A DIY Tube Preamp/Line Driver by Passinwind

[Passinwind]

Originally Posted by MAMMOTHvolume

I've looked at some semi parametric eq's have you found any that look decent? I kind've wanna avoid to much feedback as it normally ruins the dynamics a little doesn't hurt if you wanna get rid of some noise though

The only all-tube ones I've found online that looked all that promising were switched-frequency stuff meant for studio use. Lots of compromises involved, as you said. I'm not too keen on using cheap dual pots for sweeps, for instance. Since I do lots of solid state builds too, I would be pretty tempted to just do a hybrid circuit for swept frequencies.

[lneal]

Charlie: what version of spice are you using?

[Passinwind]

Originally Posted by lneal

Charlie: what version of spice are you using?

LTspice (SwitcherCAD) for the most part, but I've just started messing with Tina-TI too. The LTspice online community presence is really great, and of course free is a very good price!

Eventually I'm hoping to do my own tube models, since a good friend of mine just bought a pretty killer computerized tube testing rig.

[lneal]

Originally Posted by Passinwind

Eventually I'm hoping to do my own tube models, since a good friend of mine just bought a pretty killer computerized tube testing rig.

I'll check that LTSpice out.

Would be cool to have access to a rig like that. I'm still using a Hickok 600A from the early 1960's that works great.

[fdeck]

Charlie,

It might be interesting to look at the semi-parametric in this design:

http://personalpages.tds.net/~fdeck/bass/ebpresche.JPG

I think that with some re-jiggering of component values, something like this could be made to work with triodes, or maybe even with a combination of a triode and a single bipolar transistor.

[Passinwind]

Originally Posted by fdeck

Charlie,

It might be interesting to look at the semi-parametric in this design:

http://personalpages.tds.net/~fdeck/bass/ebpresche.JPG

I think that with some re-jiggering of component values, something like this could be made to work with triodes, or maybe even with a combination of a triode and a single bipolar transistor.

Thanks. I modeled a tube derivative of an opamp based circuit that Carvin and probably others use that's very similar as well. Guess it's time to sniff a little smoke and see how it sounds.

[OldogNewTrick]

Originally Posted by Passinwind

My own, of course...

Bass and mids are active, close to Baxandall, in the feedback loop from the second 6SL7 plate back to the grid. There is substantial treble pre-emphasis involved as well. Treble control is passive, cut-only, between the second and third stages. At midpoint you get the curve shown above, since you are cutting into the baked-in boost in the previous stage. Here's the modeled frequency response curve model with the treble control nearly all the way up:



The idea is dead-clean highs at any setting, and the ability to have variable distortion in the lows and/or mids (or not, as desired), with lots of interactivity between all the tone controls. Works great for fretless, and cabs with tweeters, which is all I care about really...

Hey Charlie, although some of the engineering aspects are above my grade, I really like how that treble curve ended up.
I also prefer that high centred bell shape, it's IMHO the most musical sounding form of treble EQ.

Bet that pre-amp sounds great !

[Passinwind]

Originally Posted by OldogNewTrick

Hey Charlie, although some of the engineering aspects are above my grade, I really like how that treble curve ended up.
I also prefer that high centred bell shape, it's IMHO the most musical sounding form of treble EQ.

Bet that pre-amp sounds great !

That EQ is actually not too far off a typical CD horn compensation curve, which made some sense to me given that I use horn tweeters in most of my cabs.

I was lucky enough to hear Michael Manring play one of his Zon basses through it and one of Duke's Thunderchild 212 cabs at a Talkbass GTG -- a pretty flattering situation for hearing a DIY piece, to say the least! I also got to try it through a Sadowsky SA200's tube power section at another GTG. Makes me really want to do a DIY all tube bass amp sooner than later.

[Foz]

Got two words for that idea: Eight 6550's

[MAMMOTHvolume]

Originally Posted by Foz

Got two words for that idea: Eight 6550's

thats 4 haha

[Passinwind]

I am now working on porting this to a two rack unit format and putting one out in the field with a fairly well known hard gigging bass player friend. I can't see this being cost effective to build and sell at this time though, unfortunately.

Seemed like a good time to try my hand at circuit board layout, so these are the line driver section and the preamp/tone stack ones. The tube sockets will still be on flying leads. More to follow in a week or two...

[Foz]

so cool... do you wear a cape?

[JGR]

Charlie, Great work (as always)! Looking forward to seeing this come together.

[Munjibunga]

Very nice work. When do they go into production?

[svtb15]

nice

Originally Posted by Passinwind

I am now working on porting this to a two rack unit format and putting one out in the field with a fairly well known hard gigging bass player friend. I can't see this being cost effective to build and sell at this time though, unfortunately.

Seemed like a good time to try my hand at circuit board layout, so these are the line driver section and the preamp/tone stack ones. The tube sockets will still be on flying leads. More to follow in a week or two...