KSP 300 60Hz Hum

[larryklipsch]

My KSP 300 developed a 60Hz hum. The speakers still put out sound. I diagnosed it to the subwoofer by disconnecting everything but power. The power cord is isolated from ground. I plugged it into the same outlet as the other speaker and it still hums.

I sent an email to customer service and they ignored some of my questions and told me where to send it for repair at a flat rate of $240.00 and that they couldn't provide any parts. There are some decent plate amps on the market to replace these with for around $100.00 so $240.00 is out of the question. I would like to keep these original if I can.

I decided to take a gamble and replace the 4700uf/63V capacitors thinking they were the likely problem. The caps had indeed leaked quite a bit. Replacing them with high quality caps didn't solve the hum problem. I notice that there's another set of wires from the xformer to the other board. I haven't looked yet but it too must have a power supply complete with decoupling caps. Before I go further it would be nice to have a set of schematics and info from others who have fixed this problem.

Has anyone out there fixed the hum problem? How?

Has anyone replaced the amps with a different plate amp? Which?

Where can I get a schematic?

[CECAA850]

Spend a little time with the search function. Somewhere there's a thread where someone used outboard amplification and another one on fixing the stock amp. They both had the same hum as yours.

[larryklipsch]

This is not a welcoming and friendly reply for a fellow audiophile in need. Also, it helps to look at the questions-all of them. I am requesting a source for schematics which would be most helpful in troubleshooting this problem. I would like to hear from people who have experienced and fixed this problem or can point me to some useful information. Others need not apply.

I have searched this forum quite extensively. I have read many posts here about hum on the KSP300 and other units both on this forum and other places on the Internet. Posting here is, as it should be, a last resort. If you can point me to something I may have missed, thanks for being helpful.

[CECAA850]

I have searched this forum quite extensively.

Jeesh.

http://community.klipsch.com/forums/p/136297/1383218.aspx#1383218

[larryklipsch]

Thanks, much more helpful though I've read this one. It comes closest to solving the problem.

Schematics?????

[larryklipsch]

OK, as I mentioned earlier I replaced the two 470uF 63V capacitors with some high-quality ones. They had definately been leaking. This didn't stop the hum. Then I noticed some xformer wires going to the other (control?) board. I detatched that board and found it had lots of electrolytics on it. There was a group of 3 of them together that I thought might be of interest. They don't look bad though. They are 2 470uF 25V and 1 100uf 50V.

Does any one know what these caps are about? It would sure be nice if I could get a SCHEMATIC!

[EdmundGTP]

Try searching for KSP-400 instead. You'll likely find many more threads dealing with this issue. Mine in particular. I used outboard amplifiers to power the subs in mine. Try not to get so bent out of shape over the fact that nobody has provided your schematic right away. This is not really a "high traffic" forum and things tend to go un-noticed for days at a time. Not to mention that Technical Data from Klipsch on these speakers is hard to find. It isn't "readily" floating around and typically you have to ask around a bit before finding anything even close. I have the schematic for the KSP400; don't know how much help that would be to you. I can tell you right off the bat that there is no aftermarket plate amp that will be a direct fit replacement, and trying to retro-fit one of similar size will simply be more fabrication work than it's worth. You're better off fixing the amps, or using outboard stand-alone amps instead. The number of people here who have taken it upon themselves to actually dive into troubleshooting the circuit boards of these amps is extraordinarily small. I know of one, maybe two.

[larryklipsch]

Thanks for the info. I see what you're saying. People don't fix things any more and there isn't much traffic here.

I can't believe a reputable company like Klipsch doesn't scan this forum and that they wouldn't be forthcoming in providing schematics! This does bend me out of shape. I keep equipment for a long time so I buy quality items. All other manufacturers have downloadable everything readily available.

It seems that I could buy an aftermarket plate amp and adapt it. I'd be willing to do the work but would much rather keep everything looking original.

Thanks for your offer. I'd like to look at the KSP-400 schematic but still think that Klipsch should make schematics readily available. What's their problem?

[larryklipsch]

I wrote an assertive email to customer service and here's the response:

Larry,I was responding to option B from your request. Since this unit has been out of production for quite a long while, I can include the service manual for this which is attached to this email. We however, can not provide tech support for the electronic components of the amp assembly. We do not scan the forums as we receive about 200-300 emails daily as well as live phone support M-Friday 8am -5:30 pm EST along with a new Live Chat option on our website as well. Hope this may help you.

The service manual contains schematics and shows power supplies on both boards. It also lists the capacitors to replace to fix hum.

I am pleased with this result and will post again after I replace the other capacitors

[txag92]

Larry,

I sent you an email and PM a few minutes ago. Was looking for exact same thing.

Thanks.

[txag92]

Here's the email I sent to Larry earlier where I basically describe my troubleshooting and ask if he can provide the schematics - I'm posting it here per his suggestion.

----------------------------

Larry,

Wow. I came across this thread late last night just after I
replaced the two large caps on the low side on mine.
Unfortunately, I still have the hum, but it changed in pitch if that makes
sense with the new caps. Both of the large caps had leaked on both
speakers.

Since I still had the hum, I proceeded to inspect the pre-amp or smaller
board and found 3 caps somewhat close together one of which had definitely
leaked on just one speaker. On the other they looked fine.

I appreciate any assist you can provide.
-------------------------------------------

Follow up: I found C6, C8 & C9 on the preamp (smaller) board. C6 is kind of tucked up just next to/under the LFE input area. It is labeled, but I had to bend the existing capacitor a little to see the label. The label is just under the LFE input, but you can reach the capacitor without having to remove the LFE input (composite/RCA) interface.

C6 is a 10mf 25v

C8 & C9 are 470mf 25v

I just double checked the Radio Shack website and these are in stock there. (I was just there this past Sunday looking for some other replacement caps for another project I'm working on and thought these were available there). Please note, you may have to purchase the 35v ones as they do not stock the 25v ones, but from the research I have done the higher voltage rating does not hurt you just don't ever want to go lower than the voltage rating. Do your own research if you don't feel comfortable with this or order from digikey corp.

I did have to order the large caps from digikey. They shipped from MN to NC in 3 days for $8 or so. I read on a different forum (badcaps) that Panasonic makes high quality capacitors, so I went with that brand.

Both of the large caps on the low board (where the power supply is located) are 4700mf 63v. These should be labeled as C6 and C8 on what we're calling the low board or large board. Again, just look for the power supply and they are right there next to it.

Also, if you are venturing out and doing repair a la DIY, make sure you get the orientation of the capacitors correct. They have a positive and a negative side. They are usually marked on the side with a broad white strip with minus signs in it. That is the negative side. Make sure you write down their orientation before you remove them or you can also just take a few pictures with your phone or camera (this is what I did). If the orientation is not correct, you will blow them, so just double check to make sure you get them right.

Again, as far as my experience so far, I figured the large caps on the low board were bad as they had leaked quite a bit, but completely missed the caps on the smaller board.

I have to get ready for work, but am planning a RS run on my way and am hoping to replace the other capacitors on the smaller board tonight. Once I replaced the large caps, the hum changed in pitch, so hopefully changing out the other 3 caps will fix the hum issue.

Thanks to Larry for encouraging me to share on here for others.

Ignacio

[larryklipsch]

Ignacio, Thanks for sharing this info. I believe you may have interpreted the manual incorrectly. Let me know if this is correct:

2 Check all filter capacitors. C6, C8, C9, C10, & C11 - from the manual

C6 and C8 refer to the filter capacitors on the power amp.

C8, C9, C10, and C11 refer to the filter capacitors on the preamp.

Also, I found high-quality capactors on Ebay and they shipped very quickly. I had to buy them from different vendors though. You are correct about the voltage. Higher volatage is ok if it fits.

Keep us up to date on how it goes.

Larry

[fini]

I'm watching this thread with great interest! I have the KSP-400s and (knock on wood) don't have the hum problem, but if it should arise it will be nice to know there's a DIY fix. Good luck!!!

[txag92]

Larry is correct. On the preamp board they are C8, C9, C10, and C11. It turns out that the C9's were bad on both speakers. They weren't bulging and didn't show any signs of leakage, but after I removed them, I could see on one of the legs where a little bit of the electrolytic fluid had leaked. Barely noticeable, but it was there.

Once I replaced these four additional caps on the preamp boards, the hum went away on both of the speakers!!!

It's my first time ever doing this type of repair although i do have some electronics/soldering experience which made the job a little less intimidating.

I did come across some great tutorials on soldering and desoldering through Google, so check there if you don't have a the background. It's not rocket science.

Anyhow, the speakers are working great now.

Thanks Larry for sharing the service manual.

Ignacio

[larryklipsch]

Ignacio,

That's great news. Not many people can fix their own amplifier.

I was out of town and just got back to find my capacitors in the mail. I installed them this morning in the failed amp and wow, it works great. I don't remember the sub sounding this good. I will be replacing the capacitors in the other one too.

It's too bad a great speaker company like Klipsch uses an amp with crappy components. The workmanship was also poor. There was lots of rosin all over the board.

Larry

[runninshine]

I had a hum with my KSW 300. I removed the amp cleaned and tightend all the grounds and the hum went away. Good to see you got it fixed. DIY is the only way to go IMO.

[ilag69]

Larry,

I'm new to this forum. I have the same problem with my ksp-300's. I have identified all of the caps except C11. Is C11 right next to C10? From what I can see this is the only one without a number under it or on the sides. Did you also change C6 on the preamp board?

[Oregon Tubes]

Larry, I am having the same problem with my KSP-300 Hummmmmmmmm. I was wondering if you could send me a copy of that service manual that Klipsch emailed to you. Thank you, Oregon Tubes

[larryklipsch]

Larry, I am having the same problem with my KSP-300 Hummmmmmmmm. I was wondering if you could send me a copy of that service manual that Klipsch emailed to you. Thank you, Oregon Tubes

You, and others, may request it from mailto:support@klipsch.com

Good luck and let us know how it goes.

[ilag69]

Larry, Thanks you for the information on fixing my KSP-300's hum problem. I replaced C8 and C9 on both the pre-amp and the amp boards. It fixed the problem and they sound better than ever. Again Thanks.