Sela T-12 inspired Mic... PSU/Transformer help!

[speakercoil]

lol... Alright you convinced me... I will mod a chinese power supply and look at the pattern switching... Maybe down the line I will build both the gus recommended changes and the JJ... For now I will do the JJ first just because... well... It can use a cheap power supply.

Yeah I figured those resistors would be large, but the body should be big enough to hold everything if I space all out correctly...

OH! I had one last question... In this design do I have to worry about using high wattage resistors anywhere, or will 1/4-1/2 watt work. So far to be safe I have been sourcing 1watt resistors. I have sourced every part so far. Total cost is around 900 so far... Using all top quality components...

Resistors are a mix a mills, vishay (bulk foil axial), Takman, and Kiwame. The caps are a mixture of Siemens NOS PIO, and Auricap.

BV8 will be from Oliver, and Capsule from Thiersch. The tube I am still debating... I know someone recommended a m8100 instead of a 6AK5, but I also was recommended a Mullard 5654.

I am very excited about this build now!!!! It went from being a "let's see if this will work" project into a full fledged new design. Thank you so much to both Gus and JJ, because without them... Well this wouldn't be possible. Also thank you to everyone else who has helped so far!!!!!

Now... To hit the drawing board again and try and implement the pattern selection circuit.

-Grant

 

[strangeandbouncy]

Go Grant!


  please keep us informed! I am very interested to hear how this sounds. I'll bet it is peachy!


  Kindest regards,



      ANdyP

 

[speakercoil]

OK... So looking at the Apex... Is it C5 and R6 which make up that circuit? Also should the values be the same as on the Apex... I mean after all it is a different capsule entirely.

Thanks...

-Grant

 

[hazmatstrat]

OK... So looking at the Apex... Is it C5 and R6 which make up that circuit? Also should the values be the same as on the Apex... I mean after all it is a different capsule entirely.

Thanks...

-Grant

R9, C5
See they go to the back of the capsule. The power supply will do the rest.

Jim Jacobsen
JJ Audio

 

[speakercoil]

Got it... OK I am going to try and add it to the circuit and post it for approval... Assuming keep the values the same, since you didn't mention differently.

-Grant

 

[speakercoil]

OK So comparing the schematics my confusion is as follows...

I am assuming this new chain should be coming from the unused side of the capsule... However being as the pinout of the Apex isn't labeled I am having trouble deciding which pinout this circuit is going to. For example and I am doing from capsule down to  Pin 3 with the the new capacitor in parallel to R1.... and if so then where would the new resistor go? For example I took a guess that I TOTALLY think is wrong... So don't laugh at how off this probably is. I didn't label the values of the new parts, because... Well... I am assuming they are in the wrong spots. lol. Well C4 might be right, but I was totally confused about R8. Both of those the numbers of my schematic and not the Apex...

So yeah... Tell me how wrong this is and let me know WHERE they should go, because I am confused about it. I think it would be easier for me to compare to the Apex if it was the same tube and capsule, etc...

-Grant

 

[speakercoil]

OK... Looking at the MK7 one... I am sort of getting it more... So do I need to use a whole other pin... I mean after all my schematic only has 6 pins I believe... one of which not even being used. lol... But I at least get where to put the cap in that circuit.

I think I am going to redo this and submit again!

 

[speakercoil]

OK so this might be wrong, but it feels slightly closer. This was modeled after the MK7 one... It still feels wrong... and I am sure it is. However I feel it's closer than the one I actually titled wrong version. lol.

-Grant

 

[hazmatstrat]

OK so this might be wrong, but it feels slightly closer. This was modeled after the MK7 one... It still feels wrong... and I am sure it is. However I feel it's closer than the one I actually titled wrong version. lol.

-Grant

Grant,
Look very closely at the MK7 and how the capsule membrane front, back and backplate are connected. Look and compare how the Apex capsule is connected. Either one will work. Make a choice. Check your schematic and re-draw.

JJ

 

[rodabod]

I know someone recommended a m8100 instead of a 6AK5

Thanks for keeping that one quiet!

 

[zebra50]

Now go find the Royer 2001 mod and look close.  You might even want to look at the power supply schematic. I suggest you google/find book(s) , Ohms law, Kirchhoff, Norton. 

Gus and a couple of others have mentioned the Royer circuit, which itself was based on classic tube mics. Your schematic is starting to look very close to it (give or take a grid resistor)

A lot of people here have built that circuit so it's a good place to start, especially in terms of future troubleshooting.

 

[speakercoil]

Didn't realize it was supposed to be a secret?!?!?!? Sorry...

AHHHHHH Now we have a schematic that I can compare a little easier... However... It is sad to see my design isn't all that unique now, but it's interesting building this circuit up. It's helping me understand the purpose of different parts of microphone circuits... When I build this, I will be sure to do a video, and I think I am going to show the different stages it went through. Going from the Sela T12, adding parts of the Sela T24, and eventually becoming almost Royer's mic mod. lol. The evolution of the design.

-Grant