Linkwitz transform w. tubes?

[markusA]

I've been wanting to build something with tubes but try as I might, it's been difficult to come up with something that would fit into my current rig.
So, here's a crazy idea... is there anyone who's tried building a LTC (Linkwitz Transform Cirquit) with tubes? Am I just being stupid for even entertaining the notion?
I really don't know if it's even a viable idea, that's why I'm asking you guys to chime in on the matter.

 

[DF96]

As I understand it, a Linkwitz transform is a filter.

Has anyone ever built a filter using valves?

 

[markusA]

Is it just silly considering this? Should I just go with opamps or all digital? I currently use digital LT...
I'm having trouble justifying a tube build since my rig is quite optimized as is.

 

[pieter t]

You are stupid, and the idea is crazy!
But challenging!
So why not give it a try?
Keeps you off the street (as we say here).
I would try to construct a tube op amp, and implement feedback to make it a LTC.
Maybe the "normal" design with SS opamps provide enough info to get you going.

 

[MarcelvdG]

I never tried it, but there is no reason why it couldn't be done with tubes. If you are not afraid of lengthy calculations and if you want to keep the number of tubes small, this could be an alternative to the Linkwitz transform circuit:

https://linearaudio.net/article-detail/2101

The advantage is that it is based on voltage followers, which could be implemented as simple cathode followers.

 

[pieter t]

Or, to honour your fellow countryman, try this one as building block:
http://www.forsselltech.com/media/attachments/VT_Opamp.PDF

 

[artosalo]

http://www.forsselltech.com/media/attachments/VT_Opamp.PDF

"Op amp" that does not work at DC is not an Op amp.

 

[pieter t]

"Op amp" that does not work at DC is not an Op amp.

???????

 

[markusA]

Thank you for the encouragement, it's nice to know I'm not the only one crazy. The Forsell link was nice, and it doesn't hurt that I have a box of Russian 6dj8 equivalents collecting dust.
4 tubes in total doesn't seam insurmountable.

 

[artosalo]

???????

Here you can find the answer.

 

[pieter t]

Here you can find the answer.

Ehm....where??

 

[stajo]

Of course. An LTC is basically a sloaping LP filter with amplification to compensate for the attenuation and boost the lower register.

 

[artosalo]

Ehm....where??

Sorry, the link was lost.

https://en.wikipedia.org/wiki/Operational_amplifier

An operational amplifier (often op-amp or opamp) is a DC-coupled high-gain electronic voltage amplifier with a differential input and...

 

[PRR]

Early op-amp theory revolved around analog computers which would do a computation (usually in time, because Integrators are powerful), and then HOLD the result so it could be read on a DC meter. (Also HOLD in the pre-set before the computation.)

While I can agree that "opamp without DC response" sounds silly, in Audio this is usaully what we want. It is "nice" to know there are no subsonic poles/zeros to skew our audio response. In practice we are smart enough to allow for them.

 

[MarcelvdG]

If you have to use op-amps, you can try to get some second-hand Philbrick devices somewhere, or try to find a Philbrick schematic and build your own.

The Philbrick Archive