First Tube Microphone Preamp Build Occilation.

[cory ponzo]

Birds nest, yea I was hopping to make it neat. Then I realized I have no idea how to do a lay out or what wires should be twisted other then the heaters. I've got parts for another ill build that one point to point right next to the sockets. First I might tear this one apart and make it point to point. I've also read somewhere that it's better to have wires come from above then have them all laying on the chassis. So once I get more experience I'll figure it out.

Thing is I'm a singer first then engineer, and lastly a diy guy so I'm not that good at this yet.

I've added a 22uf cap I had on hand from 250+ to ground and it seems to make the motorboating less so only a small place on the pot starts its engine. I assume that is a start in the right direction.

Th only good part about this project as it only cost me the price of the transformers and caps resistors. All the other parts were saved from the trash.

Thanks again

 

[cory ponzo]

I'll have to order some 10k resistor and 22uf caps to try the other stuff in the red diagram. The grounds in red are as you have drawn them.

 

[Tubetec]

Id suggest rotating the input transformer 90 degrees , so the core doesnt align with the power transformer .
You might also position the output transformer to help sheild the input from mains TX .

 

[cory ponzo]

Yes 470n is in place. Grid stoppers are on the socket. I got to get back to tracking so I'm not going to mess with this for a while. For what ever reason it sounds amazing on synth. No issues at all. I can't use it for vocals as it just clips even with the pad on. I did put a 12au7 for the first tube and the occilations stopped.

I got to get back to tracking. So I wont be Messing with the diy stuff for a few weeks. I have parts to build two more any one have a good schematic, I'm going build the next one point to point. At some point I'm going to rip everything out except the power supply and point to point it right next to the sockets.

 

[RoadrunnerOZ]

Pin 2 and 3 are through the input circuitry Balanced into the mic transformer pin 1 ground. The secondary of the mic transformer has one side grounded the other side goes to the pot.

Is the bottom of the pot actually grounded?

 

[cory ponzo]

Is the bottom of the pot actually grounded?

Yes looks like I got it all sorted out. Tried a bunch of different tubes and found a great match.

 

[cory ponzo]

I got it all sorted out. Using 2 12au7 and trying 5 different ones I found a pair that sounds good. The motor boating is no longer happening with valve 1 bring a 12au7. I'm going to build another pre just trying to decide if I want two that are the same or different.

Thanks for your input. A little direction from multiple reply seems to have sorted it. It still has plenty of gain.

 

[RoadrunnerOZ]

Transformers that are unshielded close to tube bases is always risky.

 

[cory ponzo]

Transformers that are unshielded close to tube bases is always risky.

Yea I added longer wires and removed them completely from the chassis with no improvement. So I. This situation it was not the cause.