#1
I just received an old Marshall cab that I bought from Ebay last night..... I got it for an old Randall RG100ES that I bought at a pawn shop a few months back..... it worked fine in the pawn shop.....

I was all excited to try out my new rig last night and I wasn't sure what to do about hooking up an amp with two 8-ohm outputs to a 16-ohm cabinet..... I now know that it is okay to do, but at the time i tried hooking it up to a single output jack on the back of the amp that was labeled like this:
SIGNAL OUTPUT

0 dB 600 ohms


The zero had a line through it.... I thought maybe it was the mono output, I'm a newbie to stacks...

Anyway, I got no sound.... but I'm pretty sure the red light indicating the amp was powered was lit... no sound through the speakers though... then I tried using the +6 dB input on the front of the amp instead, still no sound...

Then I tried hooking the amp up to the cab through one of the 8 ohm outputs, and turned on the amp, I could hear the hum/feedback like there was a signal coming through for just a split second.... and then the breaker that is installed in the amp popped and I lost power.....

I tried resetting the breaker in the amp but it keeps popping now every time I turn it on, after like half a second.... it doesn't matter how I hook up the amp or even if I just hook it up to the power outlet in the wall with NOTHING else hooked up.... the breaker continuously pops right after I turn it on....

So I have two questions......

A) What is going on and how do I fix it? Should I just take it in to get it fixed?

B) What is that strange SIGNAL OUTPUT jack for that is labeled as zero decibels and 600 ohms for?

I'd appreciate any help on this.... I'm lost, and Randall's website doesn't have any online manuals for this amp.... I've searched and searched the net and didn't come up with anything other than that the rack-mount version of this amp has a breaker that is prone to popping due to bad solders creating too much heat......

Suggestions? Answers?
#3
Oh good lord, I hope you didn't blow the output transformer. You have to be careful when it comes to ohm settings on amps. Pick the wrong one and you get a nice big paper weight that shaped like a guitar head. So, hopefully it's just the fuse that popped on you.

Look at the back of the marshall cab. What ohms rating is on the jack? Also, what ohms settings are on the back of the amp head? Post everything it says about the ohms.

The signal output jack is kind of like a preamp out jack.
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#4
Quote by mogar
Oh good lord, I hope you didn't blow the output transformer. You have to be careful when it comes to ohm settings on amps. Pick the wrong one and you get a nice big paper weight that shaped like a guitar head. So, hopefully it's just the fuse that popped on you.


it's a solid state amp, so it doesn't use an output transformer. It will have a minimum impedance that you aren't supposed to go under, with a power rating at that impedance, and the power will drop for any higher impedance cab you use.

I would take it in to have it looked at, it's very hard to diagnose SS amp problems unless they are really obvious. Does the amp have fx loop send/return jacks in addition to the Signal Output jack?
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#5
To answer all the questions...

Yes, the signal output jack says 600 ohms... at least, it has the same "omega" symbol that is used for ohms, like a little upside down horseshoe with tabs on the sides....

Mogar, I already posted what the ohms settings are for amp and cab, there are two 8-ohm outputs labeled "speaker" on the amp and one mono input on the cab that is 16 ohms..... I read that it is ok to plug 8 ohms into 16 ohms, or 4 ohms into 8 ohms, just not the other way around... going smaller to bigger is okay, but you will lose some volume.....

There isn't a fuse in the amp, it's a circuit breaker that can be reset by pressing a button....

And yes, the amp has send/return jacks for an effects loop...

Thank you all for the replies and please, if anyone else has any idea what happened there, please let me know.....

I will probably just take it in to my fave guitar shop and ask them if they can look at it...
#6
If it keeps popping the breaker then obviously hooking it up mismatched isnt working. The 4x12 MG cab listed on MF is an 8 ohm cab. And cabs can always be rewired. But sounds like you have other problems going on. Maybe there was a reason the amp was at a pawnshop like the last guy didnt want to get it fixed, just a thought.
#7
Yeah but it pops even when I don't have it hooked up to anything..... and when I tried it out in the pawn shop it worked fine, the breaker didn't pop......
#9
Hmmmm that's a good idea.... I was wondering about my home electricity... the place isn't exactly new and the electrical system is kinda crappy.... I will try that when I get home tonight, and will post on the results on Monday.
#10
Okay, so it wasn't a problem with the home wiring, it still popped when I had it plugged into a surge protector...

I took it in to be repaired, and it turned out to be a blown output transistor. I hope I don't have any more problems with it now, I haven't picked it up from the shop yet.