Nobel Bass Di clone or Alembic F2-B?

[Gus]

Why work out the values take the basic idea and make your own schematic. looks like two triode gain stages with stuff in the middle(HPF EQ) and after follower(s) and transformer

I don't see a SMD or leaded JFET or SMD opamp.
10 meg input resistance with a triode tube grid?

Interesting if the volume control is after the triodes. Fenders volume is after the tone stack before the 2nd triode

I would guess the two 3 term devices are regulators maybe one for the tube heaters(set to 12VDC) and one for the 9VDC supply

You could use one dual triode and a HV MOSFET as a Source follower. Did you look at the link I posted? I would add a protection Zener from gate to source in the linked schematic.

Most likely a Fender like preamp with 12AU7 triodes and an adjusted EQ. I think I figured out the EQ and HPF one value change and one more part.

My guess is the EQ is what is most different

Who every made the three schematics drew them in a confusing manner

 

[Lekky]

Noble states that the volume control only affects the 1/4" out and not the XLR out. Thus it has to be located after the 2nd triode stage where the signal is split into the output sections.
I would also recommend using MOSFET source followers. I noticed that Arkham Sound, another maker of high-quality tube bass preamps, made the switch from 12AU7 cathode followers to MOSFET source followers. From Arkham's FAQ: "I now use Mosfets as an output buffer rather than a tube Cathode Follower. In this application they are far more efficient, functionally identical, and have zero impact on the tone."

 

[Aircoutix]

Hi. For a friend, i have built a clone of the NOBLE Preamp/DI. The second tube which only aims at driving the jack output is a made of a "White cathode follower" structure (no voltage gain but very low output impedance), in order to drive any power amp low input impedance with no transmission quality loss. The first tube performs the gain, the equalisation and drives the well known Jensen transformer output. The equalisation is based on the simple schematics used in several preamps (ALEMBIC, EBS Valvedrive, ...) except that only two bands in NOBLE. I have added a trimmer based medium boost (push-pull pot switch on the front panel). The volume pot stands in between the two tubes, after the Jensen transformer, and thus does not impact the XLR/DI output. Did not find an as small tranny as the one used by NOBLE (specific design). Anyway a rather small box but not as pedalboard friendly as the original. Did not add the 9 volts pedal power supply. The other box of the picture is a double REDDI clone.

 

[CJ]

Looks like the 2.2 uf drives the Jensen and the 0.1 drives the 1/4".

Would be nice to have a vol pot on the xlr like the reddi as it also acts slightly as a tone control.

Don't see any transistors other than the regs, I agree with Gus, one for the heaters (notice the 3900 35 volt lytic) and one for the 9 v outs.

What does fender 2.5 stack mean? Bass treble and a mid resistor?

You could combine the noble and the reddi, run the noble first stage and tone stack into a 6n1p output stage, just use a parallel input jack on the input for the amp out like the reddi.

 

[PermO]

I have build the Alembic style DI a couple of years ago.
I used a 1/4W 15000/600 Edcor output transformer with a 2,2uF cap like the schematic that was posted here.

The EQ is pretty nice, the DI sounds great with guitar.

I'm not so happy how it sounds on bass though, it lacks in the bottom end.

Any recommendations on how to fix that ? ... swap the output transformer ?

I build it in an old Siemens case I found for 10,- E in a scrapyard, took the lid to a local powder coater who was doing oarange at that time and I payed him 10,- E to add it to the conveyor belt that was running.

It came out really nice;

 

[Aircoutix]

The 2,2uF drives the 1/4. It aims at keeping the low end even with the low impedance of a power amp input. Two 0,1uF/630V (before and after the vol pot) drive the high imput impedance of the White cathode follower tube.

 

[Aircoutix]

A vol pot on the XLR is not that useful in this case (it would remain maximum) since the Jensen level lost is almost 20dB (impedance conversion drawback).

 

[Aircoutix]

I have made a preamp combining both NOBLE and REDDI. But this has two drawbacks.
First the REDDI output transformer radiates a lot and this is not easily compatible with other sensitive components standing close. This would require a larger casing in order to separate the parts. I tried mumetal shield but this did not work. Mumetal only works for very low radiation levels. I had to search a lot on the transformers orientation in my dual REDDI in order to minimise the hum.
Second the White cathode follower places the upper triode cathode at a rather high voltage level (mid of the PSU high voltage, that is around 160 volts) while specification theoretically implies no more than 90 volts for a 12A_7 (and 100 volts for a 6N1P) between heater and cathode. This implies to set the heater voltage at 80 volts which induces an additional design difficulty in case of heater voltage DC control, the low voltage of the heater regulation being 80 volts above the ground level. The non regulated heater should be preferred for design simplicity but this was not the option with my PSU transformers which were delivering higher heater voltages in order to cope with the voltage lost induced by the regulation.
Anyway I stopped a bit with REDDI, NOBLE and their combining (which both sound really nice with bass, especially the REDDI) when discovering the API 500 series world.

 

[Aircoutix]

PermO, the schematic seems correct for a good result. Maybe the Edcor output transformer is the low end limiting device for bass.

 

[Aircoutix]

Except that;
1) The unbalanced 1/4 output is not isolated, contrary to what is mentioned on the output identification.
2) the 0,1uF driving the unbalanced 1/4 output does cut the low end if used toward a low impedance input such as those of power amps or most return inputs of bass heads (10k-47kOhms). This output can only provide the full bass spectrum if used in connection with a high impedance input device such as as the preamp input of a bass head.

 

[Aircoutix]

PermO, for bass, maybe you should try to run th 2.2 uF to the 1/4 output (instead of the 0.1uF) and connect it to ground with a 220 kOhms. Of course not balanced anymore (as well as the current design with the 0.1uF but with low end).
Or replace the Endcor with a Jensen 15k/600 (or close input impedance, if they have). The well known JT-DB-E would work but would lose more dB and make the low impedance tube output stage a bit useless.

 

[tinn]

Noble Bass DI:
Recently a bass Player in the studio was using the Noble Bass Di.
I did some measurements and a comparison to the active DI
used here normally ( OPA134 and a 10:1 transformer).
Maybe the saturation and distortion makes the flavour of the Noble.
But the difference is not that big:
audio DI-B is the noble DI.
The real bass was not exceeding the minus 10 level.

 

[Spencerleehorton]

I’m awaiting parts to start the noble di, I’ve planned out the turret boards but might end up doing my own pcbs.
Also been using my REDDI clone and I’m only getting quite a low level out?

What level should I expect out from the REDDI clone?

 

[Aircoutix]

Why would a clone deliver a lower output signal than the original? The REDDI output is rather high, as my clone's one. Do you use an actual clone of the output transformer?

 

[Aircoutix]

I cannot imagine one second that an OPA134 based preamp provides a similar result as the Noble DI (and generally speaking a well designed full tube based preamp). I don't use the OPA134 but I have tried a lot of OPAs among the best ones (also with metal casing which sound a bit better) and none alone provides an as good result as the Noble DI. Discrete AOPs can provide good results in well designed preamps (such as I experienced with some API 500 series ones).

 

[Spencerleehorton]

I have wound a txf to similar spec to one CJ wound.
I have used 4500 turns on primary and 625 turns on secondary and used some grease proof paper for the gap.
I’m waiting for a insurance meter to test it’s inductance but resistance is 1000ohms on primary and 170ohms on secondary.
My tube is a 6H1N-EB which I think is a 6N1P equivalent?
I do need to test the circuit to see where I’m going wrong as it does seem something is wrong!!

 

[Spencerleehorton]

I cannot imagine one second that an OPA134 based preamp provides a similar result as the Noble DI (and generally speaking a well designed full tube based preamp). I don't use the OPA134 but I have tried a lot of OPAs among the best ones (also with metal casing which sound a bit better) and none alone provides an as good result as the Noble DI. Discrete AOPs can provide good results in well designed preamps (such as I experienced with some API 500 series ones).

I thought a OPA134 was a chip? Where has that come from?

 

[tinn]

Yes, the OPA134 is a JFET Op amp.
OP amp + output Transformer 10:1
and as mentioned, the sonic difference to the noble DI was not that big.

 

[Spencerleehorton]

Just so I understand what your talking about as it is a bit vague.
are you saying you tested OPA134 on output and compared it to 12:1 output transformer and txf much better or are you saying a OPA134 based output preamp doesn’t sound as good as the noble di?

 

[Jarno]

I have build the Alembic style DI a couple of years ago.
I used a 1/4W 15000/600 Edcor output transformer with a 2,2uF cap like the schematic that was posted here.

The EQ is pretty nice, the DI sounds great with guitar.

I'm not so happy how it sounds on bass though, it lacks in the bottom end.

Any recommendations on how to fix that ? ... swap the output transformer ?

I build it in an old Siemens case I found for 10,- E in a scrapyard, took the lid to a local powder coater who was doing oarange at that time and I payed him 10,- E to add it to the conveyor belt that was running.

It came out really nice;
View attachment 108539

Did you try the signal before the output transformer (I use my F2b clone without output transformer)? What value are the bypass caps on the cathodes? What changes did you make wrt the original schematic?