Cobalt Drive - No Output

[JamesMcB]

Hi all,

New user here. Just completed my first PedalPCB build - Cobalt Drive. I have built about a dozen effects from other vendors.

I am not getting any output when the effect is switched on. All is good when the pedal is in bypass.

Based on some other threads related to this board, I suspect that I have bad and/or bogus transistors. I am using MPF102's from Tayda, as J201s are made of unobtainum nowadays. Never had a problem with any parts from Tayda before, but maybe I've just been lucky so far. Being a new builder and electronics hack, I don't have enough knowledge yet to verify this myself. Any help from more seasoned minds would be greatly appreciated...

I have double checked all component values and re-flowed any connections that looked even slightly suspect. Still no joy.

Input voltage: 9.4V. Here are the voltage measurements I have at the moment:

Q1: D: 8.49V, S: 7.79V, G: 4.46V
Q2: D: 8.42V, S: 6.65V, G: 4.14V
Q3: D: 9.15V, S: 7.79V, G: 5.48V
Q4: D: 9.15V, S: 6.65V, G: 0V

IC1:
1: 0, 2: 4.56V, 3: 4.35V, 4: 0V, 5: 0V, 6: 4.56V, 7: 9.15V, 8: 0V

Q5: E: 9.15V, B: 8.49V, C: 5.74V
Q6: E: 9.15V, B: 8.42V, C: 9.13V
Q7: E: 3.30V, B: 3.76V, C: 9.15V

Any help would be greatly appreciated. I hate unfinished business.

If there is a better alternative to the J201s than the MPF102s, please let me know.

Thanks in advance.

 

[Barry]

Not sure but it appears you didn't run the grounds from the board to the jacks, which may be ok if the ground plane is continous, maybe someone wiser than I can chime in

 

[JamesMcB]

It's kinda hard to see in this pic, but all the grounds are installed and connected. I have checked continuity on all grounds all the way back to the negative side of the power connector.

Thanks for your reply.

 

[Tha’ToneSeaQr]

Hey I’m with you, you’re not alone...
I’ve successfully built lots of pedals from other makers, But haven’t gotten any of my PedalPcb’s working (4 so far). PedalPcb has the best selection by far and I love the streamlined designs. I just don’t know where I’m going wrong w/these

Regarding your Transistors;
I don’t know where you’re from, But you can get through hole 2n5457’s from SmallBear (USA limit of 4 per purchase). Or if your adventurous.. Do like I do and buy SMD MMBFj201’s and other JFETs & solder them to “adapter boards” basically mini pcb’s for converting SMD fets to through hole. Small bear has these boards as well as Tayda and I believe they sell em here too. And you can get like 100 SMD J201’s from mouser for less than 20 bucks all 100% authentic and well within spec. Totally worth it IMO if you buy say 50+ 2n5457’s & J201’s from mouser and you’ll be set for JFETs and will have plenty to practice soldering them. Tayda has great jacks and pots but avoid their transistors!