op amp to tube conversion ?

[skal1]

1}how would i implement a parallel eq section with a pultec filter
section .
2}How do serial eq filters differ from parallel is the lata better or just different from parallel.



regards


skal1

 

[shabtek]

by series, I think you refer to a pultec/passive topology...frequency selective networks shunt (subtract/dump to ground) more or less of there respective spectral band and a make-up amp corrects for the loss imposed by the passive eq network (when it is set to flat)

please do us a favor and read through the METAs, tons of good info out there

by parallel you are talking 'bout an active topology like the S800, calrec, sontec, w492, 553, etc..(?)where frequency selective network is in the feedback path of an op-amp negative fb=cut ;positive fb=boost

can all be done with more or fewer tubes. silicon is cheaper and easier to implement for many functions.

do you want tubes to do all the magical things like 2nd harmonics, soft clipping, warmth?:
build a couple 1 bottles, milas, g9s, whatevers, omit the mic step-up transformer...build 4 1-bottles and cascade 2 pairs for extra goodness...

 

[CJ]

See if you can wrap your head around this.
If it bores you, then your in good shape.

http://home.online.no/~jaeioluf/sound/eqpassiv.htm

 

[gemini86]

after all this talk of tube opamps, got me thinking about the api312, and how it might sound with a tube opamp. so, a couple questions:

1- Would a tube opamp work in a 312 type preamp circuit? (not just dropping it into the board, actually building a 312 variant around it)

2- if so, what submini tubes would work to substitute for the ones in the forssell schematic?

3- what components in the standard api312 (2520 opamp) might take issue with the tube opamp in the 2520's place?

I'm still learning so bear with me! thanks!

 

[shabtek]

@ gemini86:
the only things one would change on the 312 to make it 'VOA' is the voltage of the power rails, the capacitance values (higher voltage rating, to cope with the new rails) maybe some resistor value tweaks, the output trans--it wants a very low source Z, not practically realized with a handful of tubes, so a different output transformer...
VOA:
try using 2x 8058 for the differential input pair and 2 or 3x 7586 in parallel to give a lowish Z drive. with one of the basic topologies as above.
I dont think you will be able to get the gain available from the 2520.I'm not up to tackling the maths (don't know how) for this but I think it is a place to start...probably need some serious I @ 6.3V--as these are .135mA each tube= 3/4 amp at 6.3 volts, probably need dc heaters

You definitely could re-use the 312 input transformer though.

try a 1 bottle. for starters! won't be disappointed.

 

[gemini86]

Well with a max gaig of 35 dB each (i'm guessing they're using a dB scale?), 2x 7586's should give me about what the api2520 puts out. Is that a correct assumption? or is it more complicated than that?

I was actually looking for a submini tubes that would make the entire board more compact, about the same size as a 312 card. and using dual triodes would make things even more compact... so any suggestions in that area? I would gladly build an output trans, or find a very close match to make the output impedance work.

This project would be used with other gear in the chain, along with a very expensive 24 track console (at least to me it is) that I want to avoid mismatching impedance and overloading something.

 

[shabtek]

everybody build a 1 bottle

 

[gemini86]

[quote author="shabtek"]everybody build a 1 bottle[/quote]

I'm not sure I follow, are you saying that everybody builds a single triode? I was thinking about trying a 6111 for the diff amp, then into a 6112 for the output, being that it's a hi-mu tube. Both of these are sub-mini dual triodes.

I can't get enough info on the tubes you suggested to see if these are at all similar. I seriously don't know enough about this to just decide what tubes to use. Maybe I'll just buy a few different ones and experiment.

thanks for all the help so far!

 

[shabtek]

http://www.groupdiy.com/index.php?topic=6711&highlight=bottle

 

[gemini86]

thanks for the link.