Hartke 3500 - Snap, Crackle & Pop

[Lownotes]

Hi All, I'm new here and looking for some help in troubleshooting my Hartke 3500. I've had this amp for years and it has served me well until a couple of gigs ago. At first I noticed a moderately loud hum coming from my speaker cab (Hartke 4X10 transporter.) It was fairly inaudible when I was playing at full volume. I figured maybe it was a voltage problem. Recently, it has started to crackle and pop. At first it was just minor. I tested different cables and guitar cords to no avail. Tried plugging into different ohms. No diff. The other night I played a gig and the crackling was so bad it sounded like it was gonna blow. Desperate to start on time, I ran it through the direct out jack to the main PA and it was fine. No crackle what so ever. I'll be the first to admit I don't know much about electronics, I'm just a silly girl! Failed tube in the preamp, loose solder connect?
Any help would be greatly appreciated. Thanks

[DrGonz78]

The fact that you ran the amp perfectly though the power amp points the finger at the preamp stage. This is good news really... There are many things on the preamp stage that need to be looked at closer. I am assuming here that the direct out takes input and bypasses all the preamp stages in the amp. In that case popping crackling could be anything... Yes solder joint or something. Popping and crackles makes me think of dried out capacitors... If I have the schematic I will post it in a bit here.

Edit: Yes the Direct output does bypass many circuits in the preamp stage... If this is the right schematic. Here it is... This narrows it down to the preamp circuitry pretty well.

[MarkusBass]

It sounds like failed tube in the preamp. I would just remove it and see whether the problem is cured (use SOLID STATE preamp only). If it is, all you need is to replace the tube.
EDIT: when you use DIRECT OUT to an external amp, you bypass a big part of the preamp and also the internal power amp. So the problem may be related either to the preamp, or to the power amp. But I would still start from replacing the tube (especially that you don't know much about electronics).

Mark

[DrGonz78]

Yeah I was just thinking about the schematic in my head just now and came back online to add more. Seems Markus helped by stating what I should have realized. Yeah the DI output is the very first stage of the preamp and the output stage has nothing to do with the Direct out. However, the fact that you are not blowing fuses is a good sign. I would not run this amp for any extended period of time, i.e. "your next show."

Another thing I would check is whether the DI makes any "working" differences between having the Post or Pre engaged. That will tell us some more about the state of the preamp. The Hum sound on the speaker makes me actually think of DC voltage on the output. Do not connect a speaker to the output if this is the case. Test the output with a voltmeter to see if there is any substantial DC on the output of the amp.

[Lownotes]

Thank you DrGonz78 and MarkusBass for the info. I will follow your instructions and post my findings. Might take me a couple of days to get around to it. I have a back-up amp I can use in the meantime, but I'd really like to get this one up and running. Your help is much appreciated!

[Enzo]

By running the direct out to the PA, I assume you mean the stage PA system, not the power amp in the head.

You can eliminate the tube by just turning the tube volume down and the solid state volume up only. If it is still noisy on solid state, then the tube is not likely at fault.

Ball up your fist and whack the top of the amp. The amp should not react. If it does or if it makes it start or stop crackling, then you have a loose connection. My primary suspect inside that amp is the row of pins along the rear edge of the preamp board, next to the power transformer. In fact a bunch of those wires are from that transformer. Try wiggling that long inline connector. Any reaction?

[Lownotes]

Ah the famous Enzo! I'm honored! I read a few of your post last night on similar problems. I will definitely get my mallet out and give it the "Enzo Wack." I believe MarkusBass also mentioned trying the solid state side only, which makes a lot of sense to me. If I end up having to take it apart you can be assured that I will wiggle the wires, check the solder points and use some contact cleaner. Thanks again gentlemen for helping a damsel in distress. I will keep you updated.

[DrGonz78]

Hey Enzo I think you should make a mold out of one of your fists all balled up. Then attach a handle to make an Enzo fist mallet whacker!! The Enzo Whacker!! Tons of people here would buy it...

Here is the prototype!!

[Lownotes]

Great idea, DrGonz! I can see the ads for it in all the guitar mags. I hope Enzo shares the wealth with you for developing the prototype

[Enzo]

Wow. I like it.