Maudio Nova circuit mod

[LevinGuitar]

I would like to try a mod on my Maudio Nova. It is the second version, with just one small pcb. So instead of going U87 way, why not to try a KM84 circuit? The fet will be 2N3819, maybe different capsule and a T8-T13 transformer.

I took the schematic of the GT55 mic form this very good thread, revised the variations of the circuit (prety much the same without pad or low cut), and did first schematic of the mod.
I did not included R5 and C6 from the original KM84 schematic, are they really needed there? Same with R11, R12 and R13?

Edit: Km84 mod not worth with the original capsule, but with a Neumann K103 or similar becomes stellar.

 

[Gus]

The best thing to do is clean up the circuit board and try the microphone again

the stock transformer is about 5:1 so think again about the 84 circuit
IMO there is nothing really wrong with the nova circuit. The first stage has selected resistors for gain and biasing
I even leave the stock poly input cap alone sometimes

I have tried different EQs and circuit changes to the ST51/151 circuit that looks to be the same as the nova/ groove tubes circuits.
I have one that I like I might make up a kit of parts for it
however
The stock circuit is OK with the 2SK30
The noise seem to drop a little if you clean the PCBs
The stock transformer is OK

For fun search for the solid state Brauner circuit threads at the forum and compare the schematics.

 

[LevinGuitar]

The microphone indeed sound very good for the price, and low noise. Just want to try improving it a bit, more details, more low end. I,m tempted to go 5840 tube but first would like to try a simple fet. I expected a lower ratio transformer, thanks for the info

P.D. Yes, will leave the 1n imput cap and original capsule wiring for now.

 

[LevinGuitar]

For now just the basic changes: removed R4, R7, R8, R9, C5 and Q2. Q1 is 2N3819 with drain voltage 12v (a bit high) with 10k on R3, C2 is Elna 22uf, C4 is 1uf MBM and chinese 9.5:1 transformer.

Will drop a bit the voltage on drain and try other capsule.

 

[LevinGuitar]

A bit of madness here following Ami M49 circuit and using few original pcb holes. I wonder if the small traces will survive a tube circuit voltage.

 

[Khron]

It's not voltage that blows up traces, but current. If anything, it's the heater wiring that you should be concerned with, if you plan on using any PCB traces for that.

Voltage rather concerns the distances between traces (traces that have large voltage differences between them).

 

[LevinGuitar]

Thanks, the heater can be wired directly to tube pin.

 

[LevinGuitar]

Here with a K103 capsule, same fet circuit as before but with 8K on R3.

Edit: 122 test without imput cap, polarization to backplate and Rifa MP 2uf in the output.

Can anyone see the attached audio files?

 

[LevinGuitar]

I realized the KM84 circuit should have a lower ratio transformer than the T13, so I tried the WGT "BV8" transformer here. Now have more gain (10v on drain finally) and seems to be well balanced. Still with the K103 capsule and without the 4pf feedback capacitor.