Recommend me a tube pre amp for guitar

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funk1980

funk1980

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Joined 2011
#1
I've gotten a lot of experience building bass tube pre- and poweramps over the last years. I want to surprise a good friend of mine (guitarist) with a simple guitar pre-amp, build from stuff I have lying around.

I know the tonal preferences but have no idea what brands/topologies fit the bill 😛. Sound has be be warm, detailed, unobtrusive and definitely not 'mid-dy'. So smooth overdrive is nice, no screaming necessary. No need for anything fancy besides gain and a simple EQ either.

Please let me know if any typical front ends spring to mind. Thanks!
 
#2
I have always loved the Valvestate front end from the Marshall Valvestate 8100.
Mine got stolen back in 2003 and I do plan on building just the preamp someday when I get more time.

I never used the poweramp much especially after I had blown it (He,he,he), But I always used to run the preamp into my heftier poweramp's after that, and sometimes even straight in to the board for a few recordings using a ART PowerPlant for its Mic/amp /Speaker simulator filters.

FWIW

jer 🙂
 
#3
Geraldfryjr, the OP wanted a tube front end. Didn't the valvestates of that era have only one tube, the rest of it solid state? I counted 9 ICs on the front end in the schematic. It seems anything but simple. Funk1980, do you want tube all the way on your front end? You could usually get by with two tubes and the PI before the power tubes. Look at schematics of late '50s and early '60s Fenders(tweed to brownface era). Usually only one or two tubes plus the phase inverter. Easy to build and gets some overdrive. Either just a tone control or just bass and treble.
 
#5
Thanks guys! I really want to keep it 'all tube'. Keeps the PSU simple too 😀.
I've been studying some guitar amp schematics. Fender, VOX, Marshall. Some striking differences and similarities as well. Like the extremely low anode load in the VOX AC series. DC coupled cathode followers. And the 12ax7 stages with 100k/820, just like in the Fender bassman. Good stuff!
 
#6
Your last observation of Marshall "just like the Fender Bassman". The very first Marshall JTM45 was, with a couple of minor exceptions,(they used a 12AX7 instead of a 12AY7 on the input and took the NFB resistor from a different OT tap) an out and out copy of the Fender Bassman. In fact, when you go to this site which is mostly dedicated to European amps-Marshall, Hiwatt,etc. the schemo for the original JTM45 is the 5F6-A Bassman schemo.
Marshall Schematics
 
#7
Hahahah that's awesome! The link you provided is from a guy (and his business) near where I live 😀. I recently visited his workshop. Great fellow with even greater knowledge about (but not limited to) tube gear. Gave me some invaluable tips&tricks for my own bass projects too and is building his own signature tube guitar amps. Small world!
 
#9
I love the Alembic FB2. It's just two Fender channels, pretty much the front end of a twin. Each is: half of a 12ax7, volume with a bright switch across it, tone stack, then the other half of the 12ax7. Some guys just build half, and you've got a Fender without reverb.

IMHO the magic is when you build the two channels like the two the Alembic has, and remove the resistors that combine the outputs (there are separate output jacks too, but just remove the mixer summing resistors for the mono output) and use it as two preamps in series instead of in parallel.
 
#10
Then you can decide whether you want a switch, pot, or coupling cap and pot between the two preamps. You can put bypass switches on the tone stacks. An input level switch for active or passive pickups. A variable input impedance "loading" pot for the passive pickup input. Tweek the plate supply and resistors. Tweek the coupling caps and grid resistors. Switchable "bright" or "deep" networks on the cathode. Output level pot. Starting with such standard building blocks as two standard Fender channels, there's no limit to how far you can take it.

Having the two tone stacks lets you control the guitar tone (which goes thru both) somewhat separately from the tone of the distortion (which is generated between the two tone stacks, and thus is mostly affected by the last tone stack). For instance, one of my favorite settings is with the guitar treble-boosted and bright in the first preamp, then the nasty fizzy treble of the distortion knocked off in the second tone stack.

Maybe add a third complete "building block" Fender channel for a side chain to mix "clean" with the "dirty" (from the original two in series) for the kind of control over how MUCH distortion (not to be confused with the guitar level where the dirt first kicks in) like the Marshall guys who double-jack the inputs to their clean and dirty channels. Add effects loop jacks between the channels (some effects like an auto-filter work great before any compression or distortion) or at the output (ambience effects like reverb sound great when applied to the final tone after distortion is added etc.). Some effects between the two channels work very nicely, especially if you put level pots before & after...very buffered, and you have a tone stack before & after.

The details and how far to take it are up to you. I like it very versatile, some people do the opposite and "voice" the amp one way and then have just one "volume" knob...

Don't just grab a schematic, consider it a starting place. And old Fender / Alembic "building blocks" are a great starting place. But my advice is for maximum fun, start with two rather than just one. Even if you just want clean tone, with just moderate gain at each stage it sounds great.
 
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#12
Hi Cycleclamper, thanks for the extensive reply! I'll look into the different options you suggested. Concerning the upgrades, I got that covered. I build tube bass amps and one of my philosophies is the use of 'current day' options. People really like 'em and so did my guitar playing friend. She told me that if I'd ever build a guitar amp with the same quality and tonal approach, she'd buy it in an instant 🙂
 
#13
funk1980 said:
simple guitar pre-amp, build from stuff I have lying around.
Sound has be be warm, detailed, unobtrusive and definitely not 'mid-dy'. So smooth overdrive is nice, no screaming necessary. No need for anything fancy besides gain and a simple EQ either.
Click to expand...

Have you looked into schematics based on EF37A / EF86 ?

20ken86.png


LBA VOX AC15

IMHO they not only sound better than triodes, they LOOK BETTER!!
 
#18
JFETs

Hi,

I know you want to build guitar TUBE preamp, nothing wrong with that, I have built some preamps for myself too. Then I discovered JFET preamps from AMT (Series 1 and Series 2). They uses jfets with some trickeries to make them behave just like triodes. With good power supply (no smps wallwarts etc.) they sound just awesome and mostly better than lots of tube preamps out there. Check it out, definately recommended!
 
#19
kacernator said:
(snip) They uses jfets with some trickeries to make them behave just like triodes. (snip)
Click to expand...

Go for the Alembic +1, it was good enough for Jerry Garcia.

Remember what everyone is comparing all the solid state pre amps to.
Just like the post I quoted. They compare them to Triodes.


Kind of like in the old days,
It runs just as good as a Chevrolet big block!
Oh really?
Ask Jim Hall or Bruce McLaren.
 
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