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).

 

[bherren]

This is actually a concern ... I built the bassdude kit with a 250V cap on the SMPS C1, but I gave the pedal to my son with a 12V supply... I worry C1 is going to pop. I might take the pedal back & swap it for a 400V or 630V rated cap

 

[Lekky]

This is actually a concern ... I built the bassdude kit with a 250V cap on the SMPS C1, but I gave the pedal to my son with a 12V supply... I worry C1 is going to pop. I might take the pedal back & swap it for a 400V or 630V rated cap

I think the voltage stays below 250V as long as the resistor values mentioned in this thread aren't changed. It can still be a good idea to put a 350V or 400V cap at C1 to have some headroom.

 

[74hc]

More worries:

1- You need to make sure the higher rated cap can fit both the footprint on the PCB, and the case.
2- You also need to select the right type of cap for C1 (not talking about axial vs radial).
3- Keep the leads on the new cap as short as you can if you are jury-rigging it.
4- If you should revisit R9 and R10 to see if you need to bump up the wattage rating if you increase B+.

Finally pertaining to earlier discussions in this thread, don't think of the power circuit behaving like a fixed linear voltage regulator. The circuit is regulated, but not in that same sense.

 

[Tassieviking]

I usually use the 10uF 400V capacitors from Tayda, they are 10mm x 16mm P5 and they fit with no problems.
I do not think you would fit anything longer then 16mm, but there might be some out there that are 17mm that could get squeezed in there.
20mm will not fit at all so don't even try, I just checked with some of the 10uF 450V ones from Tayda that are 10mm x 20mm P5 and there is no way to get them in there.
It could be that by increasing the voltage you are increasing the power that is needed to drive that circuit, the higher the voltage the less amps you can get out of this type of power supply.
You might have hit the limit of the power for the power supply so something has to give, in this case it seems the voltage can't increase enough at lower input voltages.
Maybe just stick to the original values ? (that was hard to say cause I love modding my pedals)
Cheers
Mick

Edit: it will also depend on the components you use, make sure the capacitors have low ESR etc.

 

[drew.spriggs]

I usually use the 10uF 400V capacitors from Tayda, they are 10mm x 16mm P5 and they fit with no problems.
I do not think you would fit anything longer then 16mm, but there might be some out there that are 17mm that could get squeezed in there.
20mm will not fit at all so don't even try, I just checked with some of the 10uF 450V ones from Tayda that are 10mm x 20mm P5 and there is no way to get them in there.
It could be that by increasing the voltage you are increasing the power that is needed to drive that circuit, the higher the voltage the less amps you can get out of this type of power supply.
You might have hit the limit of the power for the power supply so something has to give, in this case it seems the voltage can't increase enough at lower input voltages.
Maybe just stick to the original values ? (that was hard to say cause I love modding my pedals)
Cheers
Mick

Edit: it will also depend on the components you use, make sure the capacitors have low ESR etc.

Based on other peoples testing and what I've done, there's a couple of easy mods to squeeze some extra chooch out of it:
*change to higher current inductor (as they're already on the border of being saturated)
*change to a lower Rds MOSFET which allows more current (I use a IRFB17N50)
*modify the RC snubber network as it is a big hit to efficiency (I use 47pf/2k2)

Obviously, use the lowest ESR caps you can on the HV side too as it helps.

 

[Tassieviking]

I have some FCP20N60 in my Tayda shopping cart to try for the power supply, they have a Rds of 0.15 ohms and costs $2.29 each.
I don't know where I can get any better inductors from yet that will fit onto the Sushi C2CE PCB's.
I have a 1 watt amp that runs on the standard C2CE power supply with the same components as the BOM from Tayda so it cant be that close to saturation.
The amp should be 1 watt with a 12AU7 driving the output transformer but I am using a 12BH7 to get another 30% power out of it and I have no problems.

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