Ampeg SVT3 Pro- power amp fail?

[iKernel]

New to TB, set up an account for this particular matter:
While at practice earlier, my Ampeg SVT 3 Pro cut out. All that can be heard through the cabinet, an SVT410HLF, is sound about as powerful as a 1 watt transistor radio.

With the top cover removed and the amp powered on, the preamp tubes seem to glow as normal. Later on, inspected the board for any obvious problems, seems to be fine. Did not remove any modules and inspect leads. Acquired the schematics for the preamp and power amp section. Have yet to check test points with a voltmeter and do not have an actual oscilloscope and probe to measure wave forms (actual, meaning other than an iPhone app, oScope). I have a somewhat professional training in electronics yet tend to be a little inexperienced in troubleshooting. Need be, I will take the amp back to the music store and have their tech perform the repairs.

Any other SVT 3 Pro owners experience any problems similar to this? If so, any general ideas of where to start looking?

Tomorrow I will have a spare bass amp to verify if the problem is the amp or the cabinet. More details then.

[tom once dead]

I had a similar problem with another amp on its tube channel. I don't know what the problem was as they just fixed it under warranty. But my amp works fine now.

[sapienerabass]

Is your amp new? Has it worked ok before this? I had the same problem straight out of the box and it turned out to be a poorly wired power cord (probably the cheapest component in the rig). I used a different power cord and my svt3 pro sounded great for years. As mine was under warranty I mailed the dodgy power cord to the ampeg distributors and got a replacement cord, a sweat-shirt + stickers too!

It could also be a suspect speaker lead which could be affecting the impedance load on the poweramp? Try using a different speaker lead, a different power cord and as you suggested a different speaker cab. If these ideas don't resolve it then its probably time for a tech. Good luck.

[bstringrandy]

My SVT3-Pro had cut out on me on gigs twice before over the last 4 years and did it once again this weekend. It went out twice and was intermittant. Once when it went out, there was some sound coming out but it was very faint, I also lost the signal through the DI to the PA. I quick wiggle and replugging of the cord at the input jack seemed to fix it.

I took it out of the rack, removed the cover. Then I carefully uplugged the two connectors and undid all of the attaching hardware for the front circuit card. After turning it over and going over it with a magnifying glass, I found a cracked solder joint on one of the 4 points where the input jack goes into the board. I reflowed the solder on it and buttoned it all up. I haven't gigged with it yet, but I couldn't get it to fail in the practice room.

Cold or cracked solder joints can fail completely or introduce very high resistances at the weirdest times....

[BassmanPaul]

Are you sure that the problem lies with the amp? If the woofer(s) in your cabinet have failed all you will get is the tweeter and it'll sound much as you describe. Try another cabinet,

If the cabinet is OK try jumpering a cable between the send and return jacks of the Fx loop. They may just need cleaning.

Be careful what you are doing inside an amp. An inexperienced person can cause more damage than the original problem.

Paul

[iKernel]

Thanks for the posts! This thread has been up for less than 24 hours. I have figured out the problem here.

BassmanPaul, Sapienerabass and Bstringgrandy- your suggestions were most helpful:

After trying a different amp and cabinet, the problem is not within the amp. The problem is definitely the SVT410HLF cabinet. Hooked the amp to a 2x15 Crate cab and had no problems throughout practice. Running the amp at 8 ohm instead of 4 ohm actually required turning down the amp!

For an eleven year-old amp that cost me $400 used but factory refurbished, it has merely had one minor problem due to rack mounting. With the bottom rubber feet removed, one of the threaded inserts loosened from the chassis and landed onto the circuitry, causing a nasty arc. The tech mentioned from the first post did not even charge for finding the fault!

Now for the cabinet- I do know from professional experience that rigging electronics is meant only to be a temporary fix. With that said, here's what happened:
Two months ago, one of the bottom woofers' surround cracked all the way around. Two days from a gig and very little time to order a new speaker, or a spare cab, the problem was remedied with hockey tape and some heavy-duty adhesive. The voice coil was functionally damaged when the surround split as the woofer was still firing. The voice coil was hacked in half, solely for temporary means. The speaker sounded awfully flabby but functional. By now, the woofer has to be toast, hoping it's just the one woofer. At least it's something I can fix myself.

Any suggestions for a suitable and matched speaker replacement? I'm not completely sure of the individual speaker rating or model, just that they're Eminence. It's time to start shopping...

Also, the direct out, both XLR and 1/4" outputs are useless. Any ideas? Luckily this is *somewhat* of an easy module to remove to reflow solder on the PCB. Cold solder joints? Any input on this is greatly appreciated, especially for any sound engineer without a direct box!

[iKernel]

Incidentally, the power cable has been an issue in the past. The amp's power cable would loosen from the socket but the amp would either intermittently power off or refuse to power up period. The amp is rack mounted and the excess cables are tied, another idea from professional experience. I use a Furman power conditioner, so the amp is never meant to be unplugged, just the power cable from the conditioner, which is fixed to it's chassis. Thanks for the input, you guys aren't alone with problems with the power cable.

Never actually had to do more than simply plug the power cable into the socket nice and tight. Had thought to use superglue and "permanently" fix the problem but that could present some issues...

[rbonner]

I'm laughing so hard I hurt myself. Might need hospital visit.

This has to be a belated April Fools Post. Hacked the voice coil in half, super glue and hockey tape, still thinking the amp is malfunctioning?

May I recommend tin snips maybe a BUNZ-O-MATIC soldering torch and just heat the whole board up inside. Lots of acid core solder all over ALL the componant pads? really does an amp good.

I really don't feel good today. I'm going to bed early, you guys deal with this. I can't even read this stuff today.

BOB OUT

[iKernel]

Um, thanks, but I did clearly state the amp still works.
And aside from silicone epoxy, what else would you recommend for a disintegrated surround? Yeah, hockey tape and glue. What of it? The speaker has gone but the surround is still in it's repaired state.
Aside from putting the problem off with a "riggin'" and doing what you've got to do for a gig, I'd just have replaced the speaker right off bat.
Thanks again, Bob.

[JimmyM]

i'd use the crate for this upcoming gig, and get your 410hlf fixed right.

http://www.speakerrepair.com/ocsrepairprice.html

also, never mount a bass amp in a rack without some support on the bottom. without it, the chassis can flex and cause problems.

[iKernel]

JimmyM- thanks for the re-cone link. The only choice I had was to outright buy a new speaker. Also takes some guess work out of the process.

The gig in question here was back in the middle of May of this year. The cabinet has since sat at the practice pad of one band, used for two practices, maybe two hours total. I have yet to pick up the cabinet and get inside for further inspection. If there's any chance that the magnet and/or spider coils are inoperative, might have to go the route of a new speaker.

Side note, the 2x15 is the guitarist's cab. It was his suggestion and we did take some care to not let his cab go the way of the SVT410HLF. The other band's practice spot has an old-school (70's/80's) solid-state Peavey bass amp with a Crate 4x10, not mine personally. It's decent enough to run as a "load" with the SVT 3 Pro at 8 ohms. Most definitely will take your advice and not try to further damage the SVT410HLF.

[iKernel]

Originally Posted by rbonner

May I recommend tin snips maybe a BUNZ-O-MATIC soldering torch and just heat the whole board up inside. Lots of acid core solder all over ALL the componant pads? really does an amp good.

Umm...I've removed the top off of my Ampeg SVT 3 Pro several times, removed the modules and put it back together and it still works, never killed it once. This stuff should be done only by a skilled technician, I'm not saying that I am... Although a decade plus of experience in electronics and other related fields (not quite 30 y/o yet) has taught me many things... Like a benz-o-matic propane torch to a printed circuit board not only de-solders every component but also melts said components and circuit boards into a ball of melted, stinky plastic and metal ball. Haven't had to learn that the hard way either. So I'll accept something along the lines of "take it to a repair shop if you aren't familiar with what's inside." That's appropriate. But not this other stuff...
It's also something I've brought up to the admins here... Even though I am new to TalkBass (seriously, like a total noob), at least I did take a second to read over the rules.

[rbonner]

Oh I'm sorry let me be the first to appologize here.

You were actually serious about super gluing your power cord in, hacking your voice coil in half and hockey taping speaker parts together?

I actually thought you were just a troll trying to start a conflict on here: "It's also something I've brought up to the admins here..." Guess you are, eh?

Serious advice, wow a PROFILE, since you really are a real person, take your gear to a qualified service tech before you destroy everything.

Welcome to TB.

BOB

[JimmyM]

Originally Posted by rbonner

Oh I'm sorry let me be the first to appologize here.

You were actually serious about super gluing your power cord in, hacking your voice coil in half and hockey taping speaker parts together?

I actually thought you were just a troll trying to start a conflict on here: "It's also something I've brought up to the admins here..." Guess you are, eh?

Serious advice, wow a PROFILE, since you really are a real person, take your gear to a qualified service tech before you destroy everything.

Welcome to TB.

BOB

I'm sorry, I'm trying to not laugh but I'm unsuccessful. You are killing tonight, Bob!

[sapienerabass]

I'm kinda with Bob on this one, electronics can be lethal if not taken seriously, may I suggest trading in the amp on a blues harp or some nice pan-pipes. You can hacksaw and tape em up as often as you like and they probably won't kill you. Cheers!

[iKernel]

Wow. I came here for help and feel as if being a "starving musician" and making some "questionable" alterations is just out of the question. I wish I could just go out and plunk the $750 on a new SVT410HLF or even be able to afford shop time plus parts but it's not like that for me.
1. My bass rig is OUT of warranty at this point.
2. Aside from a mere $45 in a speaker, nothing is blown up. I have seen more damage done by bass players with "electronics" experience yet have no idea of what to do when things go wrong.
3. When I say a decade, I mean a DECADE of professional training, college and on-the-job. Spent my time in the military working with tube amps where the tubes are the size of an elementary-school age child. And the power on those things put your SVT4 stacks to shame.
4. I do emphasize safety.
5. I wouldn't do something like discharge a capacitor or measure amps without doing so properly and cautiously.
6. I've spent five years wanting to buy this rig. I'd much rather NOT blow it up when I know I'd saved about $600 or so off of what it costs new.
7. When I "hacked" the voice coil, I literally cut out the section that folded over and impeded movement. Otherwise, like I previously mentioned throughout this topic, would have left the cab with the music store in the first place. There was a slight decrease in impedance but nothing more than 0.5 ohm decrease.

So that's really nice that none of you have been to this point. I don't really care at this point, my problem is solved.

I'm done with TB already. Apparently I was in the wrong. And I'm out of a job, so money's tight. Feel better, now?

By the way, the service tech is actually a friend of mine. I'd take it to him if I had a steady income right now.

Thanks for making me feel pretty dumb for even posting this. Have a great day!

[iKernel]

And for the record, I posted the first thread. Then went to practice. Figured out the problem. So despite that there was some great advice on here, apparently it really served no useful purpose any how.

Now how do I simply delete the account without having to violate the terms of the site?
Does an admin just shut it down for me?
Back to simply reading posts on here, not actually posting. I'll stick to being a ghost.

[BassmanPaul]

Kernel, meaning no disrespect but just stating the obvious. If you have had tube electronics training it doesn't show. The statements that you made and the description of your actions shows absolutely zero knowledge of how things work with amplifiers and speaker systems. I can't even imagine how anyone could hack a voice coil in half. You have to remove the cone in order to even get at the thing. What is a spider coil supposed to be? A temporary fix is just that. You have had two months to either get the bad speaker re-coned or replaced. In the mean time you other woofers have been operation in less than ideal conditions. You could well have damaged the rest of them.

Sorry but all this shows a complete lack of common sense. Please get your cabinat repaired before you have to replace all the drivers.

Paul

[Thor]

It would be nice if we could apply rule#1, respect, to new people on the board as well.

Closed.