R
rollthebones
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Was für'n Amp?
Matzel
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n problem wirds eigentlich erst dann, wenn der verbraucher (box) weniger widerstand hat als benötigt. daher ist höhere impedanz nicht schädlich, nur geringere. wäre fast wie amp ohne box spielen
Kiview
Registrierter Benutzer
Ist kein Problem, nur ein wenig leiser.
Hast schon recht, höhere Impedanz ist nicht schlimm, nur die Mindestimpedanz muss eingehalten werden.
Hast schon recht, höhere Impedanz ist nicht schlimm, nur die Mindestimpedanz muss eingehalten werden.
R
rollthebones
Registrierter Benutzer
Leute, er spielt einen Vollröhrenamp. Was quatscht ihr da von Mindestimpedanz. Die Sache ist die, ein mismatch von einer Stufe sollte eigentlich kein Problem sein (egal, ob nach oben oder unten). Allerdings verliert der Amp an Leistung und an Bandbreite. Mismatching ist grundsätzlich nicht gut für die Röhren. (Und manch älterer Amp ist dabei auch schon abgeraucht!)
D
das_Jan
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Also ich würde's nicht machen, weils einfach nich gut für den Amp ist.
Bei nem Transistor wäre's kein Problem, aber bei Röhren sehr wohl.
Bei nem Transistor wäre's kein Problem, aber bei Röhren sehr wohl.
Breed of Killing
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Begründung?
M
Max Power
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hm wollt auch nen thread mit der selben frage machen, da klinke ich mich mal einfach ein, bzw. frag dann nur noch mal kurz nach....
Macht es sinn ne 16 ohm box ( Fender Tonemaster box) an meinem peavey bandit transencombo anzuschließen ? der bringt ja beim dem externen boxenanschluss 100 watt statt 80....
brauche mehr power aber ein entsprechendes top kann ich mir erst nächtes jahr leisten....
Macht es sinn ne 16 ohm box ( Fender Tonemaster box) an meinem peavey bandit transencombo anzuschließen ? der bringt ja beim dem externen boxenanschluss 100 watt statt 80....
brauche mehr power aber ein entsprechendes top kann ich mir erst nächtes jahr leisten....
Kiview
Registrierter Benutzer
Gerade bei einem Vollröhrenamp hat man eine Mindestimpedanz.
Wenn die Röhren nicht mit einer gewißen Last gefahren werden knallen die durch.
Eine höhere Last hat doch keinerlei Auswirkungen auf die Röhren, sie schluckt einfach nur die Leistung.
skepti
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Gerade bei einem Vollröhrenamp hat man eine Mindestimpedanz.
Wenn die Röhren nicht mit einer gewißen Last gefahren werden knallen die durch.
hi
also wenn, dann geht der aü in den himmel. aber das die röhren durchknallen
laße mich aber gerne eines besseren belehren.
gruß
skepti
R
rollthebones
Registrierter Benutzer
Zitat (AGA Faq):
"Now the primary presents a very low load to the tube, a low impedance, a vertical load-line. (...) The pentode is like a current source, so it will continue to pass the total plate current in accordance with the screen voltage and the control grid voltage. These have not changed with the alteration of the load, so the pentode will continue to merrily pump its current swings into a dead shorted load.
Take a look at some plate curves, if you need to. Find some for pentodes and for triodes. Better yet, find some for the same power pentode connected as a triode (g2 connected to anode).
First the pentode case: look at the way the curves lie on the page. Imagine a horizontal load line (infinite load, open secondary) drawn on the graph. Notice how the pentode doesn't look like it would work this way-- an infinitesimal control grid voltage change would produce a gargantuan change in plate voltage. The tube is NOT happy. Now imagine a vertical load line (zero load, shorted secondary). The pentode's peak current for a given control grid voltage doesn't change much at all-- the vg1=0 plate curve is nearly horizontal for most power pentodes, cutting right across all of the various plate voltage points. It doesn't matter what Vp is at all-- no matter where you draw that vertical line, the peak plate current is pretty much the same. The tube is happy.
(...) What the heck does all this mean? Well, hopefully you aren't running ANY tube amp into a shorted or open load... (...) As LV pointed out, you're much better off running a pentode amp into a lower load impedance than it expects. (...)For what it's worth, I've been deliberately "mismatching" load impedances by one tap for years. In other words, either a 4R or a 16R load on an 8R tap, and so on. This small mismatch will limit output power and will change the clipping points of the output tubes, but will not damage anything in a properly designed amplifier. Keep in mind that a higher load impedance in a pentode amp will put additional stress on the screens, so you may want to have at least 1k stoppers installed. A lower load impedance will cause more plate current to flow, and if you're running the tubes at the edge of acceptable quiescent plate dissipation that may push them over the edge into the red zone. If you've got an old vintage amp you'd hate to see get damaged, by all means, play it safe and don't mismatch at all. But if you're wondering about how it sounds, and the amp's got good trannies in it, then mismatch away. Just keep it within ONE TAP please, for safety's sake"
Na klar und der OT freut sich.
Hier ein kleines Zitat von Mike Soldano (der Name sagt Dir hoffentlich was):
"I wanted to know the facts on this (mismatching) so I asked Mike Soldano when I picked up my amp. After explaining it to me in detail (as he does with all my tube amp newbie questions) I asked if this was an accurate way to put it (in simple non-tech terms).... If the amp is designed for 8 ohm load and you are running it with an 8 ohm speaker load the speakers are using 100% of the power that the primary winding of the transformer is refilling to the secondary winding of the transformer. Now if you run a higher speaker load like 16 ohms or more (or no speaker load), since the resistance is higher than the transformer expects to see the power leaving the transformer can't get out as fast because its path is restricted by the higher resistance/impedance. So now only 60% (for example- I'm just making up this number) of the power has been able to leave the secondary wiring of the transformer and there is 40% left in there. The primary winding of the transformer now refills the 100% it always refills to the secondary that still has 40% in it. Obviously the transformer was not designed to cope with 140% of it's design load. Over and over this repeats with power remaining in the secondary- and it keeps stacking hihgher and higher until it gets so overloaded and hot that the insulation melts and you get arcing and all that fun stuff"
Guitar Rocker
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Vorsicht mit solchen Tips, wenn man keine richtige Ahnung hat (behaupte ich jetzt mal...)!
Ich will nicht sagen, dass ich Experte bin, ABER: Bei Transistoramps mag das stimmen, was du sagst. Wenn er das mitm Vollröhrenamp macht (ohne Box/Last spielen), dann geht der früher oder später in den A**** (AÜ überhitzt).
Wenn man ein bisschen hier im Board sucht, findet man dazu haufenweise Threads... Generell wird für Amateure bei Röhrenamps von jeglichem Mismatching abgeraten...
Also: Lieber richtig schlau machen, es geht schließlich um "Leben und Tod" der Amps der anderen!
Breed of Killing
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.. Matzel hat das genau so gesagt wie du und du wirfst ihm dann vor keine Ahnung zu haben ?!?
scottph
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Sorry, aber das ist einfach nicht die Realität.
Viele Hersteller beschreiben sogar das "safe mismatch" in ihren Bedienungsanleitungen.
http://www.geofex.com/tubeampfaq/taffram.htm
Q:Will it hurt my amp/output transformer/tubes to use a mismatched speaker load?
Simple A: Within reason, no.
Say for example you have two eight ohm speakers, and you want to hook them up to an amp with 4, 8, and 16 ohm taps. How do you hook them up?
For most power out, put them in series and tie them to the 16 ohm tap, or parallel them and tie the pair to the 4 ohm load.
For tone? Try it several different ways and see which you like best. "Tone" is not a single valued quantity, either, and in fact depends hugely on the person listening. That variation in impedance versus frequency and the variation in output power versus impedance and the variation in impedance with loading conspire to make the audio response curves a broad hump with ragged, humped ends, and those humps and dips are what makes for the "tone" you hear and interpret. Will you hurt the transformer if you parallel them to four ohms and hook them to the 8 ohm tap? Almost certainly not. If you parallel them and hook them to the 16 ohm tap? Extremely unlikely. In fact, you probably won't hurt the transformer if you short the outputs. If you series them and hook them to the 8 ohm or 4 ohm tap? Unlikely - however... the thing you CAN do to hurt a tube output transformer is to put too high an ohmage load on it. If you open the outputs, the energy that gets stored in the magnetic core has nowhere to go if there is a sudden discontinuity in the drive, and acts like a discharging inductor. This can generate voltage spikes that can punch through the insulation inside the transformer and short the windings. I would not go above double the rated load on any tap. And NEVER open circuit the output of a tube amp - it can fry the transformer in a couple of ways.
Extended A: It's almost never low impedance that kills an OT, it's too high an impedance.
The power tubes simply refuse to put out all that much more current with a lower-impedance load, so death by overheating with a too-low load is all but impossible - not totally out of the question but extremely unlikely. The power tubes simply get into a loading range where their output power goes down from the mismatched load. At 2:1 lower-than-matched load is not unreasonable at all.
If you do too high a load, the power tubes still limit what they put out, but a second order effect becomes important.
There is magnetic leakage from primary to secondary and between both half-primaries to each other. When the current in the primary is driven to be discontinuous, you get inductive kickback from the leakage inductances in the form of a voltage spike.
This voltage spike can punch through insulation or flash over sockets, and the spike is sitting on top of B+, so it's got a head start for a flashover to ground. If the punchthrough was one time, it wouldn't be a problem, but the burning residues inside the transformer make punchthrough easier at the same point on the next cycle, and eventually erode the insulation to make a conductive path between layers. The sound goes south, and with an intermittent short you can get a permanent short, or the wire can burn though to give you an open there, and now you have a dead transformer.
So how much loading is too high? For a well designed (equals interleaved, tightly coupled, low leakage inductances, like a fine, high quality hifi) OT, you can easily withstand a 2:1 mismatch high.
For a poorly designed (high leakage, poor coupling, not well insulated or potted) transformer, 2:1 may well be marginal. Worse, if you have an intermittent contact in the path to the speaker, you will introduce transients that are sharper and hence cause higher voltages. In that light, the speaker impedance selector switch could kill OT's if two ways - if it's a break befor make, the transients cause punch through; if it's a make before break, the OT is intermittently shorted and the higher currents cause burns on the switch that eventually make it into a break before make. Turning the speaker impedance selector with an amp running is something I would not chance, not once.
For why Marshalls are extra sensitive, could be the transformer design, could be that selector switch. I personally would not worry too much about a 2:1 mismatch too low, but I might not do a mismatch high on Marshalls with the observed data that they are not all that sturdy under that load. In that light, pulling two tubes and leaving the impedance switch alone might not be too bad, as the remaining tubes are running into a too-low rather than too-high load.
http://www.theguitarfiles.com/guitarfile184.html
5. Make sure that the speakers are plugged in at the proper impedance--or at the very least, a mismatch in the "safe" direction. The best scenario is to match the impedance of the speaker or cabinet with the amp--if your speaker cabinet is 8 ohms, your amp should be set for 8 ohms for best results. If you plug this same 8-ohm cabinet into the 4-ohm setting on your amp, that will also be safe, but you will generally lose about half of your power as a result of the mismatch. If you take this same 8-ohm cabinet and opt for the 16-ohm setting on your amp, you're going to likely blow the head up as it tries to produce twice as much power. again, this can result in a blown transformer and the same neutered tone if you have to replace it.
http://209.85.129.104/search?q=cach...fe+mismatch+amps&hl=en&ct=clnk&cd=11&ie=UTF-8
Kurz und gut: 4 (8) Ohm am Amp und 4 oder 8 (8 oder 16) Ohm am Cab sind ok.
Viele Hersteller beschreiben sogar das "safe mismatch" in ihren Bedienungsanleitungen.
http://www.geofex.com/tubeampfaq/taffram.htm
Q:Will it hurt my amp/output transformer/tubes to use a mismatched speaker load?
Simple A: Within reason, no.
Say for example you have two eight ohm speakers, and you want to hook them up to an amp with 4, 8, and 16 ohm taps. How do you hook them up?
For most power out, put them in series and tie them to the 16 ohm tap, or parallel them and tie the pair to the 4 ohm load.
For tone? Try it several different ways and see which you like best. "Tone" is not a single valued quantity, either, and in fact depends hugely on the person listening. That variation in impedance versus frequency and the variation in output power versus impedance and the variation in impedance with loading conspire to make the audio response curves a broad hump with ragged, humped ends, and those humps and dips are what makes for the "tone" you hear and interpret. Will you hurt the transformer if you parallel them to four ohms and hook them to the 8 ohm tap? Almost certainly not. If you parallel them and hook them to the 16 ohm tap? Extremely unlikely. In fact, you probably won't hurt the transformer if you short the outputs. If you series them and hook them to the 8 ohm or 4 ohm tap? Unlikely - however... the thing you CAN do to hurt a tube output transformer is to put too high an ohmage load on it. If you open the outputs, the energy that gets stored in the magnetic core has nowhere to go if there is a sudden discontinuity in the drive, and acts like a discharging inductor. This can generate voltage spikes that can punch through the insulation inside the transformer and short the windings. I would not go above double the rated load on any tap. And NEVER open circuit the output of a tube amp - it can fry the transformer in a couple of ways.
Extended A: It's almost never low impedance that kills an OT, it's too high an impedance.
The power tubes simply refuse to put out all that much more current with a lower-impedance load, so death by overheating with a too-low load is all but impossible - not totally out of the question but extremely unlikely. The power tubes simply get into a loading range where their output power goes down from the mismatched load. At 2:1 lower-than-matched load is not unreasonable at all.
If you do too high a load, the power tubes still limit what they put out, but a second order effect becomes important.
There is magnetic leakage from primary to secondary and between both half-primaries to each other. When the current in the primary is driven to be discontinuous, you get inductive kickback from the leakage inductances in the form of a voltage spike.
This voltage spike can punch through insulation or flash over sockets, and the spike is sitting on top of B+, so it's got a head start for a flashover to ground. If the punchthrough was one time, it wouldn't be a problem, but the burning residues inside the transformer make punchthrough easier at the same point on the next cycle, and eventually erode the insulation to make a conductive path between layers. The sound goes south, and with an intermittent short you can get a permanent short, or the wire can burn though to give you an open there, and now you have a dead transformer.
So how much loading is too high? For a well designed (equals interleaved, tightly coupled, low leakage inductances, like a fine, high quality hifi) OT, you can easily withstand a 2:1 mismatch high.
For a poorly designed (high leakage, poor coupling, not well insulated or potted) transformer, 2:1 may well be marginal. Worse, if you have an intermittent contact in the path to the speaker, you will introduce transients that are sharper and hence cause higher voltages. In that light, the speaker impedance selector switch could kill OT's if two ways - if it's a break befor make, the transients cause punch through; if it's a make before break, the OT is intermittently shorted and the higher currents cause burns on the switch that eventually make it into a break before make. Turning the speaker impedance selector with an amp running is something I would not chance, not once.
For why Marshalls are extra sensitive, could be the transformer design, could be that selector switch. I personally would not worry too much about a 2:1 mismatch too low, but I might not do a mismatch high on Marshalls with the observed data that they are not all that sturdy under that load. In that light, pulling two tubes and leaving the impedance switch alone might not be too bad, as the remaining tubes are running into a too-low rather than too-high load.
http://www.theguitarfiles.com/guitarfile184.html
5. Make sure that the speakers are plugged in at the proper impedance--or at the very least, a mismatch in the "safe" direction. The best scenario is to match the impedance of the speaker or cabinet with the amp--if your speaker cabinet is 8 ohms, your amp should be set for 8 ohms for best results. If you plug this same 8-ohm cabinet into the 4-ohm setting on your amp, that will also be safe, but you will generally lose about half of your power as a result of the mismatch. If you take this same 8-ohm cabinet and opt for the 16-ohm setting on your amp, you're going to likely blow the head up as it tries to produce twice as much power. again, this can result in a blown transformer and the same neutered tone if you have to replace it.
http://209.85.129.104/search?q=cach...fe+mismatch+amps&hl=en&ct=clnk&cd=11&ie=UTF-8
Kurz und gut: 4 (8) Ohm am Amp und 4 oder 8 (8 oder 16) Ohm am Cab sind ok.
R
rollthebones
Registrierter Benutzer
Der Tenor ist überall der gleiche: ein Mismatch von einer Stufe ist o.k., aber nur bei "well designed" OTs. Und da geht die Unsicherheit wieder los. Wer hat einen "well designed" OT? Raucht er ab, gibt's von den Protagonisten des Mismatching sicher keine Garantie!
scottph
Registrierter Benutzer
Nochmal: Mesa zB beschreibt das sogar in deren offiziellen Bedienungsanleitungen und daher ist es auch von deren Seite als kein Grund für einen Garantieverfall zu interpretieren.
Ich habe seit Jahren immer wieder mal nur mein Topteil mitgenommen und mit verschiedenen Boxen gespielt die nicht den Widerstand boten den meine Topteil gebraucht hätte und da bin ich mit 8 auf 16 Ohm nie in ein Problem gekommen, weder mit Marshall, Peavey, Mesa, oder Diezel.
Ich habe seit Jahren immer wieder mal nur mein Topteil mitgenommen und mit verschiedenen Boxen gespielt die nicht den Widerstand boten den meine Topteil gebraucht hätte und da bin ich mit 8 auf 16 Ohm nie in ein Problem gekommen, weder mit Marshall, Peavey, Mesa, oder Diezel.
Guitar Rocker
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Dann ließ nochmal. Den Eintrag kann man durchaus so verstehen, als ob man einen Vollröhrenamp ohne Probleme ohne Last laufen lassen kann. Zitat: "daher ist höhere impedanz nicht schädlich, nur geringere. wäre fast wie amp ohne box spielen". Keine Box bedeutet ja auch nicht "niedrige Impedanz", klar, trotzdem: Ohne Box spielen kann ne Zeit lang gut gut gehen. Aber nicht generell bei allen Amps, und nicht dauerhaft.
Ich zitiere mal http://www.elektronikinfo.de/strom/roehrenirrtum.htm:
Um auf das ursprüngliche Anliegen zurückzukommen: 16Ohm Box an 8Ohm Ausgang sollte gehen (allerdings garantiere ich nicht dafür; Ich kenne den Amp nicht und will hier keine pauschalen Aussagen treffen)
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