Broken Ampeg Amp into Cab?

[Ant_agonise]

Hey there!
Long time reader, first time poster.

I have an Ampeg Rocket Bass rb-210 that sadly just blew up mid gig and was out of warranty. Sent it to a Tech and they said the whole main motherboard part needs replacing, which again... seems hard to get hold of. While all that investigating was going on, I decided to go my first ever head and cab instead of getting another combo. But i'm starting to think my 4x10 is a bit big for the venues the pub covers band i'm in tend to play.

So! I was looking to potentially turn the old Ampeg into a 2x10 Cab and was wondering if I could ask you guys if there is anything I need to worry about from a power/conversion/anything i've not thought of?
As basically i'm hoping to strip the whole thing out, plug in a female twist speaker cable plug.. and that's it?
Do i need a volume on the tweeter?
The head I now have is the Fender Rumble 800HD. Is there a way to make sure I don't put too much power down the line? or is that just down to me not cranking the volume way up from the head?
Up for any links/guides if you guys have any! Thanks in advance, nervous/excited to get on it as a project.

 

[beans-on-toast]

Cost wise, I would simply buy a 210 and sell the old one.

You have to see what the nominal impedance of the speakers are in your cab. Tthere may be a label on them or you can disconnect the speaker and measure it with an ohm meter. If the 410 speakers are 32 ohms each, your 210 will have an impedance of 16 ohms, not good.

 

[UntitledProject]

Cost wise, I would simply buy a 210 and sell the old one.

You have to see what the nominal impedance of the speakers are in your cab. Tthere may be a label on them or you can disconnect the speaker and measure it with an ohm meter. If the 410 speakers are 32 ohms each, your 210 will have an impedance of 16 ohms, not good.

Why would the speaker rating of a separate 410 have any bearing on the speakers in his old combo amp?

 

[beans-on-toast]

Why would the speaker rating of a separate 410 have any bearing on the speakers in his old combo amp?

You are right, I somehow thought that some consideration was being given to cutting down the 410 to produce two 210 cabs.

The two tens in the RB-210 are 16 ohms each. They are wired in parallel to yield a total of 8 ohms. So that would work. The tweeter is not needed in a new cut down cab.

 

[UntitledProject]

You are right, I somehow thought that some consideration was being given to cutting down the 410 to produce two 210 cabs.

The two tens in the RB-210 are 16 ohms each. They are wired in parallel to yield a total of 8 ohms. So that would work. The tweeter is not needed in a new cut down cab.

Ah, I see.

OP, the only issue with the 210 is power rating. The rb put out 250 watts at 8 ohm, the fender puts out 400. Without knowing the speakers power ratings, it is possible you could be overpowering them. That said, I personally would not sweat it as any situation where I needed to be that loud, I probably would be bringing just a 210 @400 watts anyway. But it is possible you could do damage if you push it.

 

[6thplanet]

Under reasonable expectations it would work.

 

[JimChjones]

The tweeter may get complicated. I had a quick look for a circuit diagram but didn't find it. There's a block diagram in the owners manual. The easiest thing, of course, is to simply run it without the tweeter. If you want the tweeter the block diagram shows what it calls a crossover but is more likely a high pass filter. If that's on the main circuit board then you would need to construct something to replicate it. That may be more effort than you are happy getting into. Without the tweeter is just a question of installing a speakon and connecting both drivers in parallel.

Power wise, yes you will have enough power in your amp to fry the drivers, and no, there's not really any way to keep them safe other than being careful with volume. Some people claim to be able to hear incipient speaker overload and can turn down if approached. They may be correct. I only know that I cannot. Also that industry pros say that they see enough fried drivers to doubt whether the average person will succeed in turning down before it's too late.

 

[Element Zero]

Just curious if you mean the 410 cab is physically too big or if the sound is too big.

I’ve taken my 410 too all kinds of environments and things couldn’t be better. I do NOT take it to church though as much of the older members hear with their eyes which is an incredible ability in itself. I wonder if that can be taught or if it’s learned or innate.

 

[Adjectives]

You are right, I somehow thought that some consideration was being given to cutting down the 410 to produce two 210 cabs.

I got that too upon first read.

 

[agedhorse]

I do NOT take it to church though as much of the older members hear with their eyes which is an incredible ability in itself. I wonder if that can be taught or if it’s learned or innate.

It’s a miracle

 

[agedhorse]

Where is the crossover physically located?

Did the tech identify the actual fault, or just say that the board needed to be replaced because he was unwilling or unable do a component level repair? Are they an Ampeg authorized service center?

 

[Tassieviking]

You would need to blank out the hole the amp being removed leaves in the cab, and then just run the 4 wires from the woofers to a new socket on the back of the amp, make sure you connect the 2 speakers in parallel to the new socket.

If you want to use the tweeter you would need a capacitor and 2 power resistors 10W as well as what looks like a fuse or a light bulb in a fuse like shape.
Or you could just use the PCB from the busted amp and use the crossover in that, just mount it in the back of the cab somewhere.

That PCB should be repairable unless the tracks are badly damaged, get a second opinion.

You can clearly see the PCB with the crossover at 1min and 15 seconds on this youtube clip:

 

[agedhorse]

Just a note, the guy in the video has absolutely no idea what he is talking about. Any qualified tech will quickly recognize that he's a poser.

 

[wboyd68]

So much simpler to just get a 2X10 cabinet.

 

[JimChjones]

By the look of that video the crossover/hpf whichever it is is on that back panel board separate from the power amp, (together with some other stuff that's irrelevant) so with luck its good, and all you need to do is remove the other boards, blank things off and connect up a new input jack/socket to J2.

 

[KevInDaBassment]

Just a note, the guy in the video has absolutely no idea what he is talking about. Any qualified tech will quickly recognize that he's a poser.

Crikey, tell us what you REALLY think of the guy!

 

[agedhorse]

Crikey, tell us what you REALLY think of the guy!

It's actually pretty bad, looking at it from the perspective of training/supporting techs and writing service manuals. That said, I see a lot of folks that suggest that they are in way over their heads in their grasp of technology... including those who should know better.

 

[Element Zero]

It’s a miracle

 

[Tassieviking]

Just a note, the guy in the video has absolutely no idea what he is talking about. Any qualified tech will quickly recognize that he's a poser.

I did have a second look and then a laugh when he miss diagnosed what the components were, I wonder if that is a generic amplifier module that can easily be replaced.
I don't recognize it but I am not that familiar with any amp modules like ICE etc.
Perhaps it is not repairable because the tech is not an Ampeg authorized repair centre and can't get his hands on a schematic.

 

[agedhorse]

The comment about the preamp board being so simple was hilarious, considering that all of the parts are on the bottom, completely hidden.

The comments about the blue caps being low quality and needing to be replaced in 7 years was especially priceless since they are special Y rated safety parts that are specially designed and extensively tested for failure modes/lifespan (like 50+ years)