Are you implying that I should change the mic's output impedance to 150?

I've done some reading on impedance, and I guess I have a mental block (or maybe I'm just not that bright). But I don't understand the concept very well. From the reading I've done, I've gathered that the greater the discrepancy between input impedance of the preamp and output impedance of the mic, the less the load on the mic will be, and more output and bass response will be the result (your post implies this as well). But if this were true, I fail to see the need for a mic (like the 77) to even have the option to select impedance, so I must be missing something.

Feel free to enlighten me on the subject if you like (I'm all ears). But in lieu of opening that can of worms (which may best be left as a subject for another thread) another option would be to simply tell me how you would set the impedance on the mic if it were yours. I'm not afraid to experiment with the different settings, but it would be easier for me to simply take the advice of an engineer and get back to playing music.

Thanks for your input. I've had my eye on the CL-Z cloudlifter (variable impedance), and also the AEA TRP preamp, which appeals to me because of its variable impedance knob, and its high gain/low noise characteristics (although it may lack some of the vintage warmth as some of the pres you've mentioned). Would it be beneficial to use something like this to step up the gain, and then run it into another "character" pre? *Edit: It also occurs to me if I can make a clean recording without superfluous "color", I could send that track through another preamp later. Anybody have any thoughts on this?

Thanks for the clip. I haven't yet had a chance to hear it through real speakers, but you've nailed that vintage sound. You've got a bit of a Lefty Frizzell tonality to your voice.

Dude, if you ever find yourself in northwest Arkansas, you're invited to come over and jam!

I can try at the risk of getting too technical.

Two things happen. The first is that the microphone output impedance and the preamp input impedance form a voltage divider. Let's take a simple example.
Let's take a 600 ohm microphone and plug it into a true 600 ohm (resistive)
pre input. Compared to a high impedance like say 10K...you'd lose half the signal.
Six dB.

If the impedances are resistive and constant the signal loss will happen at all frequencies.

But something else happens with a ribbon. It's called the gyrator effect. I won't explain that term, but basically a low electrical resistance load is transformed into a high mechanical resistance at the ribbon. This mostly affects the bass.

Another way of looking at this: The impedance of a ribbon mic is much higher than nominal at ribbon resonance... in the low bass.

This happens with speakers too. Take an unbaffled woofer unhooked and give the cone a tap...there will be big motion and a deep thump if you put your ear near. Now short the speaker terminals with a bit of wire (still not hooked to an amp) and tap the cone again. NO motion or deep thump. The cone is locked in place.

BTW I recommend installing an XLR connector with pins 2 and 3 shorted
in our ribbon mics during transport. Just like the speaker it locks the ribbon in place.

Why did RCA put selectable impedance in the mic? There wasn't much standardization in pres. Some had input impedances in the 600 ohm range, so you'd want as low an impedance as practical to keep from loosing all the bass.
So you'd choose the 150 ohm setting. Higher pre input impedances allowed you to swith the mic to higher impedance to get more level.

For this reason many ribbon mics were 30 to 50 ohms.

In short you BRIDGE ribbon mics rather than impedance match.

One interesting side note. The early SM57 type mics were actually designed for
600 ohms. So many people wire about a 600 ohm resistor across the mic transformer secondary to get the proper sound with a higher impedance pre.

FWIW our custom ribbon pres have a differential input impedance of 10K ohms.

Les

Thank you, very interesting explanation (I have been reading along with this topic).

I especially find this interesting:

I assume this holds true for passive ribbons in general? But probably not for active ribbons?

I don't suppose anyone makes these kinds of plugs, for those of us who don't own a soldering iron?

By the way Les, I would appreciate a "heads up" know when your mics are available for shipping.

Regards, Christine

Right Christine, a simple shorting plug wouldn't work in an active ribbon. But it could be incorporated in the design.

Rather than supplying a shorting plug with our mics we will probably just have a "lock" position in the mic's EQ switch, but that will require a minor engineering change.
We came up with this because many ribbon mics are damaged in shipping.

You can follow us at:
https://www.facebook.com/LMWattsTechnology/

I use my Hardy M1 with the RCA 77 and it sounds good. I've not tried using a Cloudlifter with it since it doesn't seem to need any add'l boost. I'm sure it will sound good with just about any clean mic pre though.

Thanks for explaining this. I really appreciate your help.

How would a 77D fare if plugged into a preamp that has a low impedance? I'm looking at an old Gates tube pre that has an input impedance of "30 / 50 or 150 /250 ohms"*. I suppose in this case, you would set the 77D to its lowest setting (30 ohms), and the input impedance of the pre to its highest setting (250 ohms)? Would this work okay, or is the input impedance of the pre just not high enough? This preamp has an output of 81db, and the price sure is right.

*I'm wondering why they wrote it this way (30/50 or 150/250 ohms). I assume this means there's two options, and not four?

So, just to be clear, with a typical modern pre, the 77D would operate best set to 150 ohms?

Sorry for bugging you about all this stuff. I just want it to sound good!

I'm sure Les has a much better and technically justified explanation, and i haven't read the whole thread, but the input impedance of the preamp will always affect the mic, regardless of (the mic's) output impedance, if you want to think of that as an effect, as most things seem to be these days - this is not the propper way to go about this, in my experience.

When you start to match things, that's when you get closer to how things were used back in the day, and that will translate into the sound, in my experience anyway. Some people defend that RCA ribbons sound their "best" and like one would normally associate with the old sound (all other important signal chain and playback variables removed), at their lowest impedance possible, which has to "see" the correct and corresponding input impedance at the preamp. In my limited experience, if you're thinking about impedance and are only considering the preamp (or the mic), you're not doing it right.

If i were in your place, i'd decide (or try and see what i'd prefer) what i'd want my 77D output impedance to be (generally, either low - less output but more "old" sound/noise; or high - more output, less noise, a slightly more modern sound to my ears anyway) and then match the preamp to that.

I prefer to use my RCA ribbons at their lowest output impedance possible, but i have the valve RCA preamps to match their output impedance accordingly. I also don't record modern music where fidelity is paramount and i welcome a little noise and/or leakage at all times. In that sense, solid state amps have no place in my setup, and to my ears they don't sound right at all, especially with ribbons. But obviously your circumstances may differ and i can certainly see how a high gain, low noise amplifier would be an advantage.

But anyway, all of this to say that you should think of impedance as a match thing, you have to match it unless you're using it as an effect, and the equation should always include both the mic and the preamp, never just one or the other.

I don't mind. That's what I'm here for.

Let's go back to the heyday of the 77D...1945 to 1955.

It's likely a broadcast or recording studio would have had one or more of three
mics:
RCA77D

RCA44

Shure 55/55S

Let's start with the Shure, since i'm an alumni. The microphone was designed for impedance matching, derived from old telephone standards. So if you had the mic set to 150 ohms it was meant to be plugged into an actual 150 ohm preamp input.

The RCAs were specifically designed to be operated "open circuit" (in their words).
What does that mean practically? A preamp input impedance ten times or more
the impedance of the microphone.

Many preamps of the day had very low input impedances...again carrying over from telephone standards. I have my 1953 Radiotron designers handbook cracked open here, and i'm seeing things like 50 ohm mic pre input impedances.

Plug an RCA ribbon into that and there will be a major loading problem. And it happened enough that in October 1955 RCA wrote an AES paper about it showing the bass loss and other problems. I can't give you a link for that because it's copyrighted, but it's in the AES microphone analogy. You can buy it online or read it in a library for free.

No doubt many plugged RCAs into low impedances with little problems because the loading bass loss compensated for proximity effect. But back away from the sound source and... no bass!

The old telephone impedance matching standard that we used at Shure along with many others was basically WRONG for broadcast/studio audio. In telephones impedance matching gave max power transfer, but in a studio microphone max signal to noise ratio is the goal...and that occurs with the microphone impedance much lower than the pre input impedance. Audio grew out of telephone technology, and it wasn't in a refined state in the mid 20th century.

We know that now, so the defacto standard is a 150-250 ohm mic plugged into
a 2000 ohm input impedance pre.

Now 2000 ohm is higher but it's not open circuit. What will happen with a 77D
set to 250 ohms plugged into 2000 rather than "open circuit"? A bass loss of a
dB or two most likely. I can't give an exact number because it depends on how the ribbon was installed.

Bottom line: 250 ohm 77D into modern 2K mic pre will most likely will be fine and sound great. A dB or two is nothing compared to the proximity effect you'll be getting.

But since you are going the vintage sound route you'll probably want to use
a vintage pre. And you'll have to be careful selecting it. Like the Gates...I don't know. I'd have to see a schematic.

Sometimes "250 ohms" preamp spec means it's a higher impedance designed
for bridging with a 250 ohm load, and sometimes it means an actual 250 ohm input impedance.

A safe bet would be an RCA vintage mic pre designed for their mics.
I'll be happy to check on others like Gates, Collins, etc but i'll have to see schematics or specs.

Les

I guess I want the best of both worlds. I record digitally, and I don't have the budget or the time for the headache that would come with acquiring a miltitrack tape machine. I play mostly old-school music (honkytonk, western swing, swing jazz, blues, R&B, funk). I'm not opposed to a somewhat lo-fi sound, as long as it sounds okay in the context of my digital recordings. I suppose I'm looking for the right balance between modern fidelity and old-school vibe. In short, I want my digital recordings to sound analog, but I can't shake the concept that less noise is better.

I PM'd you the specs of the Gates preamp, as I don't want to bore the other thread participants, since we've already wandered slightly off-topic here. I'd have included the schematic in the PM as well, but I don't believe there is a provision in the message system to do so, so I've attached a JPG of the M5382 schematic, which is the circuit used in the preamp in question.

It's beyond kind of you to help out a complete stranger on the internet. The information I've gained from you and others on this thread has been invaluable. Thank you.

P.S. UPS tracking information says my package is on the truck and out for delivery. This means that sometime today I will be the proud owner of an RCA 77D!

You'll have to compromise somewhere, like someone else already said, the gear you're talking about was built in another time, for another time, etc.

I record to tape but not large format tape by any stretch, i sold the tape machines i had years ago, i don't have time nor can be bothered with the maintenance, space and investment. That said, i also record digitally occasionally, and i'll say that, if you're doing that, ribbons are absolutely the way to go. Recording with headroom and not stressing your converters will also give you a much more relaxed and natural sound.

The proper arrangement, period correct instruments and musicians will take care of the rest, and accounts for about 90% of the whole thing.

I have 2 77DX's re-ribbonned by Clarence Kane some time ago. It takes some time to learn these mics. Like mentioned above they work very well into some preamps, not so well into others depending on loading and how the mic is set up. They need lots of quiet gain. They love tubes. You can't put them right on the source like a 57. They generally have to be backed up a ways (sometimes several feet) to get the best sound. The bi-directional pattern seems to work best in most cases. Mandolins, banjos, horns and pianos can sound particularly good, even magic through these. I have also gotten great results on electric guitars (don't put it up against the grill of your Marshall 4x12 unless you want to send the mic in for service) and some vocalists. They take EQ really well. I haven't perfected their use on drums but I have heard a couple of nice recordings with only 77DX's on the drums as overheads. Great mics but don't expect them to sound like a U47 or whatever....they're their own thing.

That's great to hear that you are getting exactly what you originally wanted the 77D. Good luck!

I have noticed that if I track with the levels too hot, it sounds a bit harsh, even though it's not clipping.

I said almost exactly the same thing several posts ago. I just started a honkytonk band with some players who love the old school sound as much as I do. We've got a steel player and upright bass The other guitarist/vocalist in the band plays an old Kalamazoo acoustic archtop. I'm playing lead guitar and doing some vocals. I've got a couple of old New York Epiphone archtops, and a killer old Framus archtop that I fixed up (and an old Kay too ,which sounds pretty awesome), and some vintage Fender and Gibson amps. I just do my best to sound like Hank Garland or Jimmy Bryant. We're only just getting started, but we already sound like a real honkytonk band. I'm having a blast!

The general consensus is that 77s tend to vary sonically from one another. Do yours sound similar enough that they can be used as a matched pair? I'd love to have a U47 or something similar, but getting that sound is not quite as important to me. My musical interests lean slightly toward the era before German condensers were commonly used. That said, there's some great recordings of Marty Robbins, where I suspect they used a Neumann of some sort on his voice. Tons of other recordings too, of course. It's a beautiful sound, but for what I'm doing these days, an old RCA mic will be much more appropriate.

I'm still waiting on the UPS truck to show up, Got a beautiful 77D on the way. Holy ****. It just showed up! Gotta go...

I'm working on a production sound of classic soul/funk and I just reset my hollow body electric guitar with flat wound strings. I already had flats on my bass, but didn't really think much of trying them on guitar til recently after talking to someone on the scene and in the know. Very pleasing results

I know that doesn't relate directly to the mic, but it sounds like you're on a similar mission, so that info may be of use. I've been looking around 77DX threads after seeing pics of Al Jackson at Stax with one hanging about near his snare. I wonder what pattern they used there, but I guess we'll never know....

Thanks! It arrived this afternoon, and I had some time to try it out on vocals and guitar. Really smooth. Kinda dark sounding - a little high end EQ really helps. Output is a bit more healthy than I expected - Darren (Big D) said this one was particularly hot. I really like it, but in bi-directional mode, it makes it obvious that my living room has no acoustical treatment. I'm amazed at how deep the nulls are. I was playing guitar and singing into it, with the mic tilted slightly upwards, and my guitar was virtually inaudible because of the way it was oriented.

Hmm... a 77 on snare? I just did a quick google search of Al Jackson, and the first pic I came across had Al at his kit with a 77 on the snare. My guess is that it was in bidirectional mode (figure eight), because as I said above, the nulls on this mic are so deep that anything even close to 180 degrees off axis will be virtually inaudible. If you look at the pic and visualize the lobes of the figure eight pattern, and where the nulls would be, it's not picking up much else other than the snare. Brilliant.

I love old R&B and funk. I'm playing mainly honkytonk these days, but I listen to funk and soul way more than I listen to country music. Lots more of that in my record collection than country, too.

Regarding flatwounds - I have two electric archtops - a '53 Epiphone Zephyr Regent, and n old Framus Missouri, which is really an acoustic archtop with a super deep cutaway, that I've equipped with a Floating pickup (great guitar for swing jazz). I love the sound of flatwounds plugged in, but acoustically, they don't have as much volume. Roundwound strings tend to sound a bit harsher plugged in. The Epiphone is plywood and doesn't sound too great acoustically, so I keep it strung with flatwounds. I'd use flatwounds on the Framus, but it sounds so good acoustically that I prefer to use roundwound nickel strings on it. It's the best compromise. Bronze strings sound better to me acoustically, but string balance is uneven when plugged in.

Sorry for the off-topic guitar nerdery!

No one ever shot the messenger for saying you need a good room for these mics. A fairly decent size room and with some treatment would be optimal.

Flats were an invention that didn't really take off until after WWII for a number of reasons. And quite frankly they never really took off period. They were expensive for the average player (still are) and kinda made the axe dark and lifeless. Oh but it sure helps with the squeaky noises.
Jazz corksniffers really started talking them up in the late 60's and 70's+ but very few of the Jazz legends from the golden era used them. Same goes with other genres of years past. Very few artists actually used them.

The most used strings prior to the 60's on any acoustic (flat/archtop) or electric were nickel wounds. Look into a set of John Pearse nickel acoustic strings and never look back. Sound great, got some zing, and last a really long time.

I have a couple spuce laminate top guitars. I would never call them plywood. One's a Guild Manhattan archtop. Tones of the gods. The Guild is nice because it has so much acoustic vibe but doesn't feedback like a carved top yet is not dead like a maple laminate. Could be a dud? 1953 was not a good year for Epiphone. They also dry out if not properly humidified. Take it to a repair shop you might need some bracing adjustment or repairs.

Despite the 8' ceilings, my living room actually sounds pretty good, and it's a big enough space that it doesn't sound boxy. The oak floors help too. Sometimes I hang some blankets to deaden some of the reflections. I've made some nice sounding recordings here with just a single stereo ribbon mic (B&O BM5) in the middle of the band.

But yeah, the 77 in bi-directional mode picked up some slightly objectionable reverberations when I was singing into it this afternoon, but I'm confident this will be manageable with a bit of trial and error. The acoustics here are certainly more forgiving with a full band playing, as opposed to a single singing guitarist, for instance. This is when the makeshift room treatment really comes in handy.

https://gearspace.com/board/studio-building-acoustics/

I've said all this before in other threads, here it is again:

The input impedance on old preamps like Gates/RCA/Collins/etc specify the intended source impedance, NOT the actual input impedance of the preamp. This is true of any old audio transformer spec. The transformers almost always feed an open tube grid, so the actual input impedance is very high. They are already bridging circuits. Always greater than 5K in any measurement I've taken, sometimes up to 20K.

The exceptions are most american multi-input remote mixers, which tend to be single channel preamps with a passive mixer in front of that preamp. Those attenuators are MATCHING impedances, and load the mic exactly as stated unlike what happens with a typical single channel system. Other exceptions are pre-1960 Altec preamps, some Langevin and some Presto preamps which have matching load resistors on their inputs (can usually be removed with no adverse effects), and anything originally used as a program amp may have matching load resistors as well.

Any old Gates/RCA/Collins/etc with multiple input impedance taps allow you to match the intended source impedance for best gain into that actual high impedance. Related, the inductance of the specified tap will best match the output transformer of the ribbon mic, if you put a 50 ohm mic into a 150 input you will lose some gain while possibly forcing a resonant boost into the bottom end, for good or bad. If you have a ribbon with a choice of 50/150/600 and you have the same impedance choices on the preamp, I usually vote for the 50 setting on the basis of the preamp transformer usually being the better of the two, so let it do more of the 'transforming'. Of course in that case try them all and decide for yourself if you can. Better/worse may be a matter of sonic preference, or you may hear no difference. The occasional preamp input transformer will sound really wrong when connected for an impedance different from the source.

Hey everybody! I've had this mic for about a week now, and I had some some time to play around with it over the last few days, so I thought I'd report back with you. Thanks again for all your input and insight!

At first, I thought it sounded a bit dark - not much sparkle. However this thing takes EQ beautifully (just EQing in the box here). Another thing that bears mentioning is the huge proximity effect. Even in the V1 position, there's still a fair amount, but if you work the mic just right , the result is huge.

I just can't get over how much I love the 77D as a vocal mic - at least on my own voice. Every other mic I've ever tried, to some degree, accentuates the things I don't like about my voice, This mic makes me actually like the sound of my own voice.

I mainly concentrated on getting used to the 77D as a vocal mic, but I also tried it on an acoustic archtop guitar. It works well, but because it lacks some high frequency shimmer, a high shelf seems to help.

I tracked and mixed a couple of songs just to hear the 77D in the context of a mix. I've posted those here. I tried my hand at crooning a version of "Sweet Lorraine". I also recorded a version of "You Are my Flower" which I got off a Flatt and Scruggs record but i think it's a Carter Family song. On the guitar, I have a Beyer M160, and a Beyer M500. The 77D is running through a UA 4-710d using the tube preamp section and with compression.

I also tracked some guitar as a bed track for another tune that's not complete, but I'll post the guitar track soloed. I'll also post the first few seconds of the tune, just so you can hear it in the mix, along with some layered vocals that were also tracked using the 77D (This one is an original and I own the copyright).

The last one is a solo guitar recording. I call this one "Slim's Guitar". The guitar is miked with the 77D and a Beyer M500. The 77D is panned to the left channel.

Those are really cool, I think the mic really suits your voice and style. (Good use of the Beyer mics on guitar as well!)

Wow, great music! Thanks for sharing!
These are the first 77D clips I ever heard. It sounds like instant "good old times" to me.

And it seems like this mic (like no other mic I've heard) mimics the sound of the voice as heard by the singer. Like an inside perspective.

Let me add that I was always told to use the 250 Ohm tap on an RCA mike.

The RCA mikes never really sounded "right" on transistorized preamps.

What present-day tube preamp has the clean gain to work with a 44 or 77? My Manley sure doesn't.

Retro Instruments OP-6 is worth checking out.

Thanks guys!

I hadn't thought of it that way, but I think that's fairly accurate. The charm of this mic has to do with its proximity effect. There seems to be an invisible fuzzy bubble around the mic, and if you sing right at the edge of that bubble and work it just right, it just resonates beautifully. It's real easy to overdo it and get too close, at which point the sound becomes a muddy mess. This is where Nat King Cole, Bing Crosby, the Mills Brothers really shined. Not only were they talented vocalists, but also they were masters of mic control, which at the time was a very new concept.
This afternoon, I was listening to some early material from Smokey Robinson and the Miracles, and I got to wondering what mics were typically used for vocals at Motown. It seems that Neumann condensers hit the scene in the U.S. around the same time that Motown got its start. That said, some of the early Motown recordings sound to me like they used ribbon mics on the vocals. Could you fill us in on some of the history?

Probably U-47s with lots of Pultec eq. in the late '50s. Then U67s in the early to mid '60s along with a Neumann SM-2 used in mono. All followed by KM-86s shortly after they came out.

77 is my all time fave, but didn't Bing use the 44 ?