cory ponzo
Member
Hi everyone this is my first post.
I built the Jensen Cascode Mic pre cathode follower. I uses Edcor 1:8 input and 1:5 output. It works and sounds beautiful. Some of my best vocal sounds to date. The power supply is two nodes. 22uf 10k, 22uf 22k and 44uf on the b+![20240404_211235.jpg 20240404_211235.jpg](https://cdn.imagearchive.com/groupdiy/data/attachments/78/78453-2bf16587da7db4019ce101c9197c5fb7.jpg)
![Cascode Tube Mic Preamp From Jensen.jpg Cascode Tube Mic Preamp From Jensen.jpg](https://cdn.imagearchive.com/groupdiy/data/attachments/78/78454-bda66d302e5f241568c0be089293efcb.jpg)
but..... if I turn the pot down to 9pm it starts occilating at 2 cps. Like pop pop pop sending the speakers to full boom. I tried a capacitor between the middle wiper and the first stage it stopped. I lost all my gain. I tried different internal cable routes but this made the occilation happen at all gain settings. I tried different caps on the wiper but all messed with gain.
Luckily I don't use it at low gain so it's not the end of the world but I'd like to get it sorted.
Here's a pic of the schematic and the build. I have changed the output transformer from step down to step up since this pic was taken. I have also sorted the grounds as it had a small hum. I know my 48v is overkill but it's what I had at .5 amps it is fully adjustable supply.
Thanks for any help.
I built the Jensen Cascode Mic pre cathode follower. I uses Edcor 1:8 input and 1:5 output. It works and sounds beautiful. Some of my best vocal sounds to date. The power supply is two nodes. 22uf 10k, 22uf 22k and 44uf on the b+
![20240404_211235.jpg 20240404_211235.jpg](https://cdn.imagearchive.com/groupdiy/data/attachments/78/78453-2bf16587da7db4019ce101c9197c5fb7.jpg)
![Cascode Tube Mic Preamp From Jensen.jpg Cascode Tube Mic Preamp From Jensen.jpg](https://cdn.imagearchive.com/groupdiy/data/attachments/78/78454-bda66d302e5f241568c0be089293efcb.jpg)
but..... if I turn the pot down to 9pm it starts occilating at 2 cps. Like pop pop pop sending the speakers to full boom. I tried a capacitor between the middle wiper and the first stage it stopped. I lost all my gain. I tried different internal cable routes but this made the occilation happen at all gain settings. I tried different caps on the wiper but all messed with gain.
Luckily I don't use it at low gain so it's not the end of the world but I'd like to get it sorted.
Here's a pic of the schematic and the build. I have changed the output transformer from step down to step up since this pic was taken. I have also sorted the grounds as it had a small hum. I know my 48v is overkill but it's what I had at .5 amps it is fully adjustable supply.
Thanks for any help.