Gallien-Kruger 400RB-IV - Little Sound w/Occasional Screeching and Overload?

[Chuck H]

The tweeter protection bulb isn't something I've ever seen since I've only dealt with guitar amps. Good info. So, isn't it likely then that either a crossover circuit isn't employed correctly or has failed? I'm not sure at this point that the problem is the amplifier. I would check all connections, try the cabinet with another, equally loud amplifier under fairly equal conditions and try the amp, making sure all connections are correct, with another cabinet.

[louloomis]

Hi. Thanks again.

Here are the answers to the questions/comments since my last post:

1. Re: My not mentioning the white ring in the first post or any other.

You are totally right. I'm sorry, I completely forgot to mention this point. I thought it was in my original post, so I never mentioned it again. Sorry about that, everyone,

2. The cabinet is a Gallien-Krueger 210 RBH (2x10 inch speakers and a tweeter). It looks like it has a variable crossover because I can dial in how much high end goes to the tweeter.

3. The G-K 400RB-IV head I am using does not have a built-in crossover.

4. There is nothing else in the signal chain (i.e. just the G-K 400RB-IV head; no external compressor or eq).

5. Does the screeching occur without the bass plugged in? Just tested it (just cable in my hand - not touching the jack itself): Yes, it does.

6. Remove everything from the signal chain except your instrument. (LL: NO OTHER COMPONENTS IN CHAIN EVER.) If the problem stops it's one of the removed components. If the problem persists try the amp with nothing plugged into the input (LL: DONE. PROBLEM EXISTS - SEE #5 ABOVE.). If the problem stops, try the amp with another instrument. If the problem stops then it may be your pickups are microphonic. It's the instrument. If the problem persists make sure the cabinet is connected correctly if crossovers need to be employed.(LL: THERE IS ONLY 1 INPUT TO CAB FOR 1/4" AND 2 OUTPUTS FROM HEAD - ASSUMING THEY ARE THE SAME?). If it is, try the amp with another cabinet. If the problem stops, it's the cabinet. If the problem persists then you've isolated the problem to the amplifier. (LL: I USED ANOTHER HEAD WITH SAME BASS/CAB/CABLES AND NO ISSUE. TURNED HEAD UP TO 10 ON BOTH MASTER VOL AND VOLUME WITH STRINGS MUTED AND NO SCREECHING AT ALL NOR WAS THE WHITE LIGHT LIGHTING UP.)

7. Re: white ring is the light from the tweeter protection bulb - Understood. I thought I was hallucinating!!!!!! My goodness....

8. Re: The Enzo Whack: Just tried it: The screeching went mostly away for a bit and then came back. Right after I turned up the Master for the first time (in preparation for the first Enzo Whack (I did it 2x), the amp turned off by itself again. I turned it back on, whacked it 2x (over the Master Volume knob area of the amp) and, as mentioned, the screeching was a bit more subdued for a bit. Then I turned it up a bit more and the screeching and white light came on again.

Again, everyone. Thanks. Any other thoughts would be great.

Regards,
LL

[louloomis]

Coupla more things:

The two knobs that make it "screech" are: Master Volume and Treble. Volume knob does not cause screeching even when I turn it up to 10 with the strings muted.

LL

[52 Bill]

When you say that the amp shuts itself off, what happens? How do you turn it back on?

It sounds like there is something loose inside the amp. It could be a broken solder joint, something mechanically loose or physically broken. You can visually inspect everything to see if you can find something that fits that description. Or you can try turning on the amp and using a wooden stick, push and prod around the amp and see if pushing on anything causes the problem to start or stop.

[louloomis]

When the amp turns off - the sound goes dead, the blue light is out (power light) and this time I am sure I had to push the power button in again. It seemed like it popped out on its own. The previous times it turned off I don't remember if the power button popped out on its own or not.

I will do the wooden stick thing next.

Thanks again.
LL

[louloomis]

I started poking with a wooden stick with the amp on and no bass plugged in.

When I pushed on what I think is the 3rd plug from the front of the unit that plugs from the transformer into the board on which is mounted the fan and other stuff, the amp became quieter.

I raised the Master Volume up to the "screech level" and heard no screech.

I plugged in the bass and tested both the Master Volume and Treble up to 10 each with the bass strings muted with my hand and there was no screeching whatsoever.

Is this a plug I need to clean or do I need to resolder the connection to the piece on the board it plugs into or is there no way to tell?

If I want to clean it, even if I unplug the unit can't I get electrocuted by touching the transformer or filter caps or???

Thanks again,

LL

[J M Fahey]

Turn amp off, *unplug it from the wall*, wait 30 minutes, and open it.
Take a hard good look at the suspect connector, use good light and a loupe.
You clearly have a connection problem there, it may be either bad solder on the board underside, where the fixed pins are soldered, resolder them all.
Or the connector female part is loose and does not grip properly the corresponding male pin. In that case take a sewing needle and *slightly* bend the female wall towards the inside, as to make it grip tighter.
Or the cable which is press fit into the connector became loose.
It's more complex because you need a specialtool,the correct crimper.
Absolute worst case, if your life gets impossible, pull the connector and the pins,clean the holes,and solder cables, one by one, straight into the proper holes.
Do it carefully, use good light , a loupe, and fine pointed soldering gun, it's "very" easy to make solder bridges.

[52 Bill]

All of what JM sez is true, but I'll bet Enzo's lunch money on a bad solder joint where the connector fits to the pc board. Try and inspect it to see if the solder looks perfect and shiny or if you see any hairline cracks around the pins.

I'd try and fix that first, as it may also be the cause of the power down of the amp.

How are your soldering skills? What sort of iron do you have? If you do need to resolder the connector please be careful to not overheat the board, or to accidentally leave any solder bridges between solder pads.

[louloomis]

Here's the update:

1. I turned the amp off, unplugged it from the wall and waited more than the recommended period above.
2. I drew a diagram of the connections, and took the pc board out (the one with the fan and other stuff mounted to it).
3. I didn't have a loupe, but with the naked eye I inspected the solder joints for the row of suspect connectors. I didn't see anything.
4. My soldering skills are ok - replaced a couple of potentiometers, guitar pickups, capacitors in amps, switches in amps. Not a pro by any means. I have a Weller soldering iron that costs 15 buck from a large home renovation chain that you all know. It has a fine tip.
5. I touched up all the connections from underneath the board for everything in the row of suspect connectors. My soldering iron is nowhere near hot enough for the solder in this amp, it turns out, but I waited patiently to touch up each solder joint in the row of suspect connectors. I made sure not to inadvertently create a solder bridge.
6. I then used De-Oxit to clean the female connector plugs. Most of the plugs were VERY tight so I don't think the tightness of the plugs were an issue after all.
7. I reattached the female connector plugs.
8. I retested the amp, trying to get the screeching by turning up the amp's Volume, Treble, Master Volume to 10 (strings muted). NO screeching was heard. No white ring appeared around the speakers from the tweeter overload light either.
9. With the amp on, I then poked at the suspect plug row with the wooden stick. I heard no noise and the amp didn't turn off by itself.

So far this amp seems like it may actually be fixed. I'm stunned and thrilled. Thanks everyone, again, and I'll continue to test the amp by playing it and see if anything changes. Couldn't have done it without you!

Excellent!

Regards,
LL