Amp Tech Thread / Ask a tech Q

[ryansummit]

Well first off, I'd get an outlet tester.



I'd also take the amp home again, and see if it does the same thing there.

If it only makes the noise at the practice space, and / or the outlet tester shows something wrong, I'd get the wiring repaired, call your landlord. The power conditioner would be a quick fix option, only after you are sure it's the power. I don't use 'em myself, couldn't give you a brand or model, lotsa people use Furman.

wanted to let you know i figured out my problem(amp popping)
it was the reverb tank
when i moved it the other night the springs made a thunderous roar and pop
its definately more of an issue than normal spring noise
so i turned the reverb completely off and it all went away
now im just chasin noise in my board

[Hemisaurus]

You need to listen to more dub, then you would know the sound of a reverb tank, King Tubby, Lee Perry et al. use it all the time

Watch some of those Dub Trio videos, you'll see the guy shake his amp to get that Thunder sound.

[ryansummit]

the thunder is not what worries me
its the pop
its so loud,way louder than playing volume
and it does this when completely still,turned on,but no signal into it
even if my pedals arent plugged in, just sitting there idle ,it starts as static,then rumbles and BANG
always at the same volume,REAL FUCKING LOUD,every 2 minutes or so
lee scratch perry would not like this at all,i think he would call it "your mothers cunt" or "modascunt"

[Hemisaurus]

I think bumbahclat would be more likely, and that refers to an item a women needs to wear every mooncycle if memory serves.

So it's a pop, in the reverb circuit, but it's not the tank itself, as it happens when the amp is absolutely still, no vibrations, no nearby feet/drums/guitar noise, and it happens everywhere, not just at your practice space?

Randall Commander IV? Time to look for a schematic.

[ryansummit]

good luck finding anything about it
but yeah no vibes, we just stood there starin at it
and like i said when i dialed the reverb to zero it went away
but it has to be zero not even a smidge
i figured since it went away i didnt have to bring it home,but if you still think the power might be an issue
no other gear down there does this, but there is alot of noise with pedals
and hum from certain circuits
ill bring it back this weekend

[Hemisaurus]

Well if you email amp.support@usmusiccorp.com with your model and serial number, and ask, they will send you a manual and schematic, which you can then let me look at

[Mr. Foxen]

Sounds like something arcing, I'd get in there with alcohol and cotton buds and clean everything, especially shit that looks a bit sooty, then run it open and jab loads of stuff with a chopstick and see if it makes anything bang. Had a similar issue with an SC120 someone else recapped, and it turne dout one of the joints had a load of burned shit melted into it so it was being intermittent.

[Hemisaurus]

Solid state, less likely to be arcing, more likely to be a leaky cap

Hence the schematic.

[ryansummit]

thought i replied,shit
ill get the schematic
i was resigned to fact that the reverb wasnt gonna work no more
but if you can walk me through gettin it up and running,that'd rule
cause it sounds pretty good

[morgantician]

Cab question:  I picked up a Peavey TVX 810 off of Craigslist for a song last weekend. The owner said the tweeter wasn't acting right.

These have that active tweeter, with a potentiometer right below the input jack on the back. Here's my question:  since I could give a shit about an active tweeter, in theory could I just disconnect the leads on the tweeter and take it out of the circuit and the rest of the cab still be functional?  I'm hoping its overall impedance (4 ohms) isn't calculated including any resistance the tweeter has, and this is just an extra bell/whistle to the cab.

[Hemisaurus]

Can't you just turn the tweeter off with the pad (pot)?

Not knowing what the crossover circuit is in that cab, I'd recommend just turn the tweeter off with the pad or take the input jack plate off, and figure a way to connect the input jack direct to the woofers.

If when you open it up, the tweeter is just a piezo with a pad on it, and there is no actual crossover circuit, then yeah, go ahead and cut it out.

[SoupKitchen]

So I think I just blew a power transformer. I was replacing the bias range resistor (470 ohm between diode and B+ winding of the transformer) with a 680 ohm resistor to lower the bias range, and there was a pop and a great deal of smoke. The pop was of the first filter cap in the bias supply exploding, and the smoke came from around the power tranny (laydown mount). I'm thinking the bias supply wasn't grounded.  Moral of the story: CHECK ALL GROUNDS BEFORE YOU POWER UP! I know, stupid amateur hack mistake, but it's going to cost me $80 to replace the power transformer.

[Hemisaurus]

Well if you're savvy enough to be doing all that. I'd suggest before you remove the tranny, try disconnecting all the windings from the rest of the circuitry, and see if it runs no-load, or if it still burns. It's very hard to get smoke out of a tranny, especially without evidence like scorch marks, or melted wax running out of it. The most likely source of smoke is gonna be a carbon resistor, maybe something silicon if you have it, like a diode, voltage regulator or transistor.

So disconnect that tranny, run it up, see if the windings are all intact, if your running it no load expect the voltages to be a little high.

Hopefully you maybe just burned a voltage dropping resistor in your bias supply or something else easily replaced. Have a look and a sniff.

Fingers crossed.

[SoupKitchen]

Thanks, Hemi. I hope I smoked the rectifier diodes. It's a Marshall clone, and it has a 25A bridge diode mounted right above the transformer on the side of the chassis. I'm hoping it blew that.

[Hemisaurus]

Well silicon blows pretty quickly, so here's hoping

[morgantician]

Can't you just turn the tweeter off with the pad (pot)?

Not knowing what the crossover circuit is in that cab, I'd recommend just turn the tweeter off with the pad or take the input jack plate off, and figure a way to connect the input jack direct to the woofers.

If when you open it up, the tweeter is just a piezo with a pad on it, and there is no actual crossover circuit, then yeah, go ahead and cut it out.

There was an issue with the tweeter somewhere on its little board, so hence me wanting to take it out rather than just turn it down. I ended up just removing its electronics all together and wired the speakers to a fresh 1/4" jack. Worked perfect after that (and I won't have to worry about other things on the tweeter board going awry and having to fix something else).

[Hemisaurus]

Yep, best way 

[liquidsmoke]

Thinking about buying a micrometer to measure patch cord plugs. I'm pretty sure that fatter plugs connect way better. Not sure if getting a cheap one ($10 or so) would be wise though.

[Hemisaurus]

It's a vicious cycle, fatter plugs will make a better connection, until your jack socket stretches, and now your back where you started, except your sockets are even more stretched. You can retension them, but one they're worn out, it's only going to help so long.

$10 may get you a half dozen or so nice quality jack sockets, replace your stretched sockets instead. The bad news is a lot of modern amps use PCB mounted jacks, which need to be replaced with something with an identical pinout to fit.

I should also add that PCB mounted jack sockets are far more prone to bad solder joints, quite often the jack doesn't need replaced, just resoldered to the board.

[liquidsmoke]

Maybe I'll just stick a patch cord jack in my eyeball.

The problems never fucking end. 

It's a wonder that touring bands can get any sort of sound out of their rigs at all.

[liquidsmoke]

Some pedals get played for decades being plugged in and unplugged hundreds or thousands of times and still connect to non-fat patch cords. That is another wonder.

[Hemisaurus]

It sucks I know, but fixing the jack sockets is a better solution. Using bigger jack plugs is kinda like using a bigger value fuse in an amp that keeps blowing, it works, but it's not the right way to do it (though there are cases where mfgs mis-spec fuses).

It'll feel worth it when you can plug your cable in, it goes in firmly, and theres no scratches and crackles if you accidentally move the cable. I'm guilty of it myself, having jack sockets where you have to loop the cable to get the right angle for the socket to work, it's crappy and gets annoying.

[liquidsmoke]

It sucks I know, but fixing the jack sockets is a better solution. Using bigger jack plugs is kinda like using a bigger value fuse in an amp that keeps blowing, it works, but it's not the right way to do it (though there are cases where mfgs mis-spec fuses).

It'll feel worth it when you can plug your cable in, it goes in firmly, and theres no scratches and crackles if you accidentally move the cable. I'm guilty of it myself, having jack sockets where you have to loop the cable to get the right angle for the socket to work, it's crappy and gets annoying.

This is why I'm selling my motorcycle that needs work in the spring, too much other shit to do.

Any websites that detail how to fix or replace jack sockets?

[Hemisaurus]

Use the google if you have to, seems to be some videos and guides out there. I'd just open it up and take a look, observing the usual safety precautions, outlined elsewhere in this threaf. Your gear is SS so a bit less deadly for the most part.

[liquidsmoke]

Can one get a shock from pedals? If so that's news to me.

One thing I've noticed is that if the pedals are moving around at all on the floor or board when you are kicking them on and off they are more likely to squawk. I have a few that have not been given the velcro treatment yet, I'll get on that ASAP.