WTbuild stand alone bass preamp...request ideas

[smackoj]

hi amigos. I have a cool vintage Grommes SS power amp that is dead quiet and full of umph. I would like to build a relatively simple tube preamp to use with my Fender Jazz bass guitar which has passive pickups. Do any of you know of a good idea that I could build. I would prefer one with a tone stack on the simple side and I don't need fx loop.

thanks mucho friends

smacko   

[sluckey]

Ampeg B15N or Sunn 200. Both are one tube preamps. Probably need to add a cathode follower or source follower to drive a SS power amp.

[DummyLoad]

copy the ampeg SVT preamp or the alembic F2B.

--pete

[terminalgs]

you know what you pre-amp's input sensitivity and impedance should be (based on your passive jb p/u's),  but what is the input sensitivity and impedance of the Grommes?   It might be non-trivial to find/determine, but its important (1) to avoid a dreaded impedance mismatch,  and (2) to get the max power out of the Grommes.

++1 on Dummyload and sluckey's recommendations. 

Ampegs from the 69 and later era sometimes used switched inductors and extra triode stages for the mid-range (which might make the build more expensive $$).  the bass-boost and treble cut switches, on the other hand, are simple to incorporate,  and you can tweak the cap and resistor pairs for the freq. cut that you specifically want for your sound.

also, have a look at the PA522 transformer (330-0-330 @ 155ma,  12V@800ma) it is a good one for powering small pre-amps.

[6G6]

Another vote for Sluckey and Dummyloads suggestions.

[eleventeen]

"also, have a look at the PA522 transformer (330-0-330 @ 155ma,  12V@800ma) it is a good one for powering small pre-amps."

That's about 15-20x overkill for a one-tube preamp! Preamp tubes use 2-3-4-5 ma plate current. A much cheaper choice (if you have to buy it.... find a piece of junk little appliance >>that uses a power transformer<< or a crunched piece of 1-2-3 tube test gear that will cough up its parts, it is a very common "mode" of PT that is basically an isolation transformer (eg; 125 volt "HV" winding at 10-20 mils and maybe 800ma-1500 ma for heaters for a tube or three. Voltage doubler (or 4-diode bridge rect) on the output for B+ and you're a tad under 300 volts, fine for preamp use.

[terminalgs]

"also, have a look at the PA522 transformer (330-0-330 @ 155ma,  12V@800ma) it is a good one for powering small pre-amps."

That's about 15-20x overkill for a one-tube preamp! Preamp tubes use 2-3-4-5 ma plate current. A much cheaper choice (if you have to buy it.....

sorry, I miss quoted that transformer,  its 330-0-330 @ 15ma.  If 330 is too high, the primaries are 240 -or- 120, so you can use the 240v windings with 120v supply  to provide 165-0-165 and 6.3V if that's more suitable.   

Certainly cheaper solutions abound if used or surplus equipment is available..

[eleventeen]

15 ma = fine. All understood, no problem.

[DummyLoad]

for the 110V/120V nations...

http://triodeelectronics.com/pa2powtrandy.html

for our neighbors across the ponds and 220V americas... 

http://triodeelectronics.com/pa522.html

you will probably want some sort of delay circuit that  keeps the output(s) disconnect at turn on - turn on/off thumps can damage speakers and/or amp.

--pete

[smackoj]

ola amigos; thanks for the suggestions. I was curious if Ampeg B15 would make the list? I like the Mag Components trannies a lot so maybe the dynakit repro would be a good choice for the PT. I have some vintage iron laying about that I will check the voltage on first just to be sure.

adios for now.  jack d