Microphone boosters?

[JohnRoberts]

I have heard this myth about mic impedance dominating the noise floor but I just don't believe mic pres in interfaces are as good as you say and that's why so many people are buying mic boosters.

It may depend upon what you mean by "interfaces"....

Mic preamps inside real consoles have bettered the 3 dB NF criteria for several decades. The old school way involved a step up transformer to better match microphones low source impedance to the available electronics du jour. This century even off the shelf preamp ICs are that good without transformers.

The formulae for calculating mic preamp ein involves multiple terms. Mic source impedance factors into a couple of the important ones. First the Johnson or thermal noise of that source resistance is one noise term, then that same source impedance multiplied by the equivalent input noise current is another noise term.

Some people posting in this thread have designed multiple commercial mic preamps, so don't dismiss their advice that casually.

JR

 

[ruffrecords]

I have heard this myth about mic impedance dominating the noise floor but I just don't believe mic pres in interfaces are as good as you say and that's why so many people are buying mic boosters.

It is not a myth.. I did not say anything about interfaces. I was talking about mic pres. There are very many interfaces on the market and some of the cheaper ones are likely to cut corners which can easily result in less than optimum noise performance. That said, there are plenty that are not expensive that do turn in very good noise figures. A good starting point is this guy who has reviewed and measured many interfaces:



Rather than use a cloud lifter of dubious specification, I would advise investing in a good quality interface. After all, if your interface has cut corners in the mic pre than it is likely to have cut them in other areas.

Edit: Attached is a screen shot from one of his videos that compares EIN of several interfaces. One thing I do not like is that he quotes A weighted figures. A weighting can easily improve a noise figure by 6dB so these interfaces may well be a lot noisier than the figures suggest. If that is the case then it may well be that a really low noise figure booster could improve noise.

Cheers

Ian

 

[Ricardus]

I like my Scarlett. I mostly bought it to be a DAC for when I streamed audio, but I use it for everything when I don't need a lot of tracks.

 

[Cranehazard]

It is not a myth.. I did not say anything about interfaces. I was talking about mic pres. There are very many interfaces on the market and some of the cheaper ones are likely to cut corners which can easily result in less than optimum noise performance. That said, there are plenty that are not expensive that do turn in very good noise figures. A good starting point is this guy who has reviewed and measured many interfaces:



Rather than use a cloud lifter of dubious specification, I would advise investing in a good quality interface. After all, if your interface has cut corners in the mic pre than it is likely to have cut them in other areas.

Edit: Attached is a screen shot from one of his videos that compares EIN of several interfaces. One thing I do not like is that he quotes A weighted figures. A weighting can easily improve a noise figure by 6dB so these interfaces may well be a lot noisier than the figures suggest. If that is the case then it may well be that a really low noise figure booster could improve noise.

Cheers

Ian

I totally agree, if it turns out you need a cloudlifter with your sm7, your mic preamp (which may or may not be built ino your interface) is noisy and needs a band aid. A lot of these are sold leading me to believe MOST mic preamps (either built into the interface or not) are not making the cut. Purely speculation on my part. Just buy a good preamp and forget about it.

 

[Ricardus]

I think the takeaway here is that we all need to just eschew the SM7.

 

[soapfoot]

I can’t shake the feeling that all this debunking of “improving noise performance” might be slightly beside the point.

The reason these things exist is to approximate an unloaded condition for those ribbon microphones who need that to perform their best.

Perhaps there are circumstances where noise can be lowered (I’ve outlined one such circumstance with vintage Neve preamps), but this is an occasional side benefit at best

Is anyone really buying these things in an attempt to solve problems with noise floor?

 

[Ricardus]

I use mine (which were designed by Abbey) when I need more gain.

 

[abbey road d enfer]

I think the takeaway here is that we all need to just eschew the SM7.

That would be missing a very nice tool.
One particular case was when I recorded a singer with piano.
The fact that the singer can sing in close contact to the mic compensates the low sensitivity and allows rejecting spillage more efficiently than the directivity pattern.
And it sounds way better than a 58.
Actually, the whole album was done with two vocal mics, said SM7B and the AT4060 that is my go-to vocal mic.
No one noticed a significant difference.
Of course I wouldn't choose it for recording fly farts...

 

[Tubetec]

I found this ,

http://www.radanpro.com/Radan2400/MiscAudio/ESP - Direct Injection Box for PA Systems.htm
how much is it practicable to reduce the 6.8k feed in resistors in value before it effects the load of the output stage?
Theres a danger with 48 volts of damaging the op amps so the zener is included , would 36 volts with smaller value supply resistances (say 2.2k )be safer ,aiming to drop to around 26v at the op amp supply , then even if the full unloaded supply voltage appears at the moment of switch on its still just around the maximum rating of the chips,
In the case of the OPA chips mentioned is the driving capabillity into low loads destroyed by having relatively large resistances in series with the power rail ?

Triton fet head opperates on from 24 to 48volts ,the other electret preamp I showed works with 15-48v 3.2ma so they should still have enough to work upstream of the op amps .

 

[zmix]

The "Engineers Thumb" compressor does that. From merlin who posts here once in a great while.

I had a brief discussion with a guy on Reverb.com who was selling those assembled..

The TC Electronic Sustain+ compressor also uses that configuration ( and I have 3 of those.!)

 

[emrr]

I can’t shake the feeling that all this debunking of “improving noise performance” might be slightly beside the point.

Is anyone really buying these things in an attempt to solve problems with noise floor?

This is exactly how they’ve been marketed all along - to improve noise floor by putting ‘better’ gain upfront. It’s only recently that the ribbon loading thing has been mentioned.

The 1st product like this was from Sanken, and they actually gave a noise spec of -118dBu! Their point was more driving long lines in electrically noise environments.

if it turns out you need a cloudlifter with your sm7, your mic preamp (which may or may not be built ino your interface) is noisy and needs a band aid. A lot of these are sold leading me to believe MOST mic preamps (either built into the interface or not) are not making the cut. Purely speculation on my part.

a lot of sm7’s are sold with these specifically because retailers have widely bundling them together, it shuts down returns related to mic output being too low, and reassurances had to be made suggesting the device was as good or better than the preamp. It’s a classic case of the actual best use being too esoteric for the average consumer and retailer, so the marketing shifted. It started over 15 years ago.

I would not be surprised to learn LESS of these devices are sold with ribbons than with sm7’s.

 

[Tubetec]

I looked at the Triton site to try and find some more detailed info but when I hit the spec page it just defaulted back to home page , irritating .

Some extra info here ,
http://recordinghacks.com/2010/02/08/cloudlifter-review/
''[3000Ω] is a range much more friendly to the vast majority of ribbon mic transformers than [is] a 22k load. So, [the Cloudlifter will have a] more even response from at least 90% of ribbons, and 99% of classic ribbon mics. ''

''The 22k input impedance was decided after extensive listening; it gives dynamic and ribbon microphones a more open character.''

I think the the writer might have mixed up the comments , first one is from Triton second from Stephen Sank

Sanken HAD48 also has 20 and 40 db gain settings .

 

[frans]

Thanks for all the in-detail-technicals... even if i don't understand half of it. I also think that a quality preamp is better than to fix something that's flawed to begin with, but i also have some preamps dedicated to a lot of gain .. and some dedicated to very low gain, for high output mics and loud signals which i don't want to pad down. Looking into the issue of having a bit more gain available when those preamps are all occupied in a big session i tried a few of them. IMHO the only one that behaved like i used a good preamp with more gain is the Royer D-booster or what's it called. All of those gadgets were checked with quality preamps, but besides the Royer they didn't deliver like a good preamp with more gain. It costs a few bucks, but so what. Does the job convincingly. I also heard a report of someone who seems to have a defective Dbooster, but mine is fine.

 

[Tubetec]

Can you show us your mic booster circuit Abbey ?

There are certain situations you still might use a handheld dynamic on vocals in the studio ,
I remember one session I did many years ago with a Rap collective , we put up condensers and the guys didnt know what to do with them , they were scratching their heads , I quickly took charge of the situation and got out the 58's , bang the boys were back in the zone again . Of course theres better and worse from a technical standpoint , an Sm-7 Im sure beats a 58 but at times 'vibe' has to take precedence over other concerns .

If we used a transformer at the PSU end and apply power via primary centre tap rather than the usual resistive feed can we get more current to the op amps?

 

[abbey road d enfer]

Can you show us your mic booster circuit Abbey ?

See attachment.

If we used a transformer at the PSU end and apply power via primary centre tap rather than the usual resistive feed can we get more current to the op amps?

Yes, but that would not be P48 anymore. It could be dangerous to other mics.

 

[Tubetec]

That looks nice Abbey , what input impedence did you choose? whats the gain and expected load ?

I realise my idea is a departure from regular 48volt phantom practice and its attendant limitations , for mass market usage ,no ,not a good plan , to much chance of mishaps ,but in the hands of people who know what their doing very do-able I think.

The transformer option wont be favourable to many , you know who you are and so do we ;-) but it does at least assure many upstream 48 volt devices ,like fet heads can work .

Im a Paddy (Irishman) actually Newmarket ,but we do share many terms of indearment and otherwise with our third closest neighbours after all ,cheers for the input .

 

[Tubetec]

An elementary switched gain control over a phantom 'like' power supply is the missing link , maybe Bo has some ideas on that

 

[abbey road d enfer]

That looks nice Abbey , what input impedence did you choose? whats the gain and expected load ?

Input Z is 44k with 5nF in paralllels.
This combination may introduce resonance in the 20-30kHz area with some mics, but until now, nobody complained.
EMI/RFI protection is essential IMO.

 

[Datman]

Hi all!
I'm a new member of this forum. I was searching for a schematic and I found it here

I play with electronics since I was 14 and since 1988 it have also been my work. I played seriously with audio, but also other linear electronics, digital and RF. In 2015 I discovered Arduino and now the ATmega328p is very often in my projects. My work has been lab servicing on broadcast cameras and video mixers, then HDTV studios design and now A/V infrastructure and main switching systems.

If I would design a mic booster, the specifications would be:
- a very simple device (less components, less noise);
- unbalanced input: it is directly connected to the microphone, then a balanced input is not required;
- low input impedance (2~3kohms);
- balanced output;
- phantom power;
- gain: about 8dB.

 

[Bo Deadly]

Welcome to the list.

- a very simple device (less components, less noise);

Less components does not equate to less noise. In fact the opposite is true.

- unbalanced input: it is directly connected to the microphone, then a balanced input is not required;

Microphone outputs are almost always balanced.

Also, your question is a little bit of a deflection of the original topic which is about the merits of mic boosters in general. If you want someone to help you design a circuit, you should find a schematic to use as a starting point and submit it in a separate post.