Headphone Impedance Demystified: Do I Need a Headphone Amp ... At some point the impedance becomes too high, but a 2 to 1 mismatch either way will be fine. My favorite tube to use in it is the 5881. Impedance Mismatch - Audiogon Discussion Forum Interpreting tube load resistance - The RadioBoard Forums The smaller the mismatch, the safer it is. Into a purely resistive load, the flyback voltages aren't bad at 2x mismatch, but at 4x mismatch they can get rather high, primarily dependent upon the leakage inductance of the transformer used. An impedance mismatch between an amplifier and the speaker cabinet(s) can cause serious damage to your equipment. This super linear amplification process allows the amplifier to have a flat frequency response from 8hz to 50Khz, which is nearly . So, for example 100 ohm output impedance is a genralized measure across all frequencies. Ohm cooking 101: understanding amps, speakers and impedance Whenever you mismatch a tube amp with a much higher load (speaker) impedance, a higher signal voltage is produced across the primary of the output transformer. the output tube is loafing . When you hook up a second cab to the Ext. The impedance creates 2kΩ for the conducting tube, which is depicted by the red line. Qualified orders over $99 will ship to you without incurring a shipping . Impedance matching between the output impedance and the headphone impedance is critical for power going from the amp to the headphones. Transformer Output 7591 [20ATD9] Debunking Common Tube Amp Myths - Blue Glow How Amps Work - Rob Robinette's Car and Tube Amp Website For tube amps, I see a lot of comments like "try to match the load as much as possible" and the general feeling I get is that mismatching is discouraged, but that if it must be done, the rule is to go for a lower impedance speaker: i.e. The forty ohms in this example is the impedance that a tube would see at the primary with a 2:1 turns ratio output transformer and 10 ohms on the secondary. Tube or Solid state amp for K701 | Headphone Reviews and ... The only time a mismatch is dangerous is when using a tube (valve) amp and setting the OHM Selector higher than the speaker's impedance. The K-701 is a 62 Ohm headphone and also very inefficient. And this again applies only to fixed ohmic impedances. Mercury offers Transformer Restoration Services for rare and vintage transformers that are failing or underperforming. Tube Amps, Magnapans and Impedance - forum.audiogon.com Loudspeaker Impedance | Octave Doctor This means that the output voltage will be 8.7 times bigger, so it will be equal to 8.7 mV. The first amp like this that I built I used a 5K ohm transformer because I had one, The transformer was made for a 45 but it was a mismatch for the other tubes. A mismatch generates more heat in the output transformer, can make the tubes run harder (elevating operating temperature and lowering their lifespan) and places the amp closer to the point of tube and output transformer . Finally, in order to drive normal loudspeakers, I decided that I needed a power rating of at least 20W. So in our example the primary impedance would be 8x400 = 3200 ohms. « Reply #1 on: January 22, 2021, 02:24:38 am ». But as @beans-on-toast said, a 1:2 or 2:1 mismatch is usually not tragic with old Fenders. If the 2-k headphones you mention are classical magnetic headphones, concerns of "fidelity" -- as in "frequency response" -- are pretty much out the window. The bottom line is the greater the low impedance mismatch, the harder your amp works, and the greater the high impedance mismatch, the more likely you are to burn out your output transformer and/or power tubes. This is being driven from a 4x octal tube complement. Maximum power output is Not when the impedance is matched, if that were the case then the maximum efficiency of a amplifier would be limited to 50% as half the power would be dissipated in the amps output Z. A lot of how much/well mismatch is tolerated depends on the primary impedance of the amp in question's OT given the power tube compliment (as well as other factors like plate voltage and the OT's power bandwidth rating), which is why you will hear some manufacturers state mismatch is OK one way or another (higher/lower) - so it can and does . Example, using the amp with no speaker or no shorting jack attached to the output can damage the OT. pabloxyz Senior tube assistant Posts: 156 (8/21/03 6:34 pm) 206.231.12.101 Reply | Edit | Del Re:output impedance----- What is meant is that a tube amplifier with a specified output impedance of say, 8 Ohms, will safely work with a load of between 4 Ohms and 16 Ohms, and for many tube amplifiers this is true. To function properly, their primary winding must match the impedance of the . Re: Question about dissipation vs output and OT impedance mismatch. The opposite is generally true for solid state amps. When the primary tap is changed from 8K to 5K, the turns ratio to the NFB tap changes in addition to the power tube . Massive 5 pound (4 lb 15 oz) push pull tube output transformer came from working 7591 amp seems to have apprx 27. That's on the low side for impedance and most inexpensive OTL tube amps will struggle, due to their high output impedance. Tube amps with no output transformers (like the Bottlehead Crack), for example, . I am considering constructing a multichannel amplifier using thermionic valves for amplification. The reason is called reflected impedance and it's bad news. For tube amps a low mismatch is safer than a high mismatch, that's why most speaker jacks have a shorting switch--a short is better . Using too high an impedance is fine for solid-state (although it does reduce the potential output), but not for tube amps. It has a beautiful breakup when overdriven. Hi there. I have a 100 watt tube head that runs at either 8 or 16 ohms. Tube amps (which are coupled to the speakers via an output transformer) are different than most solid-state amps (which are generally not). A guitar speaker has no fixed impedance over the frequency range. Tube amps with no output transformers (like the Bottlehead Crack), for example, . Some of the silverface amps had two output taps and switching jacks. Impedance mismatch per se usually does not directly affect frequency response; impedance mismatch (thinking of AF power tubes) has a greater effect on power output v distortion. For tube amps a low mismatch is typically safer than a high mismatch. out, the amp would see 2:1 Amp/Cab impedance mismatch. The transformer primary impedance rating is 3,400 ohms with taps for 4,8,16 ohm speaker outputs. Output transformers (OPT's) serve a critical purpose in tube amplifier circuits. To function properly, their primary winding must match the impedance of the . Never connect a 4 ohm output to a 16 ohm speaker cabinet. The speaker impedance is always much larger than the amp output impedance. The transformer provides isolation, facilitates multiple outputs, and allows for voltage adjustment by 10. The obvious choice of output tube was the Russian designed 6C33C triode, because a single pair can deliver 2.5A into an 8Ω load from a moderate 150V rail. I've used a 4 ohm speaker to a switched impedance ss amp (with the switch at 8 ohm) and I blew a fuse. We know that class B amps have a maximum efficiency of 78%, class C and digital even higher. So you would be looking for an impedance of around 5K ohms on the primary side of a single ended transformer. . If we put 100 ohms on the secondary, the tube would see 400 ohms (100 . pabloxyz Senior tube assistant Posts: 156 (8/21/03 6:34 pm) 206.231.12.101 Reply | Edit | Del Re:output impedance----- A tube amp is happiest when the speaker load impedance matches the setting of the impedance switch on the rear of the amp. If you must mismatch, better to have a somewhat lower impedance than too high. The flyback voltage is a factor of the overall AC output voltage and the level of impedance mismatch. But the tubes are still generating power so where does it go? The output transformer is a push-pull, so I can't use it for this amp but its primary is 5700 ohms impedance @ 400Hz and the voice coil is 2.28 ohms impedance (not resistance) which makes it exactly a 50 : 1 WR output transformer. January 21, 2018. by Paul McGowan. They don't want to see a higher impedance than the rating. This varying load impedance is reflected back to the primary, so the tube, and output transformer must work into a varying impedance range. The impedance match/mismatch is rooted in the amp's output impedance facing the speaker's input impedance. To calculate the output voltage after the matching circuit, we need to know the ratio of impedance, in our case, 1500 Ω/75 Ω=20. For example, do not set a tube amp to 8 OHMS when using 4 OHM speakers. Matching always produces the most power & most even frequency response. This tube amp seems like a much more durable design since it takes both 4 and 8 ohm impedances easily. In a princeton-type amp that's able (good OT w/4 and 8 ohm taps, but no impedance switch) to run 6v6 or 6l6 tubes (after a rebias), I understand that the 6v6s output to 8 ohm, and that the 6l6 output to 4 ohm. In the case of a mismatch of 16-ohm loudspeakers with an 8-ohm output impedance, the output power for a tube amplifier decreases only to about 89% and not to 50%, as in the above calculation. The flyback voltage is a factor of the overall AC output voltage and the level of impedance mismatch. When you increase the load to 8 ohms and connect that to OPT's 4 ohm secondary tap, the primary impedance increases to 10k ohms. It increases at higher frequencies. Link Output. It usually causes a dip in output power and usually you'll get some extra distortion because of the mismatch but unless its at full power its likely nothing you'd ever notice. A well designed SS amp can easily handle a speaker load that ranges anywhere from 2 ohms to over 16 ohms. Four is the the turns ratio (2) squared. Julius Futterman's article "An Output Transformerless Power Amplifier" appeared in the October 1954 issue of the Journal of the Audio Engineering . most tube amps aren't that cranky about impedance dips honestly. Nope. I built an amp a while back with an output transformer primary impedance of 6.6K. The speaker impedance is always much larger than the amp output impedance. If we put 5 ohms on the secondary, the tube would only see 20 ohms (5 * 2^2). Chosing A Replacement Output Transformer Now lets assume we have a set that has an output transformer with an open winding that must be replaced, and the output tube is a single 6F6. for a 8 ohm amp, a 4ohm speaker is ok, but a 16 ohm speaker is a bad idea.

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