Studio Projects T3 circuit

[atomdog]

Hi guys,

What a strange coincidence !!

I decided to replace the power supply caps and had a question only to find this mic is being discussed as a live topic.

Mine is a first gen tb-1.

Im currently awaiting parts so I can replace the in/out entirely with better wire and noticed the 2 ceramic 0.1uf caps hardwired to the output socket. (Second pic)

Do I really need to copy this or can I omit them entirely ?

Thanks.

 

[Emmathom]

Hi @atomdog
Usually we see 2*10nF at XLR to supress RF noise... Note that @LevinGuitar said that its TB1 PSU's were noisy : maybe it's the opportunity to "refreh" all solders and check every connexion, etc... LM7806 can be noisy too ! But no other way to do without changing the whole thing.
For my part, not having a PSU, I have to build one from scratch but with HV & heater regulations.

Can you please provide a pict of the front pannel so one can read the XLR pins wiring ?
BR

 

[Khron]

Can you please provide a pict of the front pannel so one can read the XLR pins wiring ?

Have you considered even / at least a quick Google (image) search?

 

[Emmathom]

The modified PSU and the circuitry schematic for my TB-1.
Tube is 12AY7 NOS. Anode is 120v@1,5mA. Capsule polar. is 71v. Heater is elevated +25v.
Will use the unused wires (3 free) to supply the heater and HV minus into inside the mic.

 

[Emmathom]

PSU done and tested... Waiting for the 7 pins XLR to be delivered.

I've installed a self timer circuitry which switches HV on (and lighten the white led) about 1mn45" after heater.

It was tough to fit the 15cm x 10,5cm x 5,5cm enclosure but it's done with success. I wanted to keep these dimensions for the PSU to fit in the Studio Project original case.

Now I've got to work on the mic itself...

 

[thor.zmt]

PSU done and tested... Waiting for the 7 pins XLR to be delivered.

I've installed a self timer circuitry which switches HV on (and lighten the white led) about 1mn45" after heater.

It was tough to fit the 15cm x 10,5cm x 5,5cm enclosure but it's done with success. I wanted to keep these dimensions for the PSU to fit in the Studio Project original case.

Now I've got to work on the mic itself...

Nice work!

 

[Emmathom]

...

 

[atomdog]

PSU done and tested... Waiting for the 7 pins XLR to be delivered.

I've installed a self timer circuitry which switches HV on (and lighten the white led) about 1mn45" after heater.

It was tough to fit the 15cm x 10,5cm x 5,5cm enclosure but it's done with success. I wanted to keep these dimensions for the PSU to fit in the Studio Project original case.

Now I've got to work on the mic itself...

Nice - I ended up omitting the 2 caps hardwired to the input and the mic is dead quiet. It seems just changing all the lytics to branded caps got rid of all the noise.

Please keep us informed what you do to the actual mic. Which components actually affect audio quality ?

 

[Emmathom]

Hi @atomdog

Here is the original schematic but redrawn for more visibility (exactly the same as the one you posted)
And next is the modified schematic. Thr circuit now needs a 7 wires cable + shield .
About audio quality I changed C1 (chineese cap) for a 1uF@450v Nichicon (electrolytic) and most of all C2 (coupling cap) for a MKP (250v is ok).
C5 C6 C7 C8 are MKP 100nF@100v. No more R cathode bypass cap. Heater elevated by 23v (or so).
Just compare the 2 schematics...

EDIT : don't group pin1 (ground) with cable shield except at one place = in the mic. Cable schield will be referenced to PEN (earth) by its shell to the PSU enclosure (which is referenced to PEN for safety). So audio output XLR pin 1 is only connected to mic XLR pin 1 and not to XLR shells...

 

[Drosselmeier]

 

[Emmathom]

View attachment 140494

Yep for sure, a drawing error, thanx !