Using mic input transformer as line input transformer(noob question alert)

[orangechili]

Plz go easy on me lol.

I have a sound workshop console that has unbalanced line inputs. I have 8 extra tiny beyer mic input transformers laying around from another defunct mixer and was wondering if I can use them to balance the line-ins on the console?

I hooked one up on a whim to one of the channels and seems to sound a lot more full and louder, the signal is clean and clear from what i hear. It is considerably louder than the unbalanced signal which isn't a huge deal but was wondering if using the mic transformer has something to do with that?

I'm not too familiar with the difference between line and mic transformers obviously. I've been on Jensen's website which describes the difference a little but it's still a little hazy…

 

[JohnRoberts]

The transformer magnetic design is to accommodate input and output power levels (so pretty modest power). Besides the too large turns ratio for an output transformer application, the input transformer will not handle the flux density to pass output level power without saturating.

Different parts to accomplish different tasks.

JR

 

[gridcurrent]

They might be just fine.  Wire them "backwards".
Measure them to the best of your ability, the higher impedance side will be the input, lower Z side the output.
Post more information, DCR of each winding, Beyer part number.

 

[dmp]

I hooked one up on a whim to one of the channels and seems to sound a lot more full and louder, the signal is clean and clear from what i hear.

A transformer has a turns ratio, typically 5:1 or 10:1, that steps up the level of the input signal. A line transformer is almost always 1:1, meaning it doesn't change the signal level - what goes in goes out.
So you put in the mic transformer and heard a louder signal because of this step up.
If it sounds good, it is good (who are we to judge?) - but beware you may saturate the transformer and hear distortion or clip an amp stage later because of the earlier step up.

If you check the number on the Beyer transformer you can look up the spec. They made those peanut transformers in many different turns ratios. But they all had relatively low level handling because the core's small. But they are awesome transformers.

 

[mjrippe]

The transformer magnetic design is to accommodate input and output power levels (so pretty modest power). Besides the too large turns ratio for an output transformer application, the input transformer will not handle the flux density to pass output level power without saturating.

Different parts to accomplish different tasks.

JR

Hey John, he wants to use it for line INPUT, not output

  Still the step-up gain of a mic transformer will make the line level even hotter.  If you are using -10dB line level it *might* be ok.

 

[JohnRoberts]

The transformer magnetic design is to accommodate input and output power levels (so pretty modest power). Besides the too large turns ratio for an output transformer application, the input transformer will not handle the flux density to pass output level power without saturating.

Different parts to accomplish different tasks.

JR

Hey John, he wants to use it for line INPUT, not output

  Still the step-up gain of a mic transformer will make the line level even hotter.  If you are using -10dB line level it *might* be ok.

Oops, I mis-read that OP.

An obvious mod is to use a resistive pad before the mic primary winding that will drop the voltage level down and present the transformer with closer to the typical mic source impedance (150-200 Ohm).  To keep the input balanced two resistors in series with the transformer windings with one shunt resistor across it.

The secondary may need some make up gain or not depending on pad attenuation and transformer voltage step up.

Without the pad a hot line input is too much voltage for a mic transformer input.

JR

 

[orangechili]

Thanks guys for the info and responses, after i initially posted it dawned on me that there was likely a step-up going on with the mic transformer used as a line transformer. Using the line in with the transformer reminded me of the same volume level i would get using the mic xlr input with the pad engaged so  I would need to attenuate the level coming in somehow(or just use the pad i guess). If i wasn't careful attenuating the signal and controlling the gain staging it would definitely saturate the iron or following amp stage. I don't know the ratio of the beyers in question but if I had an educated guess based off my experience from use I'd say its likely 10:1(at least 5:1)just like the regular mic input iron on the console. I'll try to get around to measuring them soon. I'm wondering if I should just call it a day and get 1:1 line transformers. It stinks cause the beyers would fit nicely in there.

 

[gridcurrent]

Line input transformers are typically step-down.
Examples are the 31267 as found in Neve consoles, usually wired 4:1 and the 2164 found in early API consoles (10k:600).
1:1 ratio line  transformers are seldom found in consoles since the bridging input scheme was introduced the late 1960.s

 

[ruffrecords]

Line input transformers are typically step-down.
Examples are the 31267 as found in Neve consoles, usually wired 4:1 and the 2164 found in early API consoles (10k:600).

And the reason is headroom. Neve consoles worked on a 24V supply. The typical three transistor preamps in use in the 70s could output about +18dBu without distortion. To get your Neve 26dB of headroom the internal operating level had to be 26dB below this or -8dBu. It you have a line input operating at a nominal +4dBu, the to transform it to -8dBu needs 12dB of loss or a 4:1 turns ratio.

Cheers

Ian

 

[CJ]

run a 20 Hz signal into the primary of the transformer that you want to use,

put an ammeter in series and a volt meter across the primary,

slowly raise the voltage into the pri and plot voltage vs current,

it should be a straight line graph until the transformer starts to saturate,

as the transformer reaches saturation, current will go up quicker than applied voltage,

note the voltage where the graph starts to get non linear,

this will be the max level that your transformer will handle before distortion,

if you like a little saturation to your sound,

then you can exceed this level on purpose,  ;D

 

[JohnRoberts]

Characterizing the saturation point at 20 Hz will give you a clean 20-20kHz, but for typical audio mid band frequencies will be louder than 20 Hz. So that will be conservative.

That said some instruments can have strong content in the 40-100Hz region which is only one or two octaves about 20Hz so not that conservative.

There is a reason high quality audio transformers are bigger. More copper and iron will handle more bass.

JR

 

[mjrippe]

Characterizing the saturation point at 20 Hz will give you a clean 20-20kHz, but for typical audio mid band frequencies will be louder than 20 Hz. So that will be conservative.

That said some instruments can have strong content in the 40-100Hz region which is only one or two octaves about 20Hz so not that conservative.

There is a reason high quality audio transformers are bigger. More copper and iron will handle more bass.

JR

Which is exactly the reason some folks knock the Beyers - small size = earlier low end saturation.  But then there are folks who *like* that sound...

 

[JohnRoberts]

Which is exactly the reason some folks knock the Beyers - small size = earlier low end saturation.  But then there are folks who *like* that sound...

Low frequency transformer saturation in low power microphone circuits are relatively harmless. a little extra distortion here or there.  However on the output side of power amps transformer saturation can be more problematic. When I was designing for the fixed install market where audio gets stepped up to 70-100V in power transformers for distribution with lower wire losses the LF saturation in magnetics needs to be managed to prevent amp damage.

If you think 20 Hz transformers are big for line level, imagine for 50-100W or more? The practical remedy for the install market is to never even try to pass 20 Hz, but even install customers want some boom with their sizzle.

JR

PS: I think I may have used some Beyers in one early console of mine (because of the cost), but I quickly shifted to transformer less preamps as soon as I figured out how, because it was even cheaper than Beyers, with ruler flat response and low distortion.

 

[kambo]

There is a reason high quality audio transformers are bigger. More copper and iron will handle more bass.

JR

lundahl  ???

 

[orangechili]

Wow, thank all of you for the wealth of information here! I love the people on this forum 

I took the advice stated earlier and wired a beyer in reverse on another channel. I then compared the difference by ear between the two channels. The sound workshop console definitely likes a hot signal so I did miss that a little with it wired backwards but I didn't get any transformer saturation at all. I think in reverse it may have stepped down the signal a little too much for my liking. I probably would like a 4:1(or 1:1) instead of a 10:1. It does function properly though and sounds good, I just don't want to use that high of a trim setting if I don't have to on the console.