Topic: Step Up line transformer > line in or attenuator > mic in?

[ethan]

Ok I'm trying to put together my light weight travel rig and I've read what I can find on line transformers here. What I didn't see was any discussion about whether attenuating and going mic in is better or worse than amplifying and going line in.

I'm guessing step-up but want to see what others think.

Comments?

Basically I want to cover my ass in case I can't get full scale without them.

I'm planning on running:

ck91's or ck93's > MK 90/3+H 98 > SP-2 > SBM-1 > D8

The SBM-1's mic in is WAY too sensitive and the SBM-1 line in might not be sensitive enough.

So what would be best? A step up line transformer like the Hosa MIT-176 for line in or an adjustable attenuator like the the Audio Technica 8202 for mic in?

-e

[Brian Skalinder]

You're better off adding gain and running line-in than attenuating and running mic-in.

[JAH]

yup what Brian said....

[pfife]

I agree... what transformer are you thinking about getting?  I am having a similar situation going 4061 -> SP-SPSB-1 -> Mod SBM-1.  Ideally, I'd like to find a transformer that's 1/8" male on one end, 1/8" female on the other end... that maybe gives +10dbs or so...

[ethan]

I'm still researching there are a couple listed in the "Line Transformers" post.

I can see everyones point wrt to attenuation vs. gain and that was my first guess.

However, just to play devils avocate. Wouldn't whatever delivers the cleanest signal, introduce the least phase and lowest THD at the appropriate signal level be the best option even if its and attenuator? Or is the mic pre so worthless on the SBM-1 that this shouldn't even be considered?

anyhow I'm going to keep looking into it.

got to go watch 24 right now....bbl

[ethan]

Ok dug out the SBM-1 specs ad Line In is definitely the way to go given the THD, S/NR of all the inputs. But I still think all things being equal whatever gives the cleanest should be considered as an option.

-e

[pfife]

I'm actually talking with JKLabs right now about a fixed gain increase box.  I'll let you know what is decided!

[ethan]

Ok I'm getting closer to understanding this.

So now my question is the various line transformers all have variations of input / ouput impedance. How important is it to match the < 200 Ohm output impedance of my mics to the input of the transformer? Similarly my SBM-1's line in impedance is 47 KOhms. Also what's the difference between load impedance and electrical impedance?


[Edit] Found this: http://www.tape.com/Bartlett_Articles/impedance.html

So basically "bridging" source to load seems to be key according to this. So whatever transformer I get  I need to make sure it's input impedance is higher than my mics output impedance and it's output impedance is lower than the 47 KOhms of the SBM-1's line in impedance.


Hmm...this one looks sweet...no spec sheet I can find though.

http://www.tecnec.com/Product.asp?baseItem=OTL%2D1S&cat=INTERFACE&subcat=AUDINT&prodClass=IMP&mfg=&search=0&off=

Here's another interesting one:

http://www.sweetwater.com/store/detail/CleanBox/

-e

[jk labs]

I'm still researching there are a couple listed in the "Line Transformers" post.

I can see everyones point wrt to attenuation vs. gain and that was my first guess.

However, just to play devils avocate. Wouldn't whatever delivers the cleanest signal, introduce the least phase and lowest THD at the appropriate signal level be the best option even if its and attenuator?

The latter statement is true.  An attenuator in itself is a near perfect device. A mic pre can be made to have excellent specs (but it's noise performance might suffer grossly with an attenuator in front). A good transformer might be an asset to you sound.

So it boils down to comparing the actual parts you are facing. Most people seem to think the mic-pre in the sbm-1 is best avoided :-) Hopefully you can find a transformer with better specs.   

You are running with 300 bodies no? Sticking a smallish +10 .. 20 dB transformer in the chain will not upset impedances here.

[ethan]

So I just sent Tecnec email asking for specs on the "On-the-level Low to High Z" unit....sure looks like it would be great given the dual input and RCA outputs.

What is it with all these manufacturers not publishing specs....wtf...couldn't find anything for the Shure or HOSA units either.

-e

[ethan]

Here's the specs on the Tecnec Low to High Z OTL-2S:

"The impedance specs are indeed 600 ohms on the balance side and 10K on
the unbalanced side. We have not run any test for the SNR, THD or dBu
specs.  The Frequency response is 1K -10K @ -1dBm."

So now I guess my question is can I compute gain knowing the Step up values of impedance? Is 10KOhm output impedance to low for my SBM-1's 47KOhm input impedance?

-e

[leegeddy]

Here's the specs on the Tecnec Low to High Z OTL-2S:

"The impedance specs are indeed 600 ohms on the balance side and 10K on
the unbalanced side. We have not run any test for the SNR, THD or dBu
specs.  The Frequency response is 1K -10K @ -1dBm."

So now I guess my question is can I compute gain knowing the Step up values of impedance? Is 10KOhm output impedance to low for my SBM-1's 47KOhm input impedance?

-e

i'd go with a Hosa MIT-176 (50-50k)

marc

[ethan]

Here's the specs on the Tecnec Low to High Z OTL-2S:

"The impedance specs are indeed 600 ohms on the balance side and 10K on
the unbalanced side. We have not run any test for the SNR, THD or dBu
specs.  The Frequency response is 1K -10K @ -1dBm."

So now I guess my question is can I compute gain knowing the Step up values of impedance? Is 10KOhm output impedance to low for my SBM-1's 47KOhm input impedance?

-e

i'd go with a Hosa MIT-176 (50-50k)

marc

Well the problem I see with the HOSA is it's output impedance is 50K and the SBM-1 (load) will be 47K this doesn't provide the approapriate bridge and afaict would affect frequency response.

-e

[jk labs]

Transformers are coupled inductors. They are specified by such parameters as inductance, winding ratios, frequency response(!), max current before core saturation etc etc. What transformers do is to CONVERT the impedance from one port to the other. In so doing they change the voltage as well. The Bartlett article contains the formulaes no?  If not think conservation of energy (UU/R) between input and output.

You're interpreting the HOSA spec too critically. What Hosa tries to say is that if the load impedance is much lower than 50 kOhms
the core is approaching saturation (seen as brickwalling on the output side). The sbm-1 line in is probably well within what the Hosa can drive to specified levels.

[Chris K]

fwiw, i ran 

391 > b18 > line transformers (audio technica cp8201) > sbm-1 line in

when i first started concert taping, and made some great tapes.

here is a link to the audio technica site with the line transformer specs. you can get them at guitar center for about $20 a piece.

http://www.audiotechnica.com/guide/other/access/inline.html#CP8201