Hello all,
I'm looking for a way to drive a 100 foot or so cable from pre to power amp with a single triode that balances the signal. I don't need any more gain.
Possibilities:
A) A differential pair with local feedback, like a differential pair of anode followers
B) A cathodyne with just the anode output buffered, and an appropriate resistor to give both sides the same output impedance- something like a kappler phase inverter- I've read what I could find about this on th AX forum and I may in fact be "too cheap" to use two tube envelopes to get this done.
Any feedback on these possibilities? Is the first one really possible? Any hangups there?
Thank you all,
Tapehead Ted
I'm looking for a way to drive a 100 foot or so cable from pre to power amp with a single triode that balances the signal. I don't need any more gain.
Possibilities:
A) A differential pair with local feedback, like a differential pair of anode followers
B) A cathodyne with just the anode output buffered, and an appropriate resistor to give both sides the same output impedance- something like a kappler phase inverter- I've read what I could find about this on th AX forum and I may in fact be "too cheap" to use two tube envelopes to get this done.
Any feedback on these possibilities? Is the first one really possible? Any hangups there?
Thank you all,
Tapehead Ted
You must mean a single dual-triode tube.
A) perhaps with a 6AS7? Or as mentioned a smaller tube driving a transformer.
B) probably too high Zout.
100ft cable is like driving 3-4nF, which isn't as bad as I first thought, but Zout should be < 2kohms.
Long cables means equipment at each end with different AC power connections. A transformer not only gives you proper drive and optimum balance, but also galvanic isolation which eliminates ground loop problems.
A) perhaps with a 6AS7? Or as mentioned a smaller tube driving a transformer.
B) probably too high Zout.
100ft cable is like driving 3-4nF, which isn't as bad as I first thought, but Zout should be < 2kohms.
Long cables means equipment at each end with different AC power connections. A transformer not only gives you proper drive and optimum balance, but also galvanic isolation which eliminates ground loop problems.
Thanks for the replies.
I am resistant to the idea of a transformer, but it keeps coming up. I have always much preferred a transformerless option when I've had one, on some very nice gear- but 100 feet may be a different story.
I am resistant to the idea of a transformer, but it keeps coming up. I have always much preferred a transformerless option when I've had one, on some very nice gear- but 100 feet may be a different story.
> Zout should be < 2kohms.
And it should be able to drive *cleanly* into about that impedance.
Small tubes go down to maybe 5K. A 2K load is heavy work.
6AS7 goes to 300 Ohms, easily drives 1K, but is a huge hot beast of dubious linearity.
Are you sure you need Balanced? A high-quality differential ("balanced") input at the far end covers much ground-crap.
If you must balance, then two tubes in series drive the few-K load of the cable capacitance at the top of the audio band. So each tube sees half the load.
10K:600 transformers exist for a reason. A single section of 12AU7 will drive 10K with authority. 600 Ohm source will drive even longer lines.
And it should be able to drive *cleanly* into about that impedance.
Small tubes go down to maybe 5K. A 2K load is heavy work.
6AS7 goes to 300 Ohms, easily drives 1K, but is a huge hot beast of dubious linearity.
Are you sure you need Balanced? A high-quality differential ("balanced") input at the far end covers much ground-crap.
If you must balance, then two tubes in series drive the few-K load of the cable capacitance at the top of the audio band. So each tube sees half the load.
10K:600 transformers exist for a reason. A single section of 12AU7 will drive 10K with authority. 600 Ohm source will drive even longer lines.
I have build for that same pupose a hybrid solution. Get some harmonics and driving long cables.Using the newest tubes as in Korg SV-1 and Vox MV amps.
My son use the driver between DJ booth and DBX Pa2 active filter.
Below a unbalanced tryout, now i am building a Pro version with balanced signal and adjustable distorsion. Now you can use it as clean line driver or as harmonizer/tube distorsion effect.
My son use the driver between DJ booth and DBX Pa2 active filter.
Below a unbalanced tryout, now i am building a Pro version with balanced signal and adjustable distorsion. Now you can use it as clean line driver or as harmonizer/tube distorsion effect.
Attachments
Last edited:
It only takes two capacitors and three resistors to convert an unbalanced output to a balanced one.
- Status
- Not open for further replies.