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Post by jacobamerritt on May 9, 2019 9:32:11 GMT -6
I am about to get a mic pre with variable impedance- is it safe to toggle through the different impedances while a ribbon microphone is connected? Or any mic for that matter?
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Post by EmRR on May 9, 2019 12:07:43 GMT -6
sure
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Post by svart on May 9, 2019 12:16:48 GMT -6
I'd think it's no different than (un)plugging a mic.
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Post by Blackdawg on May 9, 2019 12:34:30 GMT -6
Yes, in fact on dynamic and ribbon mics I'd strongly suggest it. It can make a big difference in the sound with how the diaphragm is "loaded". Can totally change the transient response.
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Post by jacobamerritt on May 9, 2019 14:32:26 GMT -6
Yes, in fact on dynamic and ribbon mics I'd strongly suggest it. It can make a big difference in the sound with how the diaphragm is "loaded". Can totally change the transient response. Im aware of the benefits of changing impedance, just wasn't sure if toggling through impedance would be potentially problematic, like turning on phantom with a ribbon plugged in... |
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Post by Blackdawg on May 9, 2019 15:15:01 GMT -6
Yes, in fact on dynamic and ribbon mics I'd strongly suggest it. It can make a big difference in the sound with how the diaphragm is "loaded". Can totally change the transient response. Im aware of the benefits of changing impedance, just wasn't sure if toggling through impedance would be potentially problematic, like turning on phantom with a ribbon plugged in... Im not aware of it being a problem. Change away! |
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Post by shoe on May 19, 2019 16:28:18 GMT -6
Nah. The only problem would be turning on phantom power if the mic is not protected against it.
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Post by Ward on May 20, 2019 5:48:21 GMT -6
Yes, in fact on dynamic and ribbon mics I'd strongly suggest it. It can make a big difference in the sound with how the diaphragm is "loaded". Can totally change the transient response. The general consensus is, the higher you can get it - the better. markfouxman is our resident expert |
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Post by Blackdawg on May 20, 2019 9:11:10 GMT -6
Yes, in fact on dynamic and ribbon mics I'd strongly suggest it. It can make a big difference in the sound with how the diaphragm is "loaded". Can totally change the transient response. The general consensus is, the higher you can get it - the better. markfouxman is our resident expert For passive ribbons definitely. Dynamic mics it depends on the mic. |
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Post by EmRR on May 20, 2019 10:27:59 GMT -6
Yes, in fact on dynamic and ribbon mics I'd strongly suggest it. It can make a big difference in the sound with how the diaphragm is "loaded". Can totally change the transient response. The general consensus is, the higher you can get it - the better. markfouxman is our resident expert The devil is in the details, and any transformer coupled pre is on a case by case basis which cannot be evaluated strictly by the numbers on the tin, because impedance varies with frequency, and the ribbon transformer mated to the preamp transformer makes a unique case of inductive coupling. |
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Post by Ward on May 20, 2019 14:08:58 GMT -6
Thanks
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Post by shoe on May 22, 2019 6:38:58 GMT -6
The general consensus is, the higher you can get it - the better. markfouxman is our resident expert The devil is in the details, and any transformer coupled pre is on a case by case basis which cannot be evaluated strictly by the numbers on the tin, because impedance varies with frequency, and the ribbon transformer mated to the preamp transformer makes a unique case of inductive coupling. Yeah, like, strangely, even though my REDD.47s have only 200 ohm input impedance, they still sound great with ribbon mics and dynamic mics. I think, probably, the rest of the pre is designed in such a way that it works well with that low input impedance. Originally they were expecting them to be matched exactly 200 ohm to 200 ohm in/out everywhere. |
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Post by EmRR on May 22, 2019 6:45:02 GMT -6
The devil is in the details, and any transformer coupled pre is on a case by case basis which cannot be evaluated strictly by the numbers on the tin, because impedance varies with frequency, and the ribbon transformer mated to the preamp transformer makes a unique case of inductive coupling. Yeah, like, strangely, even though my REDD.47s have only 200 ohm input impedance, they still sound great with ribbon mics and dynamic mics. I think, probably, the rest of the pre is designed in such a way that it works well with that low input impedance. Originally they were expecting them to be matched exactly 200 ohm to 200 ohm in/out everywhere. There's that pesky tin: 200Ω is the expected source impedance, NOT the preamp input impedance. It's a bridging input Z as expected, with 200Ω being actual in the -3 to -6 dB range of the rolloff at top and bottom of the response curve. It may be 20KΩ at 1kHz. |
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ericn
Temp
Balance Engineer
Posts: 14,934 
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Post by ericn on May 22, 2019 7:10:20 GMT -6
The general consensus is, the higher you can get it - the better. markfouxman is our resident expert The devil is in the details, and any transformer coupled pre is on a case by case basis which cannot be evaluated strictly by the numbers on the tin, because impedance varies with frequency, and the ribbon transformer mated to the preamp transformer makes a unique case of inductive coupling. The first sentence of this should be a general audio sticky before any gear discussion ! |
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Post by markfouxman on May 22, 2019 11:31:42 GMT -6
Yes, in fact on dynamic and ribbon mics I'd strongly suggest it. It can make a big difference in the sound with how the diaphragm is "loaded". Can totally change the transient response. The general consensus is, the higher you can get it - the better. markfouxman is our resident expert As Doug (EmRR) has said, the devil is in details. That is, the passive ribbon is a two way system, so it not only passes the signal to the preamp, but also preamp input impedance goes back and loads it, restricting ribbon's movement. Needless to notice, while ribbon impedance is pure resistive (except at tuning frequency), we are also going through a transformer, which impedance changes with frequency. Because of that the loading is also frequency dependent. On the other hand, the ribbon has resonances, which need to be damped. Usually, it is done by means of acoustic screens, which additionally protect the ribbon from air blasts, making much safer operation. The trick is, there is no difference between aforementioned electrical loading and mechanical one (screen), so careful balance between those two will ensure linear and resonance free response. For example, because of construction old RCA77s ribbons were way overdamped, so they insisted to measure response with unloaded input preamp. Our ribbons were designed to work with 'normal' 1.5kΩ-3kΩ input impedance of modern preamps--that's where we specify their response. Of course, they will work fine with higher impedances and depending on application, source, or taste some might find it preferable. As always, use your ears and they will tell you everything))) Best, M |
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Post by shoe on May 22, 2019 20:05:24 GMT -6
Yeah, like, strangely, even though my REDD.47s have only 200 ohm input impedance, they still sound great with ribbon mics and dynamic mics. I think, probably, the rest of the pre is designed in such a way that it works well with that low input impedance. Originally they were expecting them to be matched exactly 200 ohm to 200 ohm in/out everywhere. There's that pesky tin: 200Ω is the expected source impedance, NOT the preamp input impedance. It's a bridging input Z as expected, with 200Ω being actual in the -3 to -6 dB range of the rolloff at top and bottom of the response curve. It may be 20KΩ at 1kHz. That's strange...I thought the idea was the EMI equipment all had 200 ohm input and output impedance for exact matching. |
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Post by EmRR on May 22, 2019 20:15:29 GMT -6
There's that pesky tin: 200Ω is the expected source impedance, NOT the preamp input impedance. It's a bridging input Z as expected, with 200Ω being actual in the -3 to -6 dB range of the rolloff at top and bottom of the response curve. It may be 20KΩ at 1kHz. That's strange...I thought the idea was the EMI equipment all had 200 ohm input and output impedance for exact matching. Maybe except for mics. Yeah, it's way more confusing than the tin label. Very few 200Ω outputs are actually 200Ω either, unless there are build out resistors to make it exactly so. It's no small feat to make a tube circuit have an exact output impedance AND have it do what you want it to do; if it's a no/low feedback circuit the 200Ω designation comes from the assumption that you will load it with such, NOT that it is, and the transformer inductance is specified so it performs best with that loading. If it's a high feedback circuit it's easily 75-100Ω, and it takes series resistance to make it be 200Ω. Usually neither is exact, and many times vary far from it, but the two mating transformers are expecting an inductive load that suits 200Ω, so they at least don't misbehave with one another. |
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