Kustom KPS4100

[goldtop5]

I have a Kustom KPS4100 powered mixer head that's making a squealing noise at the speaker output. I figured maybe it could be one of the filter caps. I replaced all of them except the 2 caps at the bridge rectifier (I didn't have them in stock). It still makes a squealing noise. Just give the amp time to warm up and it gradually gets worse. Do you think maybe those 2 reaming caps (4700uf, 50v) that I haven't change could be the cause or is it something else?

[Enzo]

No, I wouldn't think it was a cap at all really.

perhaps KPM4100?


isolate the problem. Does it still do it with ALL the controls set to zero?

If ANY of the controls affect the noise in ANY way, which ones do what?

Does turning down the reverb help?

[goldtop5]

Yes, it is a KPM, not a KPS. My mistake. No wonder I couldn't find any info on it. Duh! Anyways, it doesn't matter where the controls are set to, even with the whole preamp disconnected. It still makes a squealing noise.

[Enzo]

With the preamp disconnected? is that a small 2-pin connector?

Up front: I do not know this piece, I am working from a general impression of similar things.

Some of these amps require the preamp connection to supply a ground to the power amp input stages. If you go without the preamp, then at least ground the input with a clip wire.


I have few KPM series drawings, but none have separate power amp. I see a number with a TDA72xx power amp IC.

This really is a time to call Kustom and ask of they can provide you drawings.

Got a scope?

Are both main power rails up to similar voltages and fairly clear of ripple? If the power amp uses an op amp or other IC, then check the +/-15v rails. heck, do that anyway.

Look where the speaker output connects to the board, or if the jack is right on there, follow the traces. Somewhere there ought to be a low value resistor in series with a cap. They are wired from the output to ground. We call that a zobel stability network. See if the resistor is now open. I have no idea, they are usually no higher than maybe 22 ohms and could be as low as 1 ohm? But not open.

[soundguruman]

I have a Kustom KPS4100 powered mixer head that's making a squealing noise at the speaker output. I figured maybe it could be one of the filter caps. I replaced all of them except the 2 caps at the bridge rectifier (I didn't have them in stock). It still makes a squealing noise. Just give the amp time to warm up and it gradually gets worse. Do you think maybe those 2 reaming caps (4700uf, 50v) that I haven't change could be the cause or is it something else?

It's caused by the negative 15V regulator failing.
The heatsink is inadequate and it overheats.
The positive regulator is just as hot and bound to fail also...

The trick is to increase the voltage drop resistor to the regulator inputs, and try not to overvolage them so much.
I used 5 watt resistors and mounted them on a little terminal strip, but I would have rather used chassis mount resistors.

Then, I used flying leads, from the board, to mount the voltage regulators to the amp chassis...
To provide a better heat sink, Then the regulators barely even get warm.
And the squealing noise stops...

But the whole thing hot, so I also installed a little fan on the heatsink.

(It's actually a Sanyo Mixer), and it's intended to run on 100 volts.
Which is why it runs hot as Hades...
And this is why the voltage regulators are over-voltage, hence the larger voltage drop resistors to the input of the regulators.
This mod is recommended by Sanyo.

However I talked it over with the techs at Kustom Service Dept. and we basically agreed that a fan was needed.

If it was running on 100V, the heat sink would be adequate I suppose barely.
But mounting the regs on the chassis for a heat sink was my idea.
After I did the Sanyo Mods, it still ran too hot for my tastes.
That's how I wound up moving the regulators...and it really did solve the problem in a more permanent sense.

The mixer has worked for about 3-1/2 years now. But I think it was silly to go to all that trouble to make it reliable.

But you still have the problem of the PC mounted plastic pots, that wear out, and can't be cleaned.
So this mixer is overall, a dog. It's not really worth fixing.

Kustom ECO_0343-1_Sanyo100W_Oscillation_21OCT03-1.pdf
Kustom Service Bulletin_061031-1_-15V Reg Failure_100W_SanyoModule-2.pdf

Yeah I'm sorry if documents do not attach correctly.
PM me your e mail and I will send you the 3 service bulletin documents I have. I think I do have the schematic.

[J M Fahey]

Hey SGM, aren't you bored sick of posting the same inaccurate information over and over?
Now we have a new member worrying about "a 100V amp being used on a 120V line" bullshit.
Dear goldtop, don't waste time or risk your amp following the dubious "advice" from the Forum idiot.

The file he can't attach is:
http://www.kustom.com/Content/20082/...on_21OCT03.pdf
which of course does not say a single word about overheating or "100V power lines" which are just his obsession .

[J M Fahey]

Dear goldtop5, to get a taste of the useless crap SGM posts about nonexistent *Sanyo amplifiers" , 100V Japanese power , etc, first read:
http://music-electronics-forum.com/t28492/

Data posted by others, *specially* Enzo, is accurate and will help you.

[Enzo]

What SGM refers to is this:
http://www.kustom.com/Content/20082/...on_21OCT03.pdf

Kustom can buy power modules from Sanyo, just as others buy them from B&O. Companies buy ready made power amps all the time. From that he decides that the whole product is from Sanyo, and then that it must have been made for 100v operation.

Credit where due, if your Vregs are unstable, this mod will help. Note it does not involve temperature.



Note in the schematic, the power supply is not designed for 100v, 120v, 240v, whatever. The power supply is designed to work from a proper transformer. In this case, looks like 32-0-32vAC. Such a transformer is easily made with any primary voltage you like. If one chooses to think that Sanyo is too stupid to design products for the largest electronics market in the world, well, they have my sympathy.


Oh, sorry Juan, you already said those things, your post was scrolled off my screen.

[km6xz]

It is really a strange obcession. Of all the things someone could latch onto and obsess about, why "100V"? I guess the fact that a vast majority of Japanese production is for 230 volts and a bit less for the 120-130 volt world, does not register.