Transformers berfore a mic pre

[FilmDingo]

I've seen the odd post suggesting using transformers on the inserts to try and get some vibe into a clean pre.

I've not actually found anyone who has done it! Anyone gone beyond thinking about this and actually wired up a test?

So now we get to the really NooB q.

Can I put a transformer in the signal path between a mic and the pre on my MOTU 896? I'm getting the Black Lion Mod, so it should be a nice clean pre - I just get annoyed at the thought of buying 8 more pres than I need for a different color.

Any thoughts? Will it float? Seen a white paper that hit this? I'd like to learn more, and so far I have not found this covered on any Transformer websites.

Many thanks
Deane

[Matt Syson]

hi
You could collect a variety of transformers and try them in various positions to get a 'sound' you want. Small cores will saturate earlier and info can be found on the net about them (www.canford.co.uk for sowter and Lundahl for instance).
Get them wired in a box with XLR or jacks so that you can plug them quickly and experiment away. If it is to be used before the mic amp then they must be well shielded to reduce hum pickup and of course the signal will be low level here so is less likely to saturate although different core material makeup will affect the sound.
If you are looking for a saturation 'effect' use it on the insert and chose models that have lower rated signal level, say 0 or +6dB. A version which is rated for +24dB or thereabouts will be far more subtle effect.
All good clean fun and safe so get playing.
Matt S

[FilmDingo]

small core sounds great. I am using a MOTU 896 so there are NO inserts .

So I will have no choice but to put 'em before the pre, but with a hot condener that should give it a fair whack ' o signal to choke on.

Any actually done any of this?

Thanks for the 2 previous replys, we are off to a great start.

[hrn]

I had an idea in a similar way discussed at:

http://www.prodigy-pro.com/forum/vie...549&highlight=

I was thinking about the options to play with the impedance loads and of course the tranny sound.

Guess a 1:1 tranny would be easier.....

Hans

[FilmDingo]

Thanks Hans - now I have a couple of model numbers to look up. How far did you get with your experiments?

[Tim Farrant]

If you place a transformer in the mic line, you will need to organise an external phantom power source if using mics that require it. Neutrik make some little mic input transformers with small cores that might do the job.

Tim.

[FilmDingo]

Holy Crap - talk about missing the obvious.

Yeah, my entire mic collection is very fond of phantom power. The cost of that alone makes me stop worrying about getting 8 new pres.

If I had inserts, the tranny thing would be worth a shot, but I am mad keen on a robust source of phantom - and having built those little kits 10 years ago, I really can't be buggered to go halfway to building a new pre when I could have...a new pre.

Well, that's what this board is for...nattering about my beautifull theories untill thay are murdered by a gang of ugly facts.

MOTU for not putting $2.00 worth of connectors on the box for frikken inserts. I roundly chastised a Mackie rep the other day - their older 400f firewire thingy has inserts on all 4 mic pres - the new 12ch version only has 2. I guess firewire interfaces (on the whole) are not designed by recording people. Just musicians who really love to go direct and use an amp sim and have never heard of compression in the tracking process.

OK - rant is over.

[Tim Farrant]

Maybe you should consider getting into an API 500 series rack and adding preamps as you can afford it?

[FilmDingo]

yeah, that was always an idea, it's just my Dunedin heritage that makes me cheap. There is no way around the "get what you pay for" factor this time.

Well the OSA racks are cheap, but there are a lot of good 4ch pres too - Sebatron, UA, Vintech and so on...

Thanks Tim

[Lucas]

here's a link to a +48V phantom power supply...however I'm not sure how robust it is.

http://sound.westhost.com/project96.htm

[hrn]

It's easy to find external phantom power supplies, and the prices are kind of low:

Googled this among others:

http://www.zzounds.com/cat--Phantom-...Supplies--2829
http://www.samedaymusic.com/browse--...Supplies--2829
http://www.bhphotovideo.com/bnh/cont...75&Q=&O=NavBar

Hans

[Matt Syson]

Hi
Adding an insert point is not cheap if you are doing it properly.
You would need an amplifier stage to be able to 'drive' the insert send, the internals are probably already busy and you should be doing it balanced. Then you need a balanced return amp to get it back to 'system' level. All in all a pain, and then your punters want it for next to nothing....
Getting phantom power across a transformer is done by having centre tapped primaries and secondaries. Link the centre taps directly and the job is done.

Matt S

[Jim Williams]

See the Jensen Transformers application note AS015. It shows how to do this.

Jim Williams
Audio Upgrades

[username]

well this has all got me rather interested!..

what I gather from this thread (I know very little about electronics) is that if I grab a 1:1 ratio audio transformer (of reasonably quality).. with a 1% THD rating of about +18 or +20 and wire it up with xlr in and outs.. then go an plug it into the insert of a preamp.. it will most likely add some of the saturation and tone generaly associated with Transformer gear?

This sounds too good to be true.. I'm assuming I'm either wrong.. or suitable transformers for this task are rediculously expensive??.. otherwise this would be an amazingly cool toy to have around..

[Matt Syson]

Hi Username
Basically yes, and you certainly won't break anything by playing.
It depends on how subtle you want the effect to be although for a mild effect you won't be far off. The distortion level is often quoted at 50 Hz and there may not be a large level at this frequency so for an 'effects' transformer you may want to go for 1% at say +12dB. You may also need a samll amount of experimentation to add a resistor or resistor and capacitor combination to overcome ringing although it in itself is an 'effect' so you may want it. Transformer manufacturers usually give typical values to use (Lundahl and Sowter do certainly ). A transformer type with a variety of tappings may be more 'fun' for experiments although you will probably add gain or attenuation (not necessarily a problem). For transformers without their own shielding can, you will probably need to mount it in a steel box to reduce stray hum pickup, and even so you may have to position it carefully.
Have fun
Matt S

[username]

okay.. so I'd be looking at something similar to this?

http://www.sowter.co.uk/specs/3292.htm

what do you mean about ringing?.. I don't realy quite understand (I'm pretty ignorant of electronics)

[Matt Syson]

Hi
Yes that transformer looks interesting. I am afraid you will have to try one to see if it does what you would like it to do.
Ringing. An inductor (transformer for example) and capacitance (the cabling etc) will form a 'tuned circuit' at one particular frequency )(1/2.pi.F.L) and in the case of a transformer used conventionally will give a frequency response boost at the frequency determined by the inductance and capacitance. This may be in the audio band or anywhere from a few KHz to 100KHz or more. This effect is often referred to as ringing (like a bell). To stop it, or at least tame the response a load resistor can be used.. For the transformer you indicated the load could well be 600 ohm resistive in which case it does not ring excessively. If you were to omit the resistor (actually using a much larger resistor) then it may have a rising response and ring. You can check for this by using a REAL VU meter and oscillator capable of up to 50KHz or more and look for an increase in level at high frequencies. You need a real VU unless you are using 192K converters, 48K will automatically filter anything over 24K. The effect is only like a HF boost and won't damage anything so play away!
Matt S

[sleestack]

Does anyone build boxes with just transformers that you can put after an intrument? Is there something cheap I can buy that happens to have transformers that saturate nicely when overdriven?

[sleestack]

bump

[emrr]

I keep all kinds of odd 1:1 ratio transformers around for this purpose, but always use them after the fact as additional color at line level.