Dummy Load Danger?

SteveD · #1 01-26-2012, 04:24 PM

In my neverending search for tone, I whined to my tech, "My Ampeg B-15N sounds better than any amp I've ever tried, but it's only 30 watts. My Carvin BX1200 has huge power, but it's transparent and dry sounding."

Tech: I'll build you a magic box. It will have an input and and an output and a 'dummy load' inside to fool the Ampeg and keep it from blowing up. A line level signal will come from the output, which you will connect to the input of your Carvin. Then you will have the B-15N for a front end and all the power you want with the Ampeg tone and sag."

Some other wags are saying this is dangerous and still liable to damage the Ampeg.

I love the feel and tone of a tube amp, but don't want to carry a heavy tube amp around, that's how this all got started.

Comments?

billfitzmaurice · #2 01-26-2012, 04:31 PM

Get a tube pre-amp to use with the Carvin. Try a few until you find one you like. An emulator is another possibility. Some find them OK, some don't.

lowfreq33 · #3 01-26-2012, 04:33 PM

As long as it's done properly this shouldn't hurt the amp at all.

SteveD · #4 01-26-2012, 04:39 PM

Quote:

Originally Posted by billfitzmaurice

Get a tube pre-amp to use with the Carvin. Try a few until you find one you like. An emulator is another possibility. Some find them OK, some don't.

Thanks Bill, that's an obvious and proper solution. I have a Tech 21 VT Deluxe, it clones the tone fairly well, but of course it can't do that natural compression saggy thing that only tubes seem to do. My tech calls the B-15 sound "spongy". It's a heavenly thing.

SteveD · #5 01-26-2012, 04:43 PM

Quote:

Originally Posted by lowfreq33

As long as it's done properly this shouldn't hurt the amp at all.

Thanks, lowfreq33, my tech has been very good over the years, but that makes me feel better. That Ampeg is my
bay-bee, since 1975 (she's a 67).

I've had a bad 38 year habit of paying a lot more attention to my playing than techie-type stuff. I know how to plug in a cord, change a fuse and that's about it.

will33 · #6 01-26-2012, 04:45 PM

Assuming he remembers to carry his naught and calculates the resistance and power handling right, it's perfectly fine. Techs use dummy loads to work on amps all the time. All it is is a group of resistors that take the place of the speaker. As long as you make it with a proper resistance for the amp (4ohm/8ohm, etc.) and use enough to be sure they can handle the power (dissipate the heat) the amp is sending their way, it's perfectly fine. Just in the interest of reliability/safety, tell him to over-engineer it a little bit, meaning make one that'll handle a little more power than yoir B-15 has to give, just so your not making the components work their hardest. A small heatsink or cooling fan would be a double-guaranty for constant use, 4 hour gig, etc.

sevdog · #7 01-26-2012, 04:47 PM

Not more than a couple of weeks ago I was just asking here on TB and at a shop in Austin about doing a similar thing with an Ashdown Little Bastard and a power amp. I was told the answer was a power attenuator which is exactly what your tech told you he would build...to me it became cost prohibitive at that point but if I had the $$$ I'd probably do it. So, I say do it and post a video review on Youtube for us to all see.

SteveD · #8 01-26-2012, 04:53 PM

Quote:

Originally Posted by sevdog

Not more than a couple of weeks ago I was just asking here on TB and at a shop in Austin about doing a similar thing with an Ashdown Little Bastard and a power amp. I was told the answer was a power attenuator which is exactly what your tech told you he would build...to me it became cost prohibitive at that point but if I had the $$$ I'd probably do it. So, I say do it and post a video review on Youtube for us to all see.

Great idea. The magic box is $200. Just got word he's got it done. Picking it up tomorrow and will try it at tomorrow night's gig and give verbal report Saturday.

This place is the greatest, thanks everyone.

will33 · #9 01-26-2012, 05:10 PM

Quote:

Originally Posted by sevdog

Not more than a couple of weeks ago I was just asking here on TB and at a shop in Austin about doing a similar thing with an Ashdown Little Bastard and a power amp. I was told the answer was a power attenuator which is exactly what your tech told you he would build...to me it became cost prohibitive at that point but if I had the $$$ I'd probably do it. So, I say do it and post a video review on Youtube for us to all see.

That sounds more like a Marshall Powerbrake or other tyoe device. They let the tubes run at full output and then soak up some of that power before it hits the speaker without changing the impedance, kind of like a giant L-pad. That's a different deal and yeah, they do kill tubes.

The dummy load is simply a resistor(s) instead of a speaker. It's actually a more "friendly" load on the amp than the speaker is....of course, it doesn't make any sound.

will33 · #10 01-26-2012, 05:14 PM

Hmm.....I have a typo on the word "type".....wierd.

SteveD · #11 01-26-2012, 05:27 PM

Quote:

Originally Posted by will33

That sounds more like a Marshall Powerbrake or other tyoe device. They let the tubes run at full output and then soak up some of that power before it hits the speaker without changing the impedance, kind of like a giant L-pad. That's a different deal and yeah, they do kill tubes.

The dummy load is simply a resistor(s) instead of a speaker. It's actually a more "friendly" load on the amp than the speaker is....of course, it doesn't make any sound.

Ah HA! That's what one of the guys was worried about. He said guys put these "power soaks" on Marshalls trying to get bloody tone at lower volumes and it hurts things.

will33 · #12 01-26-2012, 05:30 PM

Quote:

Originally Posted by SteveD

Ah HA! That's what one of the guys was worried about. He said guys put these "power soaks" on Marshalls trying to get bloody tone at lower volumes and it hurts things.

Yes.

Your dummy load will allow you to run your B15 without a speaker at all and won't hurt it. Your tech will explain it to you. Make sure he's giving you a dummy load and not a power soak.

P Town · #13 01-26-2012, 05:46 PM

The sound of the tube output is created by the interaction of the output transformer, and the inductive, + resistive + speker mechanical + cabinet effect on the sound. A resistive load probably would not present the same voltage signal, (not to mention phase relationship with the current flow seen by the solid state amplifer). And I would bet it would not produce the desired effect. You could take the signal from the tube preamplifier, and switch the power to the output section of the tube amplifier off, and send that to a solid state power amplifier, but it really is not worth it.

SteveD · #14 01-26-2012, 05:50 PM

Yep, it's a dummy load. I'm getting kind of excited now. I took the B-15 to a quiet jazz casual last week and it sounded so sweet. I'm interested to hear what this setup will sound like through my two Avatar BR210 cabs, stacked vertical of course. This will be at my classic rock gig.

I'll take my old Fender Mystery Jazz and my MIM fretless Jazz. The Mystery Jazz has 61 pots, a 63 neck and a 65 serial number. Got it that way in 84, no idea what happened there, but she's a good 'un.

JGR · #15 01-26-2012, 05:54 PM

The dummy load, especially if it is purely resistive, will totally change the sound and feel/responsiveness of the amp, and not in a good way. The right way to do it is to tap a slave signal from the speaker jack and keep the internal amp speaker connected. Otherwise you loose all the dynamics of the amp's power section reacting with the speaker/cab, which has a HUGE impact. Send that signal to another power amp and cab. That will allow you to get the tone you love at higher volumes. I've spent a lot of time and money buying attenuators and building custom reactive and resistive dummy loads, and running all sorts of re-amp configurations, and that is by far the best way. You have the advantage of wanting more volume rather than trying to reduce it which makes things easier; use the small amp as a monitor.

billfitzmaurice · #16 01-26-2012, 05:56 PM

Quote:

Originally Posted by P Town

The sound of the tube output is created by the interaction of the output transformer, and the inductive, + resistive + speker mechanical + cabinet effect on the sound. A resistive load probably would not present the same voltage signal

A resistive plus inductive load would, and a good techie can come up with that no problem. Well, I could, so make that a really good techie.

But I still wouldn't lug around a 30 plus pound amp and a ten pound dummy load.

Quote:

I have a Tech 21 VT Deluxe, it clones the tone fairly well, but of course it can't do that natural compression saggy thing that only tubes seem to do.

A tube compressor will. I wouldn't spend a few k$ on a Fairchild, but I imagine there must be a decent one out there that isn't too pricey.

P Town · #17 01-26-2012, 06:00 PM

Or, get a PF500.

SteveD · #18 01-26-2012, 06:02 PM

I thought about an SVT and a teenager to carry it, but couldn't find a teenager who would leave his x-box/facebook/texting/WarCraft etc. long enough to help me.

will33 · #19 01-26-2012, 06:13 PM

Those guys points about your dummy load not sounding the same are spot on. It may not have all the B-15 character you expect. Although, for $200, I'd assume your tech is putting together something more involved like these guys are describing and not just a box with $10 worth of resistors in it. In that case, it should do what you're wanting to do.

beans-on-toast · #20 01-26-2012, 06:19 PM

You can build an inductive dummy load out of a speaker motor which approximates a real speaker.