New Tube Preamp Design/Build

[kurtlives]

Introducing my new tube preamp design......."Top Drive"

What makes this little tube powered pre-amp different, unique, rocking? Well for one it's voiced in interesting way. The pre-amp sounds very much like a Vox/Dumble amp. Its got that great top end "jangley" character with that nice tight bottom end. It has great clarity and character all the way up the volume control. When the volume control is maxed out there is great "singing" distortion. "Top Drive" is very much like an old Vox (AC30 for example) in the sense that is has a single volume control. No master (gain) control, this means you need to crank up the volume for that great tube saturation. There is something about a non-master volume amp that just makes it special and sound different. Along with the volume control there is also a three band equalizer consisting of treble, middle and bass controls.

Another really cool part is the preamp is tiny. It is very small and I have fit a ton of circuitry into this solid little enclosure.

I mentioned Dumble though, yes Dumble. What makes "Top Drive" unique is it has a footswitch-able gain stage in the form of a FET boost. With the high impedence FET booster driving the front end of the pre-amp you get tons of added gain, saturation and sustain. The distortion and break up are incredible, its like a pushed over the top Vox mixed with a smooth overdriven Dumble. The FET boost stage also has a volume control. Now this means you now have a volume control at the beginning of the circuit and the normal one at the end. So when you switch on the FET boost stage you now have a master volume amp! You can now dial in the perfect amount of gain without having to crank the volume.

As well as the volume control for the FET boost stage there is a voicing control. The voicing control affects the FET's source bypass cap. A switch allows you to select bright, flat or fat boosted gain tones. This is all made possible by putting different RC filters in parallel to the FET's source resistor. What's nice about the bright control is it stays bright and clear all the way through the volume control's sweep, it's not like an old Fender bright control where the bright affect faded as the volume increased.

I have now designed a two switch external switching box. using relays It lets you bypass "Top Drive" totally in a true bypass manner. It also allows you to turn on and off the FET boost stage. This is really useful as depending on how you set the FET volume and normal volume the footswitch can then act as a clean/dirty channel switch. The switching system even allows one to use just the FET boost by itself. Both switches have activate LEDs mounted on the front of the pre-amp to tell you when which switch is activated.






It's not easy fitting so much stuff into such a small enclosure!



This gives an idea of how small the unit actually is. (ignore my akwardness!)


For schematics and even more info see my site: here


Anyways the tone is incredible. It is very tight sounding but with a nice amount of highs and clarity on the top end. With just the tube signal path (no FET boost) the tone can range from clean to great tube distortion. When the volume controls hits 3 o'clock the unit starts to break up and this great natural distortion hits you. It is not overly heavy, just the right amount of gain. I would describe the max gain as a early 60's British Vox or Marshall that is cranked. All the while the tone remains tight and clear. Even if the tone isn't spot on it can be tweaked by the simple but the very effect three band EQ.

With the FET stage engaged things let loose! With the FET gain rolled up to about 2 o'clock there is a serious increase in gain. The sound becomes bigger chunkier and there is a lot more gain. Now with the voicing switch set flat the frequency response is well flat, nothing is boost. This helps retain the character of the tube circuitry. With the voicing control set to fat boosted gain there is even more gain than the flat setting. The tone also becomes even bigger and the bass is boosted. The sounding is very tight and raw, it provides a great Texas blues type of tone. Finally with the voicing control set to bright well the sound is bright! Very clear and articulate, not piecing or shrill at all. It sounds pretty good with the bright on and some gain, kinda like a 70s Hiwatt. It sounds even better if the preamp is set clean, resembles more of a Blackface style amp.

The FET booster can also be used all by itself. This means you can bypass the tube circuit with the footswitch and then turn on the FET boost with the footswitch so it's on all by itself, kind of a neat feature.



Really proud of this one. Took a long time to design and then build. In the end it was all worth it though because it works perfectly and sounds incredible.

[davent]

Chris, nice job, that looks great How long did you end up spending  designing, building and tweaking it to your satisfaction?

dave

[petemoore]

Really proud of this one.
  You should be, it looks superb !
  Took a long time to design and then build.
  It looks like it. fine job packing it in there !
  Looks great in pictures, and I bet is sounds great too !
  Looks like a nice place to work, and whatever is under the black tolex probably really likes your new Top Drive Preamp System! WOW!

[kurtlives]

Chris, nice job, that looks great How long did you end up spending  designing, building and tweaking it to your satisfaction?

dave

I had a rough idea of what I wanted with in my head. From there I spent my free week nights tweaking. Find tweaking to my satisfaction took probably 20hrs. That's probably how long I had my guitar in hand while I changed components on the breadboard. If you go to my site I linked to you can see the circuit on the bread, you cal also see how the circuit evolved from the original schem.

Probably spent 12hrs actually building it. Took a long time to work my way through it. Hit a few snags.



Thanks Pete!
That black amp there is a Deluxe Reverb I am building that is so CLOSE to beng done!

[frequencycentral]

That looks terrific Chris, really well done! It's bed time here in the UK, so I'll check out the schemo (and soundclips?) tomorrow. Great work, you're coming up with some really inteesting stuff!  

[Renegadrian]

Damn, that thing looks so good...Congrats, man...THX for sharing that...

[kurtlives]

Thanks!

The footswitch uses an XLR cable so now I have no cable for my mic. I am going to pick one up soon though and get some soundclips up.

[mnordbye]

That looks like a lot of work! Thanks for sharing it!

[Renegadrian]

Hey now THAT'S a nice workplace!!! You'd have to see mine - actually it doesn't exist, I usually solder and wire in front of my PC...

[panterica]

I'd love to hear what this sounds like.. everything from clean to full gain. It looks great!

[Ben N]

Beautiful project--thanks for sharing it.

[frank_p]

That is a good looking one.  Congrats.  Is there some audio clips on your site ?
Inspiring... I like.

[biggy boy]

That looks great! Very nicely laid out.
I'm looking forward to hearing some sound clips too.

Glen

[Ice-9]

Congrats , that a great looking and well designed piece of kit.

[kurtlives]

Soundclips:

Ok I am not a recording tech an no guitar wizard. I managed to somehow increase floor noise. Playing isn't the best but your listening to the tone right 

I talk a bit to try and explain the settings. You'll have to turn up your volume to hear me.

Anyways very easily tweak able design, if there is some portion of the sound you don't like it is generally a quick fix.

http://www.soundclick.com/bands/default.cfm?bandID=649289

[liddokun]

 Sounds great. Can't wait for the summer to come so I can start building again too. 

[kurtlives]

Thanks man!

[kurtlives]

Any more opinions on the sound?

[jacobyjd]

Hey man, this preamp sounds fantastic. I'm definitely impressed

I didn't see it listed anywhere else, so sorry if someone already asked, but what's your signal chain for recording? are you running this preamp into a clean amp, then mic'ing, or are you running through a cab sim of some sort?

[kurtlives]

Running a tele I built into it, then into a 75W Randall SS amp. Idea was the crappy SS amp would show the difference more. O then I miced the amp with a Shure SM57

Thanks!