[SOLVED] Connecting a hi-z "blues harp" mic to an audio interface?

4

4tracker

Guest
Can someone tell me how to do this?

I have a switchcraft 332a adapter, so I can plug the harp mic into a guitar cable and the into the input on the interface, but will this signal be the appropriate impedance?

I'm using a focusrite 18i8 interface. It has the option of "instrument" or "line" input level. Would I use the instrument or line input setting? I'm not really sure how to get everything to match best.

Thank you
 
Last edited:
arcaxis said:
I would use the "instrument" input setting on the interface since the mic is Hi-Z.
Click to expand...

Thanks.

Actually, that makes sense.

Are guitars/instruments technically hi-z (from what I remember, hi-z and instrument are slightly different)?
The reason I ask is will using the instrument still result in some impedance issues? Would I be better off adding a transformer/adapter for a better match? If so, which should I use?

The microphone is a very old crystal mic that I want to use for harp and vocal, but I don't want to mess up the element by having a mismatch.
 
It won't hurt the element. It'll either sound good or not. If it doesn't, then it might be because of the impedance mismatch or just that the mic sucks.

A passive electric guitar is pretty much the definition of a high-impedance source and inputs meant for such instruments are always the highest Z holes in the studio. The kinds of hi-Z mics made for harmonicas are pretty specifically intended to be plugged into a guitar amp, so...
 
arcaxis said:
have you given thought to plugging the mic into the amp and micing the amp for the harp?
Click to expand...

Yeah I have, but I live in an apt and amps aren't an option for me, unfortunately.

Thanks, guys. I now know what to do.

The mic is from the 1940s (shure 707a if that helps with the impedance questions), so I don't know how it will perform. I wish I could mic it. This is the info I found: http://cdn.shure.com/user_guide/upload/564/us_pro_707a_ug.pdf

Internal Output Impedance:
Equivalent to a
900 micro-microfarad condenser

Recommended Load Impedance:
1 to 5 megohms

Voltage Sensitivity:
3.15 millivolts r.m.s. per
microbar at the end of a 7-foot (2.1 m) cable across 1 to
5 megohms at 1000 cycles. This is equivalent to 50 db
below I volt per microbar at the terminals of the 7-foot
(2. I m) cable.
 
It say that its output is "equivalent to a 900 micro-microfarad condenser", which in modern English means a 900pf capacitor. Into a 1M load, this will give you a high pass filter with a cutoff of 176Hz, which is probably fine - maybe good! - for a harmonica held right up to it as intended. If your interface input is 500K, that cutoff moves up an octave, which feels a bit high to me, but this is not a super steep filter, so it's easily undone. Like I said, these are used straight into 470K guitar amps all the time and nobody really complains. If anything, they just turn up the knob marked Bass.

It's gonna be a weak signal, but that's just the nature of the beast. The 9-10db boost that your interface undoubtedly puts on the Instrument input will help a bit there, but the noise floor kind of is what it is.
 
ashcat_lt said:
It say that its output is "equivalent to a 900 micro-microfarad condenser", which in modern English means a 900pf capacitor. Into a 1M load, this will give you a high pass filter with a cutoff of 176Hz, which is probably fine - maybe good! - for a harmonica held right up to it as intended. If your interface input is 500K, that cutoff moves up an octave, which feels a bit high to me, but this is not a super steep filter, so it's easily undone. Like I said, these are used straight into 470K guitar amps all the time and nobody really complains. If anything, they just turn up the knob marked Bass.

It's gonna be a weak signal, but that's just the nature of the beast. The 9-10db boost that your interface undoubtedly puts on the Instrument input will help a bit there, but the noise floor kind of is what it is.
Click to expand...

Cool, thanks. How would you unleash the low end on this without an amp? Is there any way?

The specs are 30hz to 7000k, but from what I am reading, you say the best I can hope for is 176hz and nothing lower? I would like some of that lower end since it sounds nice on harp and vocals, which I want to use the mic for.

What about if using this on a Tascam 244 4-track -- would it definitely require a preamp or micing an amp? The machine only has mic/line levels no instrument level.
 
Last edited:
Into 4M, it would give you 40Hz. I think honestly that proximity effect will give you all the bass you need, and a bit of EQ will get you the rest of the way. ITB I would run it through a decent amp sims and use its tone controls like you would with an amp. The Tascam will probably want a preamp of some sort. I might grab one of my SansAmps. You won't find 4M anywhere except maybe one of those active DIs that are specifically meant to interface with raw piezos. Ooo, or maybe look for the preamp modules meant to go in an acoustic-electric guitar! Probably overkill, though.

Edit - Most of the fun of these mics is their honky character and the way they sound through an a guitar amp. That said, I once used one of these for a top snare mic. Pretty sure I just plugged into the line input (I was young, and it was the hole that fit) and cranked the input all the way up. It was actually pretty awesome for a couple of the songs... Or at least it wasn't the worst thing wrong with the drum mix. ;)
 
ashcat_lt said:
Into 4M, it would give you 40Hz.
Click to expand...

Embarrassing question, but what is 4M?


I think honestly that proximity effect will give you all the bass you need
Click to expand...

That is true. Do the old crystals have proximity effect?

Most of the fun of these mics is their honky character and the way they sound through an a guitar amp.
Click to expand...

I agree. If I can't get what I want now, I will save it for when I move somewhere I can play louder. I LOVE the old-timey sound of these mics through a guitar amp. I love how they break up vocals. It's almost like M.Ward or The Strokes in terms of modern sounds, (or any of the old blues players).

I was looking at the Bugera 5v as maybe a small apartment amp to use the mic with...do you think that would be doable? It has a .1w attenuator...
 
4MegaOhm input-Z.

My AC4 sounds like ass on the 1/4W setting. Maybe the Bugera is better?

Seriously, though. A decent amp sim will get you most of the way there with a lot less hassle. Those SansAmp pedals really still are great sounding, fairly convincing devices as well. You will probably miss the sheer SPL, but it'll work fine for bedroom recordings.
 
ashcat_lt said:
4MegaOhm input-Z.

My AC4 sounds like ass on the 1/4W setting. Maybe the Bugera is better?

Seriously, though. A decent amp sim will get you most of the way there with a lot less hassle. Those SansAmp pedals really still are great sounding, fairly convincing devices as well. You will probably miss the sheer SPL, but it'll work fine for bedroom recordings.
Click to expand...

Thanks, buddy. I am in somewhat uncharted territory here. I have an old Shure Spherodyne hi-z that sounds good through my interface, but it's from the 70s or so. I've never used a really old mic. Appreciate it.

Can you link me or name the model of the exact sanamp pedal you have and like?
 
ashcat_lt said:
It say that its output is "equivalent to a 900 micro-microfarad condenser", which in modern English means a 900pf capacitor. Into a 1M load, this will give you a high pass filter with a cutoff of 176Hz, which is probably fine - maybe good! - for a harmonica held right up to it as intended. If your interface input is 500K, that cutoff moves up an octave, which feels a bit high to me
Click to expand...

Here are the specs: Specifications | Focusrite

I don't see the load listed. I'm curious if by reading this you can tell if it will cut at 176hz or up an octave.
 
4tracker said:
Here are the specs: Specifications | Focusrite

I don't see the load listed. I'm curious if by reading this you can tell if it will cut at 176hz or up an octave.
Click to expand...

It isn't listed, neither are any other input or output impedances nor does the user manual tell you any more. They really are a Curate's Egg of a company! Probably IS one meg Ohm there is no technical reason (save cheap arseness!) to make it lower and that is what git'ists will expect.

FYI should you come across one the A&H ZED 10 mixer has 10meg inputs. If you have a pedal, not of the daft "true" bypass variety and it uses a j-fet input IC such as the venerable TL072 it is usually quite simple to change the input bias resistor from what should be 1meg to 5 or 10meg. Or you can build a simple opamp buffer/preamp using a TL0XX but there are much better fet chips around now.

Dave.
 
The load for the mic would of course be the input impedance for whatever hole you're plugging into. It really sucks that the manufacturer can't be bothered to tell you. Many "Instrument" inputs are 1M, but it's not completely uncommon to see something around 700K or even 500K. There is a way to figure out what you've got, but it's tedious and probably not worth the bother. In fact, while I appreciate your desire to learn, I strongly believe that you're thinking too hard about this. If you wanted a hifi recording you'd use a real mic. You want funky. Plug it in, turn the knobs till it sounds good, push record. If you can't get it to sound good, maybe then look for a solution, but I'm sure you'll get something you can work with.

Honestly, all of the Sansamps use the same basic circuitry to get the sounds they get, and they all do a fine job. I have a GT2 from the 90s that ocassionaly decides to play nice long enough to still be useable. I also have their Tri-OD, which doesn't have all of the options but allows you to cycle through the different amps from a footswitch. But I also have the Behringer clone of the GT2 - the TM300 - which is exactly the same as the original except I just saw it on amazon for $25.
 
Thanks, guys. I wrote focusrite to ask the load. I will post results so those in the future will know.
 
A decent active direct box would make that hi-z mic work with any lo-z mic input and be a useful tool for other things. Some instruments need substantially higher loading than 1M, something like 10M, which a good active direct box provides.
 
bouldersoundguy said:
A decent active direct box would make that hi-z mic work with any lo-z mic input and be a useful tool for other things. Some instruments need substantially higher loading than 1M, something like 10M, which a good active direct box provides.
Click to expand...
I mentioned that above. I personally can't think of any off the top of my head, and am not gonna bother to google it. I'm sure Radial probably has a couple that'll do it.
 
Radial J48 and Pro48 (as in 48 volt phantom powered), Countryman Type 85 (though they have newer models now), BSS AR-133 etc.
 
arcaxis said:
4tracker...

Have you tried plugging the mic into the interface yet and give it a listen?

I took a look at some other Focusrite interfaces specs and most generally just stated >1.0 megohm. Would guess yours will be similar.
Click to expand...

No not yet. I am waiting for it to arrive via mail.
 
For future users, input impedance for the 18i8 is as follows:
- Mic: 2K
- Line: 10K
- Instrument: 1M

From fr tech support.
 
The mics arrived. Thanks for your help, guys. The Shure 707a works great. The frequency response is 100-7k, so I really lucked out and got a good crystal, I think. But I won't know for sure until I test it through an amp, but that's the frequency response direct into the digital interface.

I hear it's hard to find these in good working order so I feel lucky with this. I'm about to test the Brown Bullet I purchased, so we'll see if my luck ran out.
 
You must log in or register to reply here.
Back
Top