Cathodyne inverter as a balanced output?

[Hellhammer]

I'm designing a standalone pre-amp for bass. As it is now I have a cathode follower as the last stage. I started thinking a balanced output would be a nice addition.

Can I convert the cathode follower into a cathodyne inverter and use the outputs for this? If this is possible I guess using one of the outputs for unbalanced output simultaneously is out of the question as the loading of the outputs would be different... or?

Thanks

[Phil_S]

I'm not sure I understand the question. A cathodyne inverter is designed to balance current on the plate and cathode. Voltages will be quite far apart. By contrast the LTPI produces more consistent voltage to each half.

[Andy Le Blanc]

I did a bass line out using a little DI transformer sourced after a CF

simple, cheap, didn't take up chassis space and had a predictable balance

[Firestorm]

Yes, you can use a cathodyne inverter as the source for a balanced line out. Just connect the outputs to your hi and low pins. Use large enough coupling caps to assure full-band performance and choose load resistors for the impedance you need. I think you're right that you don't want to use balanced and unbalanced outputs simultaneously, so for the unbalanced line out, you should probably use a switching jack to interrupt one leg or the other (after the load resistors).

All that said, I have no idea how the noise performance of this would stack up to a transformer coupled output, which might be a better choice.

[jon]

I'm designing a standalone pre-amp for bass. As it is now I have a cathode follower as the last stage. I started thinking a balanced output would be a nice addition.

Can I convert the cathode follower into a cathodyne inverter and use the outputs for this? If this is possible I guess using one of the outputs for unbalanced output simultaneously is out of the question as the loading of the outputs would be different... or?

Thanks

Just curious, what is the preamp based on?

[Ian444]

The cathodyne needs equal loading top and bottom to stay balanced, so you could only do balanced out or unbalanced out, but not both at the same time, unless the unbalanced input you are driving has a really high input impedance. A mosfet source follower on each output from the cathodyne might be a solution if you need both outputs at the same time.

[FUCHSAUDIO]

most balanced outputs are expected to be 600 ohms. Use a transformer, it's a safer bet, and offers isolation and the right impedances.

[Hellhammer]

Thank you all!

I did a bass line out using a little DI transformer sourced after a CF

simple, cheap, didn't take up chassis space and had a predictable balance

I'm building this as a stomp box with no extra space at all. So a tranformer that takes NO space would be nice!

Yes, you can use a cathodyne inverter as the source for a balanced line out. Just connect the outputs to your hi and low pins. Use large enough coupling caps to assure full-band performance and choose load resistors for the impedance you need. I think you're right that you don't want to use balanced and unbalanced outputs simultaneously, so for the unbalanced line out, you should probably use a switching jack to interrupt one leg or the other (after the load resistors).

I would use a combojack i guess.

Just curious, what is the preamp based on?

Not based on any existing design, but nothing revolutionary I guess. DC-coupling and several gain stages are key elements, lots of tweaking still before I have a good design. I like distortion!

The cathodyne needs equal loading top and bottom to stay balanced, so you could only do balanced out or unbalanced out, but not both at the same time, unless the unbalanced input you are driving has a really high input impedance. A mosfet source follower on each output from the cathodyne might be a solution if you need both outputs at the same time.

I'll keep that in mind thanks!

most balanced outputs are expected to be 600 ohms. Use a transformer, it's a safer bet, and offers isolation and the right impedances.

Using a 12au7 I should get close enough I think?

[FUCHSAUDIO]

not sure if the AU7 would be that low. I'm guessing a few k (maybe 5 or 10-K ) but not 600 ohms. Maybe follow with an FET or an IC buffer.

[Hellhammer]

not sure if the AU7 would be that low. I'm guessing a few k (maybe 5 or 10-K ) but not 600 ohms. Maybe follow with an FET or an IC buffer.

When equally loaded, the output impedance from anode and cathode is roughly 1/gm, the same as a cathode follower.

http://www.freewebs.com/valvewizard/cathodyne.html

Using the gm value of 2,2mA/V from a ECC82 datasheet:
1/0,0022=454 ohms

Am I doing something wrong?

[FUCHSAUDIO]

Hey, if that's what the internet says, we all know it must be true....lol.

It's possible; Again, I was speculating. It sounded low imho. It could not hurt to rig one up on a bread board, or build it and try to drive a 600 ohm balanced input with it. It just strikes me as unusually low to expect from especially the plate side. And, are they equal impedances too ? A dual op amp would do the job and save you a tube/socket/current etc. But, have fun !

[Hellhammer]

Hey, if that's what the internet says, we all know it must be true....lol.

It's possible; Again, I was speculating. It sounded low imho. It could not hurt to rig one up on a bread board, or build it and try to drive a 600 ohm balanced input with it. It just strikes me as unusually low to expect from especially the plate side. And, are they equal impedances too ? A dual op amp would do the job and save you a tube/socket/current etc. But, have fun !

I know you have to be critical regarding sources especially on the net. I've read this from a couple of different sources though, even Merlins book and I have that in print. Now I'm not pretending I get it so I might be interpreting it all wrong.

I know op-amps, tranformers etc would get me there and probably do a better job but since I have half a 12au7 I was going to use for a CF and this seems like an option to get balanced out for the cost of an XLR-socket and a resistor I thought why not? I wil probably try it out in time.

[Ian444]

600 ohms is a tough load, I forgot about that. Hmmm, give it a try without some sort of buffer/s, thats how we learn stuff. Or use a mosfet instead of the tube as a cathodyne, I've done that before.

[FUCHSAUDIO]

That's why I suggested building and trying it. You could build that triode into a small single ended amp, driving a balanced output transformer as well. How bout a single ended small output with 4-8-16 ohm connections. Ground the 8 ohm tap and take the output push pull off 16 and 0....now thats a cool little lo-Z drive... Musical Power Supplies, Hammond and possibly Weber have them.

[rob@tele]

Keep in mind that the frequency of the high pass filter made by the coupling (output) caps and the load impedance is sufficiently low. With a load of 600Ohms you will need 47uF to obtain a high pass frequency of 5.6Hz.

E.g. I think this is also a tricky part of the D-lator send circuit. The send potmeter is 250k and with a low impedance load you get different high pass frequencies based on the wiper position.