Input vs Output transformers

[Trench Recordings]

So if transformers are passive and can be run backwards in some cases. Why is there input and output transformers? Would one type of transformer work for both? Output transformers seem physical larger in general.

 

[Echo North]

Page one right side:

http://www.jensen-transformers.com/an/an002.pdf

 

[JohnRoberts]

So if transformers are passive and can be run backwards in some cases. Why is there input and output transformers? Would one type of transformer work for both? Output transformers seem physical larger in general.

Transformer size reflects the power they can pass cleanly. Line level transformers are larger than Mic level transformers. Output transformers are larger (in general) to drive potentially lower load impedances, while input transformers can be terminated with relatively high impedances to always keep power requirements modest.

JR

 

[Trench Recordings]

So I have a great sounding older late 60's - 70's designed mixer with unbalanced monitor outs. It is inherently noisy with ground loops and hum but I managed to get it quiet with xlr and power ground lifts. I recently bought more speakers and a passive xlr speaker switch box to switch between speakers. Now the hum is a problem.

So I guess an output transformer after the monitor out of the mixer is the solution. I had some carnhill input transforms I wired up but the sound was not ideal. Any recommendations ?

 

[ruffrecords]

Difficult to without seeing the monitor output schematic - it may not be man enough to drive an output  transformer. If you use a 10k:10k bridging transformer at the monitor amp input end it should solve your hum problems although I would advise you never to lift power grounds. You can solve all hum problems by lifting signal screens. Lifting power screens is a safety hazard. Which Car hill transformer did you try.

Cheers

Ian

 

[gyraf]

I'm not sure that you'd like transformers in the monitor outputs - after all, you want to monitor exactly what you have - no more, no less.

Maybe try cheating: impedance balancing

Jakob E.

 

[Meathands]

I'm not sure that you'd like transformers in the monitor outputs - after all, you want to monitor exactly what you have - no more, no less.

Why not? A well made transformer can have better specs than many active balancing/receiving schemes.

 

[Trench Recordings]

The general brochure specs are posted in this thread I started a few months back. http://www.groupdiy.com/index.php?topic=49429.msg626831#msg626831

Today I wired up some EA2503 from a build I haven't got around to yet. I wired them 1:1  or 75omh:75omh. They sounds quite good, a bit scooped in the low mids and a bit crunchy in the high mids at times but all in all not that bad.

Way better than the carnhill VTB9046 which just sounded wrong. I'm sure its just the wrong transformer for the purpose or I just wired it up wrong. I tried the carnhill in a 10k:2K4 and in a 2K4:2K4

Both transformers solved my ground hum issue between the speakers and switch box. And I was able to reground the xlrs and power ground. But your right gyraf, I'm not sure if i want to hear the transformers all the time.

So maybe a balancing circuit like the JLM dINgO kit. That way I can keep it DOA and not IC based.

I also have ground hum issues in the unbalanced line in that I'm trying to solve. 

 

[gyraf]

Why not? A well made transformer can have better specs than many active balancing/receiving schemes.

Yes, but only if it is perfectly matched for the job - and in this case we're integrating into already-designed in- and outputs.

Jakob E.

 

[ruffrecords]

Balancing will not solve ground loop problems. You can only to that by isolating grounds and you can only do that by either lifting shields or including transformers.

Cheers

Ian

 

[Trench Recordings]

So what if I where to impedance balance the monitor out and lift the screen/ground at the speaker switchbox ? Whats the best way figure out the resistor value to impedance balance ?

Monitor Out C +---Hot ---------------------------- Line In  + Balance
                    \
                      Cold-- Res Value----------------- Line In -
                        \
                          Ground--------------------------- Lifted

 

[CJ]

so that mixer puts out a line level signal on the monitor jacks and that goes to powered speakers or a power amp and then a switch box?

you might try the 2503 again, only wired for more input Z,

that is a quad wound xfmr, so you could take three windings and put them in series for your pri,  then use the one wind as your output, you will have to make up for the voltage drop,

that transformer is pretty clean, flat from 10 cps to 1 megahertz,(helical coil) probably as transparent as you will find, so you would not have a huge differential in sound, DCR is very low so no smearing of the hi end,

 

[ruffrecords]

So what if I where to impedance balance the monitor out and lift the screen/ground at the speaker switchbox ? Whats the best way figure out the resistor value to impedance balance ?

Monitor Out C +---Hot ---------------------------- Line In  + Balance
                    \
                      Cold-- Res Value----------------- Line In -
                        \
                          Ground--------------------------- Lifted

To make it balance, the resistor value needs to be equal to their hot output impedance.

Cheers

Ian