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I am building a bass amp for a friend, and his guitar has a balanced line out which I would like to pair with the amp. I know that with a simple transformer is used to make a balanced line out, but is it the exact same thing in reverse to make a line in???

Thanks for your help, this has been causing me some major head aches.

I work with balanced lines in broadcast, and the simplest way
to do this would be a simple 10K to 10K (or higher) transformer
on the input of your amp. A balanced guitar makes lots of sense,
since hum always seems to be a problem.

Excellent, i was hoping it would be that simple. I found a kit on webers site that i am using to do the balanced out, will these parts work as well for the line in?

https://taweber.powweb.com/store/modkits.htm#balun

Yep - that should work, I am assuming the transformer they
supply is probably high impedance on both sides, judging
by the high value of the pot.

fantastic, thanks a heap!!!

ioginy wrote:I am building a bass amp for a friend, and his guitar has a balanced line out which I would like to pair with the amp. I know that with a simple transformer is used to make a balanced line out, but is it the exact same thing in reverse to make a line in???

Thanks for your help, this has been causing me some major head aches.

Did you ever build this amp?

I'm thinking "why convert the balance input to single ended?" It seems a waste because you are only going to send the SE signel into a phase splitter and make the balanced again? If tyou leave off the transformers you can also loose the phase splitter. It's win/win.

What you do is build a balanced preamp. Basically each side of the balanced input goes to it's own triode gain stage then these directly drive the power tubes. (I'm assuming the bass has an active preamp, go you don't need a ton of gain in the bass amp)

Hammond build their big church organs this way. You get better sound and maybe even lower cost.

I think if Electrioc guitar had been invented today any decent engineer would have thought to run BOTH ends of the pickup coil to an XLR jack and then use a standard mic cable to the amp

ChrisAlbertson wrote:I think if Electrioc guitar had been invented today any decent engineer would have thought to run BOTH ends of the pickup coil to an XLR jack and then use a standard mic cable to the amp

I'm currently upgrading parts of my guitar, and this is giving me too many non-backwards-compatible ideas.

ChrisAlbertson wrote:

ioginy wrote:I am building a bass amp for a friend, and his guitar has a balanced line out which I would like to pair with the amp. I know that with a simple transformer is used to make a balanced line out, but is it the exact same thing in reverse to make a line in???

Thanks for your help, this has been causing me some major head aches.

Did you ever build this amp?

I'm thinking "why convert the balance input to single ended?" It seems a waste because you are only going to send the SE signel into a phase splitter and make the balanced again? If tyou leave off the transformers you can also loose the phase splitter. It's win/win.

What you do is build a balanced preamp. Basically each side of the balanced input goes to it's own triode gain stage then these directly drive the power tubes. (I'm assuming the bass has an active preamp, go you don't need a ton of gain in the bass amp)

Hammond build their big church organs this way. You get better sound and maybe even lower cost.

I think if Electrioc guitar had been invented today any decent engineer would have thought to run BOTH ends of the pickup coil to an XLR jack and then use a standard mic cable to the amp

Wow, that's a brilliant idea. I haven't built the amp yet. I left it too long and got my brain working on a different preamp design so I scrapped the old one and started working on a new one. The curse of an over active imagination. None the less, I'll look into that set up. It sounds great.

Sorry to break your bubble, but if you try to maintain a balanced amp throughout the preamp tone controls are almost impossible. The only way they could be done is with switches to select highly matched componets. This is one of the reasons high end preamps have dropped tone controls.

Also, the circuit requires twice as many gain stages and require a means for balancing the gain between the two signal paths (+ and -).

I wonder if the Hammond 124B interstage transformer might be useful for this application.

It has a nominally 10K primary and 90K CT secondary, so the total winding ratio is 1:3, or 1:1.5 either side of CT. THis trannie has some nickel lams, so the overall freq response is a bit better than the standard 124, and it is open frame, so some kind od shielding may be necessary, especially for low level signals and high gain stages, in order to prevent or at least seriously reduce any magnetic field AC hum pickup problems. . Maybe a small steel box, or even a snall "tin" steel can, like the type that tomato paste comes in.

Friend of mine here, who plays in a Christian rock band, has an acoustic guitar with both balanced XLR output and standard single-ended 1/4 inch jack. It has some on-board electronics, has the treble and bass controls as well as volume, and pickup selectors, as well as a built-in "tuner".

/ed B