Tone control buffer sugestion

[catalin gramada]

Hello.
I want to use a buffer to drive a James tone control. Thinking more a ac coupled cathode follower able to say 100V pk-pk clear swing I wonder if an 12au7 is a good candidate ? What should be a good load line keeping the h-k potential into safe region please ? Usable B+ supply 350v around. Thanks

[pdf64]

If you’re not wanting the asymmetry thing of a dccf, how about using a self balancing paraphase type inverting amp, eg v4b of https://el34world.com/charts/Schemat...Vox_ac50_2.pdf
It should have very good linearity and available signal swing.

[Helmholtz]

If you’re not wanting the asymmetry thing of a dccf, how about using a self balancing paraphase type inverting amp, eg v4b of https://el34world.com/charts/Schemat...Vox_ac50_2.pdf
It should have very good linearity and available signal swing.

What would be the advantage of a paraphase over a common cathode stage as you could use only one plate output?
(BTW, the first real guitar amp I had was an AC50, bought around '69. Never liked it, maybe due to Fane speakers. Wouldn't sing with my Hornby-Skewes treble booster. Was a decent bass rig, though.
The 1970 AC30 I traded it for was so much better. The only vintage tube amp I liked even less was a Selmer Zodiac.)

And what's wrong with an AC coupled CF? It should be very linear because of local NFB.

But my first question would be, how low the source impedance needs to be: 1k,10k, 20k?

[catalin gramada]

Thinking to use the both halves of tubes as follow: first half buffer for tone stack with maximised headroom, 10 k source impedance should be right , and second as preamp line out buffer 1 k at least . I.ll put a schematic in a sec...

[catalin gramada]

Something like this, more or less. The second cf act as a line out buffer.

[Helmholtz]

The ECC82 has a Vhk limit of 180V (same as ECC83).
So you should bias for a cathode voltage of around 90V. Output impedance will be around 1.5k. An ECC83 would give even lower impedance.

[pdf64]

What would be the advantage of a paraphase over a common cathode stage as you could use only one plate output?
(BTW, the first real guitar amp I had was an AC50, bought around '69. Never liked it, maybe due to Fane speakers. Wouldn't sing with my Hornby-Skewes treble booster. Was a decent bass rig, though....

Sorry if the reference to the paraphase was misleading, I was thinking of a single triode section common cathode stage, configured as an inverting feedback amp, possibly as per V4B of that AC50. A link to the Aiken page on the topic would have been a better idea http://www.aikenamps.com/index.php/d...ack-amplifiers
Yes, AC50 can be amazing bass amps, though I've never really tried one for guitar, as they seem too beefy.

[Helmholtz]

I was thinking of a single triode section common cathode stage, configured as an inverting feedback amp, possibly as per V4B of that AC50. A link to the Aiken page on the topic would have been a better idea http://www.aikenamps.com/index.php/d...ack-amplifiers

So you're suggesting a common cathode stage with local voltage NFB.
That would be an interesting option if a little gain is required.
Generally it would have a considerably lower input impedance and a higher output impedance than the CF.
The output impedance of an ECC83 (Ip=2mA, Rk=47k) calculates as 460 Ohm.
At such low plate current the ECC83 makes a better CF than the ECC82.

[pdf64]

If the inverting CC feedback was configured with 1M input and feedback resistors (Ri and Rf in the Aiken page), the input impedance shouldn’t be a problem for most applications, and its output impedance should be down around1k. Plus the cathode - heater voltage wouldn’t be an issue.

[Helmholtz]

If the inverting CC feedback was configured with 1M input and feedback resistors (Ri and Rf in the Aiken page), the input impedance shouldn’t be a problem for most applications, and its output impedance should be down around1k. Plus the cathode - heater voltage wouldn’t be an issue.

But that would mean a gain of 1, so no advantage here. More gain would require to lower the input impedance (Ri).

If as suggested above, the cathode voltage of the CF is chosen to be below 90V, cathode-heater voltage shouldn't be an issue.

No doubt, your proposal is a serious alternative to the CF.

But the CF needs less components .