Yet another 12B4 line stage, or is the 12B4 better than the Grounded Grid.....

[Shoog]

Sounds about what I got on my third try. Still would take you down to the hundreds of hertz.

Bummer !!!!

Power supply filtering I think.

Shoog

[pengboon]

If this 12B4a preamp was hooked up to a current output DAC (like Monica2), will it work well? I read somewhere that this type of DAC prefers a lower input impedance, like the GG design? So I need a I/V resistor that will solve the problem?

thanks!

[Pjotr]

Originally posted by Shoog
Just a simple question. I am toying with the idea of building a 12B4 preamp. I have some big light ballast tranformers which I would like to try as plate chokes. I expect them to be good down to at least 400hz. The question is could I put a simple single transistor CCS before the choke (ie +B - CCS - CHOKE - PLATE) to take up the slack.

Shoog

Uhhh,

What do you think what’s left from the inductance when biased with the DC anode current? These ballasts are not designed for DC bias and probably driven into saturation right away.

Cheers

[Mark A. Gulbrandsen]

If this 12B4a preamp was hooked up to a current output DAC (like Monica2), will it work well?

You need a voltage output type DAC and then it'll work fine. HGo back and look for BRian BEck's schematic in this thread. Thats exactly what he's using this line stage for!!

Mark

[icebear]

Hi

I'm thinking of making a 4 channel preamp after my behringer dcx 2496. I have baypassed the analog section like this:
As it is now, i run the signal directly into my 6 deck pot(I use only 4), and directly to each amp. The pot is 20k.
Would the 12B4 circuit have any problems matching the DACs (AKM 4393) output? Shold the pot be placed before or after the 12B4?

Cheers
bjorn

[pengboon]

Originally posted by Mark A. Gulbrandsen


You need a voltage output type DAC and then it'll work fine. HGo back and look for BRian BEck's schematic in this thread. Thats exactly what he's using this line stage for!!

Mark

Ok, gotcha.

Brian,
Can you show me how do you compute the values of R10, R21, L1 and C3? Would this values be applicable to Monica2?

thanks!

[BGcap]

Hello,
My first time posting although have been reading for a while. I am building a 12b4 pre. Does anyone know if when using a CCS at the cathode it is best to have be one CCS for each tube or just one shared CCS for both tubes?
Tom

[blaaberg]

Hey,

Mark, you haved try the RNT-400 from thiel in combination with a DC load from your powersupply, can I see :-)

Have you try it with a 220Vac load?
I wonder if the noise floor is still low, if it would be an option for me as a supply on my 12b4a preamp.

Venlig hilsen Jan Jensen

[Mark A. Gulbrandsen]

Mark-there it is

OK Choky,

I hook up your gas tube regulator diagram and nothing happens....the glow tubes don't glow.... or shall we say there is no ignition.... any idea what might be wrong?

Thanks!
Mark

[ErikdeBest]

Originally posted by BGcap
Hello,
My first time posting although have been reading for a while. I am building a 12b4 pre. Does anyone know if when using a CCS at the cathode it is best to have be one CCS for each tube or just one shared CCS for both tubes?
Tom

HI BGcap

Welcome! You must use one CCS for each cathode. Circuits with two cathodes sharing one CCS have an other function, namely phase inversion to drive PP stages.

Erik