KGSS Problem

[RockCity]

I'm hoping Justin, Mr. Gilmore or Spritzer will see this thread and hopefully tell me what's wrong with this KGSS. This unit is over 7 years old and features Alps volume controls as opposed to the newer DACT controls. The serial no. written in red pen on the circuit is #1000.

The issue with the amp is a noisy humming emitting from both channels past 0 position. The humming sound is distinctive to the transformer and is very audible at modest volume. I've isolated the issue without plugging in a source. I've made sure my SR-007 is working properly on the SRM-007t and SRM-717. The problem persists on both RCA and XLR.

I've taken several pictures. I have not touched the inside or done any cleaning. Please help

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020513.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020512.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020511.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020509.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020508.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020507.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020505.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020504.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020502.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020500.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020499.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020498.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020497.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020495.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020493.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020492.jpg

Edited March 13, 2011 by RockCity

[justin]

do you have a DMM capable of measuring DC and AC volts up to 1000V? you could get very far in troubleshooting if you have one

[RockCity]

Hi Justin. I can pick up one but which points would I be measuring? To clarify, the humming is identical to the sound of a power supply; not transformer. In some amps, the power supply has a soft humming noise heard outside the chassis. However, this amp is physically dead silent but both channels emit a constant floor noise.

[justin]

and this is a new issue? are all LEDs lit up on the amp board? what about on the PSU board?

[RockCity]

The lights are lit on both boards.

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020514.jpg

This is the exact same KGSS that attended Denver, NC meet 02/20/11. The previous owner said he did not notice this issue before shipment.

Justin, is there anyway I can send it in for repairs? The seller offered to take it back but I'd much rather have an operational unit. Regards.

Edited March 13, 2011 by RockCity

[spritzer]

First thing I'd check is the LED on the front panel. Are the leads touching the chassis? After that, check all ground wires and make sure they are secure.

[RockCity]

Hi spritzer, the LED wires are clear. The ground or green wires appear to be in place although I cannot see underneath the boards. The amp has no distortion. The issue is the unusually high floor noise. The sound is a constant humming and does change or go away with warm-up.

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020521.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020520.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020519.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020518.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020517.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020516.jpg

[spritzer]

Have you checked the DC offset and balance? Hum could be caused by a capacitor approaching end of its life.

[The Monkey]

Could it be a ground loop?

[spritzer]

It's there without any input present so it doesn't appear to be the case.

[kevin gilmore]

The power transformer has clearly shifted in shipping.

This needs to be fixed first. If the bolt is touching the

inside of the transformer, all sorts of ground current

and vibration is getting into the chassis.

[RockCity]

Hi Mr. Gilmore, I assume the power transformer is the big round doughnut? It is fastened very tightly and it is sitting on circular rubbers top and bottom. Is there any way I can make sure it is in its proper position?

Spritzer, I am not sure about the capacitor since I have no way to check. Will a bad capacitor start to whine like in certain TVs and monitors? So far, the machine is dead quiet.

The humming is much louder without plugging in a source than connected. Flipping between XLR and RCA worsens the noise. On XLR, it is very loud compared to RCA.

Again, I want to clarify that I am complaining about the floor noise in both channels and not the machine noise for those reading this post first.

Edited March 13, 2011 by RockCity

[Pars]

In this pic

the transformer looks like it has clearly shifted towards the back corner of the case. I would loosen the nut/bolt and slide the transformer so it is centered in the rubber disc and hold downs, then re-tighten the bolt.

Edited March 13, 2011 by Pars

[RockCity]

Hi Pars, I carefully undid the bolt, realigned the center, and fastened it. The problem persists, no better and no worse than before.

Here is the realignment:

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020524.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020523.jpg

[mypasswordis]

Check the ground wiring to make sure everything is probably grounded (looks like the green wires). Also try grounding the chassis to see if maybe chassis ground is not at 0V.

[RockCity]

Hi mypasswordis, I can only find one ground fastened to the chassis. The wire connects the C14 inlet connector to a washer. The ground wires on the board are difficult to follow, but I do not see any bad solders.

Here is one of the ground wires you're talking about?

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020528.jpg

[The Monkey]

I think mine has a different switch for the input selection, but that was one of the things that Justin replaced on mine. Does the toggle switch feel right mechanically?

[RockCity]

The toggle switch feels right mechanically. I've checked the grid wires and they are intact.

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020535.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020534.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020533.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020532.jpg

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020531.jpg

[mypasswordis]

Hi mypasswordis, I can only find one ground fastened to the chassis. The wire connects the C14 inlet connector to a washer. The ground wires on the board are difficult to follow, but I do not see any bad solders.

Here is one of the ground wires you're talking about?

http://i1099.photobucket.com/albums/g397/staxspeakers/P1020528.jpg

Are you sure none of the other green ground wires are connected to that one green wire in the pic, which would make it a star ground? Once you have a multimeter try measuring the resistance from the GND solder points on the PCBs to that nut in the pic, should measure close to 0. That one ground wire in the pic doesn't exactly look like a great connection from what I see but maybe it is electrically solid, also would be quick to figure out with a multimeter. Also there is one ground connection on the amp PCB that has no wire soldered, next to the 2SC2240s. Have you tried grounding the chassis itself?

And unrelated but are those compensation caps next to the -350V trimpot?

[RockCity]

Unfortunately, I can only answer one of those questions with certainty. There is a vacant GND spot next to the 2SC2240, however, the same spot is vacant on HeadAmp's website images. I have not been able to find a voltmeter. Please explain how I can ground it? Is it much like a PC?

Secondly, are you referring to the four small caps? http://i1099.photobucket.com/albums/g397/staxspeakers/P1020536.jpg

Thanks for the patience.

[RockCity]

I borrowed a DMM. I believe it is rated for 500V AC, DC so I am not sure if this is helpful, Justin.

Voltmeter

http://img225.imageshack.us/img225/3006/p1020560u.jpg

Here is an overview of the system. If anyone wants to circle which points I should measure, please let me know. Please tell me how I should set up the voltmeter as well.

http://img202.imageshack.us/img202/6131/p1020538y.jpg

[justin]

...

Edited March 14, 2011 by justin

[n3rdling]

Friendly reminder, please be careful while measuring RockCity. Best of luck, hope you get it all worked out!

[RockCity]

Thank you Justin and n3rdling. To verify before I get started, I set up the voltmeter with the black prong plugged into the COMM and the red next to it. I believe the picture I posted had this setting in reverse.

Should I power on the amp first and get started or position the prongs first and then turn the amp on?

Justin, are you talking about the four flat screw blocks on the bottom of power supply board that have the black and red wires leading to it? Should I touch the prongs to the screws coordinating to the same color wires on each block? Or are you telling me I need to touch a GND (green) with one prong and the other prong to the screw head?

[Pars]

It sounds like you are inexperienced in electronic measurement, and probably also in safety when dealing with high voltage equipment? If you do proceed on this, please do a google on safety. At a bare minimum, NEVER perform measurements with both hands. Keep one hand in your pocket or away from the equipment (and not touching metal, etc.) If it were me, I would use some clip leads of appropriate voltage rating and clip them onto the test points with the amp off/unplugged. Be aware that without bleeder resistors, capacitors can remain charged up to high levels, even with the equipment off and unplugged. They could stay that way for days without being properly discharged.

My advice would be to leave this to someone with experience.

Is this an amp that you just received, or have you owned this for some time? Not clear from your postings whether this is something that just occurred under your ownership, or if you bought it and it arrived working like this?