Active ribbon-mic

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abbey road d enfer

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I've been telling everyone who asks about cloudlifter type devices, "If you have a mic pre that will do 65dB or 70dB of gain you don't need one."
There are 2 instances where such a gizmo is useful, and I've been faced with both.
  • The source impedance id too high for a mic input. This shouldn't generally happen, but my incursion in this domain was prompted by having bought a Thomann ribbon mic, which clearly didn't work satisfactorily. After some head-scratching I found its impedance was 2.5k. The 40+k input Z of a Fethead solved the problem.
  • The line to the preamp is noisy. Adding about 20dB to the mic signal improves S/N.
In general, I agree with both statements "If you have a mic pre that will do 65dB or 70dB of gain you don't need one." and "these additions might/will be used where they're often not needed at all.", but there are some cases where they are useful.
One thing is for sure: none of these has a better noise figure than a good preamp coupled with a good mic and a good cable.
 

Whoops

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having bought a Thomann ribbon mic, which clearly didn't work satisfactorily. After some head-scratching I found its impedance was 2.5k.

Do you remember the model of the Thomann mic?

They have 3 models, the cheapest is bad, but the other 2 are very nice, the lollypop style and the bigger one.
I never thought about limitations of my preamps impedance with those mics, but I will try it out for sure.

Why did you feel it didn’t work well? What did improve?

Thanks
 

abbey road d enfer

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Do you remember the model of the Thomann mic?

They have 3 models, the cheapest is bad, but the other 2 are very nice, the lollypop style and the bigger one.
I never thought about limitations of my preamps impedance with those mics, but I will try it out for sure.

Why did you feel it didn’t work well? What did improve?
It's a RB500.
It seems like there's been at least 3 different builds of this model. Most are genuine 200r, but mine is 2500r. I believe it was an attempt at increasing the sensitivity (or an inventory problem - we won't hold a shipment because we are short on xfmrs; put just any other and let's ship the damn things). Anyway, a real f..k-up.
It results in a muffled sound and high susceptibility to any interference.
Paired with the FetHead, the frequency response is incomparably better (even with my 72 yo ears, I can clearly hear the difference) and the S/N is much improved. A typical mic pre meeting a source of 2k+ does not perform as it should in terms of noise.
It sounds even better with my MicBooster, than with the 1st-generation FetHead, that suffers from gate-drain leakage noise, due to improper bias of the FET's in it. They have corrected it later, but not as they should have.
I don't doubt there are good RB500's. Actually, I bought it because of some unbiased reviews.
Using my MicBooster is actually cheaper than replacing the xfmr in the mic.
 

Whoops

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Thanks Abbey, I was not aware of that problem in the RB500, the 2500R at the output is also reported by other people or you were just unlucky in the model/batch you got?

Sorry if this is a really basic question, but how can I measure an RB500 output to check if the impedance is 200R or 2500R?

Thanks

I used the RB500 mics quite a few times and it's a really nice Ribbon mic for the price, the other I also like a lot is the RM700.

I recorded a well know portuguese piano player some years ago, I used 3 stereo pairs on the Piano.
A pair of Neumann U67, a pair of Schoeps CMC6 and a pair of TBone RB500.
The piano player come to the control room to have a listen, and I played for him every Pair for him to choose, he had no idea about what mics I was using or the pricing of the mics, he choose the RB500, he loved the sound, so those were the ones used on the final mix for his record.
I guess he doesn't like too much high end and the condensers were not fitting his taste.
So I'm not saying that the cheap RB500 is better than Neumann or Schoeps (mics that I trully love) just that sometimes a 80€ mic might be the best tool for a specific job.
 

ricardo

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but how can I measure an RB500 output to check if the impedance is 200R or 2500R?
A really good transformer would have its resistive (DC) losses small compared to the 'designed impedances' eg 10% and 'equally' distributed between primary & secondary. 5% of 2k5 is 125R while 5% of 200R is 10R.

Most small signal transformers are not quite as good .. maybe 2x or 3x more DC resistance.

If the DC resistance of the secondary is under 100R, it's the 200R version. If much more than 125Rdc, the 2k5 version.

You can also sweep the mike from 20Hz - 20kHz with a SMALL AC current and measure the voltage across it. This give exact info on impedance and how it changes with frequency but is riskier cos you are treating the microphone like a speaker.

If you stretch or blow the ribbon on your genuine STC 4038, don't blame me :)
 

ricardo

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"If you have a mic pre that will do 65dB or 70dB of gain you don't need one."
That should be "65dB or 70dB of Low Noise gain" so non est tantum facile.

I show how to modify a M-Audio DMP3 into such a beast in my MicBuilders Forum Files. DMP3s used to be less than $100 but seem to have disappeared from eBay.

Also there, is my own take on Active Ribbons.
 
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Winston OBoogie

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OK!!! I guess your answer settles my question of whether or not to build this circuit!!! My now knowing that this circuit - could - be improved upon in different ways, but that such information is being withheld for whatever reasoning, I will just abandon the idea of building this circuit and instead go buy a "Cloud-Lifter" or something.

While you're ordering a Cloud-Lifter, see if they also have any books on etiquette.
 

kato

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What circuit is this?
I'm not totally sure. I think it's this one?

Edit: Here's the original, without my resistors poking out of the paper.

Some of the images from this thread appear to be missing so I can't locate the original.

It also might be this Alctron one that Rog's drew up:

Alctron.MA.1.jpg

I believe this was the one. I'm remembering that S2, which I used a jumper for.

I'm re-doing my studio now so I still haven't had a chance to plug it in. But if anyone's interested, I can report back on how it works.
 
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abbey road d enfer

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Thanks Abbey, I was not aware of that problem in the RB500, the 2500R at the output is also reported by other people or you were just unlucky in the model/batch you got?
I don't know of anyone having actually measured the same impedance, but there were reports of 500-600 ohms versions.. Mine may be the only one on earth with 2k5...
Sorry if this is a really basic question, but how can I measure an RB500 output to check if the impedance is 200R or 2500R?
Ricardo's suggestion is good for an estimate. I measured mine with a generator, millivoltmeter and a large resistor in series. It's not a very difficult measurement but still it takes method to do it correctly. REW has a procedure and set-up to do that.
I used the RB500 mics quite a few times and it's a really nice Ribbon mic for the price,
This is consistent with many user feedbacks.
I have other T-bone mics, in particular a trio of Retro (not made anymore), that I bought about 15 years ago, large diaphragm FET mics that are permanently installed in my Yamaha C7 grand. 3 or 4 years ago I decided to improve the set-up and bought a trio of C414XLS. They didn't stay long, and I quickly reisnstalled the T-bones.
 

Whoops

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I decided to improve the set-up and bought a trio of C414XLS. They didn't stay long, and I quickly reinstalled the T-bones.

I have a pair os 414XLS, I was never impressed by the sound, although I always liked the sound of older AKG 414 models.
These new Harman 414 mics are not that great
 

mylesgm

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I'm not totally sure. I think it's this one?

Edit: Here's the original, without my resistors poking out of the paper.

Some of the images from this thread appear to be missing so I can't locate the original.

It also might be this Alctron one that Rog's drew up:

View attachment 81685

I believe this was the one. I'm remembering that S2, which I used a jumper for.

I'm re-doing my studio now so I still haven't had a chance to plug it in. But if anyone's interested, I can report back on how it works.
Thanks! I may one day get around to making one.
 

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