Topic: gain with transformers

[dklein]

Who can give me the lowdown on this?  How much actual gain can these provide and what are people using.  Lots of folks with JB3s need some gain for mics without a pre.  I looked up the math on transformers and gain.  The popular Hosa transformers will yield 24dB less the load loss.  Anyone got real world results?  It depends on gear impedance and all that, but is 12-18 dB realistic?  And what's the cost...it almost seems to good to be true.

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

[bhtoque]

Who can give me the lowdown on this?  How much actual gain can these provide and what are people using.  Lots of folks with JB3s need some gain for mics without a pre.  I looked up the math on transformers and gain.  The popular Hosa transformers will yield 24dB less the load loss.  Anyone got real world results?  It depends on gear impedance and all that, but is 12-18 dB realistic?  And what's the cost...it almost seems to good to be true.

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

I can't give you an actual number, but when I run my Oktava MC012's>PS-2>transformers(Audio Technica CP8201's)> JB3, I end up having to run the jb3 with the gain set to -2 or -3 to keep it from clipping at most shows.

I think they ran me about $20 each at guitar center.

JAson

[twatts (pants are so over-rated...)]

I'm curious about this too.  I just picked up some Giant Squids and need something to add some gain...  I thought about an AD20, but trasnformers would be alot smaller.

Squids > Hosa Ts () > Nomad 3 (line-in)

Terry

[BobW]

Don't forget that transformers block DC, as in they do not pass Phantom.
In fact, this will usually short out the phantom supply causing damage to the pre.
Not sure why anyone would use both, but might be worth mentioning.

[bhtoque]

yeah, you would not want to pass phantom through them. The ones I use are xlr f and 1/4" m
I have 1/4">rca adapters and an rca>1/8" cable to go to the deck.

Works great and the transformers are no bigger than a pack of cigs.


They are also handy for unballancing xlr sbd feeds

JAson

[dklein]

Understood about relationship with phantom (Using transformers is one way of blocking the 48vdc, an alternative to blocking caps)

I guess the questions are specific to running stealthy ecms (CSBs, SP mics, squids etc) into a high impedance line input device like the JB3.  I'm assuming the mics are receving appropriate bias from a battery box (but no preamp).

What transformers are you using?
How much gain are you getting vs no transformer (anyone drive a test signal in both ways and measure it?)
What effect do the transformers have on the sound if any?

These things are always described as "impedance matching" as opposed to "signal boosting" so I'm curious if this is a good approach to gain or if there are obvious tradeoffs vs a little premp.

JK's suggestions seam to lead to transformers that are appropriate to use in preamp construction but not as a 'inline device'.  And they seem to cost $100 a piece too!

[bhtoque]

Understood about relationship with phantom (Using transformers is one way of blocking the 48vdc, an alternative to blocking caps)

I guess the questions are specific to running stealthy ecms (CSBs, SP mics, squids etc) into a high impedance line input device like the JB3.  I'm assuming the mics are receving appropriate bias from a battery box (but no preamp).

The mic>batt box connection (or mic>phantom power) is not changed in any way. You are using the transformers after the batt box, but before the deck.

What transformers are you using?
How much gain are you getting vs no transformer (anyone drive a test signal in both ways and measure it?)
What effect do the transformers have on the sound if any?

These things are always described as "impedance matching" as opposed to "signal boosting" so I'm curious if this is a good approach to gain or if there are obvious tradeoffs vs a little premp.

The ones I use are Audio Technica CP8201's. You can get them at guitar center, and radio shack carries similar ones. Not sure why impedance matching boosts the signal to line level, but it works. I can't give you a gain number, but I can guarantee that it will work for any rock show. Might be too soft for acoustic stuff though.

There is almost no effect on the sound. Very colorless source of amplification

JAson

[jk labs]

Understood about relationship with phantom (Using transformers is one way of blocking the 48vdc, an alternative to blocking caps)

I guess the questions are specific to running stealthy ecms (CSBs, SP mics, squids etc) into a high impedance line input device like the JB3.  I'm assuming the mics are receving appropriate bias from a battery box (but no preamp).

What transformers are you using?
How much gain are you getting vs no transformer (anyone drive a test signal in both ways and measure it?)
What effect do the transformers have on the sound if any?

These things are always described as "impedance matching" as opposed to "signal boosting" so I'm curious if this is a good approach to gain or if there are obvious tradeoffs vs a little premp.

JK's suggestions seam to lead to transformers that are appropriate to use in preamp construction but not as a 'inline device'.  And they seem to cost $100 a piece too!

Hi there!

And your music isn't worth another $200? 

Your intended application is identical in every respect to that of a 20 dB step-up transformer sitting in the front end of a transformer coupled mic-preamp. (Possibly barring issues related to phantom powering but I take it you have sorted those out).

Reading up on the information available at the sites I mentioned will allow you to understand a little more of what to pay attention to when experimenting.

Don't misunderstand, I am all for going with a small & really cheap transformer, at least for starters, but you ought to have insight into what it does and also how to "optimize" it for your application.

Seen from the primary side, the transformer transforms the load impedance down and presents a much harder load to the batterybox. With a low impedance source (which you might NOT have) and a high impedance line-input, both the signal source and the transformer will suffer little internal losses and you get close to the theoretical gain.

With a high source impedance, the transformer steals so much of the available current => the mic&battery box don't manage to develop the full signal voltage => reduced voltage out from batterybox => reduced voltage delivered to the line-input..

With a low impedance line-input the battle is lost anyways. There just isn't enough current available to transfom the voltage up 20 dB. . 

The reason I can't be more specific is that there is no standard mic & batterybox!  Some mic& batt boxes drive just about any load and others suffers loss of amplitude already into a 10 kOhms load. I think this ought to be your starting point: can your batterybox drive 1 kOhms loads without going belly up? 

[leegeddy]

my very first rig was: AT831b > AT8531 (battbox, xlr out) > Hosa MIT-167 Xformer > D100 (line in). i didn't like the setup too much. i got bass distortions in few instances; therefore, ditched the setup for mic/preamp setup.

marc