iMic volume/noise issues

[kozikowski]

<<<he has a rather "unorthodox" style (read "grumpy") >>>

Grumpy and irritable!

This thread drags from January 23rd through now. In that time, we've helped thousands of other people out of trouble and I, personally can't keep all that in my head and still remember where my car keys are.

<<<and that the preamp itself has to be plugged into an extension cord to reach the nearest wall socket.>>>

Ding!!!

Not the same socket as everything else is plugged? Didn't you say earlier that you were in a very old house with iffy wiring? Does everything have three-wire plugs and sockets?

Did you ever say where you were? US? Do you have or can get one of these...

http://www.tessco.com/products/displayP ... ventPage=1

The object is to get all electrical parts of the system plugged into the same wall outlet, even if you have to generate a power octopus to do it. You're not running six hair dryers and a microwave oven so there's no danger of circuit overload, besides, the power strip has a circuit breaker to guard against overload damage.

AC Power Problems can cause even top quality broadcast and recording equipment to behave funny.

Is the computer portable? Can you briefly run batteries and see if the hum level changes? Not even gets better, just does Something Else.

==[irritable]
<<<Believe me, if it had changed, I would have told everyone.>>>

You were supposed to respond with a neat orderly listing of the equipment you are currently using with model numbers.

<<<Oh, yes, the ribbon owner. >>>

Remember that post? I don't remember details from 7 month old posts and few of us do.
==[/irritable]

Koz

[steve]

This all started with the microphone - a very nice, but expensive ribbon mic.

People that use them would often rather sell their children that part with their ribbon mic, but they have a couple of drawbacks. They are usually rather delicate, and they produce a very low level signal. The first of these is not too serious so long as you take care, but the second can cause headaches. This is because you need to use a lot of gain (voltage amplification) in order to get a usable signal, which in turn can mean problems with noise and hum. A well designed and well made microphone should not be a source of noise, and I doubt that it is the problem in this case, but "hum" is a funny thing and can enter the system anywhere (through an input, through a power supply, even through the output or through the casing). My suspicion was that the noise is coming in through the pre-amp output as this is using an unbalanced lead.

XLR leads are great for eliminating electrical noise, not only because they are usually well shielded and have eXtra Low Resistance connectors, but because they are balanced. Balanced microphone leads send the signal through two signal wires that are twisted around each other (and are shielded on top of that). The signal works as a push/pull through the two wires so the signal in one wire is always exactly 180 degrees out of phase from the other. The great thing about that is that if any electrical interference (hum) gets past the shielding, then it will affect both wires pretty much the same (in phase), but a balanced input on an amplifier only responds to the difference between the two signals and largely ignores any common signal, so the hum is rejected by phase cancellation.

So anyway, I did a bit of digging and bingo:

When I first powered on the preamp, I connected it to a Digi001 with an XLR to TS cable. This immediately led to an annoying electrical hum, even before connecting a microphone to the input. So, I tried using an unbalanced 1/4" to 1/4" cable. This made the hum even worse. Fortunately, using either a balanced 1/4" to 1/4" or an XLR to 1/4" cable eliminated the hum. The manual states that you can use unbalanced cabling, but I personally did not find that to be the case. There are other users who have had hum problems with this preamp, so I do not believe that this was an isolated issue on mine.

You can read the rest of the review here: http://jerfocom.blogspot.com/2005/07/el ... eview.html

The problem is that your iMic does not have a balanced input, so you can not use a balanced cable to connect the output of the pre-amp to the input of your sound card.
There are a couple of things that may help here - you could perhaps use a DI box between the pre-amp and the iMic, or you could get a better sound card that has an XLR input.

Avoid cheap passive DI boxes as they use poor quality audio transformers, tend to be noisy and have poor frequency response. The cheapest one that I have found to be any good is this: http://www.thomann.de/gb/millenium_dip_ ... di_box.htm
You can also get "Active" DI boxes which use powered electronics rather than a transformer to provide a balanced input. An inexpensive example of this is the Behringer DI-20.There is no guarantee that either of these will provide a suitable solution as they are not really designed for this, but in theory they should work. I notice that one of the replies to the review made a similar suggestion (use an ART Cleanbox).

Personally I would probably go for the more expensive solution of getting a sound card that has XLR inputs.

Whichever solution you decide to go for, I would suggest taking your microphone and pre-amp along to a music shop so that you can try it out before you buy.

[kozikowski]

<<<The manual states that you can use unbalanced cabling>>>

You can, but with conditions. The technology used to create the preamplifier balanced output dictates the wiring of the adapter cable.

If you have a line-level transformer in the output of your preamp, it is required that you tie XLR pins one and three together and to ground and get the unbalanced signal from pin 2. The show will be a little hot, but it should be well within the abilities of the downstream electronics to deal with.

If you have an electronic balance instead of the transformer, you are required to get the signal from pin two with pin one grounded and don't do anything with pin three. Note you can't freely move these adapter cables back and forth between the two preamps. The wrong connection in one case will cause sound damage and in the other case the show will vanish. Either error could cause hum.

This comes up regularly and I swear I'm going to make my fortune by soldering these cables together and selling them.

<<< ¼” OUTPUT LEVEL – This separate, buffered output with a dedicated level control
is “balanced out,” which can provide +18dBu. Shorting the ring to the sleeve allows
for use of single-ended unbalance cables in some equipment. Test for best results. >>>

That's a direct quote from the instruction book.

The instructions are not perfectly clear which is why they throw it open to individual personal testing. They claim a transformerless design, yet they also claim an adapter cable designed for transformers. If you guess right, I'm sure the thing works a treat. If you guess wrong, it may give you your condition.

Koz

[kozikowski]

I'm arm-wrestling with my website host, so I can't post pictures for a while.

I was reading the instructions for the microphone and they leave out a couple of really important items. They suggest, but don't come right out and tell you that the microphone, typical of ribbons, has no pickup from the sides or the top, and has more or less equal pickup from the front and back.

http://en.wikipedia.org/wiki/File:Polar ... _eight.png

This is the response of a typical ribbon looking down from the top. If you happen to be standing at 90 or 270, all the microphone is going to get from you is room echoes. No voice.

In early broadcasting, they would park one of these ribbon microphones directly between two voice actors, one in one response peak and one in the other. That's the illustration I won't be getting to for a while.

So you need to be talking directly into the front and back of the mic and not either side or the rounded top. I know you probably know that already, but we're covering all the bases.

Koz

[kozikowski]

http://kozco.com/tech/audacity/Fibber6.jpg

That's the microphone that I have. RCA 44BX. Classic ribbon. It only responds from the two flat sides, not the sides with the logos or the top.

http://www.apb.org/RCA%2044%20BX%20Micr ... 20Sale.htm

Koz

[tymime]

Hum has suddenly almost disappeared. Nothing has changed as far as I know. I'm guessing that the preamp is just temperamental. >_<

[tymime]

Hum still comes and goes, but has been especially (and frustratingly) stubborn lately. Looking into getting this to eliminate it entirely: http://www.amazon.com/Ebtech-LLS-2-XLR- ... 886&sr=8-5

Simple questions in need of simple answers:
1. Will this do the job? If not, what?
2. Is there a cheaper alternative that will do the job just as well?

[waxcylinder]

I think Steve suggested a similar device a while back in this thread.

And personally I agree with one of Steve's earlier comments in this thread in that the iMic is the weak link in your recording chain - the forum is littered with folk who have problems with iMics. I put iMic on my shortlist (along with the Behringer device that SteveTF runs and the Edirol that I finally bought) - but soon discarded the iMic from the short-list after reading several poor reviews on t'interweb.

So if you have this sort of $$ to spend I would be thinking about getting a better external soundcard.

Oh, and do you still have these bits of kit plugged into different sockets around your house - or have you consolidated? I run my rig, recording gear and PC, off a ten-way drop with power-surge (and lightning) protection, fed from a single wall socket.

WC

[stearman65]

I've already said this on this thread & thought it had gone away, so I think it's worth repeating. I started with the Imic which gave problems from day one & sent it back for a re-fund. I then bought the Behringer USB device and never looked back, The Imic uses the jack commection which are notorious for problem of noise, the USB connection of the Behringer circumvents this and after 18 months use I am still happy.
Stearman65

[tymime]

Commence gigantic eyeroll.

THE IMIC IS NOT THE PROBLEM.

I can say for certain that the preamp is entirely at fault here. Lots of people have had the same problem. The hum only disappears when the <i>preamp</i> is removed from the chain.
I found out about the EBTech converter through this review (2nd from the bottom): http://pro-audio.musiciansfriend.com/pr ... te&so=desc And no, I don't have "this sort of $$"- I might not be able to get it until my birthday.
I will say it again (since we're all into repeating ourselves): the iMic does exactly what I want it to, and I have had no problems with it in the time I've owned it. So please, just answer my questions...

Ranting aside, yes, I have dealt with the socket problem. I got a nice new surge protector with more sockets and now everything computer-related goes into the same wall.
Is this what you mean?: http://www.thomann.de/gb/millenium_dia_ ... di_box.htm It does the same thing then? Is it available in the US?