Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Colas LeGrippa on October 10, 2012, 04:04:04 pm

Title: Modifying a guitar amp input to balanced XLR input
Post by: Colas LeGrippa on October 10, 2012, 04:04:04 pm

Hello my friends,

the idea here is to amplify a sound coming out of a rackmount studio sound processing device which outputs are balanced. I just wanna know what type of input transformer to use here and how to hook it up, thanks folks.

Colas

Title: Re: Modifying a guitar amp input to balanced XLR input
Post by: HotBluePlates on October 10, 2012, 07:07:48 pm

You'll want a single-ended primary and a single-ended secondary. The difference between the two is the shield/ground on the primary will connect only to the chassis (and not to the transformer primary), while the secondary will have one end as the hot and the other as the ground.

But what is the intended output impedance of the gear you'll be plugging in, and what is its output level? These two things will determine the ratio between primary and secondary, as well as the build-out resistor to place across the secondary (if needed).

Is this being plugged into the input jack of a full guitar amp (including preamp), or just feeding the phase inverter? Or would you want to keep the signal balanced, and feed it to a push-pull driver stage?

Title: Re: Modifying a guitar amp input to balanced XLR input
Post by: Colas LeGrippa on October 10, 2012, 07:35:01 pm

Ideally, there would be 2 inputs: one for a guitar ( 1/4 ) and one balanced XLR. If it is useful to use the whole amp or just necessary to hook up the line transformer to the phase inverter, I don't know. I haven't bought the unit yet but it will be a  time delay effect that I could use for recording as well. So, if I compare a regular guitar amp to a mixing board, I would need the preamp and the power amp. The mixing board being a preamp, and the powered monitor speakers being the power amp.

Thanks, bro.

Colas

Title: Re: Modifying a guitar amp input to balanced XLR input
Post by: xm52 on October 10, 2012, 08:00:16 pm

You might find what you are looking at the application schematic page at Jensen: http://www.jensen-transformers.com/apps_sc.html (http://www.jensen-transformers.com/apps_sc.html)

Title: Re: Modifying a guitar amp input to balanced XLR input
Post by: HotBluePlates on October 10, 2012, 08:01:38 pm

In the end, all you're doing is going from balanced to unbalanced operation, so the wiring is easy.

What is the effect? Maybe we can find some specs online for the output level.

Title: Re: Modifying a guitar amp input to balanced XLR input
Post by: PRR on October 10, 2012, 10:49:42 pm

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Title: Re: Modifying a guitar amp input to balanced XLR input
Post by: Colas LeGrippa on October 11, 2012, 08:01:55 am

Good-a Morning-a ,

Wow this is simple, a 10:1 voltage divider, that's all ? No line transformer needed ? And what about the noise ? Any advantage in replacing the first 2 resistors  by a pot, if yes what would be an ideal value ?

( I have worn out the question mark on my keypad )


Thank-a.

Col-a

PS: PRR, what is your brain CPU make ?

Title: Re: Modifying a guitar amp input to balanced XLR input
Post by: PRR on October 11, 2012, 10:52:30 pm

> No line transformer needed ?

There are SO many ways this can go wrong, I can't cover all cases.

However it is a 36 cent experiment/investment. Worth a try.

Title: Re: Modifying a guitar amp input to balanced XLR input
Post by: Colas LeGrippa on October 12, 2012, 08:37:30 am

Hi,

Yeah sure it's worth a try , thanks a million.

Colas