Bass pre-amp

[David Schwab]

OMG, Stanley Clarke! I'm about to try and build a bass preamp to go with a Class-D power amp I recently acquired, and I can't decide whether to try the Albert Kreuzer JFET preamp, or one channel of the Alembic F2B. I'm a big fan of Stanley Clarke, though I think my favourite tone is one I heard on a live recording of "All Blues" and I have no idea what he used for that. Probably mostly raw talent

Steve, Stanley always plays through the F2B. That's part of his sound. He runs each pickup into a channel. I've read he then runs those into an SWR power amp and cabs. I'm a big Clarke fan.

I've looked at that JFET preamp... look pretty good, except he copied the tone stack from an Ampeg... I never liked their tone controls. I dislike them even more than G-K's! Ugly center frequencies. I owed an 800RB for years and ended up using a Yamaha rack guitar preamp with it most of the time!

If people complained about the F2B lacking output, I guess it would be because the output jack is fed straight from the tube plate in the published schematic. That gives a very high output impedance, which would be loaded down a lot by the input impedance of whatever you connect. A cathode follower stage, or the guts of an active DI box, would help. I see Alembic built the guts of a DI box into the F1X.

My BlueTube pedal has the same problem. I have to plug it into a high impedance source, like an effect pedal, to get any level out of it.

[Steve Conner]

Well, if the F2B is good enough for Stanley Clarke it's good enough for me!

If I used the Kreuzer preamp, I was planning to just use the Baxandall bass and treble, and replace his mid EQ with a parametric EQ. Likewise, with the F2B, I'd probably put a parametric midrange control after it.

Recording is one thing, you can EQ and compress the bass with plugins on your computer, but at rehearsals and gigs, sometimes my midrange just sucks. My old bass had a real midrange growl around 400Hz that needed cut, but my new one just wants to boom and twang, and I have to boost it.

Maybe I should make a parametric EQ as a stomp box instead.

BTW, David, what do you like to use as a preamp? I got the impression you were an "Active bass straight into power amp" kind of guy.

[David Schwab]

Well, if the F2B is good enough for Stanley Clarke it's good enough for me!

Of course playing an Alembic bass through the thing helps!

If I used the Kreuzer preamp, I was planning to just use the Baxandall bass and treble, and replace his mid EQ with a parametric EQ. Likewise, with the F2B, I'd probably put a parametric midrange control after it.

Yeah, those Ampeg Ultra-Hi and Ultra-Lo switches always annoyed me. I loved my old B-15N, but the later Ampegs just had annoying tone controls. They always mess up the tone too much. It's all variations of the same Ampeg sound.

Recording is one thing, you can EQ and compress the bass with plugins on your computer, but at rehearsals and gigs, sometimes my midrange just sucks. My old bass had a real midrange growl around 400Hz that needed cut, but my new one just wants to boom and twang, and I have to boost it.

You know, when I was using EMG pickups, I could never EQ them and make them sound different. I had to do all these drastic mid boosts and stuff.

Now I mostly just plug into the board and maybe goose the lows or mids a bit. And some compression of course.

BTW, David, what do you like to use as a preamp? I got the impression you were an "Active bass straight into power amp" kind of guy.

Right now I play through a Trace Elliot combo. I've been on this search for a transparent amp. I spend a whole afternoon trying out amps last year and hated almost everyone of them! Almost every amp I tried did something to the sound of my bass that I didn't like, and couldn't undo. The most accurate amp was (surprisingly) a SWR LA12 combo (and not the LA10 or 15)... tiny little thing. Too small to use as a main amp. Runner ups included a Peavey and Harkie amps. Of course I didn't get to try every amp made... no Edens for example. My main gripe is that most amps seem to impart too much of their own sound. This is great for guitar, but it's not what I want from a bass amp. I want to start off pretty neutral, and then I can EQ or dirty the tone up as needed... not being stuck with the same type of tone all the time.

I used a GK for years, and then picked up a Mesa 400+ (back when I was in my vintage tone period... complete with flatwounds). I sold the GK and bought the TE because the Mesa is too damn heavy. Sometimes I plug directly into the effect return on the TE, just because the preamp section never seems to go high enough.

I was thinking of building that preamp and picking up a power amp, and making a new 2X12 cab or something.

I want to check out those MarkBass amps and the new Roland DBass combos.

I have to say though that bass amps these days in general are better than when I started playing bass!

[Steve Conner]

Yay, thanks for all the info. So you don't like the Ultra Hi and Ultra Lo's? I've never used an Ampeg long enough to really figure out what they do. Whenever I plug into a SVT at a rehearsal place or whatever, I just fiddle with the volume and tone knobs at random until the rest of the band stop yelling at me to turn down. The volume is usually around 2 by then

About compression, do you think a compressor should be an integral part of a good bass preamp? Or do you prefer to use a stomp box for it? What kind of characteristic do you like? I ask because I tried to build a bass compressor before, but it never seemed to sound right. The tube compressor from the Trace Elliot V-8 looks interesting, but I'm struggling to understand how it works or find a clear schematic.

I have a Marshall ED-1 compressor stomp box that works OK, but I think it's really meant for guitar rather than bass.

[bob p]

back in the RTF days i saw Stanley playing in a small venue. of all things, he was plugged into an Acoustic 136 solid state combo, 100W with 1x15. that surprised the hell out of me as i had the same amp. that is not to say our tone was at all similar ... no matter how hard i tried we sounded different.

[David Schwab]

Yay, thanks for all the info. So you don't like the Ultra Hi and Ultra Lo's? I've never used an Ampeg long enough to really figure out what they do. Whenever I plug into a SVT at a rehearsal place or whatever, I just fiddle with the volume and tone knobs at random until the rest of the band stop yelling at me to turn down. The volume is usually around 2 by then

The ultra switches shift the frequency of the controls, so the ultra lo makes it really deep. But you lose the mids. It's just too gimmicky sounding to me.

About compression, do you think a compressor should be an integral part of a good bass preamp? Or do you prefer to use a stomp box for it? What kind of characteristic do you like? I ask because I tried to build a bass compressor before, but it never seemed to sound right. The tube compressor from the Trace Elliot V-8 looks interesting, but I'm struggling to understand how it works or find a clear schematic.

The multiband compressor in the Trace is really nice. I have that on all the time. You don't actually hear it though. Sometimes I like more squash, you know, like using the compressor as an effect, so I have an old MXR AC Limiter that I use. When I'm recording I usually either use the compressor in my Roland VM-3100Pro digital mixer, or an Alesis Nanocompressor.

I have a Marshall ED-1 compressor stomp box that works OK, but I think it's really meant for guitar rather than bass.

That can be a cool sound, as long as you get good low end. I used to use a lot of effects... I had this elaborate signal chain.. my bass went to the MXR Limiter, and an old script logo Phase 90, and then into the GK-800RB head. The effect send on that went to a Peavey biamp chorus pedal, that had a crossover that split the signal and applied the effect on the high frequencies only. It had a high and low out. The low channel went to an Electro Harmonix Microsynth, mostly for sub octave, and the high frequency channel went to a Blue Tube pedal. The outs from these went to a two channel mixer I made, and then back to the GK! Whew!

I used the same setup for recording, using the direct out on the GK head.

Now I just plug into the amp. Every now and then I use some chorus, but I've been letting our singer use it on her acoustic guitar...

[David Schwab]

back in the RTF days i saw Stanley playing in a small venue. of all things, he was plugged into an Acoustic 136 solid state combo, 100W with 1x15. that surprised the hell out of me as i had the same amp. that is not to say our tone was at all similar ... no matter how hard i tried we sounded different.

I had the head version of that amp! I used to use it with my old B-15 cab loaded with a JBL. That was a great sounding amp. When I saw him with RTF (Romantic Warrior tour) and on the School Days tour, he had an Electro Voice cab.. I think it was a 3-way setup. Damn they were scary good! I didn't know if I wanted to go home and practice, or quit! lol

The closest I got to his tone was my Ric 4001 with a Bart Hi-A pickup in the bridge, TC-1 preamp, into my old Peavey "Bass" amp (the first one they made). I called that Ric my "baby Alembic" lol

Being the Stanley fan that I am, I modeled my basses loosely on Alembics. I can kind of get that tone, but there's something about his high end that has a certain character that's hard to nail down.

He also likes to put his action really high when he slaps. He said it was so high when he recorded Silly Putty, that he almost couldn't play it! You can hear him slip up a little in the intro too.

I like my action really low. But the lowest action I ever felt was Jeff Berlin's Dean bass! Everyone who tried it said "oh shit"! It was crazy. It buzzed quite a bit, but you couldn't hear it when he played. he probably has a light touch, as compared to me... I pluck hard. I like that Stanley snap!

[RPmanen]

Anyway, I've been looking around for toroids thatare available over here, and found one with 230V/60mA - 6,3V/2,5A secondaries, 230V primary, would this be ok or would it be a hazard (Ivan was good point)? Its one made by amplimo, I've heard good things about them.

Rob

[R.G.]

Anyway, I've been looking around for toroids thatare available over here, and found one with 230V/60mA - 6,3V/2,5A secondaries, 230V primary, would this be ok or would it be a hazard (Ivan was good point)? Its one made by amplimo, I've heard good things about them.

Rob

That would be fine. You'll get a bit less than 230*1.414 = 263V for your tube plates, and the 6.3V/2.5A is plenty. That transformer will put out far more power than the circuit really needs, but that's fine - a transformer that will do the job that you can actually get is worth 12,347 transformers that are perfect, but unobtainable.

Be sure to do your AC power wiring properly and safely. The real primary side can make an Ivan out of any of us if we're not careful.

[bob p]

I had the head version of that amp! I used to use it with my old B-15 cab loaded with a JBL. That was a great sounding amp. When I saw him with RTF (Romantic Warrior tour) and on the School Days tour, he had an Electro Voice cab.. I think it was a 3-way setup. Damn they were scary good!

Those EV bass rigs used either 1 or 2 EVM-15L in a Thiele-Small array, plus a VMR vented midrange driver that was originally designed for the Interface D studio monitor. The VMR made the popping sounds HUGE!

When I first discovered Stanley I removed the crappy 15" Eminence speaker from my Acoustic combo amp and replaced it with an EVM-15L. I was in heaven! The problem was that the huge vented reflex Acoustic "combo" was about 3-1/2 feet tall, about 30" wide, and it weighed more than a Twin Reverb. The amp had casters, but it had ONE HANDLE on the side, like they expected The Governator to carry it for you!

To manage getting my bass rig into and out of a 2-door car, I had to put that head into a homemade head-only cab, and I needed a small/portable a 1x15 cab. I knew some of the engineers at EV from a separate Hifi project I had been working on, so they helped me by drawing up plans for a little 1x15 cab for my EVM-15L and I built the prototype.

As it turns out, I was a little ahead of the curve. A year or two later was when EV came out with those Thiele-Small / VMR bass rigs, and later on EV marketed the original T-S cab design that we had worked on to Mesa. Although the original EV rig with the VMR never seemed to catch on, Mesa hit it big with the EVM-15L/TL-606 cabinet as one of their compact bass rigs. The EVM design with the VMR was better, but the Mesa rig without the VMR fared better because it was less expensive and it because was aggressively marketed. EVs marketing for MI has always seemed half-hearted, IMO.

That was back in 1976 or 78. I've still got that head/cab setup and I still using it for practice and small venues 30+ years later...

[RPmanen]

That would be fine. You'll get a bit less than 230*1.414 = 263V for your tube plates, and the 6.3V/2.5A is plenty. That transformer will put out far more power than the circuit really needs, but that's fine - a transformer that will do the job that you can actually get is worth 12,347 transformers that are perfect, but unobtainable.

Not trying to be a pain, but 230*1.414= 325, and running the numbers through duncans PSU designer, I get around 300V (although I'm not sure how much ripple to allow).

Sooo, am I missing valuable psu info? Also, how much ripple do you guys allow/ how much capacitance/RC stages do you use?

Love the forum btw, lots of good info

[RPmanen]

Shameless kick

[R.G.]

Not trying to be a pain, but 230*1.414= 325, and running the numbers through duncans PSU designer, I get around 300V (although I'm not sure how much ripple to allow).

Sooo, am I missing valuable psu info? Also, how much ripple do you guys allow/ how much capacitance/RC stages do you use?

Love the forum btw, lots of good info

So your point is I can't multiply? You're right, I can't.

230*1.414 is actually325.22, as you correctly note. You'll get peaks of around 325, less the losses in the wire resistances and diodes. 300's a fair guess.

Ripple is the enemy. Keep ripple under 5-10% on your first capacitor. That's 0.05*325 = 16.25V to 32.5V. Then put in another section and reduce it again.

To compute the reduction, consider the R-C section as a voltage divider. The lowest frequency going through is 120Hz or 100Hz if you live in a 50Hz country. So the DC drop is the I*R across the resistor R, but the ripple is reduced by the ratio of |Xc|/(R+|Xc|) approximately. Dial in a 10% DC loss, about 32V and ...er... maybe 6ma, for 32/0.006 = 5.3K, then a 47uF cap for Xc = 1/(47E-6 *2 * pi *100) = 33.9 ohms, or the attenuation of 100Hz ripple is 33.9/(5134) = 0.0066 = 6.6E-3, 50+ db of attenuation. A couple of stages of this will get the ripple right out of what you feed to your input stage.

32V of ripple becomes 211mV - which is stlll too much for your first stage.

Your first stage will have a gain of maybe 30, guessing, so your 100mV guitar signal will get up to 3V. 211mV of ripple, which rides right through, it's on the plate, becomes a hum only 0.211/3.00 = 0.07 of the desired signal peaks, about 30db down. That's way too much ripple. You need it down another 20 db at least, preferably 40, so you need a minimum of two 40-50db ripple reduction sections if you allow 5-10% ripple on the input filter.

If all that sound chaotic, it was stream of consiousness as I thought and calculated what would be needed.

You could get the necessary ripple reduction in one stage with a MOSFET source follower regulator to knock a lot of the ripple off.

You can let the ripple run high on the first rectifier, then reduce it a lot with a couple of R-C stages.

[RPmanen]

Thanks for that, it was a bit chaotic, but at least now I know where to start designing my psu. I'll play around with some numbers in PSUII later.

ROb

[jaysg]

It amazes me a little how full of gossip the internet is. Several people have complained that I didn't specify a power transformer for that schematic. I couldn't - the original was a custom unit, made for the box. And there is almost never a mention of that schemo without someone vaguely remembering something somewhere was wrong with it.

R.G., that would be my doing. I sent you an email immediately after noticing that the Plate and Cathode numbers were reversed on one of the triodes. You never fixed it afaik.

Beyond that, I found an at TubeCAD about the voltage doubler circuit as shown on the GEO schematic. Iirc, the concept is something like magnetically unbalancing the PT. A different configuration with the exact same parts, pulls current through evenly in each direction.