Bass Preamp advice, please

[titanicslim]

Hey, Gang

It looks like I'm gonna be needing another "big" amp, 'cause the band I've been playing with has decided they want to play some big rooms.

For the time being, at least, I'm thinking of making a tube preamp and mating it to a Crown power amp. This will mean my rig will be in four major pieces (including speakers) but all of them manageable pieces.

Anybody have any ideas about a good circuit for the pre?

There is, of course, the Alembic F2B, and I may end up doing that anyway, but I'm curious if anybody knows of a significantly different (i.e. not a Fender or Marshall clone) unit I could try. Barring that, have you got any good ideas or mods for the Alembic/Showman circuit that would be interesting.

Dave

[jaysg]

There is, of course, the Alembic F2B, and I may end up doing that anyway, but I'm curious if anybody knows of a significantly different (i.e. not a Fender or Marshall clone) unit I could try. Barring that, have you got any good ideas or mods for the Alembic/Showman circuit that would be interesting.

Depending on the power amp, the F2-B circuit may not do a good job driving. You'll have to add a cathode follower or some other circuit with a lower output impedance.

[TGA-3]

Demeter makes several Bass Preamps. I have an original VTBP-201. You might want to check out his circuits.

[LeftyStrat]

The FB-2 is a good one. As jaysg said you may want to add something at the end to drive longer cables. I've been toying with building one using the first stage of the dumbleator as the output driver.

Another bass amp that I always hear raves about is the Sunn 200s. Now that might be because of the ultralinear output stage and Dynaco OT, but it still might be worth experimenting with that preamp.

Lastly, if you have Kevin O'Connor's TUT3, you might look at his modern take on the SVT and Portaflex, and use the preamp sections from those.

Most bass preamps use two gain stages (a single 12ax7), if it was me I'd pick a couple or three that struck my fancy and then use one extra tube as a mixer stage and low impedance driver stage.

You could either blend them or use some relays to switch between them.

The Sunn preamp has hi-boost and lo-boost switches, which a lot of people think gets you into the ampeg territory, so the Sunn and Alembic preamps together with mixer and driver would only be three tubes and probably cover a lot of tonal territory.

[titanicslim]

Thanks, everybody, for the input What you are saying makes a lot of sense and has given me a lot to think about.

Lefty, I think you get the gold star for the two channel rig with a Dumbleator driving Add a footswitch and there isn't an amp in the world that covers it better. I was on the road for about a dozen years and 90% of the time used either a 2000s or an SVT. The only thing I disliked about either was replacing the output tubes

I've got a couple of projects to get off the bench first, but I'll be back with many s when I start on this one

Dave

[LeftyStrat]

I was on the road for about a dozen years and 90% of the time used either a 2000s or an SVT. The only thing I disliked about either was replacing the output tubes

I used to lug around an Ampeg VT22 "88 Pounds of Devotion". I always thought that the Ampeg tone controls pretty much left every other tone stack in the dust.

I scored an old Dynaco A431 (Same OT as used in the 200S), and at some point I'm going to build a bass amp around it.

I'd be curious to know how your preamp turns out. For my bass amp I plan on going either dual or triple channel preamp, mostly to capture the classic bass tones (Sunn, Fender/Alembic, Ampeg).

[titanicslim]

First time I left home to play, the bandleader noticed that, at practice, I was always fiddling with the controls on my borrowed Fender amp, my head resting on my other arm, staring at the knobs, unable to hypnotize the pots.

He took me to a dealer in Tacoma (I wish I could remember the name) and he let me try every amp in the store, sold me a 2000s w/JBLs for a great price, then let me take it for no down payment (this was about 1972) and I sent him payments from six or eight different cities until it was paid for

I also am collecting large specimens of Dynaco iron

Dave

[LeftyStrat]

I have an original A470, and I recently bought a Dynaclone A470 from triode. Haven't quite figured out what I am going to do with them. Half of me wants to build a nice stereo tube amp. The other half keeps looking at the original for a rocket or liverpool clone, or a combo built into a cab like this:

http://www.vintone.com/rc_ac30_o

There used to be a store here in Seattle called "Old Technology Shop", that had all these NOS tubes and transformers. The guy closed up shop about a year ago, and towards the end was discounting things like crazy. In the last days he was selling iron by the pound. For twenty bucks I picked up everything I could even possibly ever use. Some are power transformers with very high B+, so I'm not sure about those, but I picked up the one A470, a Stancor OT and some nice old chokes.

Bought every one of his Mullards and Telfunkens, and literally a grocery bag full of NOS 12SN7's, which makes a nice 1 watt output tube for miniamps.

I was in heaven at the time, but it quickly faded, I really miss the store. It is quite a luxury to be able to drive ten blocks to a store to pick up a nice NOS EF86 for that latest project.

This guy knew every ham and hifi hound in Seattle, and would go to their estate sales when they passed. Tube testers, iron, tubes, old radios and stereos, tag boards, big hefty rheostats... heaven.

The place even smelled great, just like a warm tube amp.

[LeftyStrat]

Well I waxed poetic and forgot why I was posting. Another tone stack to consider for a bass preamp is this:

http://members.aol.com/sbench101/Batter ... estac.html

This would be similar to the SVT tonestack without having a special tapped inductor for the midrange.

The values given are for guitar, but it could be adapted to bass. My idea would be to use this and instead of the switchable mid, dupe the mid-range band (hi and lo) for a four band tone stack. Dump the hearing aid tubes and use a single 12ax7 for pre and recovery.

Might be a good 'modern' channel for a preamp.

[titanicslim]

Well I waxed poetic and forgot why I was posting. Another tone stack to consider for a bass preamp is this:

http://members.aol.com/sbench101/Batter ... estac.html

This would be similar to the SVT tonestack without having a special tapped inductor for the midrange.

The values given are for guitar, but it could be adapted to bass. My idea would be to use this and instead of the switchable mid, dupe the mid-range band (hi and lo) for a four band tone stack. Dump the hearing aid tubes and use a single 12ax7 for pre and recovery.

Might be a good 'modern' channel for a preamp.

Does he intend this to be some sort of onboard rig?

[LeftyStrat]

I think it was part of a larger project to product a battery powered amp. However, you could replace the tubes he uses with 12ax7's. The inductors he uses are available at Mouser for pretty cheap.

Just thought I would throw it out. The original inductor used for the midrange in the SVT is a multi-tapped beast that is impossible to find. This design uses easily found parts and with some tuning could get close to the SVT tone stack.

[titanicslim]

Hmmm..... Well, I've got odds and sods enough to created a reasonable fax,emily. And I've actually got a trannie with disused 45 watt outs, but its HV taps are currently being employed in a Liverpool clone.... I'll rig something if it doesn't get too complicated.

Thanks If it produces something like an SVT pre, you'll get one of the pups

Dave

[mhuss]

Another option is the Hiwatt AP preamp -- the tone controls are much more responsive then the normal Fender/Marshall stack, and they truly are all-purpose; sounds good for guitar or bass.

http://mhuss.com/Hiwatt/Schematics/DR_Pre4Input_v1.pdf

--mark

[titanicslim]

Mark

Thanks very much for that one. That's very intriguing indeed. My only deep personal involvement with a Hiwatt was one belonging to a guitar player a long time ago who insisted upon always playing a little too loud, and the leader, naturally, insisted it go on my side of the bandstand. No question that, over the years, I haven't given these amps a fair shake. I hate playing with cotton in my ears.

I can't quit staring at this schemo! I think you guys may have given me the answer- don't go A-B with your amps- do it with your preamp channels on a rotary footswitch! I wonder how many I can get away with... This will require some thought, and that's shaky ground for me.

Dave

[LeftyStrat]

Build 'em all, let the ears sort them out. Nice thing about preamps is other than the tonestack, it is just a few component changes. Build a few and let us all know what you think.