Gswitz Posted March 9, 2019 Share Posted March 9, 2019 (edited) I have some preamp choices and they all have different specs etc. One of my preamps is an Audient ASP 880 which I've messed with quite a bit by now. In general, it seems like using the highest impedance most of the time makes sense. If you want to gently roll off bass, maybe use 220 or so with dynamics (?), but they work just fine with 2800 Ohms (high). Mid is 1200 ohms. This manual describes and shows some frequency charts for a sm57 at different impedances...https://d9w4fhj63j193.cloudfront.net/ASP880/1.+Manuals/ASP880+Manual+(En).pdf I can definitely see that using higher impedance gives you more level as relates to noise when using ribbons. I've always used high impedance with my ribbons. AEA says use high on this link...https://www.aearibbonmics.com/how-impedance-affects-ribbon-microphones/ But in this video today, the guy says use low impedance with your ribbons and that's why there's a low-z button a Neve pre. This Neve Pre talks about 9K Ohms impedance when 48 phantom is not engaged. So what is it when phantom is on? Why doesn't it matter? I can't even find it on the web what it is with phantom engaged. Is it just the same (9k) but doesn't matter?https://www.sweetwater.com/store/detail/5211--rupert-neve-designs-5211-2-channel-microphone-preamp I also read this one...https://www.gearslutz.com/board/so-much-gear-so-little-time/121838-impedance-setting-neve-1073dpa.html which talks about a Neve pre with switchable impedance between 300 and 1200https://vintageking.com/neve-1073-dpa Anyway, I find preamp choosing and setting a little puzzling. I recognize that the lower impedance settings are maybe a touch more feedback resistant and have a bit of bass roll-off. My RME UCX has 470K ohm on the instrument input. 2k ohm on the mic pres. 8k ohm on the TRS.http://www.rme-audio.de/en/products/fireface_ucx.php The instrument input on the Audient ASP880 is 1000k ohms. "Therefore we need at least a 400kΩ load to get the most signal and tone from our instruments. It should then come as no surprise that most classic valve guitar amplifiers have a very high input impedance - 1MegΩ!" My RME Quad Mic Pre has 2 kOhm and TRS 4 kOhm. Seems like 2 kOhm is kinda normal for a mic pre that may or may not have phantom. ................................... Right now, I'm feeling like using high impedance for just about everything except drum dynamic mics, feedback type situations for vocal dynamics especially with female vocalists where bass frequencies are less important, or dynamics being paired with another mic that will carry the bass. Could some of you nice folks set me straight? Edited March 9, 2019 by Gswitz Link to comment Share on other sites More sharing options...
craigb Posted March 9, 2019 Share Posted March 9, 2019 I'm sensing you have some resistance here... ? Cue the amp builders!!! 2 Link to comment Share on other sites More sharing options...
Gswitz Posted March 9, 2019 Author Share Posted March 9, 2019 I know someone will say 'listen'. I can assure you I do listen. But I often set up a bunch of mics and roll tape and hope for the best. I don't listen to every mic. I have to go on gut and practice for placement and impedance and etc etc. Link to comment Share on other sites More sharing options...
Gswitz Posted March 9, 2019 Author Share Posted March 9, 2019 https://www.soundonsound.com/reviews/neve-4081 This one also talks about low-impedance mode intended for ribbon mics. Link to comment Share on other sites More sharing options...
Gswitz Posted March 9, 2019 Author Share Posted March 9, 2019 (edited) Another AEA link https://www.aearibbonmics.com/how-impedance-affects-ribbon-microphones/ "Passive ribbon mics are dependent on the impedance of the preamp. Since 2005, AEA has been producing preamps that have extremely high input impedance that ranges from 10k ohms up to 63k ohms. This is optimal for passive ribbon mics." "The basic rule is: the higher the preamp’s input impedance, the better it is suited to reproduce the full range of a ribbon microphone." Edited March 9, 2019 by Gswitz Link to comment Share on other sites More sharing options...
Gswitz Posted March 9, 2019 Author Share Posted March 9, 2019 I'm starting to think that the volume of the source for a ribbon might make a big difference. A screaming guitar might go just fine with a lower impedance setting where a soft acoustic or singer might need the crazy high impedance. Yes? Link to comment Share on other sites More sharing options...
Gswitz Posted March 9, 2019 Author Share Posted March 9, 2019 And then this link... https://www.soundonsound.com/techniques/understanding-impedance Makes me think I've learned all this before and forgotten it. Link to comment Share on other sites More sharing options...
Gswitz Posted March 9, 2019 Author Share Posted March 9, 2019 (edited) 9 hours ago, Gswitz said: I'm starting to think that the volume of the source for a ribbon might make a big difference. A screaming guitar might go just fine with a lower impedance setting where a soft acoustic or singer might need the crazy high impedance. Yes? Maybe. I found an aea link that says the impedance varies by frequency. This means for passive ribbon mics when you don't use a pre with extremely high impedance you are choosing to distort the bass and high end. The lower the impedance the more the distortion. I feel sure lots of great recordings have been made with passive ribbons plugged into pres with insufficiently high impedance so it's a sound you can mimic for that reason. Insufficiently high impedance will distort and reduce high end and low end. Because you impact how these transients are captured by the ribbon, you can't just add them back with eq later to get the same sound with more noise. It will sound different as well as be diminished in volume. All of this makes me think active ribbons might make sense for many ribbon users. I also add that I've now been enjoying passive ribbons for yikes ten years? using pres as low as 2 kohms and loving the sound. I do not own an active ribbon for comparison. I suppose the freedom to use a passive ribbon with a preamp with lower impedance might be the nice thing you get for using passive ribbons. In other words, the freedom to intentionally distort and diminish some frequencies could be seen as a good thing even if aea never says so. Edited March 9, 2019 by Gswitz Link to comment Share on other sites More sharing options...
craigb Posted March 9, 2019 Share Posted March 9, 2019 I'm also sensing a feedback loop now! Will SOMEONE please help Gswitz out here??? ? 1 1 Link to comment Share on other sites More sharing options...
synkrotron Posted March 9, 2019 Share Posted March 9, 2019 I wish I could. I've got microphones but I rarely use them and certainly don't know enough to bring anything to the party here. I'll get me coat 1 Link to comment Share on other sites More sharing options...
Gswitz Posted March 9, 2019 Author Share Posted March 9, 2019 (edited) Thanks folks. I think I'm going to try to answer the question with my gear, at least for guitar at a healthy volume. I'm going to go ahead and record something, position some mics and switch the pre-amps and impedances until I have at least one nice sample with my gear. I'll make a video when I'm done showing the mics on the different pres so you can see too. Edited March 9, 2019 by Gswitz Link to comment Share on other sites More sharing options...
JohnG Posted March 10, 2019 Share Posted March 10, 2019 The simple key to understanding this is that low impedance to low impedance there is a significant current flow, this can lead to distortion. (N.B. simple) Low to hi means that it's predominantly a voltage flow. Pre-amps are primarily built to allow sufficient headroom over the normal voltage generated. It doesn't matter how loud the sound is it's about the underlying electronics design. Ribbons are low impedance like pickup coils so it's not unusual to have a guitar pre-amp impedance up at 1 MegOhm. Any help? 1 Link to comment Share on other sites More sharing options...
Gswitz Posted March 10, 2019 Author Share Posted March 10, 2019 I don't know what N.B. simple means. I think this chart showing impedance differences by frequency means it isn't possible to correctly match a low impedance preamp to this mic. I guess the fact that the Rupert neve 5211 doesn't have a low impedance switch might mean it isn't necessary. It helps that you say volume doesn't compensate for an impedance mismatch. JohnG, in what cases do you use a low impedance setting in a preamp? Link to comment Share on other sites More sharing options...
JohnG Posted March 10, 2019 Share Posted March 10, 2019 (edited) Hmmm! Crikey, I'm digging back a long way and I'm not really a studio techy, more some PA stuff a while back (and aircraft electronics which was my initial work background). I remember building a low impedance pre-amp for a moving coil cartridge, but that was back in the 70s. The cartridge was about 10 Ohms and ultra low output, just a few micro volts as I recall. So that should give me a clue. No ... I'll look it up in my reference docs, if I can find them, and get back to you. (Being of a certain age, you might have to remind me!!!) You don't want to know about motor driven ailerons on the Concorde by any chance do you? The current required to overcome air pressure at supersonic speeds. No, I thought not. Obsolete, redundant. Time for a cuppa. Toodle-pip. JohnG. P.S. All electrical transducers show a varying impedance with reference to frequency. Take a look at the impedance curve of any non-amplified loudspeaker. Impedance can dive below 2 Ohms and go way above 40 Ohms for a 'nominal' 8 Ohm impedance. I would say that, what, 300 Ohms to 2 k Ohms is not an unnatural impedance for such a transducer. Edited March 10, 2019 by JohnG Shpeling. Link to comment Share on other sites More sharing options...
JohnG Posted March 11, 2019 Share Posted March 11, 2019 Well, I can't find my reference book. Did I dump it before moving back to the UK or is it packed in a tea chest at the back of the garage? Dunno. Anyway, some thoughts. It's about the amount of current that can be generated by the analogue to electrical transducer. Consider a bass guitar string waggling back and forth above the pickup coil. That mechanism can generate large amounts of current (no, not enough to heat the home), but sufficient, potentially to cause damage to the components in an electronic circuit, especially when amplified. (These components have a current rating measured in fractions of a watt). In this case we want to block current flow, but allow voltage swings, so the coil must see a very high impedance, in the order of hundreds of kilohms to a megohm. In a pickup for record (LP) transduction, a moving coil cartridge will not 'see' these high amplitude movements. They are limited, deliberately, by the RIAA equalisation curve applied to the coil of the cutting stylus, as much to reduce the width of grooves as to reduce current transfer. Bass reduced by degrees, treble amplified by degrees. As there's no danger of high current flow we can more closely match the pre-amp impedance to the transducer. Pre-amp always higher. The same, I believe, is true for a ribbon mic. It's transducing air movement to electrical energy. The movement of the ribbon is not excessive, so little current is generated. In fact, high transitions can result in damage to the ribbon. "Don't blow the mic!" used to be the shouted command from BBC engineers in the past, according to anecdote. So I would expect a ribbon mic pre-amp to be a relatively low impedance. "Relative" in relation to the ribbon mic. But always higher than the transducer. Is that of any help? JohnG. Link to comment Share on other sites More sharing options...
Gswitz Posted March 12, 2019 Author Share Posted March 12, 2019 John, I totally appreciate the lesson. I'm not really sure how much help it is to be honest because the AES link (above) suggests 10k to 63k Ohms for preamp impedance for their ribbons. I've never before had something close to that, but I just picked up a new pre-amp. The Rupert Neve 5211, which has 9k impedance. I'm going to try a recording soon (re-amped) where I shift a ribbon between various preamps recording the identical guitar part. Then I'll switch between them to sample them and see what I think. I just got it racked up today. I'll share a link to a video breaking down the different recordings once I've had a chance to make it. Today, I'm done. I spent hours re-organizing my rack and testing all the inputs and outputs. ? I'm always nervous when I pull the whole thing apart, but happy when it's done. Especially when everything works when I'm done. The compressor can't be between hot things, so I'm just putting it on top. I can screw it in before going out and then put it on top when I get there. ? That's why the 2u hole. Link to comment Share on other sites More sharing options...
Gswitz Posted March 12, 2019 Author Share Posted March 12, 2019 I made a first pass effort of recording the same reamped passage using first the Neve 5211 and then the Audient asp880. I set the Audient to low impedance and frankly had a tough time hearing differences between the two tracks. I didn't move the mics between recordings. It was much easier to get a good level with the neve. I normalized the tracks after recording so they were close in volume. Link to comment Share on other sites More sharing options...
JohnG Posted March 12, 2019 Share Posted March 12, 2019 (edited) My suspicion is, without hard evidence to back it up, that their microphones have different characteristic impedances. Therefore the pre-amps have variabilty in order to most closely match mic to amp. Using different impedance set-ups will, most likely, affect frequency response in subtle ways. Again, from memory of long ago, possibly inaccurate, bass roll-off or high frequency gain may be slightly altered. Possibly even a lift in the 'presence' region. My memory of these things cannot be relied upon though, I moved into a totally different area of expertise, dealing with CCITT Q.921 D channel signalling, both terrestrial and via satellite, sometime in the late '80s, and that's getting 'dim' too! JohnG. Edited March 12, 2019 by JohnG 1 Link to comment Share on other sites More sharing options...
Gswitz Posted March 12, 2019 Author Share Posted March 12, 2019 (edited) http://gswitz.blob.core.windows.net/tunes/20190312_Preamps_A.wav http://gswitz.blob.core.windows.net/tunes/20190312_Preamps_B.wav http://gswitz.blob.core.windows.net/tunes/20190312_Preamps_C.wav http://gswitz.blob.core.windows.net/tunes/20190312_Preamps_D.wav I recorded a ribbon mic and a small diaphragm condenser. I used the identical guitar passage re-amped. I used the identical analog to digital converter. The only difference was the preamps. On both preamps, I used the high-pass filter set around the same place. I didn't move the mics between the two; I only unplugged the mics from one pre and plugged them into the other. Then I normalized the tracks to -3 dB. The ldc was recorded at high impedance on the Audient ASP 880 which is 2800 Ohms. The ribbon on the Audient was recorded at low impedance or 220 Ohms. On the Neve, both had an input impedance of 9600 or so. What do you think? Edited March 13, 2019 by Gswitz Link to comment Share on other sites More sharing options...
JohnG Posted March 12, 2019 Share Posted March 12, 2019 I'm not going to even try to assess your tracks, so sorry. At my age, my hearing is so far beyond it's best that assessment would just be guesswork. I can't hear anything beyond about 6kHz. I have hyperaccusis too. Maybe some others can help. My hearing was damaged a long time ago when testing the generators that attach to jet engines without their silencers. Ouch! I defer to younger people. Link to comment Share on other sites More sharing options...
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