanks for the suggestions! You guys are great! I'm aware this is a very odd issue. At first I thought it was a bad connection in the signal chain prior to the speakers, but I am 99% certain that is not it. I went through all that twice. Pulling the SDA cable and having them work perfectly should eliminate that as a variable. That, to me, said SDA crossover or SDA speaker drivers. The shrieking and apparent problem in both speakers leaves me a little mystified. But, I'm going to try a Denon home theater receiver tonight to doubly rule out electronics.

To be fair, I'm only 90% certain it was BOTH speakers. It's a little hard to isolate since I need to have the volume up and both speakers going with SDA for it to happen. I'll play with swapping and disconnecting cables tonight, along with hooking up the Denon.

Clipdat

I believe the issue will not happen with the Denon AVR.

SeleniumFalcon

From your description what seems to be happening is that the amplifier is going into parasitic oscillation. This happens when part of the amplifier's output is fed back into the input at just the right phase and amplitude to cause positive feedback. In looking at the schematic there is a resistor and capacitor to roll off the output at a very high frequency to avoid this, but maybe something is not working correctly.
There is a Stereophile review that mentions noise present when the amp was tested with a CAT preamp:

https://www.stereophile.com/solidpoweramps/100parasound/index.html

Emlyn

Long shot and no offense intended, but based on some other member experiences with vendors not always selling these in matched pairs, did you get both a left side and right side speaker from where you bought the L800s?

ryanmh1

Will report back. Amp seems unlike since it works in regular old stereo, but who knows. One thing I have plenty of is amplifiers. I'll also swap SDA cables just for grins. And toss some other speakers on the HCA3500 although I don't know if that's necessary since it's fine with the L800s in regular old stereo.

Assuming a different amp does not resolve this, has anyone reported whether it is kosher to hook up the positive lead from the amp directly to the SDA input to eliminate a variable? I assume the crossover to run the SDA speakers for a particular channel must be in that channel, and the SDA cable is just carrying, for example, SPEAKER INPUT LEFT over to SDA INPUT RIGHT. Then again, there is both SDA IN and SDA OUT on the crossover per posted photos, so hypothetically they could be doing something for each channel on both crossovers...

Will do a detailed log tonight and update. Fingers crossed.

mhardy6647

ryanmh1 wrote: »

Will report back. Amp seems unlike since it works in regular old stereo, but who knows. One thing I have plenty of is amplifiers. I'll also swap SDA cables just for grins. And toss some other speakers on the HCA3500 although I don't know if that's necessary since it's fine with the L800s in regular old stereo.

Assuming a different amp does not resolve this, has anyone reported whether it is kosher to hook up the positive lead from the amp directly to the SDA input to eliminate a variable? I assume the crossover to run the SDA speakers for a particular channel must be in that channel, and the SDA cable is just carrying, for example, SPEAKER INPUT LEFT over to SDA INPUT RIGHT. Then again, there is both SDA IN and SDA OUT on the crossover per posted photos, so hypothetically they could be doing something for each channel on both crossovers...

Will do a detailed log tonight and update. Fingers crossed.

@ryanmh1
1) from an electrical perspective, the interconnection of amplifier and loudspeakers is quite different with the SDA cable connected vs. not connected. I.e., the behavior of the amp in stereo vs. "SDA mode" could well be different.
2) You were asked if you have a LEFT and RIGHT loudspeaker. Mis-shipment of incorrect pairs (e.g., two LEFT loudspeakers) has been documented on this forum. Check the box and/or serial number plate and ensure you have a LEFT and a RIGHT.
https://forum.polkaudio.com/discussion/194983/l800-l-r/p1

ryanmh1

Left and right was the first thing I checked when the crate arrived and when I opened the box. Confirmed.

At least with the old SDA design for which there are a few schematics in the wild, AMP OUT 1 was basically pushing SPEAKER 1 and SDA 2, which was all then tied back with a common ground internally to AMP OUT 2. Vice versa for AMP OUT 2. I need to test again with SDA connected and one of the amp channels off. It *should* cause one speaker to play, and one SDA to play, with the crackling on the SDA channel. If it doesn't, the crossover is more complex. Heading home to try more configurations and pieces of gear to (hopefully) figure out what's gone wrong.

ryanmh1

I did some more testing. My test notes confusing, to say the least. I thought that when the left channel was playing, the only other speakers playing should be the right SDA speakers. That doesn't seem to be the case. But that might have been amplifier misbehavior. What it comes down to is that no matter what I did, I could not seem to trigger the misbehavior with the Parasound with the SDA disconnected. I suppose it does draw more power with SDA connected for the same volume, so that could have had an impact? But, I still had crackle in stereo no matter what I did, once SDA was connected for a bit with the volume up. It would be fine for a bit, but then go to crap the longer it went. No shrieking this time.

Frustrated, I finally caved and hooked it up to a plain vanilla Denon X3500H receiver. Very, very limited testing since by this point it was getting late and the testing was getting ... less and less appreciated. But, it seems not to to do it. So perhaps I was wrong and the problem is electronics. I was only able to drive it hard for a couple of minutes, but if that holds, I guess it must be that this 100 pound amp just does not like whatever is in that SDA crossover. Fingers crossed that's all it is. But, I still need a good half hour to drive them hard to confirm, and test with some other amps.

pitdogg2

The Parasound HCA-3500 is an old amp. If it has not been serviced, it is well past it's prime, no matter what the weight is. Electronics age and wear out plain and simple. If it were mine I find an authorized service center and have them go through it and replace ALL resistors, capacitors and miscellaneous parts that have worn out and all service bulletins issued on the amp. That should get you another 20+ years

Maybe start with contacting Parasound, they've in the past have been very helpful with helping finding or having you ship directly to them. Excellent customer service.

nooshinjohn

If it is a differential balanced design, the Parasound is not going to work regardless...

HzTweaker

nooshinjohn wrote: »

If it is a differential balanced design, the Parasound is not going to work regardless...

That's what I was going to say. Is the OP running the amp with it's balanced XLRs inputs?

edit: I run my pre/amp with the balanced XLRs and don't have this issue, but my SDAs are old school 2Bs.

ryanmh1

It's not a differential output amplifier. XLRs will also work fine with L800s. The negative speaker terminal just has to return to earth since there are only positive connections in the SDA cable. Each side uses the ground coming from the speaker cables going to the speaker.

Clipdat

You seem to be well informed and very knowledgeable.

pitdogg2

How are you using these inputs?

ryanmh1

[tl;dr: Issue likely is due to difficulty of the load, not the amp design. Read on if you enjoy technical stuff.]

The input to the amplifier does not matter. XLR or balanced input is irrelevant. What Polk is concerned about is the output stage topology. Most amplifiers will have the entire "signal" in the positive terminal. The black terminal is referenced to ground. Some amplifiers, though, will essentially "float" the black terminal, and the black terminal will actually carry half the "signal" to the speakers. This is what happens when you bridge an amplifier externally, but some amplifiers also do this internally. This is various referred to as a "quad differential", differential, dual differential, or "bridge tied load/BTL" output". All of these amplifiers effectively use two amplifiers two drive a single speaker, which allows roughly half the voltage that a single amplifier would require. Most amps rated over 350 or 400wpc into 8 ohms is likely doing this unless it's an old class G pro amp. There is no grounded speaker terminal. If you use an amplifier like this, you will lose 6dB output from the SDA array, but generally speaking there should not be other effects. Why? Primarily, Polk does not run a pair of "negatives" in the SDA cables. So if you are driving the speaker with the black terminal, you lose half the voltage to the SDA, and drive it with 1/4 the power of the main speakers. That's 6dB. The Parasound has a ground-referenced negative terminal. That's not the issue here.

[begin boring navel gazing]

What the issue is, I still don't know, but it appears to be some other interaction between the speakers and the amplifier. I still haven't had it happen with the Denon receiver. I have to assume there's some sort of misbehavior that either exists in the Parasound which a normal crossover "masks" or which is being induced by something in the SDA crossover (in which I am including the cable). The only other possibility here is that the Parasound will happily drive a light load an easier load at quite high volumes, but not drive a harder, lower impedence load at lesser volumes because something has gone wrong in the amp or amp/speaker interaction. The only simple way I have of testing this is by dragging out 100 pound of speaker from the attic which is the sort of punishing load I originally bought it for years ago. It's easier and a better idea just to drag the amp over to a tech for a going through and upgrade since they came with some bad design elements from the factory.

But let's dig into that load issue, a bit. Polk appears to have used the "corporate" parts for these. Midwoofers are supposedly the same as those in the L100 and R100, and for tweeters those in literally every other and Lx00, Rx00 speaker, except the L900 modules which use a 3/4" variant. Woofers are unique. So, if we can find impedance/phase measurements for other speakers in the line, maybe we can get close. Erin's Audio Corner did nice impedance/phase plots for the R700, R500, and R200. The R500 and R200 aren't exactly easy loads, but that aren't horrible. The EPDR (a combined metric of phase angle and impedance) never drops much below about 2 ohms. See https://www.stereophile.com/content/heavy-load-how-loudspeakers-torture-amplifiers-page-2 for an explanation of this. But the R700, well that's a load. It drops to an EPDR of 1.6 which is pretty low. And that's with a speaker than has a minimum impedance of 3.5 ohms.

The L800 has a minimum of apparently 2.8 ohms. Assuming that's in the range or 80Hz through say 250Hz where the R700 is at its most difficult, the load could be punishing. And if that's without SDA connected and SDA adds a parallel load, it could be a really tough load. I doubt they did that, but that at least is something I should be able to check with a DMM. Whatever the case, it could be a bad cracked solder joint that gets a bit noise and does all sort of who-knows-what when the current demands hit it. That's all speculation, but it would explain why a fairly benign track with loud female vocals really gets the amp all bothered, while playing the same thing without SDA causes no issues.

[/end boring navel gazing]

Now, I almost used all of this as an excuse to buy a McIntosh MC302 or 312. I don't need one versus what I already have, I just want one. Instead, I bought one of those Chinese VU meter units for $125 that I'm hoping will cure my need for meters. Plus, I almost certainly won't hear a difference over the Denon 60% of the time! Although, realizing just how difficult this load could be makes me wonder whether a receiver is up the task. Perhaps not so much. Fortunately, I also have another amp or two lying around that will be more than sufficient. And I'm not really convinced there's all that much point in having that much power on tap since the tweeter runs out of gas pretty quick.

The real shame of it all is just how good these speakers are, and that they appear to be out of production now. That was a short run. Audiophiles tend to really pride imaging and soundstaging, and these are just the best at that. Polk needs to upgrade the tweeter, put an "SDA OFF" switch on teh cabinet, make another run, and just drop three pairs on the doorstep of high end audio reviewers. Some of the best speakers ever literally cost less than some cables.

mhardy6647

The L-800s (introduced in 2019) were in production for a reasonable amount of time, especially given the turmoil in ownership of the brand in the interim.

If one amp has trouble with a given load, and another one doesn't -- it is certainly fair to consider that an amplifier issue.
It really depends on which component one is more wedded to -- the amp or the loudspeakers.

nooshinjohn

Given the Covid shutdowns and supply issues, it’s a wonder the Legend series lasted as long as it did

ryanmh1

It's not like it isn't just the same drivers as the Reserve.... I'm just saying it would be a shame if this was the last of SDA. They never really got a fair shake. This is the speaker most audiophiles wish they had but don't, and they don't even know it.

I'm still a little chagrined it may have been the amplifier. I'm almost hoping I go home and crank it up with the crummy Denon on there and the crackle fest starts again! Then I might get to open 'em up without voiding the warranty!

pitdogg2

They are the last SDA's. I'll be shocked if they ever visit it ever again.

nooshinjohn

pitdogg2 wrote: »

They are the last SDA's. I'll be shocked if they ever visit it ever again.

That would all depend upon any potential new ownership for Polk Audio. I would like to see new ownership come in and continue in SDA line, but with Massimo, dragging their feet about how they’re going to get out from underneath their consumer division, and back to focusing what they want to focus on which is medical products I don’t know how it would all shake out hopefully whoever steps in the breach will be an audio file first as opposed to a Beancounter

pitdogg2

Had it not been for a retirement, I doubt they would have had them in the Legend line this time around.
I'm with you on the Massimo foot dragging and almost incompetence at running this company.

VR3

Gamestop has 4 billon on tap, to the moon as they say!

vader540is

Those L800 are toast. Sell them to me thx.

ryanmh1

pitdogg2 wrote: »

Had it not been for a retirement, I doubt they would have had them in the Legend line this time around.
I'm with you on the Massimo foot dragging and almost incompetence at running this company.

Hopefully a new owner will for an upgrade of the tweeter and a repeat in a "version 2". I think the (presumably) not great sales of the L800 was due to lack of proper marking and need for an in-home audition program setup, which some manufacturers have done before.

Plus, they really just needed to iron out the amplification issue. If it was just a matter of adding in two more conductors to the SDA cable to be able to use a BTL amplifier, that was an opportunity lost. It confused too many people in this day and aged where internally bridged amps are more common. Polk had no sufficient amps in the entire Sound United portfolio to recommend. Oops. Denon/Marantz receivers as well as their separate amps are all out of gas at or before 200W into 4 ohms.

This Denon receiver I'm using works, but it will not properly drive these things at anything above "medium loud", and every current compatible Denon/Marantz amp is similarly underpowered. I haven't had the distortion issue again, but the receiver is unhappy to go very loud, and listening is very volume constrained. When I put in some actual power again next week, hopefully it all goes well. I'll have a solid 800W on tap into 4 ohms, which should be enough.

Clipdat

What amp did you get that does 800 into 4ohm?

Emlyn

A 4 ohm stable receiver like the Marantz Cinema 30 or the older SR-8015 would be fine with the L800s but I'd want to run a separate multichannel amp for the rest of the speakers and just have the receiver power the L800s if it's a large home theater setup.

Masimo also owns Classe Audio. Their Delta amp is considerably more upmarket than Polk's speakers though. I think they are building the Classe products at the same top notch factory in Japan that Marantz and Denon use for their best products.

It's normal for someone to use a receiver with a different brand of separate amplifier when a system needs the extra power. I agree that the L800s don't fit well in the same stable as the Marantz/Denon product lines without bringing in more power with a compatible high current and suitable design.

nooshinjohn

My Carver tube amps paired with the Arcam AVR20 does a fine job of driving my Legends.