Nobel Bass Di clone or Alembic F2-B?

[Spencerleehorton]

Hi All,

Just completed a Reddi tube bass di clone and it sounds rather nice, was also interested in building a Nobel bass di which uses two tubes and has bass and treble pots and a low cut switch.
Can’t see any schematics online so far so thought I’d ask here to see if this build or something fairly similar was possible.
I think it uses the 5963 tubes? Which I think is a variant of the 12AU7?
Also thinking about a Alembic F2-B
Any info would be appreciated.

 

[CJ]

I built an Alembic di, it had a cap output but it was noisy and had no bass so I wound a 5:1 on some utc lams and that did the trick.

Used a big cap to drive the transformer.

 

[Spencerleehorton]

If you have anymore details on the output txf and cap value that would help me as I could wind something on these ei75?
I’m gonna start putting together the turret boards in the next week or so, have a local company that can wind me the toroidal 260v 0.09A and 2 x 6.3v @ 2A main txf.

 

[Spencerleehorton]

 

[Spencerleehorton]

 

[Spencerleehorton]

 

[Spencerleehorton]

The psu schematic is obviously 110v but mine will be 220v

 

[Jarno]

I built a single channel F2b, without output transformer, it had a bit too much gain for my active basses, so I lowered the plate resistor (well, tacked one in parallel). Quite high output impedance, but mine goes to my power amp, with 10cm patch cables.
I've made a proposal to add a cathode follower stage to it, to lower the output impedance, you could do this with a mosfet as well, see the mosfet follies article.

A Reddi is still on my list to try, did you post your build here somewhere?

Those Noble di's look interesting as well, really compact! Did have to chuckle about the marketing blurb regarding shielding though. It's true that aluminium is a better choice if you look at electrical conductivity, but that goes for pure aluminium. Conductivity of the die cast alloys usually are a lot worse (which is still totally fine for shielding).

 

[CJ]

i used a nickel core for the OPT but you could wind a single ended gapped xfmr on EI 75 and do way with the cap, kind of like the reddi di only for guitar. in fact, you could use the same xfmr for the FB 2 as you used in the reddi

just add 50% more turns of smaller wire.

12ax7a plate R is more than the 6N1P so you need more primary Z. (impedance)

 

[Spencerleehorton]

you did say you used a 5:1 ratio on yours CJ, the Reddi/Zod txf was only 3.67:1 so are we saying rather than 4500 on pri, change to 6750 on pri and 1420 on sec? That’s 4.7:1 so could go a bit more?
7200:1420

I do have some nickel core as well, how big were yours?

 

[CJ]

I used type 31UI

This is the same lam used in the utc a 10, ha 100x etc.

But you could use .EI lams , but nickel does like DC so you need a cap. 20 uf cap eill work.

If you use Ni you can drop your turns down to a bout 2000.

 

[Spencerleehorton]

So nickel lams pri - 2000T sec- 400T
M6 lams pri - 7200T sec - 1420T

M6 version gapped nickel version with 20uf cap

 

[CJ]

sounds good! use a few sections on that 7200 T primary so you do not lose hi end due to capacitance,

 

[Gus]

Maybe something like this with a output transformer
https://www.thallenbeck.com/blog/posts/sortaflex-d-i-y-tube-bass-preamp/

 

[MidnightArrakis]

Do you guys prefer something like -- THIS -- to put your bass guitar preamp circuitry in???


Or, something more along the lines of the ALEMBIC preamp in a 1U rack-chassis???

FUN FACT!!! --- Way back during the mid-1970's, a friend of mine who was a bass player wanted me to design and build for him a bass guitar preamp similar to the ALEMBIC guitar preamp that was available at that time. I did so, BUT..........since I was also a BOSE Professional Products dealer at that time, I had also included the BOSE EQ circuitry that was used to EQ the BOSE 802 speakers that I was selling back then. To say that my friend's bass guitar preamp ended up being "unique" would be a significant understatement, to say the least!!!

SO!!!.....my friends' band had a gig one night at a local nightclub and it was the very first time that he was going to be using his new bass preamp during a show. I don't remember the exact song title, but my friend had a particular song in mind that he wanted to be playing when he stepped on the pedal-switch to "kick-in" the BOSE EQ circuit portion of his new preamp. Even I was wondering what this was going to sound like!!!

In any case.....the song my friend had in mind finally came up in the set and he is really "going to town" on his playing. Meanwhile, I am off to the side-stage watching both him and the audience dancing and standing in front of the stage. This one part of the song comes up.....my friend walks over to the pedal-switch and.....he steps on the pedal-switch that activates the BOSE EQ circuitry within the preamp AN-N-N-NDD..........>> THE AUDIENCE WAS SHOVED BACK ABOUT 3-FEET FROM THE FRONT OF THE STAGE DUE TO THE PRESSURE OF ALL OF THE AIR COMING OUT OF HIS BASS RIG!!! <<

>>> MAN!!! OH!!! MAN!!! <<< I didn't see THAT coming!!!

Now.....you would need to understand how the BOSE speakers operate and why they need this EQ circuitry, but all that I can say is, when that EQ circuitry is used with a "regular" speaker.....LOOK OUT!!!

/

 

[Lekky]

Speaking of the Noble preamp: I've been curious about the circuit after all the praise on Talkbass. Somebody posted gut shots, but the circuit can't be figured out as the PCB is vertical. Based on the description of the unit, I guess the signal flow is something like this:
Input -> first gain stage -> HPF and tone stack -> second gain stage -> split into 1) volume control -> cathode follower #1 -> 1/4" out and 2) cathode follower #2 -> Jensen transformer -> XLR out.

 

[Gus]

Found this web page

https://www.bassgearmag.com/zen-personified-noble-amplifier-company-preamp/
Interesting part is the 2.5 Fender tone stack and the EQ is flat at min on the tone controls if I understand the write up
I would GUESS the input goes to a JFET source follower or some other follower circuit before the first tube. This is because of the 10meg input resistance.

It looks to be well made. I do like the 9VDC supply for effects

EDIT
I did some more searching. If what I have found on the web the main differences seems to be the tone stack and tubes.
So you can take a stock F tone stack and use Duncan's or sim the circuit to match what the EQ is.
I am simming a few ideas about what the tone stack might be.

 

[Spencerleehorton]

Speaking of the Noble preamp: I've been curious about the circuit after all the praise on Talkbass. Somebody posted gut shots, but the circuit can't be figured out as the PCB is vertical. Based on the description of the unit, I guess the signal flow is something like this:
Input -> first gain stage -> HPF and tone stack -> second gain stage -> split into 1) volume control -> cathode follower #1 -> 1/4" out and 2) cathode follower #2 -> Jensen transformer -> XLR out.

Would like to very much know the specific circuit as blind tests for me put this and the Nobel top of the pile.

 

[Lekky]

Here are some gut shots of the Noble preamp from a thread on Talkbass. Some components are visible, but nothing that can reveal details about the circuit: https://www.talkbass.com/threads/noble-amps-preamp.1006334/page-75#post-21218203

 

[Spencerleehorton]

Thanks I can work out some of the components from those pictures