EL84 as Preamp and as Crossover

[navin]

I am thinking of building a tube preamp, crossover and power amp.

the pre amp will be about 15 meters from the crossover and power amp.

Since the distance between the preamp and crossover is so long would it make sense to use a EL84 as a preamp?

Also could the EL84 be used as a Crossover (12db/oct)?

If so does anyone know of a schematic using the EL84 as a preamp and/or crossover?

I assume that 1 EL84 per channel would suffice for a preamp and 1 EL84 (triode) would suffice for the crossover.

[hacknet]

i don`t know if you can get 12dB/oct with 1 stage. from what i know. 1 RC filter will get you only 6dB/oct. you`ll have to stack if you want more.

[navin]

Originally posted by hacknet
i don`t know if you can get 12dB/oct with 1 stage. from what i know. 1 RC filter will get you only 6dB/oct. you`ll have to stack if you want more.

ok so i will need 2 EL84 to get a 12db/oct slope. thanks.

any schematic that you know of?

[hacknet]

why would you want to use a el84 as a crossover? its rather distortion ridden and microphonic. why not go for something more efficient like an opamp?

[ilimzn]

Originally posted by hacknet
i don`t know if you can get 12dB/oct with 1 stage. from what i know. 1 RC filter will get you only 6dB/oct. you`ll have to stack if you want more.

If you don't know it, it does not mean it is not possible
One of the implementations of a 12dB/oct active filter requires an amplifier with Av=1, i.e. a follower - which should be fairly easy to do with an EL84. Triode mode will have a gain somewat less than 1, which will produce an error in the filter's transfer characteristic, but this could be reasonably compensated.

[rdf]

I've played around with triode connected EL84s as drivers for an EL84SE. Of the brands tried (EH, JJ, Sovtek and Russian EL84M) my experience was hacknet is right when he says they're too microphonic at that signal level.

[Wodgy]

15 meters? If you're planning a line-level cable run that long, your priority should be building a preamp with balanced outputs.

[ErikdeBest]

15 meters? If you're planning a line-level cable run that long, your priority should be building a preamp with balanced outputs.

Agree on that - and while you're also thinking about building power amps, I would suggest them to be along the lines of this one: as far as my knowledge goes you could easily turn them into balanced amplifiers.
http://www.wdehaan.demon.nl/tubeamps/el84dc/

For higher power with EL34.
http://www.vacuumstate.com/schematics/pp-1c_s.gif

For the low output impedance needed to drive the 15m of cable a white cathode follower with a regulated PS would be good, even using some 'small' tube (a double triode).

And in case you haven't seen it yet...
http://www.tubecad.com/articles_2001...s_and_Filters/
http://www.tubecad.com/articles_2001...ed_Crossovers/

Erik

[anatech]

Hi navin,
Unless there is a good reason to run the signal that far, move the amp(s) back to the rest of the equipment. The signal between the pre and power amps is the most delicate, unless we talk about a turntable. The difference between 2 feet of wire and 20 feet of wire is tiny and overshadowed by other negative things.

-Chris

[navin]

Originally posted by anatech
Hi navin,
Unless there is a good reason to run the signal that far, move the amp(s) back to the rest of the equipment. The signal between the pre and power amps is the most delicate, unless we talk about a turntable. The difference between 2 feet of wire and 20 feet of wire is tiny and overshadowed by other negative things.

-Chris

thanks everyone. wow what a response! I feel special.

the object of locating the power amp that far away is to located them behind the speaker and make them more discrete. this way WAF only sees the preamp and that too is only because of the volume control.

Presently I have a home made SS preamp and 200W SS power amp. The preamp uses relay switching a pair of OP275 and an ALPS pot. The power amp uses Hitachi MOSFETS (3 pair per channel) and is similar to B&K ST140 in topology. Both were built by a friend.

Anyway my wife wonders why I need such large equipment when most of our friends are happy with their Bose Acoustimass and B&W VM1.

Tube power amps will be bigger considering that I am thinking of using an active XO and biamping. OPTs and such are not really WAF compatible.

I got interested in tubes when the same friend got a Prima Luna Prologue 2 KT88 40W amp to replace his 200W solid state. Yes the max SPL is lower but the sound quality is nice. I cannot afford the Prima Luna he has.

Any other options?
SS preamp feeding tube power amps perhaps?
Tube preamp feeding small gain clones?