Increasing B+ on Bassdude

[Valiesh]

This is strange.

After reading all the information I could find on this forum (and on Talkbass), it seemed to me that lowering resistor 560R (R6 on the schematic, printed R7 on the PCB) would increase my B+ voltage.

I'm aiming for a voltage of around 320V, and I've read that a 390R resistor could be more or less in that zone.
So I powered my Bassdude PCB directly with this 390R resistor, which gave 269VDC in the end.

That's not quite right.

So I decided to replace the resistor with an even lower value.
Searching through my stash, found a 330R...
Mmmh... I read somewhere that @vigilante398 generally put a 359R in series with the 4K7.

This can raise the voltage above 350VDC.

Anyway, I took the risk of replacing the 390R with the 330R and...... still 270VDC....

Ok...

I searched my reserve and found a 220R that replaced the 330R, I activated the pedal and.... still 270-ish VDC...


Comparing with what I've read so far, I think I'm missing something. Are these results possible?



Thank you all in advance for your valuable help,

 

[Creach]

Hello Valiesh,

Right now I 'm finishing a Black eye, 430R gave me 312 VDC.

Is your power supply strong enough? Maybe not enough juice to get over the 270V?

 

[Valiesh]

Hello Valiesh,

Right now I 'm finishing a Black eye, 430R gave me 312 VDC.

Is your power supply strong enough? Maybe not enough juice to get over the 270V?

Thanks for your reply,

I'd be surprised if my power supply had anything to do with it. After measurement, it delivers 9.32V (1Spot 9V 1700mA).


Just for the sake of it, I tried it with an MXR mini-brick which has an output that delivers exactly 9.0V 800mA. The VDC on B+ is slightly lower at 267.5VDC.

Also tried with a CIOKS DC7 @9V : 274.3 VDC


Finally, I tried it with a T-Rex 12V 1.25A power supply and... that's it: 327.4 VDC (the tube filaments are also visually brighter).


I still find this a little strange, as I'd understood that the rail voltage should be the same whether the circuit is powered by 9V or 12V, which is clearly not the case here...

 

[Valiesh]

Quick update.

I've runned the same testing on my Nobelium build and stated the same phenomenon : The output voltage vary greatly depending on the input voltage.

Approx. 254 VDC with 9V input and 318V with 12V input.

According to @vigilante398 on the thread https://forum.pedalpcb.com/threads/tubes-102-intro-to-power-supplies-for-tube-circuits.10652/
It is stated that "SMPS have a regulated output, which means the output voltage is independent of the input voltage."

I really do think that something is wrong with my builds.


Is anyone experiencing the same phenomenon as I am ?

 

[Creach]

So you also changed the 560R resistor to your Nobelium?

Now i have a 12V psu, i will go to pick up my 9V and test it.

 

[Creach]

Test done with my Black Eye, the B+ is going up when I increase the input voltage from 9V to 12V, and down when going back to 9V.

So it not regulated, your build have nothing wrong.

240V at 9V, 310V at 12V.

A link to the video of my test (hope the link is working) : https://drive.google.com/file/d/12aZeGrSWPR2IfmsfRit-1M4hskR2K8Yw/view?usp=drivesdk

Edit : Quick test with my Diplomat : 300V at 9V, 335V at 12V.

 

[Valiesh]

Test done with my Black Eye, the B+ is going up when I increase the input voltage from 9V to 12V, and down when going back to 9V.

So it not regulated, your build have nothing wrong.

240V at 9V, 310V at 12V.

A link to the video of my test (hope the link is working) : https://drive.google.com/file/d/12aZeGrSWPR2IfmsfRit-1M4hskR2K8Yw/view?usp=drivesdk

Edit : Quick test with my Diplomat : 300V at 9V, 335V at 12V.

Thank you so much for taking the time to test it out

(Yes, my Nobelium is also equipped with a 390R instead of the 560R)

It's really interesting. I think I need to learn more on how this SMPS design works because I'm still convinced somehow that the output voltage should be regulated.

Another strange thing is that when I lower the resistance below 390R, the B+ doesn't change (I've tested 330R and 220R).