XL6009 based DC/DC Converter for sensitive audio voltages like e.g. phantom power?

[rock soderstrom]

Hi guys,

modern switched-mode power supplies are slowly arriving in my archaic tube audio world. Lately, I've been trying to question my cherished habits and take a different approach to realizing my projects.

Out of curiosity, I bought two of these DC/DC up converter boards on aliexpress.

https://de.aliexpress.com/item/1005...t_main.11.21ef5c5fshABJR&gatewayAdapt=glo2deu

As supplied, these boards can convert over 38V from 9V. The promised 52V can only be achieved after a feedback resistor hack.



52VDC minus some filtering makes good 48V?

What do you think, are such boards suitable for obtaining a clean phantom voltage from lets say the heater voltage (or a separate DC voltage)?

Could you heat an unusual single tube (P or U tubes) with these boards to operate them with other conventional E-tubes?

...or would it be better to stay away from such solutions, as they contaminate everything in their vicinity with HF noise?


20mV/5muS per division, Vout=24V

What do you think? Does anyone have experience with this?



PS: I'm a beginner with this stuff and have almost no experience with it. So, dear experts, bear with me. (Yes, you too Khron )

 

[rock soderstrom]

I played a bit more with the DCDC converter board and would like to show my new findings here.

I try simulate a phantom power supply, since the board is not yet hacked (I don't have the right SMT resistors yet), here only with approx. 38V instead of 48V.


My test circuit looks like this, I have installed an RC filter to see what effect I can achieve with it.



What is noticeable (at least to me) is that the switching peaks of the DC DC board rise sharply with a light load (such as an LDC microphone).

Comparison idle vs light load without filter: (20mV/5muS)


Here now with light load and 50mV per division

Now the 470R/4700uF filter comes into play and clearly shows its effect (back in the original 20mV setting!)


To make the signal more visible, now in the highest resolution of my scope 5mV.

For me this is pretty interesting

 

[rock soderstrom]

My learning odyssey continues, this time a test to use the DCDC board as a heater supply for a nice PCL86.

According to the data sheets, the PCL86 needs 13-14.5V with series heating at 300mA. What if you wanted to use this tube (as an example) in a device with only 6.3V DC tubes?


Let's try it out. It works for the most part without any problems. My lab power supply provides the 6.3V DC, the tube and the DC board together draw 0.75A. The output voltage of the board is exactly 13V. The chip stays cool after the (hot) start

This is the only problematic point, the moment of power up, the cold tube is at first a short circuit and makes the XL6009 sweat a lot, it reacts with a soft start mode and draws a whopping 2.5A or more.

After a short time this normalizes, a small series resistor for starting could bring advantages.

The chip is tough, I have tortured it several times and it is still alive.

The scope picture now looks like this, at 0.2V/ 5muS per division, without further filter.

 

[rock soderstrom]

Now with my single-stage, super inefficient RC filter with 18 ohms and 4700uF. Its a disaster in terms of energy, too. The laboratory power supply now delivers 1.26A at 6.3V, because I had to increase the output voltage of the DCDC board by 5V, I had no better suitable resistor of this size. Very warm affair...still 0.2V per division. The chip still stays cool.

Learning by doing.

 

[rock soderstrom]

1muS per division


Edit:

I think this is a valid way to replace the now very expensive ECL86 with the much cheaper PCL86 in old radios and R2R recorders. These boards are very inexpensive and small. There are versions without a display that are even smaller and cheaper.

 

[nashkato]

According to the data sheets, the PCL86 needs 13-14.5V with series heating at 300mA. What if you wanted to use this tube (as an example) in a device with only 6.3V DC tubes?

i guess one would use ecl86 then

 

[rock soderstrom]

i guess one would use ecl86 then

Take a look at today's prices and availability and BTW it was just an example (as mentioned). Thanks for feedback

 

[nashkato]

i'm very sorry if i interrupted your oh so very serious scientific monologue with my ridiculous comment.
stupid,stupid , stupid me !