JGR's custom built rock bass tube preamp is done!

[JGR]

OK, so I started building my own custom guitar amps about 10 years ago in search of that elusive perfect high gain sound (finally nailed it a year or so ago). Anyway, about four years ago, I decided I should build my own bass preamp as well - especially since there aren't many commercial ones in production anymore. I've had parts laying around for several years now, but with weddings, funerals, mortgages, new jobs, cross country moves, selling homes, building new homes, - you get the idea - it has been pretty busy the last few years. A few weeks ago, I decided to take a break for all the household projects including finishing the basement (need to get it done, most of my gear is in storage), and tackle this project.

I've owned the following preamps: Aguilar DB659, SWR IOD, Ampeg SVP CL, Ashdown RPM, and the Tech 21 RPM and RBI. At this point, I only still have a pair of RPM's which work very well for me. I play rock. I like to play with a pick. I like grindy midrange and some OD. So I want a no frills, all tube preamp built to rock.

So I've put together a preamp with three 12ax7's running with a high voltage supply (300V+) and managed to cram it into a single rack space only 8 inches deep. Controls are gain, master, bass (~40Hz), treble (~4kHz), and dual Fasel inductor driven midranges - I think the inductor midrange is a key component of the venerable SVT sound. I voiced the low-mid around 400Hz and the high-mid around 1.5 kHz as these frequencies are where I find a lot of the rock tone is for me. Normally I like to cut the 400Hz, but it sounds killer boosted on this preamp - actually, all of the controls do. Also sounds great with everything at noon as it should.

I've incorporated a couple of tricks with the input stages that I picked up designing my guitar amps which keep things nice and clear at both low and high gain settings - no loading, no murky tones. I also incorporated a design idea I've been kicking around for a parallel gain structure so that I could add extra gain emphasis to the midrange frequencies only for grind without harshness or the mud, and still keep the fullness and fidelity intact. It was an idea that seemed good on paper, and actually worked exactly as I had hoped (how often does that happen?) I'm probably going to add a Jensen DI with pre/post switch just for good measure, though it probably isn't something I will use, but other folks might want it if I crank out a few more down the road (I have no aspirations to start an amp company, but have always wanted to do low volume stuff here and there).

I'd say the tone is like a more clear SVT with more grind. I need to crank it through my big cabs - all I've got out right now is a pair of Bag End S15D's - they do sound great though. I may farm this thing out to some of you guys for beta testing if you are interested and promise to give it back!

I've been swaping components in and out over the last few days, fine tuning the design, so some of the wiring has gotten a bit messy, but it is a proto anyway for proof of concept, so no biggie. I'm going to build another unit, and probably have some faceplates made to finish it off. I just recorded a clip that I am posting to Youtube - it is hard to get decent sound quality (can't wait for my Zoom Q3 HD to arrive!!), but (hopefully) it will serve to provide a basic idea of the tone.
I'll post the video link as soon as it loads - here is a gut shot (not keeping the chicken heads - just what I had laying around).

http://www.youtube.com/watch?v=oCC50lqQ600

http://www.youtube.com/watch?v=SL_RgFHhufU

http://www.youtube.com/watch?v=oizXgFooWpQ

http://www.youtube.com/watch?v=pWo9wtBmCqs this one has the corrected cap value

http://www.youtube.com/watch?v=I6RfhJ7k09M latest through the Berg NV412 with normal/deep voicing switch added

http://www.youtube.com/watch?v=NCxtP3bSe4I Check out the latest clip from the DI output!

http://www.youtube.com/watch?v=KpN_kBeg4z0 Unbalanced pre-EQ output into power amp and cab - nice, warm, and relatively clean!

http://www.youtube.com/watch?v=sSQMGv-4dKY Here's the latest with the new Zoom Q3 HD!!!!!!!!

http://www.youtube.com/watch?v=7XhmzeynKDE Another one with the new Zoom

http://www.youtube.com/watch?v=bZ8xF1FrLco clean/dirty split into CA9 into NV215+NV412

http://www.youtube.com/watch?v=uPNIn5cVYeU updated low mid control into CA9 into NV215+NV412 (both post EQ signal)

http://www.youtube.com/watch?v=cn89xKpO4ss fingerstyle only

http://www.youtube.com/watch?v=IAirXB-pl7E fingerstyle using overdriven tone from preamp

[Jazzdogg]

Fantastic!

I'm curious to hear how it pairs with various power amps, and eager to hear your clips.

Is there a mute switch?

What's the input impedance?

[interstatejoe]

Subscribed!! I sooooo want to hear this thing, and I may be first in line if you decide to make a few more.

Let's hear it!!!!!

[JimmyM]

looks cool as all getout, jgr! nice!

[JGR]

Originally Posted by Jazzdogg

Fantastic!

I'm curious to hear how it pairs with various power amps, and eager to hear your clips.

Is there a mute switch?

What's the input impedance?

Good idea about the mute switch - I will put one in. The output uses a cathode follower design so it is low impedance and can drive long cables no problem. With all the EQ flat (noon), I can drive the SWR Power amp to full power using the unbalanced inputs with gain settings of around 10 'clock (master cranked) or higher (decrease master accordingly). With EQ boosted, output is boosted as well. I've been tweaking it the last few days to maximize output, and I think it is in pretty good shape at this point. The above is with a passive bass too. Input impedance is 2.2M.

[JGR]

Bump for Youtube link added. Please keep in mind it is a cheap camera and mic, so it is hard to record bass without it distorting. The sound is much fuller in real life and at higher volumes where the cabs open up.

[Jim C]

Love the idea; low parts count, 3 tubes, and high voltage!

I'm in Rockville, MD so feel free to PM if you want to compare it to my SVT-CL; SVP pre, SWR or LMII; have a Berg HT322 and TL606 for cabs all tied to an Ampeg speaker selector for quick changes while the tone is still in your head
PS- Also have a Diaz CD100 tube guitar amp that's kind of interesting

[JGR]

Originally Posted by Jim C

Love the idea; low parts count, 3 tubes, and high voltage!

I'm in Rockville, MD so feel free to PM if you want to compare it to my SVT-CL; SVP pre, SWR or LMII; have a Berg HT322 and TL606 for cabs all tied to an Ampeg speaker selector for quick changes while the tone is still in your head
PS- Also have a Diaz CD100 tube guitar amp that's kind of interesting

That sounds like a plan!

[kringle77]

Thats sounds really good! Similar to my 70's svt in character. Great job!

[DanRJBrasil]

very nice congrats

[animal52]

Originally Posted by Jim C

Love the idea; low parts count, 3 tubes, and high voltage!

I'm in Rockville, MD so feel free to PM if you want to compare it to my SVT-CL; SVP pre, SWR or LMII; have a Berg HT322 and TL606 for cabs all tied to an Ampeg speaker selector for quick changes while the tone is still in your head

Holy crap, that is pure awesome. Sounds like a mesa and an SVT got together and dirty things.

I'm in Rockville MD too... PM me if you'd like to A/B against my SVT-CL/Berg NV610. I don't get nearly enough opportunities to let the SVT off the leash.

[Jim C]

Hmmm
Bunches of tube power and Berg cabs all in the same neighborhood
Dare I say; "rule the world"

[chadds]

I like the knobs.....

[synaesthesia]

Nice. I cannot resist a good 1 U unit. If you are posting your schematic, I'm sure several woul be willing to try your design, i.e. if you are not commercialising it.

I'd add a Neutrik locking input socket for that take no prisoners look. And yes, I am aware that Kern did that.

Will you add a Jensen transformer for XLR DI out?

[tocs100]

Why is it all the builders with talent and drive never wanna go commercial? I've been thru 2 builders in 5 years and still can't get a simple 3-band eq/ bandsplit loop pedal made.

(One stole--then thankfully modified--the design, the other won't finish OR mail back the half-done protos. And I'm functionally blind so I solder my fingers more than my circuits, lol.)

Info is at this aging Harmony Central thread:
http://acapella.harmony-central.com/....php?t=2340201
I have build-pics, I just can't get 'em loaded to photobucket right now. Any builders seriously curious--pm me!

[animal52]

So have you tried 12AU7's in place of the 12AX7's? They'd be mellower, but probably still sound great as well.

[beans-on-toast]

Very nice! Sounds great.

[Fuzzbass]

I am VERY interested. Subscribed!

[sammyfallen]

If you wanna send it south to KY I'd give it a run with some hardcore punk / doom metal. We're scheduled to go into the studio soon so you could get some ace recordings to use. It sounds FANTASTIC, especially when the gain is cranked, I love me some good grinding tone...

[Sliderbass]

Originally Posted by JGR

OK, so I started building my own custom guitar amps about 10 years ago in search of that elusive perfect high gain sound (finally nailed it a year or so ago). Anyway, about four years ago, I decided I should build my own bass preamp as well - especially since there aren't many commercial ones in production anymore. I've had parts laying around for several years now, but with weddings, funerals, mortgages, new jobs, cross country moves, selling homes, building new homes, - you get the idea - it has been pretty busy the last few years. A few weeks ago, I decided to take a break for all the household projects including finishing the basement (need to get it done, most of my gear is in storage), and tackle this project.

I've owned the following preamps: Aguilar DB659, SWR IOD, Ampeg SVP CL, Ashdown RPM, and the Tech 21 RPM and RBI. At this point, I only still have a pair of RPM's which work very well for me. I play rock. I like to play with a pick. I like grindy midrange and some OD. So I want a no frills, all tube preamp built to rock.

So I've put together a preamp with three 12ax7's running with a high voltage supply (300V+) and managed to cram it into a single rack space only 8 inches deep. Controls are gain, master, bass (~40Hz), treble (~4kHz), and dual Fasel inductor driven midranges - I think the inductor midrange is a key component of the venerable SVT sound. I voiced the low-mid around 400Hz and the high-mid around 1.5 kHz as these frequencies are where I find a lot of the rock tone is for me. Normally I like to cut the 400Hz, but it sounds killer boosted on this preamp - actually, all of the controls do. Also sounds great with everything at noon as it should.

I've incorporated a couple of tricks with the input stages that I picked up designing my guitar amps which keep things nice and clear at both low and high gain settings - no loading, no murky tones. I also incorporated a design idea I've been kicking around for a parallel gain structure so that I could add extra gain emphasis to the midrange frequencies only for grind without harshness or the mud, and still keep the fullness and fidelity intact. It was an idea that seemed good on paper, and actually worked exactly as I had hoped (how often does that happen?) I'm probably going to add a Jensen DI with pre/post switch just for good measure, though it probably isn't something I will use, but other folks might want it if I crank out a few more down the road (I have no aspirations to start an amp company, but have always wanted to do low volume stuff here and there).

I'd say the tone is like a more clear SVT with more grind. I need to crank it through my big cabs - all I've got out right now is a pair of Bag End S15D's - they do sound great though. I may farm this thing out to some of you guys for beta testing if you are interested and promise to give it back!

I've been swaping components in and out over the last few days, fine tuning the design, so some of the wiring has gotten a bit messy, but it is a proto anyway for proof of concept, so no biggie. I'm going to build another unit, and probably have some faceplates made to finish it off. I just recorded a clip that I am posting to Youtube - it is hard to get decent sound quality (can't wait for my Zoom Q3 HD to arrive!!), but (hopefully) it will serve to provide a basic idea of the tone.
I'll post the video link as soon as it loads - here is a gut shot (not keeping the chicken heads - just what I had laying around).

http://www.youtube.com/watch?v=oCC50lqQ600

I wonder how you pre would sound with, lets say, a DB-728?