mic pre concepts

[Svart]

yes i totally agree Tamas.

PRR got me thinking in a new light, which i think was his whole intent here.

maybe we should be looking at alternate ideas to the "accepted" preamp solutions of today? maybe we should be looking to change the WAY things are done instead of how we fix problems that keep coming up time and time again using the same old tired ideas..? I know that it could mean that a lot of people would not like it since most are VERY set in their ways, but like the phonograph, sometimes we just have to toss out the old outdated crapin order to move ahead.

 

[tmbg]

In a roundabout way, that was sort of my point in starting this thread... I'm still trying to learn a lot of this stuff, but I'm trying to learn it in a way where I discover what exactly a mic preamp needs to DO, then try to figure out on my own how to accomplish those goals. It's a horribly inefficient way to try to design gear, but it goes the furthest in helping me understand HOW to design gear.

 

[Svart]

hmm i've just come up with more opinion...

it seems that the computer industry is driven by the new and inventive, but otherwise needed ideas, such as the new PCI-E to replace pci and agp, just like all the scsi interfaces and the various processors etc.

Pro audio has no such driving force other than rather simple improvements in already maxed out design structures. HOW much better can we make a microphone? Sure we can buy "better" parts to put in them etc, but how much better can they get when we reach the limitations of other hardware? this leads to the next point.

we can already BUY the "best" of everything, which is really just a version of something else with better parts when you boil it all down. How about, are the original designs of the boxes we clone really worth as much as they are sold for? nope.

we as consumers strive to have the "best" of what's availiable, but it always seems that the "best" is too expensive for everyone but a few to own. this creates a "must have" situation where everyone who is serious about audio must have it, but will probably never come close to getting it. this is the force that is killing the evolution of pro audio. very few people have the best things out there, and since there is no competition, there is no innovation.

sure you can argue about the digital revolution, yadda, yadda, but is it really changing things at a pace that refreshes the gear market every couple of years? I think not. how about going back to older topologies like valves, and such? if they fit what you are looking for then ok, but what if we discover something else that tops everything we have now? we would never know without innovation.... the innovation that isn't happening.

the author is not responsible for electrical shocks caused by:
1. crying on your keyboard
2. laughing so hard snot drips out of your nose and onto your keyboard
3. other bodily functions in direct association with websites of German ladies with large breasts.

:guinness:

 

[Gus]

I have an Idea for a different condenser capsule. Maybe there is room for microphone preamp changes. I have a simple preamp almost done being protoed. It was made for high ouput condensers it will suck for lower output microphones.

PRR has hinted and posted about how good noise is a trade off again some circuit designs.

 

[tk@halmi]

[quote author="Gus"]PRR has hinted and posted about how good noise is a trade off again some circuit designs.[/quote]

This is entirely true for designing anything in this world. A design is a series of trade-offs balancing one constraint against another. In fact, for 99% of the products you ever buy budget is the #1 constraint. Yet there are usually new ideas that make more of that budget in creative ways.
Studio electronics has had a lot of incremental improvement, but not many braktrhough innovations.

 

[Svart]

Studio electronics has had a lot of incremental improvement, but not many braktrhough innovations

Exactly what i was saying Tamas!

:guinness: great minds think alike i say! :green:

 

[Consul]

You know, I've often wondered why 48 volt phantom power became the standard when it would've been much easier to send any voltage up an extra conductor or two. I can only guess it had to do with what was available off the shelf to designers at the time.

Of course, changing the entire industry at this point can't be expected, but for those of us building our own gear from the ground up, the idea of playing with completely new design concepts is appealing.

 

[Svart]

they stole the idea from the phone company.. balanced signal, 48v..

 

[CJ]

OK, is this thread going to get anywhere, or just turn into another brainstorm session? Let's pretend that we will arrrive at a project after all is said and done. That means starting at the Very beginning.

1)Who will be the audience for this thing? Public? Engineers? DIY people?
2)What kind of music is it for?
3)What kind of microphone will be plugged into it
4)What will the micpre be plugged into?

You have to ask these questions first in order to draft up an archetecture statement.

Obviously, we won't arrive at micpre nirvana where one size fits all.
So we have to target a specific goal. Then we can start.

Some basic questions: Are we going to use tubes, transistors, or both?
How about transformers?

Once we get the basics answered, we can throw something together.
Lame post, but realistic.

 

[Gus]

Its my understanding the german condenser microphones were designed for 200 om output strapping, The german condenser microphone wants a 2K or larger load.

Want is on my bench now a 24V circuit (why 24V I have a spare 24 V ps) a single transistor 10 collector R 1K emitter R not bypssed. The 10K and 1K set the transistor gain at about x10 or 20Db. The input R will be the hfe x 1K now I need to find a transformer at 1:2 to 1:4 I want the input R to be about 2K or greater. The bias string will be a 150K to +24V and a selected resistor from the end of the 150K to ground the "bottom" R will be selected for were we want the colltor to sit for the distortion we want or don't want. The "bottom" R will be Bypassed by a nice cap to keep the resistor node stable.

The transformer secondary will connect at the resistor node and the other side at the base. Now here is one of the problems there will be some current flow into the base the higher the hfe the less current.

One will note this is based on some older solid state preamps and a circuit PRR posted at the old site.

Now some other fun we can place install a direct coupled EF to the collector and pick a emitter E and go out unbalence or we can place a linear pot of 100K or so and send the wiper to another EF or gain stage with an input R of X3 to X5 the loading of the vol with an R of 3 to 5 times greater makes a nice log vol.

Lots of stuff to try one could use a cap and resistor that you could switch in the emitter leg of the first transistor for more gain but the input R will change.

One could do the math for a higher voltage circuit but other parts will change etc........ The circuit is simple with only local feedback. I have a 2n4401 in it now

So what do we want for a high output condenser? I think around 20DB will be a good place to start.

We can use a current source instead of an emitter resistor and.........................................................................

 

[tk@halmi]

Some interface "standards" need to be estabilished before diving into design.

1. What range of electronic levels should a microphone output given some dBs of acoustic signal?
2. What range should a preamp accomodate on its input (dictated by #1) and provide on the output?
3. Should a micpre provide power to a microphone at all?
4. Should a pre still provide phantom power through traditional means or should it provide it through separate lines.

Suggestions are welcome!

 

[CJ]

Also to consider, do we keep the preamp near the mic and put the volume control in the control room? This is what that Gordon amp does in case long runs with certain mic types give problems.

Being a tube head retro freak, I was horrified to read that post about going into a A/D then D/A, but after thinking about itf or awhile, I bet thats exactly where we end up within the next 50 years. Or maybe even a didital mic like PRR was talking about a while back. Get some resolution and use some dsp's to manipulate the signal to sound like whatever you want..

 

[Svart]

ok before we get started, I restate My opinion in hopes that we can do something completely different and new.

We already have pre designs readily avaliable with both clean and colored trafos, both clean an semi-colored semiconductor based, and various kinds of tubes. why rehash the old designs over and over?

maybe we should look at building a mic circuit that ouputs *line* level or something of that nature? phantom power or general power is easy enough to design into the whole picture after we decide the important aspects of what we expect this setup to do. I don't see why we can't design a mic and console interface together. we can use any number of different topologies, however i am a fan of FET based circuits.

condenser mics do a degree of amplification before the output, why can't we add the second gain stage there instead of putting another 2 or more in the preamp?

 

[tk@halmi]

Line level is good. Some things that we are used to in micpres are pad and phase. Most condenser mics have a 10dB pad already. Why not make it a 20dB pad? Then you just need an additional phase switch on the mike.
Power supplies become local affairs and they can be anything depending on the components inside the mic.

 

[StephenGiles]

.............all very theoretical but assumes that whatever the microphone is picking up is worth recording in the first place, if it's all the same to you!
For christs sake, or whoever takes your fancy, I turn on my guitar amp, stick a mic in front of the speaker and record through my BEHRINGER preamp into my recorder, with a What compressor in the insert. If I like it I keep the track and clean up the grunge, if I don't I erase. I just wish I had the time to worry about the fancy stuff. I'm sure there are dozens of other people who do the same.

Right now, my wife is in "getting ready to go out mode" if you know what I mean - another 4 hours I could have been building a decent preamp!!!
Stephen

 

[Kev]

[quote author="tmbg"]Lets start a nice thread all about the hows and whys of mic pre design![/quote]

a quote from the very first post in this thread

It was a hypothetical and not necessarily for the purpose of actually designing a project.

I wanted to get the ball rolling to aim at say 3 or 4 very typical and popular microphones and look at how to interface to them and then provide that very first main step of gain.

Don't even think about output sections except that it was vaguely going to have to interface to the rest of our gear which would of assumed -10 to +4 perhaps 600 ohm but it is NOT important.

Then we could have discussed some older topologies and why they went that way and PERHAPS looked at some new ideas with new components.

I'm sure along the way someone would have pointed out that you can now purchase a Microphone that only has AES EBU.
That's right ... only digital audio out !

:shock:
THAT begs the question ... "what circuitry did they use to get from Capsule to AtoD converter. Bearing in mind they had complete control and choice and don't have to sell it to anyone and can keep it under wraps.

to wit ... see the above and original question .... :roll:

 

[Gus]

Kev

I wonder if neumann used some ideas from RF condenser microphone circuits Maybe they can us the capsule in a circuit that generates digital word dirrectly and not capsule to amp to a to d to some logic and then out..

One reason I am thinking of this there are direct changing capactance measuring devices. The company that owns neumann is known for the RF microphone design(not a transmitter)

I wonder if they use the rf freg as a clock ................................................................

 

[dayvel]

I think one of the problems with designing preamps is that we feel compelled to come up with something that will work with any combination of mic, hardware and application, just like the big boys. But the beauty of DIY is that we don't have to do that. We can use simpler designs that are optimized for specific mics going into whatever hardware we want to use or happen to have.
A preamp that's taking the output of an SM57 into a consumer level input on a soundcard doesn't need phantom power or to be able to swing +24dBV at the output, while a condenser mic going into tape deck may.
It makes sense to me to have different boxes for different jobs rather than coming up with a "one-size-fits-all" solution. Building things yourself allows you to come up with cost-effective solutions that perform better because they are optimized for the task at hand.

 

[Kev]

[quote author="Gus"]One reason I am thinking of this there are direct changing capactance measuring devices. [/quote]

if you can keep linearity, then why not .
clock ??
:roll: - now here is where we get into trouble.

I'll go braodcast for a minute just to keep away from your Golden Ears in the music biz ...
... generally our gear have a ref input and it is here that clock distribution happens. I don't personally think the ref sunc is fast enough to make for top audio clock sync - moving on.

An AES digital output Mic will now need an input if it is to slave from the main system. Think multiple mics.
This could get out of hand very quickly but it is fun to think about.


[quote author="dayvel"] But the beauty of DIY is that we don't have to do that. We can use simpler designs that are optimized for specific mics going into whatever hardware we want to use or happen to have.
A preamp that's taking the output of an SM57 into a consumer level input on a soundcard doesn't need phantom power or to be able to swing +24dBV at the output, while a condenser mic going into tape deck may.[/quote]
dead right
and this is where I wanted the thread to end up after first establishing want needs the various mics might have.

 

[CJ]

I was thinking we should design twoo micpre's, one tube version for some color, and one solid state version for clean.
What say?
Can we beat anything thats already out there?