Our native mobile app has a new name: Fora Communities. Learn more.

Diagnose/repair buzz/hum from Logitech Z2300 subwoofer

15443 Views 29 Replies 10 Participants Last post by Tesla1856, 1 mo ago

fizikz

Discussion Starter · Sep 3, 2019

My Z2300 works fine but has developed an annoying buzz/hum coming from the subwoofer which can be heard when it is on in a quiet room but not playing anything. The hum has been gradually increasing over the past several years.

Some posts on the internet suggested removing a couple of wire crimp connectors and soldering them instead. I did this but it did not change anything.

There's the typical suggestion of checking for bulging capacitors, but nothing sticks out to my eyes. I've taken some photos to show as much of the board as possible. Pardon the image quality, as I have not freed the board from the wires keeping it captive to the cabinet. For reference here is another post of someone else's Z2300 with clearer photos of the whole board.

The tops of the capacitors look flat to my eyes. The two large Sanxon capacitors have a black "cardboard" on top which is slightly loose, but it's hard to tell if the surface below them is anything but flat.

Any tips on how to eliminate the hum? Does anything stand out in the photos?

See less See more

9

1 - 20 of 30 Posts

kombat

· #2 · Sep 3, 2019

I'll be interested in this thread. My subwoofer in the living room developed a hum too, but it isn't the subwoofer itself as I've tried another subwoofer there that I know doesn't hum in the basement theater and it hums also. And it just started one day out of the blue. I put in a ground loop thingy and it seemed to take it away for a bit but it gradually started humming again. And like yours, it's only when nothing is playing. I've never tried a different receiver though.

amn2110

· #3 · Sep 4, 2019

I had a similar buzz coming from both the sub as well as the satellite speakers on my Z-2300 system. Removing the crimp and soldering the connectors did not address my issue either.

What did work was replacing those two large Sanxon capacitors. They did not appear to be deformed, but I guess they started malfunctioning after 10 years.

It's a bit of effort to remove the board from the back panel (you have to unscrew the heat sink as well) but I replaced those capacitors with some that I found on Amazon (search 2pcs Nover LA 35V 10000uF 30x36mm LA Audio Grade Power Capacitor-5665), soldered them in, put it back together, and now the system is working again with no buzz on any components.

fizikz

Discussion Starter · #4 · Sep 5, 2019

amn2110 said:
I had a similar buzz coming from both the sub as well as the satellite speakers on my Z-2300 system. Removing the crimp and soldering the connectors did not address my issue either.

What did work was replacing those two large Sanxon capacitors. They did not appear to be deformed, but I guess they started malfunctioning after 10 years.

It's a bit of effort to remove the board from the back panel (you have to unscrew the heat sink as well) but I replaced those capacitors with some that I found on Amazon (search 2pcs Nover LA 35V 10000uF 30x36mm LA Audio Grade Power Capacitor-5665), soldered them in, put it back together, and now the system is working again with no buzz on any components.

Thanks so much for joining to reply, @amn2110 ! Your comment gives me confidence to try replacing those two large 10000 uF capacitors.

Did you manage to remove the board without cutting wires? If I am forced to cut wires, I hope using connectors is ok in case I need to disassemble things again. Suggestions?

As you described, I can also hear the hum from the satellite speakers, but it goes away if I switch off the sub, which is why I suspect the sub (or its circuitry) as the source.

The noise has been bugging me for a long time, especially as it's in the bedroom. I've noticed a dramatic improvement in sleep quality in the couple of days since I unplugged it. I hope the fix can achieve silence, because otherwise I quite like these speakers.

fizikz

Discussion Starter · #5 · Sep 7, 2019 (Edited)

I changed the two large capacitors, but unfortunately the hum is still there.

In case it makes a difference, the sound comes from, or is loudest at, the toroidal transformer. Any other suggestions to try?

Finding replacements locally was not easy, as most stores don't seem to stock 10000 uF units. Finally one store had some: Illinois Capacitor (IC) 10000 uF 50V 85C 35x35mm snap-in. They also had 35V-rated ones, but they were a fair bit smaller (maybe 30x30mm or less, I didn't measure) than the original's 35x30mm.

The Samxons both measured at ~12000 uF by my multimeter. At the store I also asked them to use an ESR meter and the resistance was very low, better than the replacements I bought. So it seems the Samxons are fine. The guy at the store was kind enough to suggest I could return the ones I bought if they didn't solve my problem.

For reference, I'll drop in this thread with lots of info and photos on the Z-2300 and its components: https://www.electro-tech-online.com...-logitech-z-2300-toroidal-transformer.114427/

As for the disassembly, I managed to remove the board by cutting only one wire--ironically the black wire on which I had previously removed a crimp and soldered together. It was quite a pain: dozens of screws, nuts, tons of glue all over securing many components, and even something like epoxy under the D-Sub connector. There is also what I assume is thermal paste applied with some strange plastic between each amp IC and the heatsink. That made a bit of a mess. I wonder if that needs to be reapplied after disassembly...

I also managed to remove the speaker wire without removing the speaker (getting the grill off is a pain since apparently it is glued). It required a lot of patience, contortions, and using a webcam for remote viewing. I've included a (blurry, not enough space to focus!) photo of the inside of the (upside down) sub, which at least shows the wire order: red then black, going clockwise from behind the speaker.

I'm really not looking forward to disassembling everything again to swap out the capacitors again... and mostly just disappointed the problem isn't solved.

See less See more

amn2110

· #6 · Sep 10, 2019

I did not have to cut any wires but I did disconnect the the board from the power when accessing the board to solder in the new capacitors (the 4 pin connector near the top left with the red, yellow, orange, green wires coming out of it).

I saw the same weird plastic pieces near the heatsink and tried to put them back as best as possible (didn't add any additional thermal paste). Agree with you that it was quite a pain to disassemble with all the glue.

Not sure where else to go - maybe it is related to one of the smaller capacitors. This video on Youtube titled "The sound of bad filter caps - hum and ghost notes" had a similar sound to the buzz that I was hearing, which led me to replace the 10000 uF capacitors. Not sure if that is the same buzz you hear?

fizikz

Discussion Starter · #7 · Sep 12, 2019

amn2110 said:
This video on Youtube titled "The sound of bad filter caps - hum and ghost notes" had a similar sound to the buzz that I was hearing

Thanks for the reference. That's a great video and perfectly describes the buzz:

I also compared to a 120 Hz test tone and it matches, as explained in the video.

Unfortunately, I made things a lot worse. I swapped back in the original Samxon 10000 uF capacitors. In addition to the usual hum from the transformer, I now hear the buzz loudly amplified through all speakers (satellites and sub) if I switch the power on at the control pod. Right now this makes the speakers totally unusable.

Maybe my soldering went badly or I kept the iron on the board too long. I think a couple of metal sleeves came out of the through-holes for one of the capacitors which was a bit difficult to remove. I tried resoldering to no avail.

The smaller capacitors look ok. I don't see loose wires or bad solder joints, which was an issue I previously fixed for the headphone jack on the control pod.

Perhaps it's time to take it to a repair shop, because I can't think of what else to try.

See less See more

amn2110

· #8 · Sep 12, 2019

Darn sorry to hear that. Yeah, repair shop seems like the best bet.

fizikz

Discussion Starter · #9 · Oct 1, 2019

Repair shops wouldn't deal with PC speakers. They said they can't get replacement parts and suggested buying new.. I'm guessing their repair bill would possibly rival the cost of these speakers anyway.

With some help from the DIY subforum, my speakers are working again after soldering wire between the top and bottom PCB holes which lost their copper sleeves.

Now I'm back to the original humming problem. I'm out of ideas on solving it directly. One workaround I've thought of is plugging in the speakers to a switched outlet which I can easily turn off at night (the back of the sub is a bit hard to reach). Another is to buy a cheap used Z-2300 sub unit that doesn't have the hum (for now...).

Erik99

· #10 · Oct 26, 2020

The Z-2300 has a design flaw. The chassis should be earthed next to the signal input only. This is done by two screws holding the PCB. (See picture 'PCB to chassis earthing'). However, the PCB is also grounded with a green wire to the cooling assembly. (see picture 'Power unit earthing disconnected' where this wire is already cut). To get rid of the hum you can tighten the screws on the PCB to restore good contact, cut the green wire, or both. I did both and the hum completely disappeared!

Be aware that when you cut the green wire and the insulation between one of the amplifier units on the cooling rail fails, a large DC current will flow though the PCB. This can cause fire.

See less See more

3

fizikz

Discussion Starter · #11 · Oct 26, 2020

Erik99 said:
The Z-2300 has a design flaw. The chassis should be earthed next to the signal input only. This is done by two screws holding the PCB. (See picture 'PCB to chassis earthing'). However, the PCB is also grounded with a green wire to the cooling assembly. (see picture 'Power unit earthing disconnected' where this wire is already cut). To get rid of the hum you can tighten the screws on the PCB to restore good contact, cut the green wire, or both. I did both and the hum completely disappeared!

Be aware that when you cut the green wire and the insulation between one of the amplifier units on the cooling rail fails, a large DC current will flow though the PCB. This can cause fire.

Thanks for posting! I'll give this a try later.

Note that the green wire can be detached without cutting. It is secured to the heatsink by a screw through a ring terminal and is very easy to remove. I think your picture shows the intact ring terminal under the insulation.

Any suggestions to avoid the potential fire hazard?

Erik99

· #12 · Oct 26, 2020

Hi Fizikz,

Yes, you can detach the green wire without cutting. That is what I did. Cover the end of the lose wire with plastic tube or tape to prevent any contact.

The fire hazard is theoretical. I wanted to think of a reason for the existence of that wire. I have not taken out the PCB. If the ground connection over the board from the input range (near the nuts) to the large capacitors is at some point narrow (say only a few mils wide) that spot can melt when the insulation between one of the amplifier modules and the heat-sink fails and the fuse in the power line does not break in time.

If you do not want to take that risk than just tighten the nuts to improve the contact with the PCB ground surface. That will not remove the ground loop, but the voltage induced to the input signal will be minimized. The hum will be the same as of a newly bought unit.

Please confirm if you had success,
Erik

See less See more

fizikz

Discussion Starter · #13 · Oct 27, 2020

Unfortunately disconnecting the green wire did not stop the hum for me, and I noticed no difference in its volume. I checked with a multimeter that the washers and nuts make contact with the ground pads on the PCB.

As a side note, the green wire connects to a pad on the PCB labelled "WA17". No idea what that means.

The sound, at least in my case, comes especially from the toroidal transformer when the power is switched on, and then gets amplified a bit through the subwoofer and satellite speakers when the switch on the control pod is on.

This time noted that the PCB is marked:

T3-2 Sub
DATE 4/05/04
211874-000 REVA0

Do you have the same revision?

Thanks anyway for the suggestion. Maybe it will help others. If it works, it's an easy solution.

See less See more

Erik99

· #14 · Oct 27, 2020

I am sorry to hear that your problem is not solved. I found this:
1. A loosely wound transformer can vibrate/hum. If this is mechanically coupled into the chassis it will be amplified by the casework. It coupled into valves it can come out of the speakers. Refit the traffo, try soft mounts, pads, tight/loose screw mounting.
2. DC riding on the mains. if it adjusts in sound during the day then this is likely, could be over voltage though. Get a DC blocker, get one rated to handle up to 3 volts. Soljstrom audio do a couple, they work. DC on the trafo can couple into the core and come through as noise from subsequent stages.
3. Overvoltage, can saturate the core, cause physical hum and can come through subsequent stages. Not much you can do here other than measure it and respec new trafo's.
4. Toroids have a gap in the winding where the wires go through, this is usually a quiet spot. If you have 100hz noise coupling into the system try rotating the traffo, if wire length allows, so you can point the quiet bit at the sensitive wires. (Honestly though, fix your ground loops, minimize your loop area and take care of circuit decoupling properly).
here Power amp transformer hum [Archive] - The Art of Sound Forum.

But I cannot understand that mechanical noise generated by the transformer is audible through your satellite speakers. Try to unplug/plugin the satellite speaker to make sure.

BTW: I do not know the revision of my PCB. I think it will not make a difference to the ground loop resolution I suggested.

See less See more

fizikz

Discussion Starter · #15 · Oct 27, 2020

Nice find. I think my speaker has both mechanical and electrical hums. Maybe one is even caused by the other.

I previously put a couple of layers of foam-like material between the toroidal transformer and the cabinet, and also below the metal bracket that secures the transformer, and that reduced the hum moderately.

Over time the damping effect must have worn off because the hum is nearly back to the original level.

bumpy said:
EI transformers can be noisy because the laminations rattle. Tightening them and potting them will cure that.

The above is mechanical noise coming straight off the transformer. Electrical noise is something else completely. The magnetic field radiated from the transformer can cause nearby circuits to hum, and rotating the transformer (particularly an EI type) can redirect the magnetic field away from circuit and reduce hum. However, it won't have any impact on mechanical buzzing.

Power amp transformer hum [Archive] - The Art of Sound Forum

metalshreds

· #16 · Nov 7, 2020

fizikz, I'm wondering if I'm having the same issue as you. Could you install a spectrum analyzer app on your phone and pick out the frequency of the hum? Mine is at exactly 240Hz, I replaced the two caps and soldered the crimp connection and it's still there, although I can only hear it when I'm <2ft from it and no hum through the satellites. Doing a bit of research, I think It may just be the toroidal transformer which probably isn't the highest quality

fizikz

Discussion Starter · #17 · Nov 7, 2020

@metalshreds Interesting. I used the Oscilloscope app and here is my result:

I thought it sounded more like 120Hz based on comparisons with test tones, but now I can hear 60Hz too. It flips in my mind as I listen to it, and the spectrum shows both. But not 240Hz. That is perhaps yet another issue.

See less See more

metalshreds

· #18 · Nov 8, 2020

In my research, I found this post where this person mentions that failing power filter caps can be traced to 60hz or any multiples of that. Unfortunately for me I closed everything quite well even with semi permanent loctite thinking replacing the large caps and soldering the crimp connections would have fixed the problem 😣 It could be that replacing all caps would fix the issue but I'm not an electrical engineer to say that would fix it. Also it took me like 4+ hrs for the whole disassembly/repair assembly so I'm not excite to open it up again.

240Hz hum in a power amp???

With no signal going in, upon warming up a couple minutes after power on, this amplifier starts outputting a low level hum at exactly 240 hertz. 60Hz or 120Hz would make sense, but any theories what could cause this at 4x AC line freq? http://www.theatreorgans.com/hammond/faq/a-100/schem3.jpg...

groupdiy.com

fizikz

Discussion Starter · #19 · Nov 8, 2020

I wonder if there are other capacitors, other than the two largest ones, which also act as filter capacitors. A complete list would be nice. It's been tempting to get a budget ESR meter that is hopefully able to test in-circuit to check all the capacitors.

On the other hand it could be the toroidal transformer, because the sound seems to me to come from there.

metalshreds said:
Unfortunately for me I closed everything quite well even with semi permanent loctite thinking replacing the large caps and soldering the crimp connections would have fixed the problem 😣

Ouch. But you'll get used to this dis/re-assembly. 😛 I've taken it apart so many times, I've lost count.

metalshreds

· #20 · Nov 8, 2020

Exactly! now it would probably take me half an hour to disassemble and put back together

(not that I want to!)

Not sure if you came across this post in your search. It list various specs, someone said that the two large caps are the ripple filters, but they don't point out other caps that are filters. They do conclude that the toroidal transformer is underpowered so it could be the source of the hum.

At this point I'm wondering if it would be cheaper to just get a new subwoofer 🙃

Help required on Logitech Z-2300 toroidal transformer

Hi, i am a newbie in this forum, and require help on my Logitech Z-2300 2.1 multimedia speaker system. My Z-2300 toroidal transformer have died and i need a replacement. But i do not know the VA rating of this transformer. I opened my Z-2300 subwoofer and clicked some pictures, which i am...

www.diyaudio.com

1 - 20 of 30 Posts