Ribbon mic. I need a preamp schematic ( or a brain... ) .

[5ynth3t1k]

I was given a really cool sports commentator mic, it's probably very collectable... but I pulled to bits. ( !! )

and way, so it has a transformer, it does work, BUT it's insanely quiet. I used my Triton Fethead preamp but that didn't really make much a difference.
( yes it is a ribbon mic, 100% sure on that. I seen the ribbon, oh you want photos ? )

So yes, without having to rob a bank to get a super duper preamp... anybody made any preamps that actually work ?

hmmm. let me look at it... for one second...

ah ha ! It's a Coles 4104 !!!! I have one ! but... it does not like my Focusrite ADC preamp...

Help ?

 

[SSS]

Viewing the spec of this mic shows that it has to be used quite near the lips and with a strong voice. At a distance I think there will be not much output. Further there is a reduced frequency band 60 - 12000 Hz. This mic is made just for voice. But it should work with a standard mic input.

 

[5ynth3t1k]

Viewing the spec of this mic shows that it has to be used quite near the lips and with a strong voice. At a distance I think there will be not much output. Further there is a reduced frequency band 60 - 12000 Hz. This mic is made just for voice. But it should work with a standard mic input.

sure but it's rilly rilly rilly quiet. I compared it to my SM58 ( which is also a quiet mic ) and the mic was in the noise floor. It may have a duff transformer I guess... I might take the cable off and use a know one, and /or I might borrow the SM58 transformer and see if that helps ( maybe for impedance balancing...)

Thanks for the help !

 

[SSS]

What I know is that a magnet can deteriorate over time when the mic is really old. This would mean the sensitivity is reduced. Also a defect in the transformer may happen like a winding short. Without measuring it is not easy to find the cause.

 

[DVDdoug]

Maybe the mic is broken/defective... Ribbons have a reputation of being fragile but I don't know about that particular one.

Dynamic and ribbon mics are typically 20dB "weaker" than condensers. It should be about the same as the SM58. Most interfaces are designed for condensers. You may not get a good signal unless you are recording a loud drum or guitar amp but the FetHead is supposed to take care of that. Or you can boost digitally after recording but of course any preamp noise gets boosted too, and the Focusrite's preamp is probably noisier than the FetHead.

I used my Triton Fethead preamp but that didn't really make much a difference.

It's supposed to have 27dB of gain. That's a lot of gain and it should make a BIG difference even if it's not enough... Does the FetHead work with the SM58? Is phantom power turned-on on the Focusrite? The FetHead needs power.

 

[5ynth3t1k]

Maybe the mic is broken/defective... Ribbons have a reputation of being fragile but I don't know about that particular one.

Dynamic and ribbon mics are typically 20dB "weaker" than condensers. It should be about the same as the SM58. Most interfaces are designed for condensers. You may not get a good signal unless you are recording a loud drum or guitar amp but the FetHead is supposed to take care of that. Or you can boost digitally after recording but of course any preamp noise gets boosted too, and the Focusrite's preamp is probably noisier than the FetHead.


It's supposed to have 27dB of gain. That's a lot of gain and it should make a BIG difference even if it's not enough... Does the FetHead work with the SM58? Is phantom power turned-on on the Focusrite? The FetHead needs power.

Yes. The FET head does nothing with the power off. So if I say the mic is very quiet with the FET head on. then yeah the mic is very quiet. I'm not fooling around...

The SM58 with the FET head is not super loud. With the Focusrite on 50% on the gain knob and the FET head and I sing ( at a normal loud but not yelling program ) at about 200mm from the mic I get about -6 Db on the input in REAPER. Close to hitting the 0 mark. That's a pretty darn quiet mic. AND the 4140 mic is still in the noise floor.

Obviously this is an impedance thing, etc etc. Which is why I'm interested in a preamp made for a ribbon mic.

The transformer is the Key, I suspect. I will inspect the Mic again with a closer eye.

Thanks for the help !

 

[5ynth3t1k]

What I know is that a magnet can deteriorate over time when the mic is really old. This would mean the sensitivity is reduced. Also a defect in the transformer may happen like a winding short. Without measuring it is not easy to find the cause.

How do you test a transformer ? Input vs output. I have a really budget CRO. but to test the tranny... what can I feed it that is a know source ?? I do not have a lab power supply...

Thanks !

 

[DVDdoug]

How do you test a transformer ? Input vs output.

Yes, but it's hard to measure a few millivolts or less. And I believe it's a step-up transformer so the even-lower primary voltage is probably impossible to measure "at home".

You can check the resistance on both sides but you'll have to disconnect the microphone from the primary side. If you've got it disconnected you can also check the microphone (ribbon) resistance. I don't know what to expect but if you measure an open on either side of the transformer or directly across the ribbon, it's bad. The DC resistance should be lower than the 300 Ohm impedance rating and the primary side and the ribbon should be a lot lower than the secondary side.

The transformer shouldn't fail unless it's corroded from moisture or something... There's not enough energy to burn it out and it should survive dropping the mic, etc.

...Unless you burn it out with phantom power but there should be no current-path for phantom power so phantom power shouldn't hurt it, unless the cable is wired wrong. There are "rumors" of phantom power killing dynamic or ribbon mics but it's not supposed to happen. And it could happen if the mic is high-impedance, unbalanced.

The SM58 has a sensitivity of -56dBV (1.6mV) at 94dB SPL (1Pa)
The Coles 4104 is -50dB (3.2mV)

So the Coles SHOULD BE 6dB louder.

The SM58 with the FET head is not super loud. With the Focusrite on 50% on the gain knob and the FET head and I sing ( at a normal loud but not yelling program ) at about 200mm from the mic I get about -6 Db on the input in REAPER. Close to hitting the 0 mark. That's a pretty darn quiet mic.

That seems about right. And "50%" on the gain knob is probably much lower than 50% gain. It's probably an Audio Taper pot where most of the "action" or change is near maximum rotation.

Obviously this is an impedance thing, etc etc. Which is why I'm interested in a preamp made for a ribbon mic.

I don't think it's an "impedance" problem". (Unless it's open or shorted.)
Both mics are 300 Ohms (although the Sure specs are "strange").

Generally the preamp input impedance is higher than the mic. You can check the Focusrite and FetHead specs but I'd guess they are around 1K.
You can check the input impedance

I have a really budget CRO.

I don't know what that is.

 

[AnalogSteph]

I don't know what that is.

A scope. (OP must be from 'straya.)

 

[Bugg100]

sure but it's rilly rilly rilly quiet. I compared it to my SM58 ( which is also a quiet mic ) and the mic was in the noise floor. It may have a duff transformer I guess... I might take the cable off and use a know one, and /or I might borrow the SM58 transformer and see if that helps ( maybe for impedance balancing...)

Thanks for the help !

That is an announcers "lip mic". It is built to be TOUCHING under the announcers nose and not overloading with a loud voice. Think about f1 race announcer, horse racing announcer and the like. Sort its own form of compression and noise rejection all in the design.

Put the thing touching your face and yell at it, then decide if your Fethead is enough or not.....

 

[5ynth3t1k]

That is an announcers "lip mic". It is built to be TOUCHING under the announcers nose and not overloading with a loud voice. Think about f1 race announcer, horse racing announcer and the like. Sort its own form of compression and noise rejection all in the design.

Put the thing touching your face and yell at it, then decide if your Fethead is enough or not.....

Sure, but it's wildly too quiet. Like bonkers. To make it even vaguely "normal" you would have to jack the hell out of it.

I understand the idea behind the mic, the way it is used etc but a mic that is toooooo quiet starts to create other problems.
Such as the signal being so close to the noise floor and the preamp being so jacked that it's going to go nuts if it gets a spike or
noise or some not cool freak out.

Even if you yelled into this mic nothing useable would come out. Maybe it's broken. The trannie is porked... I tested the foil and it's conducting
so it's not blown. Maybe the magnets have demagnetised ?

I wonder if I can apply new bar magnets...

Fun !

 

[JayGilb]

A mic booster like the Cloud lifter might help if your mic is not broken. It provides a 25 dB boost.

 

[JayGilb]

I tested the foil and it's conducting
so it's not blown.

Maybe the ribbon is stretched and needs to be tensioned correctly.

 

[5ynth3t1k]

I have a FET head. That marginally helped. It's still dragging the signal through the noise floor. The mic does make this nice warm rumble down low.

Tension... right. The thing is tiny. I kind of don't feel comfortable fiddling with it.

A new transformer.. I wonder where I get one of those from .

Cheers !

A mic booster like the Cloud lifter might help if your mic is not broken. It provides a 25 dB boost.