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

[ethan]

I found the formula here:

http://www.shure.com/support/technotes/app-transform.html


Gain = 20 * log (sqrt(ImpedanceOut/ImpedanceIn))

So the Tecnec box is a approximately a 12 dB gain.

-e

[redbook]

do these AT transformers provide gain? Same levels as Hosa ones?

[ethan]

Basically they match impedance but the affect of matching 600 Ohm -> 50 KOhm is they provide gain up to 25 dB from what I've read.



BTW, I've decided to give the "On-the-level" line transformer from Tecnec a try. I'll let ya'll know.

-e

[hexyjones]

 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.

That statement seems to be at odds with itself...? (perfect device/suffers grossly)?

Also - is this really "adding gain", or just changing the way the signal looks to the subsequent device...?

Would there be any loss/distortion along the way in the transformer...?(even though the recorder might see more gain)

(I probably dont fully understand the concept of gain...electrically speaking...beyond the obvious..)

[ethan]

Read that impedance FAQ...it'll answer some questions for ya.

-e

[Todd R]

I also used the AT transformers mentioned above when I first started taping.  Went line in to an Aiwa HDX3000 DAT (same as the marantz brick and Aiwa HHB1) and made many great tapes.  I lost those transformers and used the Radioshack version for a few shows, but then moved to a beyer MV100.  The ratshack ones were ok, but I'd recommend the AT ones for sure.

[Todd R]

BTW, I've decided to give the "On-the-level" line transformer from Tecnec a try. I'll let ya'll know.

Didn't you say the freq response on these was 1K-10K?  I'd go with the AT or Radioshack ones (20-20k and 50-20k) before going with ones with such limited range as 1k-10k.

BTW, I've got the RS ones packed away somewhere.  You can borrow them if you'd like.

[ethan]

Todd the Tecnec one has a 20 Hz - 20 KHz range.

The 10K refered to the output impedance.

-e

[Todd R]

The Frequency response is 1K -10K @ -1dBm

Just checking -- so this info you posted before was for a different TecNec transformer?

Also, gotta nix that offer for borrowing my RS transformers.  I just looked for them, but can't find them.  Must have lent or sold them to someone else, though it escapes my mind to whom.

[jk labs]

 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.

That statement seems to be at odds with itself...? (perfect device/suffers grossly)?

Also - is this really "adding gain", or just changing the way the signal looks to the subsequent device...?

Would there be any loss/distortion along the way in the transformer...?(even though the recorder might see more gain)

(I probably dont fully understand the concept of gain...electrically speaking...beyond the obvious..)

A transformer is a passive device: You cannot get more energy out of it than you put in. But the transformer can amplify the voltage (step-up transformer).  Now total energy (voltage x current) is conserved so you get correspondingly less current out.

Most all audio circuits these days measure the voltage. So when a device has a gain of say 20 dB it's implied that we are talking about the voltage. A transformer with 20 dB gain (meaning voltage gain) is a 20 dB attenuator of the current. 

Audio transformers are not ideal devices. It cannot pass DC. At high frequencies the core material sets limitations. I think you’ll find near infinite amounts of info on the net on this very topic. 

A way to visualise voltage and current is to think of voltage as water pressure and current as the amount of water flowing per second. 

[hexyjones]

Thanks - that makes lots of sense now...thanks.

Does that apply for both balanced and unbalanced lines alike...?

Also - isnt the quality of the transformer pretty important?...at one point someone was reccommending using Radio Shack transformers - which I was always told - sucked...and were to be avoided. Dont these things need to be matched to some extent - like mics?

I thought maybe that advice needed to be reconsidered...?

[jk labs]

Thanks - that makes lots of sense now...thanks.

Does that apply for both balanced and unbalanced lines alike...?

Also - isnt the quality of the transformer pretty important?...at one point someone was reccommending using Radio Shack transformers - which I was always told - sucked...and were to be avoided. Dont these things need to be matched to some extent - like mics?

I thought maybe that advice needed to be reconsidered...?

Hi there. Balanced line you say. The transformer doesn't care (nor does it have any way of finding out) if one side is at ground or is fed a signal of inverted phase. So the analysis does not change. 

on the issue of recommending RS transfomers, or calling them crap.
I think this is exactly like all other gear discussions. It comes down to what you need/want/can hear/enjoy/can afford ..   People don't put a lot of cosmetics into transformers so there is a correlation between cost and measured performance.

The only thing that really matters is what you are happy with. A working transformer needs not cost much. You can even make your own easily. But it will affect the lows and the highs and add it's own sonic footprint. I'm sure that some will say "wow, sounds good in my system". Maybe attenuated highs and rolled off bass is  just what is needed. Then the mid-band colorations seem a small price to pay.

Regards
Jon

[hexyjones]

well - I admit - I own some Shack transformers and might use them occasionally...

A mentor of mine is the source of the "crap" comment - he thought it was hard to get a pair that sounded alike...

So - keep an eye out for stuff like this?

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=3278&item=7303101938&rd=1

Do you have any preference? the sonic footprint of a transformer or the noise penalty with the attenuator...? or is this, as you said, "what you need/want/can hear/enjoy/can afford"?

Thanks for all the helpful info!

[jk labs]

well - I admit - I own some Shack transformers and might use them occasionally...

A mentor of mine is the source of the "crap" comment - he thought it was hard to get a pair that sounded alike...

So - keep an eye out for stuff like this?

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=3278&item=7303101938&rd=1

Do you have any preference? the sonic footprint of a transformer or the noise penalty with the attenuator...? or is this, as you said, "what you need/want/can hear/enjoy/can afford"?

Thanks for all the helpful info!

You're asking the wrong person. I rip things open to see how I can make it a perfect match for the device sitting downstream. Then I go to the device downstream...

In general you want to get the signal amplitude *up* as early in the signal chain as possible. Then downstream you provide just sufficient gain to reach 0 dB FS. Going through stages with 0 dB gain is not optimal as I see it unless you have a good reason for so doing.   

I.e. I do agree with those who recommended an external transformer ahead of the line stage instead of going attenuator + mic-in & then line stage of the sbm-1.  I hold this view irrespective of mods done to the sbm-1.

I encourage experimentation. Buy those Sowters and try (if they provide ballpark 20 dB gain and handles 50 kOhms loads [which I think they do judging from their size]).

Jon
PS Of course the RS xformers are crap, especially in the bass. We must assume they are produced for RS by the lowest bidder in the entire world. Every penny they can save on materials, production and quality control contributes to their profit. But remember that the sound tapers capture have gone through a complex signal chain including speakers with considerable TDH and deviation from flat. And maybe the mics used were omnis with excessive bass. So it must be YOU who decide if the RS transformers are ok to use in YOUR setup. Sample to sample variations may make their use somewhat more of a challenge :-)

[Todd R]

Just to clarify, since I think I was the only one mentioning RS transformers in this thread.  I am not really recommending them.  I'd recommend the AT transformers that I used for awhile.  But I only picked up the RS ones in a pinch after losing the AT ones.  Ran the RS ones only a couple times before I switched to a Beyer MV100 preamp.

I would however, as I mentioned before, use the RS transformers before I used a pair of transformers that only provided a signal in the 1000Hz-10,000Hz range (assuming that information is correct).

Jon -- thanks for all your input on this.  I'm not following you in regards to your statements on transformers and the SBM1.  If you are better off stepping up the signal amplitude earlier in the chain, wouldn't that argue for using transformers rather than attenuators?  Also, the unmodified SBM1 uses a 4580 op-amp based gain stage for the mic pre input and another 4580 gain stage for the line input.  So a transformer-boosted signal going line into the SBM1 would go through the transformer gain stage and then the single 4580 gain stage in the SBM1.  If you went the attenuator> mic-in route, you'd be going mics> attenuator> 4580 gain stage> 4580 gain stage.  So by using the transformers, you skip one 4580-based gain stage, opting instead for the line transformers.  I have no idea whether line transformers would sound better than a 4580 op amp, but it seems that if they do there might be merit to going with the line transformers rather than going through an attenuator and then mic in.  I'm curious why you'd always prefer the attenuator > mic-in route.