vibroverb reissue into 425A Cab

[classic rock]

I want to hook up my 63 reissue vibroverb to my 425a cab. In the manual (http://media.musicalplanet.com/pdf/FEN302.PDF) it says the amp needs a total of 4ohms. I know the 425a cab can do 4ohms mono, left input on cab is for 4 ohm and right input is for 16 ohms, am I safe if i just disconnect the internal speakers and hook up the cab to the speaker jack of the vibro? Also is it safe to have the my VM plugged into the 425a 16ohm input and my virboverb into the 4ohm to share the cab so i can use my a/b amp switch to switch between amps? I am just real scared to ruin my amps or speakers. I know there are a lot of guys on this forum that know there stuff when it comes to this especially steve d. Hope you guys can help me out.

[slowpokerhino]

I know it is safe to hook up the 425 (4 ohm mono) to the Fender if you disconnect the internal speaker. I've done it many times with my Twin without issue (make sure you plug it into the right jack though, one time I hooked it up to the wrong one (16 ohm?) and it blew the fuse in my Twin).
As far as hooking up both, I don't know but that would be cool.

[classic rock]

Thanks for the reply. The greenbacks sound so damn good with this amp. I dont see a problem if I were to hook up both amps the VM and Vibro to the 425a cab so I dont have to keep unplugging and plugging the amps back in. As long as I am not playing through both amps at the same time? can anyone else shed some light?

[SteveD]

Thanks for the reply. The greenbacks sound so damn good with this amp. I dont see a problem if I were to hook up both amps the VM and Vibro to the 425a cab so I dont have to keep unplugging and plugging the amps back in. As long as I am not playing through both amps at the same time? can anyone else shed some light?

No you can't have something plugged into both sockets in mono mode as each jack socket depends on the configuration of the other unused socket's switching contacts.

[classic rock]

Thanks steve for the information. Unfortunately I tried it tho this morning playing 2 amps through the same cab, had the day off thanks to this monsoon and when i would played through my VM it sounded good no problem but then when i switched to the vibroverb which was connected to the 4ohm mono the sound was all distorted and fuzzy and very low volume so I quickly disconnected it. I guess I will just stick with the stock speakers, they are pretty good anyway. it would be too much work disconnecting and reconnecting the amps to 425a. steve, could i have done some damage to the speakers or amps connecting both amps to the 425a? thanks again.

[SteveD]

Basically all you ended up doing was running both amps at 8 ohms as the grounds must have been commoned through your A/B switcher.

Obviously the Vintage Modern didn't sound bad driving 8 ohms while you had it set to 16 ohms, but the Vibroverb mustn't like 8 ohms at all.

It's best not to just take a chance like that, it could have cost you a lot of money if you hadn't been so lucky!

[ClubAndCountry]

A Vibroverb will be perfectly happy at 8 ohms, I don't think that's the problem. (Fender amps are usually fine with between half and double the correct impedance, by design.)

If the switch was set to Mono the two amps would have been connected together in some way (I think the 16-ohm input with the 4-ohm Fender output transformer in series with the speakers, but it has a very low impedance when not producing signal, which is why the Marshall sounded OK, but the 4-ohm input would have run the signal from the Fender in parallel with the Marshall's output transformer, basically shorting it... I think! I'd need to check the wiring diagram to be completely sure), not each to 8 ohms.

NEVER, EVER connect two amplifiers into the same cabinet, *unless* it's specifically set for stereo operation, or connect the outputs of two amps together in any other way. You will quite likely damage one or both amps, and if you haven't then as SteveD said you've been lucky. That's why it specifically states on the back of the cab "Do not switch to mono with stereo inputs"!

You *can* do this with your cab but you *must* have it set to stereo, and each amp will only drive two speakers, at 8 ohms per amp. This won't sound very good with only one amp running because the other two speakers will try to act as out-of-phase 'passive speakers'.