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B-15n & Avalon U5

NickyBass

NickyBass

Supporting Member
Nov 28, 2005
6,525
4,131
Southern New Jersey
#1
I read something in another thread, and decided not to hijack that thread, so I'm starting a new one. I'm not sure if this would work, but it seems like a cool idea. (I blame Tom Bowlus for my latest GAS--Imagine that.)

The Avalon U5 ( [Invalid or Expired Link Removed] ) has an input jack that can handle 400 watts, so you could hypothetically plug a tube head into it and run that into a SS power amp. Is this correct?

My question is, if that's correct, then would the B-15n need a dummy load? If so, how can that be accomplished?
 
#4
Well basically, in this scenario, you connect the amp out to the input. Then you connect the cab to the thru jack. This is very important in that it insures that the tube amp gets the correct load from the speaker. (The extremely high impedence of the U5 input puts very little load on the amp.) Then you connect the mic input to the lo-z output of the DI. This sends the power amp signal to the console.
 
#5
There are silent "dummy load" devices which might be able to substitute for the actual speaker load, but I've never tried it, nor have I heard anybody say they'd done it successfully. Just throwing it out there as a potential option, maybe somebody who's tried it can confirm or deny.
 
#6
BFunk said:
Well basically, in this scenario, you connect the amp out to the input. Then you connect the cab to the thru jack. This is very important in that it insures that the tube amp gets the correct load from the speaker...
Click to expand...

Not with the U5. It has a dedicated speaker level input jack on the rear, which doesn't have a thru jack to connect the cab. You still need to connect the speaker to the amp as the U5 doesn't provide the load.
 
#8
Munji is right. If you do wihat you suggest, you will end up with 2 very expensive boat anchors. Please look over the Avalon manual very carefully. I am sure they go out of thier way to make this very clear.

el_Kabong said:
Not with the U5. It has a dedicated speaker level input jack on the rear, which doesn't have a thru jack to connect the cab. You still need to connect the speaker to the amp as the U5 doesn't provide the load.
Click to expand...
 
#9
BFunk said:
Munji is right. If you do wihat you suggest, you will end up with 2 very expensive boat anchors. Please look over the Avalon manual very carefully. I am sure they go out of thier way to make this very clear.
Click to expand...

Huh? I'm saying the same thing as Munji.

edit, oh I see now. It's your post that Munji is refering to as the bum scoop, not mine. Pretty funny actually. :D
 
#10
Shoot, there I go saying something stupid again\! :rolleyes:

Yeah, I just re-read the Radial JDI manual. (I could not find the Avalon U5 manual online.) It states that you should use the parallel speaker out to attach the speaker, and not the thru jack. Sorry about the misstatement.
 
#12
Trouble is that a B15N has a 4 pole XLR as the speaker connector. The extention speaker jack is connected in series with the internal 15" and switches the amp to 16 ohms. However if you connect the line out jack (make that the external amp jack) to the Avalon and use the Ampeg as a monitor you get what you need.

Paul
 
#14
bongomania said:
No, that defeats the whole point. The "external amp jack" is a preamp output only, and the goal here is to get the entire sound of both pre and power tube sections.
Click to expand...

Indeed it is Bongo but it IS the simplest way of getting round the connector problem. Remember that this amp will not work without the speaker connected as the ground circuit is completed by the cabinet. To me the sound of the B15 is a combination of both amp and cabinet (including the speaker) but mostly by the cabinet. Therefore the best way to get the complete sound is to mic the thing. I have used the Ext. Amp. jack to drive a PA and it sounded sweet but not fully B15'y.

If the OP wants just the sound of the electonics he will have to make a 'Lil box'. Buy an aluminum box of sufficient size to hold a 8 ohm dummy load resistor (Parts Express #019-020 for 100W or #019-030 for the 200W version which is the one I would use). Buy a 4 pole XLR as is mounted on the cabinet, a phone socket and a 1K 10W resistor. By unscrewing the socket from the cabinet and gently pulling it out you will see that two pins are wired to the speaker and the other two are shorted together. I'm sorry I can't remember the actual pin numbers but the connections will be obvious. Wire your new box the same way with the dummy load connected to the XLR pins the speaker is connected to and the other pins shorted. Connect the phone socket sleeve to the XLR speaker ground which will probably be pin 1 and the 1K 10W resistor between the phone socket tip and the other speaker connection on the XLR. Put every thing back together making sure you have no shorts in your wiring.

Plugging the cable from the amp into this contraption will allow the amp to operate and see an 8 ohm load. Taking a cable from the phone socket will allow you to drive almost any load you like. Remember that this is a full speaker level signal heading on for 20V. The 1K resistor will protect the B15 from you using a shorted cable or trying to drive too low an impedence. In operation this box will get hot as the dummy load dissipates the power of the amplifier.

Paul
 
#15
Thanks for the replies. This is just an idea, so I'm not getting gung-ho about it----yet.

I have a cable from Fliptops.net that converts the Ampeg jack to 1/4". If I plug that into the input on the U5 (that can handle up to 400 watts) would the U5 act as the dummy load? Then take the signal out of the U5 into a power amp, then into a cabinet. Since the input jack can handle 400 watts, the Ampeg would still be putting out it's full wattage---so, would that be sufficient for protecting the amp?

Edit: I am not very technical, so I don't know if this makes any sense.
 
#16
Oh, and for the cabinet, I could mount all the external gear right in the cabinet. It would need a new speaker to handle the higher power, but there is alot of room in the box. Especially with an Acoustic Image power amp. The weight could be offset by using a Neo speaker.

This would be a pricey undertaking, but would be an insane setup---it's the closest I've come to finding a solution to the low wattage of the B-15 (aside from micing it) No biggie though. Maybe it's not possible to get that tone at high volumes, but it's worth a try.
 
#17
NickyBass said:
Thanks for the replies. This is just an idea, so I'm not getting gung-ho about it----yet.

I have a cable from Fliptops.net that converts the Ampeg jack to 1/4". If I plug that into the input on the U5 (that can handle up to 400 watts) would the U5 act as the dummy load? Then take the signal out of the U5 into a power amp, then into a cabinet. Since the input jack can handle 400 watts, the Ampeg would still be putting out it's full wattage---so, would that be sufficient for protecting the amp?

Edit: I am not very technical, so I don't know if this makes any sense.
Click to expand...

The Avalon is NOT a dummy load it's a pre-amp. When it refers to 400W it is in terms of voltage ie the voltage sufficient to dissipate 400W into probably an 8 ohm load. Most pre's would burn something out with that sort of voltage applied to it. If in actual fact you want to just drive a solid state power amp why use the Avalon at all. Assuming that you teminate the B15 with a dummy load there will be approaching 20V across it as I said previously. As most SS power amps will give full output with 0.5 - 2V going in, all you actually need is an attenuator. 10K top resistor with a 1K on the bottom would work fine.

Paul
 
#18
Interesting. It may only take attenuation to take 20V down to 2V, but then what about proper loading of the tube head?

IOW, since the Avalon and a few other DI's are in fact designed to take a speaker level output and convert it to a line or mic level signal; and since the Ampeg needs a proper load; what is the best/proper way to terminate the Ampeg? Is a speaker the only option? Or will a dummy load do the job? And what is the best way to connect this specific amp to both the attenuator (DI or otherwise) and the load simultaneously?
 
#19
NickyBass said:
Oh, and for the cabinet, I could mount all the external gear right in the cabinet. It would need a new speaker to handle the higher power, but there is alot of room in the box. Especially with an Acoustic Image power amp. The weight could be offset by using a Neo speaker.

This would be a pricey undertaking, but would be an insane setup---it's the closest I've come to finding a solution to the low wattage of the B-15 (aside from micing it) No biggie though. Maybe it's not possible to get that tone at high volumes, but it's worth a try.
Click to expand...

NOW I see what you are trying to do!!!!! Use the B15 amp to drive a SS power amp and THEN use the SS amp to drive the B15 cabinet. Is that right???

Assuming it is, it doesn't have to be that pricey. I replaced my original CTS speaker with a JBL 2205 that I bought blown for $25 via Ebay. I had it reconed with a 2225 kit for $120. This gave the speaker a 400W handling ability.

When I rebuilt my B15, I replaced the XLR with a 4 pole speakon wired the same way. Thus I can connect the cabinet to any power amp in my arsenal. Driven with one channel of a Carvin DCM1000 (about 225W) the cabinet is very punchy and very loud. Well capable of handling the low B of my six string. If I bridged the Carvin it would be even louder. The Ampeg is still a single 15 cabinet and there is only so much you can do with one speaker IMO.

Would I do what you are suggesting? No I would not. The B15 is a classic amp and I would not want to risk the damage that is inevitable to working equipment. Mine stays home and my smaller and lighter Acme B2's go everywhere with me.

Paul
 
#20
bongomania said:
Interesting. It may only take attenuation to take 20V down to 2V, but then what about proper loading of the tube head?

IOW, since the Avalon and a few other DI's are in fact designed to take a speaker level output and convert it to a line or mic level signal; and since the Ampeg needs a proper load; what is the best/proper way to terminate the Ampeg? Is a speaker the only option? Or will a dummy load do the job? And what is the best way to connect this specific amp to both the attenuator (DI or otherwise) and the load simultaneously?
Click to expand...

A dummy load is fine for running the amp silently. I do this with any tube amp that I build or repair. Running any amp full out with a sine wave into a speaker is a recipe for a headache not to mention a divorce.

As the OP has the just mentioned cable, the lil box I described earlier will do the job except the XLR is replaced with another phone socket labelled "Input". Wired across this is the dummy load. The other jack labelled "Output" is wired with a 1K 1W resistor across it. The tip connection is then connected to to tip of the Input jack using a 10K 1W resistor. Grounds are completed by the metal box itself. The input jack goes to the amp via the new Fliptops cable while the output jack can be used to drive a DI or a power amp. Output voltage will be dependant on the B15's volume setting.

Paul
 

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