Ampeg B15N: Using the Ext Amp Out

[Robal]

I recently acquired a B15N, probably a 1966, in very good shape. The tone is great but, of course, it isn't all that loud.
For band use I have a much louder and cleaner rig: an Avalon U5 DI/Preamp into a Crest CA9 power amp driving a Bag End 4x10 cab. Is there an optimal way to use the Ext Amp Out from the B15 to drive the Crest/Bag End rig?
I find that when I plug into the Ext Amp Out the volume to the B15N's own cab is cut a lot. Still sounds great. Is this an ok way to operate the B15N?
Alternatively, should I pull the power tubes on the B15N or disconnect with B15N's speaker cab while using the Ext Amp Out?
The Ext Amp Out does not provide a very hot signal but I can turn up the CA9's gain so that the output to the Bag End is fairly substantial. Alternatively, I could run the Ext Amp Out through the Avalon U5 to add some gain before the signal hits the CA9.
I will try all these alternatives but I thought it would be good to ask here first in case (1) any of them may actually harm my gear; (2) others have already gone through this process and found a winning combination or a better alternative.
Thanks for your thoughts on this.

 

[JimmyM]

it's an ok way to do it but certainly not optimal imho, nor easy to set up. this is why svt's caught on

 

[BassmanPaul]

The amp out was designed to run a slave tube amp. Trying to drive a SS power amp will load down the circuit and cut volume in the B15. If you wish to use the output with SS devices you'll need some sort of a buffer with a high impedance input to avoid the loading issues.

 

[aborgman]

The amp out was designed to run a slave tube amp. Trying to drive a SS power amp will load down the circuit and cut volume in the B15. If you wish to use the output with SS devices you'll need some sort of a buffer with a high impedance input to avoid the loading issues.

Exactamundo.

The B15 ext amp out/in expects to see a tube grid - impedance >1 megaohm.

Your standard power amp input impedance? About 20-30Kohm.

The last stage in the preamp section can't sink enough current to drive that load impedance.

Stick a DI between the ext. amp jack and your power amp and you'll be golden.

 

[Robal]

Exactamundo.

The B15 ext amp out/in expects to see a tube grid - impedance >1 megaohm.

Your standard power amp input impedance? About 20-30Kohm.

The last stage in the preamp section can't sink enough current to drive that load impedance.

Stick a DI between the ext. amp jack and your power amp and you'll be golden.

So, running my Avalon U5 between the Ext Speaker Out and the Power Amp will do the trick, as far as impedance matching? Or would a passive DI be better?

 

[aborgman]

So, running my Avalon U5 between the Ext Speaker Out and the Power Amp will do the trick, as far as impedance matching?

Yep, it has a claimed 3Megaohm input impedance.

Or would a passive DI be better?

Probably no different.

 

[NecroticImbecil]

Interested in this as well, though I've never tried it. More generally, could this be plugged into another amp's normal input, where you would plug in the bass?

 

[aborgman]

Interested in this as well, though I've never tried it. More generally, could this be plugged into another amp's normal input, where you would plug in the bass?

Yes.

Anything you can drive with a passive pickup bass, you'll be able to drive with the ext. amp connection of a B15/B18.

Anything that requires a preamp/buffer, you won't be able to drive.

 

[NecroticImbecil]

Awesome. Thank you very much!

 

[Mendouza]

Hi, im reviving this old thread to see if i can upgrade my live setup. I have an Ampeg B15N 64´hooked to the original cab and from the 8ohm external speaker from B15N head to an Ampeg SVT 410HE to push it a little bit and i would like to incorporate an Ampeg SVT DI (12AX7 Vacum tube DI) sent to the mixer and finally to the PA. I would like to know if it´s possible to use de ext amp out jack from B15N into The SVT DI box>mixer>PA or would this harm my gear. Or what would be the best setup trying to keep the signal from the 6SL7 pre tube from the B15N togheter with the 12AX7 tube of the SVTDI box.
On the SVT DI box spec sheet it says mawimum input signal 2.5V RMS, Maximum Bal. out signal 0.5V RMS. I would be greatfull if anyone could help me out as i don´t want to mess up my gear. Thanxs

ps: here in South America we use 220V

 

[beans-on-toast]

You won't damage your B-15 by connecting the SVT DI box to the ext amp output on the amp. The output signal is well below the maximum 2.5 VRMS​ specified.

With some B-15's the signal going to the speakers is reduced when you lug a DI in. This is because of an impedance mismatch which tells you that the DI may not be the best one to use. You have the option of selecting a path of through a tube in the DI or direct to a transformer. Try each one. Also at the input, you can select 0 or -6db (a padding) based on what you hear.

It won't hurt anything though so just give it a try and see how it sounds.

 

[Mendouza]

You won't damage your B-15 by connecting the SVT DI box to the ext amp output on the amp. The output signal is well below the maximum 2.5 VRMS​ specified.

With some B-15's the signal going to the speakers is reduced when you lug a DI in. This is because of an impedance mismatch which tells you that the DI may not be the best one to use. You have the option of selecting a path of through a tube in the DI or direct to a transformer. Try each one. Also at the input, you can select 0 or -6db (a padding) based on what you hear.

It won't hurt anything though so just give it a try and see how it sounds.

I tried it out in my home studio and this set up reduced the signal a lot, tried turning the volume up on the amp and even jumpering the two channles but the signal out of de B15 was still low. I did get a cranked warm round tone recording on my mac but it seems not to work out this way on live setups, it´ll sure work for recording as it sounded really good. I even put my pedalboard and it sounded great. So i will probably use it as trough as it´s meant to be as in terms of tone and sound shaping you just can´t go wrong with this Ampeg set up.
Thanks for the heads up

 

[beans-on-toast]

There are DI's like the Countryman 85 that go inline with the speaker out. You wouldn't have the impedance mismatch and subsequent loss of volume. There is an added advantage in that you get power amp distortion and not just pre in the DI signal.

Other DI's also have a thru so you can plug your instrument into the DI, then out to the board via the balanced line and out to the B-15 via the thru.

 

[Mendouza]

There are DI's like the Countryman 85 that go inline with the speaker out. You wouldn't have the impedance mismatch and subsequent loss of volume. There is an added advantage in that you get power amp distortion and not just pre in the DI signal.

Other DI's also have a thru so you can plug your instrument into the DI, then out to the board via the balanced line and out to the B-15 via the thru.

I'm totally new in terms of di boxes, so following this idea of the Countryman 85, couldn't i send the signal from the B15N 8ohm speaker out to the SVT DI 2.5V rms input attenuating the -6db switch to get power amp distortion along with pre's to the board? Or would the load harm the DI? I dont know if you're familiar to this DI but it also has a trhu, but i think setting it up this way will only send line+di tube?

 

[beans-on-toast]

...following this idea of the Countryman 85, couldn't i send the signal from the B15N 8ohm speaker out to the SVT DI 2.5V rms input attenuating the -6db switch to get power amp distortion along with pre's to the board?

What you are proposing sounds reasonable but isn't a good thing to try.

The DI's that can be hooked to the speaker out do it in a way that is safe for the DI and won't affect the sound of the amp. Basically they put a high resistance in parallel with the amps output and pull off a very small amount of signal. The SVTDI doesn't work that way.

The thru on your unit should allow you to plug in your bass into the SVTDI and connect the thru to the input of the B-15. If you select direct at the input, the 12AU7 tube won't color the sound of the B-15's pre-amp. I believe that the output goes both to the thru and the balanced out and that you can select any combination of direct or tube.

If you want a really nice DI, check out the REDDI. There is a thread discussing it here. JimmyM has one that he uses with his B-15. He would be able to give you some insight as to how well the combination works.

 

[JimmyM]

Insight on using a REDDI with a B-15? Awesome, but if I understand it right, you're wanting to put amp distortion out to the PA from the B-15. I'm going to recommend against it for one reason and one reason only...high frequencies with distortion can easily clip and blow PA tweeters. And if that's your goal, I'd rule out the REDDI, too. The REDDI is the most awesome sounding DI I've ever plugged into, and for my money it sounds identical to a B-15 being run clean through a speaker out DI, but the REDDI can't be run through a speaker out, and it doesn't do dirt. This is why when I play live, I use a dirt pedal that has a rolloff of the tweeter blowing highs (5k and above). Also gives you the option of turning it off and playing clean, whereas you're kind of stuck with dirt unless you want to drive the soundman crazy with levels.

But if you're dead set on using power tube distortion, the best way to make it happen is to mic a tweeterless cab.

 

[tonynoriega]

This topic is timely for my situation since I'm a new owner of a B15n and want to use it next Wednesday, gigging for the first time since I've had it. The concern is that it won't have the volume I need for the room. I'll be using a 4x10 cab (8ohm) since it sounds much better than the Ampeg's 15.

I'll be taking my trusted GK800rb as a backup and just to clarify, can I go from the Amp Out on the back of the B15n direct to the Bass In on my GK using a line cable? If so, should my settings (on the GK) all be set flat?

With the B15n stacked on top of the GK, I would be ready to make a quick connection if needed. Please let me know your thoughts on this and thank you.

 

[Mendouza]

Insight on using a REDDI with a B-15? Awesome, but if I understand it right, you're wanting to put amp distortion out to the PA from the B-15. I'm going to recommend against it for one reason and one reason only...

But if you're dead set on using power tube distortion, the best way to make it happen is to mic a tweeterless cab.

Great insight on di's folks, never tried the Reddi di but will definitly have it in mind, as by now i'll be using my recently aquired SVT DI without experimenting so much with it as it also sounds great. Thankfully there are places like this forums and experienced people with great attitude like beans-on-toast and JimmyM that really helped me out.
Thanxs a lot