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Gear / Technical Help => Microphones & Setup => Topic started by: scoper on March 10, 2006, 02:57:41 PM
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After reading many threads here about using line transformers to add signal gain, I decided to check it out.
I went to RadShack and bought the following:
274-016 - 3 pin XLR(F) to 1/4" phono plug
274-909 - 1/4" mono phono jack to RCA female
274-897 - RCA Male to 1/8" mini plug
Since the mics on hand (SP-BMC-3 omnis) terminate in 1/8" plugs, I used a 1/8" to XLR conversion cable I had from Sound Professionals, and made two passes of a recording, with no adjustments to mic positioning or volume from the speakers.
Pass 1: Mics > BB > jb3 analog in
Pass 2: Mics > BB > converter cable > piggyback transformers (as above) > jb3 analog in
Absolutely NO gain difference in the two passes. I only bought one set of plugs, and thus used left channel only.
Pass 1::
Mono
Min Sample Value: -1301
Max Sample Value: 1717
Peak Amplitude: -25.61 dB
Possibly Clipped: 0
DC Offset: -.002
Minimum RMS Power: -89.02 dB
Maximum RMS Power: -35.53 dB
Average RMS Power: -49.45 dB
Total RMS Power: -47.61 dB
Actual Bit Depth: 16 Bits
Using RMS Window of 50 ms
Pass 2:
Mono
Min Sample Value: -1681
Max Sample Value: 1333
Peak Amplitude: -25.8 dB
Possibly Clipped: 0
DC Offset: -.002
Minimum RMS Power: -91.16 dB
Maximum RMS Power: -35.09 dB
Average RMS Power: -48.29 dB
Total RMS Power: -46.7 dB
Actual Bit Depth: 16 Bits
Using RMS Window of 50 ms
Help, please! Did I do this wrong?
Scott
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I went to RadShack and bought the following:
274-016 - 3 pin XLR(F) to 1/4" phono plug
274-909 - 1/4" mono phono jack to RCA female
274-897 - RCA Male to 1/8" mini plug
Since the mics on hand (SP-BMC-3 omnis) terminate in 1/8" plugs, I used a 1/8" to XLR conversion cable I had from Sound Professionals, and made two passes of a recording, with no adjustments to mic positioning or volume from the speakers.
What transformers did you use... there should be mics, connectors, battery box, pri/sec transformer, more connectors, recording device.
the "gain" is determined by the ratio of the number of primary windings to the number of secondary windings
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The transformer was the XLR to 1/4" connector - low impedence to high impedence. Nothing else in the signal path changed.
Everything is detailed in the original post.
Scott
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The Hosa MIT-176 line transformers use all three wires on the female XLR side.
I have done the following succesfully though.
soundcard mini out > stereo mini/RCA Y Adapter > RCA barrels > DIY RCA/XLRmale cable (x2 [pin 1 & 3 ground pin 2 hot]) > Hosa MIT-176(x2 terminated to a single mini stereo jack) > Computer Speakers
There was a noticable clean gain boost w/ the line transformers in the chain.
You are only feeding pin 1[ground] and pin 2[hot] a signal from your 1/8 mini output + adapters. For it to work properly I would imagine you would need to cross pin 1 & 3 in the transformer.
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After reading many threads here about using line transformers to add signal gain, I decided to check it out.
I went to RadShack and bought the following:
274-016 - 3 pin XLR(F) to 1/4" phono plug
274-909 - 1/4" mono phono jack to RCA female
274-897 - RCA Male to 1/8" mini plug
Since the mics on hand (SP-BMC-3 omnis) terminate in 1/8" plugs, I used a 1/8" to XLR conversion cable I had from Sound Professionals, and made two passes of a recording, with no adjustments to mic positioning or volume from the speakers.
Pass 1: Mics > BB > jb3 analog in
Pass 2: Mics > BB > converter cable > piggyback transformers (as above) > jb3 analog in
Absolutely NO gain difference in the two passes. I only bought one set of plugs, and thus used left channel only.
Pass 1::
Mono
Min Sample Value: -1301
Max Sample Value: 1717
Peak Amplitude: -25.61 dB
Possibly Clipped: 0
DC Offset: -.002
Minimum RMS Power: -89.02 dB
Maximum RMS Power: -35.53 dB
Average RMS Power: -49.45 dB
Total RMS Power: -47.61 dB
Actual Bit Depth: 16 Bits
Using RMS Window of 50 ms
Pass 2:
Mono
Min Sample Value: -1681
Max Sample Value: 1333
Peak Amplitude: -25.8 dB
Possibly Clipped: 0
DC Offset: -.002
Minimum RMS Power: -91.16 dB
Maximum RMS Power: -35.09 dB
Average RMS Power: -48.29 dB
Total RMS Power: -46.7 dB
Actual Bit Depth: 16 Bits
Using RMS Window of 50 ms
Help, please! Did I do this wrong?
Scott
I tried something similar and got the same result as you (ie., no gain!)
Then I thought back to my training in Electrical Engineering: To get gain, you need a *low impedance* source that matches the low impedance input of your transformers. A battery box does *not* provide a low impedance source.
To get gain, you need a regular (ie., phantom powered) condenser or dynamic mic. A dynamic mic has low impedance (it is just like a speaker or earphone, a coil of wire around a permanent magnet). A condenser mic will have either a transformer, or a discrete transistor output stage. Both of these are low impedance and will work with transformers.
So, in our "taping" world, you will probably need either a phantom powered condenser mic + transformers, an battery operated mic with a preamp, or a battery operated mic with a very loud sound source! oh yeah, maybe an AKG C1000 or an AT822/825 would work with transformers. They have battery power, but there is presumeabley an output buffer to strengthen the signal.
Richard
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I don't pretend to understand all this -
Once I get my 3 wire box and modded mics back from sanjay, would it work then?
BTW, it looks like he had some difficulties getting the AT853's to solder correctly to the minixlrs, so I guess I'll have to wait an extra week until he returns from out of town. I knew it would be a rush for him to get it done in a week, so I'll have either use my standby mics (as above), or borrow Jason's DPA 4060's, which I'm afraid to do for fear of wanting to never return them <g>.
Scott
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Then I thought back to my training in Electrical Engineering: To get gain, you need a *low impedance* source that matches the low impedance input of your transformers. A battery box does *not* provide a low impedance source.
To get gain, you need a regular (ie., phantom powered) condenser or dynamic mic. A dynamic mic has low impedance (it is just like a speaker or earphone, a coil of wire around a permanent magnet). A condenser mic will have either a transformer, or a discrete transistor output stage. Both of these are low impedance and will work with transformers.
So, in our "taping" world, you will probably need either a phantom powered condenser mic + transformers, an battery operated mic with a preamp, or a battery operated mic with a very loud sound source! oh yeah, maybe an AKG C1000 or an AT822/825 would work with transformers. They have battery power, but there is presumeabley an output buffer to strengthen the signal.
Richard
I had succesfull results using the output of the soundcard built into my motherboard, which I am guessing is high impedance, thus transforming it to higher impedence. I doubt the output of your battery box is at a seriously high Impedence.
I dropped out of college way before we got to this stuff so correct me if I'm going in the wrong direction.
With the "higher impedence" you now have a higher voltage (louder) signal with less current(more succeptable to interferece). If you are not already overloading the input of the transformer I imagine it would succesfully be able to "transform" the signal. I would imagine there is a point at which you would also be overloading your recording device and/or you get to a point that the current flow would reach a point too low to efectively push current into your recording device (it has some resistance too)
How would this effect the frequence response of the chain?
Your soundcard *output* will be low impedance. The *input* may be low or high.
Think of low impedance = "high current" = "strong signal" = "voltage not reduced by loading".
Think of high impedance = "low current" = "weak signal" = "voltage reduced by loading".
A battery box is not very high impedance, but it is say, 10K. The input impedance of the transformer is 300Ohms, or 0.3K. What happens is the voltage into the transformer is 0.3/(10 + 0.3) ~= 1/30 reduction. So any gain in the transformer is lost at the input...
Richard