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A DIY Tube Preamp/Line Driver by Passinwind

#61
MAMMOTHvolume said:
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 :)
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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.
 
#63
lneal said:
Charlie: what version of spice are you using?
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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.
 
#65
Charlie,

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

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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.
 
#66
fdeck said:
Charlie,

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

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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.
Click to expand...

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. ;)
 
#67
Passinwind said:
My own, of course...:cool:

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:

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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...;)
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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 ! :bassist:
 
#68
OldogNewTrick said:
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 ! :bassist:
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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. :cool:
 
#74
nice
Passinwind said:
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...:cool:

PW6B_PCBs.jpg
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#75
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.
Click to expand...

And now I'm just about finishing up this build:

PW6B_DESE_inprogress.jpg


Lots of "learning opportunities" here, and it's been even more work than I expected. Hope to be making some noise in the next day or so though...:bassist:
 
#77
beans-on-toast said:
Looking great Charlie. Those gold turrets are a nice touch and the icing on the cake.
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Thanks David. Of course, I'm already contemplating replacing the turret boards with purple and gold PCBs...:cool:

This build was complicated a lot by my friend wanting the output jack on the front panel. Hence the upside-down circuit board on the right, and some other "creative" design changes I had to come up with on the fly.

BTW, the teflon composite tube sockets I used feel really great for my horizontal tube mounting scheme. They are super tight yet have some give that should help dampen microphonics. May make tube rolling a bit of a hassle though.
 
#78
Designs are never done. Designers just can't stop wanting to change things. :p Some time in the field will no doubt provide some additional insights as to how the pre-amp is performing which might lead to further enhancements.

How did you decide to mount the teflon sockets in the end. Are the two socket holes or the plates that you used mounted with small rubber grommets under them?

Do you anticipate any issues with heat?
 
#80
beans-on-toast said:
Designs are never done. Designers just can't stop wanting to change things. :p Some time in the field will no doubt provide some additional insights as to how the pre-amp is performing which might lead to further enhancements.

How did you decide to mount the teflon sockets in the end. Are the two socket holes or the plates that you used mounted with small rubber grommets under them?

Do you anticipate any issues with heat?
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Presently the whole tube cage assembly is sitting on rubber washers. I have several levels of isolation ready to add as needed, including well nuts under the cage and grommets in either or both of the places you mentioned, and also possibly under the transformers. I'm also keeping the vibration killers you sent me the link for in mind. The Hammond power transformers seem very quiet mechanically so far, a relief since I've never tried these particular pieces before.

All the hot bits have convection cooling ducts more or less directly above and below them. Lots of aluminium to spread the heat around too. Heat has never been a problem with the 3RU one so far, but space is definitely more cramped this time.

I hear you on the never ending quest for mo bettah tweaks. This new one already puts out even more clean level (8+ volts RMS 200Hz sine) on the bench than the earlier one, but I won't get to actually listen to it until tomorrow. ;)
 
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