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Post by jcourtjr on Oct 23, 2005 15:21:16 GMT -7
I understand that the manual states that you can use the airbrake as long as you match the ohm setting on your amp and the speaker load you are plugging into the airbrake, but i dont get the suggestion on vintage amps. I have a 50 jmp marshall. The suggestion is to set the ohms selector on the amp to 8ohms while using a 16 ohm cab (100W marshall) what should I do in my case with a 50 watter? I dont get it?
How about the '64 bassman that is fixed at 4 ohms. I will be using a 4 ohm cab with that?
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Post by charlienc on Oct 23, 2005 15:53:53 GMT -7
uh... i'm going to take a stab in the dark here, but i think you're making things too complicated. basically, you need to make sure that your ohm rating coming out the amp is the correct ohm rating for the speaker cab.
you know, like my z-best cab is 8 ohms so i use the 8 ohm speaker out on my Maz Jr. so the Airbrake would go right in between the two, as if it's not really there.
basically just hook your amp and speaker cab up the exact way you would without the airbrake. make sense?
i'm not exactly sure of the dangers of not-matching up the correct ohm rating for a head and a cab and i've never wanted to find out. i figure those numbers are there for a reason.
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Post by jcourtjr on Oct 23, 2005 16:10:31 GMT -7
uh... i'm going to take a stab in the dark here, but i think you're making things too complicated. basically, you need to make sure that your ohm rating coming out the amp is the correct ohm rating for the speaker cab. you know, like my z-best cab is 8 ohms so i use the 8 ohm speaker out on my Maz Jr. so the Airbrake would go right in between the two, as if it's not really there. basically just hook your amp and speaker cab up the exact way you would without the airbrake. make sense? i'm not exactly sure of the dangers of not-matching up the correct ohm rating for a head and a cab and i've never wanted to find out. i figure those numbers are there for a reason. yeah but the instruction manual states that is true until you start using "Vintage amps" its in the helpful hints section. I just dont want to screw up my amps.
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Post by Deleted on Dec 11, 2005 15:55:06 GMT -7
I forget where I heard this but I was told to plug my 16ohm Private Jack into the Air Brake into the 8ohm output on the amp.
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Post by Paul (TRANE) on Dec 16, 2005 9:13:59 GMT -7
What the Dr is talking about is an old trick to take the stress off of the output transformer on older amps. If you run old amps flat out at full power on their highest ohm level you can wear out the transformer quicker. On older amps if you do what the manual says you will be taking some of the load off of the output transformer. Now, it is best to run with matching ohms 16 Ohm head to 16 ohm cab. However, you can run an 8 ohm head into a 16 ohm cab. This will cut your output power by about 1/2 though. DO NOT EVER REVERSE THIS THOUGH. If you run a 16 OHM head into an 8 ohm cab you will burn up your head. In this state the head tries to produce about twice the power it has and will burn up something....transformer, tubes, etc. Hope that clears things up.
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Post by billyguitar on Dec 16, 2005 12:39:11 GMT -7
I believe you are confusing impedance mismatching of a tube amp with a solid state amp. You won't lose much with a tube amp. The output transformer is what makes the difference, solid state amps don't have one. A 100% impedance mismatch just makes a tube amp inefficient and not sound it's best. An overbuilt amp like an old Fender or Dr Z won't be harmed but something like a Marshall or Vox needs the correct load. I also don't think output tranformers wear out unless they get overheated or rusty. A speaker with a higher impedance is the safer mismatch. I wouldn't make a habit of using speakers that are lower impedance than the taps on the OT allow, just to be safe. A match always gives the best tone and makes the amp most efficient. I hope I'm right about all of this! We need Myles or the Dr to confirm or deny.
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Post by Paul (TRANE) on Dec 20, 2005 11:10:55 GMT -7
Per the DRs instruction manual with the AIRBRAKE
"Helpful Hints: When using the Airbrake with older vintage amps, mismatching the load will be a safer way to operate. This will eliminate any overheating of the output transformer. Example: a vintage Vox AC-30, switch to the 8 Ohm output impedance, and then instert the speakers to the airbrake. THis will eliminate any stress on the old output transformer and allow full output distortion at an attenuated level."
This is from the back page of the instruction manual.
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Post by Lefty on Jan 7, 2006 8:40:37 GMT -7
Maybe this will help... Ohm's Law Ohm's Law defines the relationships between (P) power, (E) voltage, (I) current, and (R) resistance. One ohm is the resistance value through which one volt will maintain a current of one ampere. ( I ) Current is what flows on a wire or conductor like water flowing down a river. Current flows from points of high voltage to points of low voltage on the surface of a conductor. Current is measured in (A) amperes or amps. ( E ) Voltage is the difference in electrical potential between two points in a circuit. It's the push or pressure behind current flow through a circuit, and is measured in (V) volts. ( R ) Resistance determines how much current will flow through a component. Resistors are used to control voltage and current levels. A very high resistance allows a small amount of current to flow. A very low resistance allows a large amount of current to flow. Resistance is measured in ohms. ( P ) Power is the amount of current times the voltage level at a given point measured in wattage or watts.
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Post by sparrowhawk (Bob) on Jan 9, 2006 15:56:44 GMT -7
trane - I just got my Brake and read that tip. It is indeed confusing. Fortunately for me I'm not using it wht a vintage amp. Being an engineer by training, I think I could give you an answer. But maybe best to ask the Doc what to do. Let him know the amp, the impedance of your speaker(s), and ask him what output from the amp should be used with the Brake.
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