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Topic: Amp heads into A/B box |
Garry Pugh
From:
Nashville Indiana
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Posted 28 Mar 2015 7:44 am |
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Is there any problem running the power out from 2 amps, one into each side of an A/B box then out into a speaker cabinet? I do this off and on when space on stage is a problem and not enough room for another speaker. It allows me to use 2 amps (one for guitar and one for steel) into one speaker. I switch back and forth between amps when I change instruments.
I had a guy tell me last night this was not a good thing to do as it could damage something. I've done it off and on for years.
Are there potential problems doing this?
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Emmons PP D10 8X5, GFI Ultra D10,both are setup up "Emmons" style. Quilter 202 Tone Block, Nashville 400, Milkman 85, Stewart PA200, BW and JBL speakers, Profex II
cell # 812-603-1612 |
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James Hartman
From:
Pennsylvania, USA
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Posted 28 Mar 2015 8:00 am
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| If I understand what you're proposing here, the amp not in use at any given time would be without a speaker load. You can probably (maybe?) get away with that using solid state amps; but it's a quick way to destroy a tube amp. |
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Garry Pugh
From:
Nashville Indiana
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Posted 28 Mar 2015 8:52 am
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Are you saying the amp not in use, not switched on, needs an impedence load or it could be damaged?
What is the difference between doing that vs having an amp on but unplugged from the speaker cabinet is that potentially damaging as well?
_________________
Emmons PP D10 8X5, GFI Ultra D10,both are setup up "Emmons" style. Quilter 202 Tone Block, Nashville 400, Milkman 85, Stewart PA200, BW and JBL speakers, Profex II
cell # 812-603-1612 |
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James Hartman
From:
Pennsylvania, USA
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Posted 28 Mar 2015 9:30 am
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| Garry Pugh wrote: |
Are you saying the amp not in use, not switched on, needs an impedence load or it could be damaged?
What is the difference between doing that vs having an amp on but unplugged from the speaker cabinet is that potentially damaging as well? |
Yes. A tube amp always needs a speaker load.
"... not switched on" ??? Well, if you're not actually powering up both amps simultaneously, I guess there wouldn't be a problem. But you should never turn on a tube amp without impedence load.
I have almost no experience of solid state amps, so I can't speak to those. |
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mike nolan
From:
Forest Hills, NY USA
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Posted 28 Mar 2015 10:26 am
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| Radial makes a box for this..... The Headbone, it comes in three flavors , tube only, solid state only, or tube/SS. |
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Clyde Mattocks
From:
Kinston, North Carolina, USA
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Posted 29 Mar 2015 8:49 am
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I did this for years using a Session 400 for steel and a Fender Pro Reverb head for guitar without any ill effects. Both went thru an A/B box and into the Peavey's Black Widow. Loud!! The two amps were never receiving a signal at the same time.
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LeGrande II, Nash. 112, Fender Twin Tone Master, Session 400, Harlow Dobro, R.Q.Jones Dobro |
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Clete Ritta
From:
San Antonio, Texas
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Posted 29 Mar 2015 11:35 am Re: Amp heads into A/B box
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| Garry Pugh wrote: |
| Is there any problem running the power out from 2 amps, one into each side of an A/B box then out into a speaker cabinet?... |
When you say "power out" I assume you are not referring to the AC power plugs. The A/B box implies you mean "speaker out" of both amps into one speaker.
| Garry Pugh wrote: |
| ...the amp not in use, not switched on... |
Do you physically switch amp power on and off? If the power is off, then no harm. In short, don't power up an amp without a speaker hooked up first. |
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Richard Sinkler
From:
aka: Rusty Strings -- Missoula, Montana
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Posted 29 Mar 2015 12:38 pm
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| mike nolan wrote: |
| Radial makes a box for this..... The Headbone, it comes in three flavors , tube only, solid state only, or tube/SS. |
Heck... Radial makes things for just about any situation you have. Great products. I have a Radial Big Shot loop switcher, so you can set up different effect in a loop separate from you normal signal path. It works really good when you have more than 1 effect turned on at one time. It has 2 switchable loops, that you can use loop 1, loop 2 or I believe even both together. I can vouch for the quality of Radial's products.
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Carter D10 8p/8k, Dekley S10 3p/4k C6 setup,Regal RD40 Dobro, Recording King Professional Dobro, NV400, NV112,Ibanez Gio guitar, Epiphone SG Special (open D slide guitar) . Playing for 54 years and still counting. |
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Garry Pugh
From:
Nashville Indiana
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Posted 30 Mar 2015 9:23 am
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I am not talking about the voltage or the AC outlets.
The A/B box acts to toggle between the 2 amplifiers and I am doing this as I only have one speaker.
On the A/B box you have side A and side B. In the situation I am referring to side A is coming from the power out (the output to the speaker cabinet) of one amp; side B is coming from the power out of the other amplifier.
When I say "switched off or on" I'm talking about the A/B box not the amp. When you step on the switch one side (of the A/B box) is off and the other is on and vise versa.
The situation is actually as Clyde mentioned but different amps involved. As a result of this post I have started turning the tube amp to standby when it is not switched on (engaged) at the A/B box.
_________________
Emmons PP D10 8X5, GFI Ultra D10,both are setup up "Emmons" style. Quilter 202 Tone Block, Nashville 400, Milkman 85, Stewart PA200, BW and JBL speakers, Profex II
cell # 812-603-1612 |
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Dave Mudgett
From:
Central Pennsylvania and Gallatin, Tennessee
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Posted 30 Mar 2015 2:38 pm
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It makes all the difference what types of amps you're talking about.
For a typical solid-state amp, there's no problem having the amp on with no speaker load. There's typically no output transformer (there are exceptions, but probably nothing we'd see here), so if you have transistors directly coupled to the load, if that load becomes infinite impedance, no problem - no current flows. For this type of an amp, the enemy is too small a load impedance, which causes too much current to flow through the transistors, and kaboom.
But for a typical tube amp, you absolutely must not allow the power tubes to be putting out current with no load impedance. Basically, you're hitting the primary of the output transformer with a large current, it's inducing a large voltage in the secondary which has nowhere to go. The short story is that your output transformer will be history pretty quickly.
So to know what to tell you, we need to know the particulars of your amps. Your sig reads Milkman half-and-half and a Stewart (power amp, I presume?). I think the output sections of both of these are Class D solid-state?
The best guy to ask about the Milkman is, of course, Tim Marcus. But my guess is that if these are both normal solid-state amps, it's not a big deal as long as you're very careful to make sure you're never letting the amps short out somehow. But if I were you, I'd look over the particulars of your setup very carefully before I assumed anything.
I have one of the tube/tube Radial Headbone amp head switchers. I typically stick a lower-power head (or a lower-power combo) that will give me a bit of juice for guitar and slide on top of a clean combo for steel, and share the clean combo's speaker(s). No problems so far. |
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Clete Ritta
From:
San Antonio, Texas
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Posted 31 Mar 2015 12:05 am
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| Garry Pugh wrote: |
| ...the power out (the output to the speaker cabinet)... |
Just for clarification and to avoid confusion, the term power out usually refers to the AC wall outlet. Speaker out to the cabinet (1/4" low resistance cable). |
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Garry Pugh
From:
Nashville Indiana
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Posted 31 Mar 2015 4:04 am
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In summary: It's my understanding a solid state amplifier can be plugged into the A/B box and whether the box is toggled (switched) on or off for that channel makes no difference in terms of potential damage to the amp.
The other amplifier, in my case a tube preamp and tube power amp, has the potential to be damaged if there is not a load (impedance?) from a speaker. Correct???
Again in my case I am turning the standby switch on this amp off and on in relation to the which channel of the A/B box is selected.
_________________
Emmons PP D10 8X5, GFI Ultra D10,both are setup up "Emmons" style. Quilter 202 Tone Block, Nashville 400, Milkman 85, Stewart PA200, BW and JBL speakers, Profex II
cell # 812-603-1612 |
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Clete Ritta
From:
San Antonio, Texas
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Posted 31 Mar 2015 5:10 am
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Initially I wasn't quite sure if you had a power AB switch, but I soon understood your term "Power Out" to mean "Speaker Output". I just never call the speaker out a "power out" since theres no power coming out of the speaker jack. I'll try to explain via this image:
| Garry Pugh wrote: |
| ...The other amplifier, in my case a tube preamp and tube power amp has the potential to be damaged if there is not a load (impedance?) from a speaker. Correct??? Again in my case I am turning the standby switch on this amp off and on in relation to the which channel of the A/B box is selected... |
Yes that is correct, you can damage your tube amp if "on" with no speaker connected. Standby is safe, but not as safe as turning the power off. If you forget to hit standby and smoke starts coming out its too late! I'm no expert either, but you've been doing it for years so it appears you are doing it right.  |
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Marty Broussard
From:
Broussard, Louisiana, USA
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Posted 1 Apr 2015 2:16 pm
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Gary I have a Weber device made for this that has never been used. I scrapped the project before using it. Let me know if ur interested. I'll send you the info and make you a heck of a deal.
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RETIRED
"Technique is really the elimination of the unnecessary..it is a constant effort to avoid any personal impediment or obstacle to achieve the smooth flow of energy and intent" Yehudi Menuhin |
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Garry Pugh
From:
Nashville Indiana
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Posted 2 Apr 2015 2:54 am
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I emailed Tim Marcus about this scenario and this is what he said.
"They are correct. The Half and Half (his Milkman tube preamp, solid state power amp) can have a switch on the output *as long as the switch does not short the output*
That would be bad
The Creamer (his Milkman tube preamp, tube power amp) can not be powered on without a speaker load. I can modify the amp to safely run with no load by adding a resistor to the output. I do this to the head versions of my amps to be safe. It's still not ideal, and placing a switch at the output is always going to be risky, but it will help protect the output transformer from melting down. You do not want to replace that part!"
_________________
Emmons PP D10 8X5, GFI Ultra D10,both are setup up "Emmons" style. Quilter 202 Tone Block, Nashville 400, Milkman 85, Stewart PA200, BW and JBL speakers, Profex II
cell # 812-603-1612 |
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