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The YARRA Preamplifier/HPA for Melbourne DB Group Buy

Member
Joined 2010
Paid Member
Hi Vunce,

I am going to have to lower the voltage from the Yarra psu to 24v for the Hakuin. You had posted the following for member meanie"
Hi Meanie,
I also run 22v trafos in the Yarra capMx psu. The way I reduced the voltage is increase the CRCRC resistors on the daughter board itself to lower the voltage.
My PCA’s use 47R and 33R in those locations for approximately a 7-8v drop. I don’t remember what my Hakuin values are. Use Ohms Law to calculate what the resistor values need to be for your voltage drop.

If using Ohm's Law V=IxR, solving for R saying I need a 4 volt drop would be R=4V / I . What is a good value for I ?

Thanks for the help,
 
Member
Joined 2010
Paid Member
Hi Builders of the Yarra/Hakuin preamp,

Is the procedure for dropping the voltage thru the CRCRC of the Hakuin a trial procedure where one hooks up a 22R resistor using alligator clips to complete the circuit and then adjusts the voltage to the required value of 24 volts. If the voltage does not lower to 24 volts, another resistor is used and the process begins again ?

I assume that this will require test leads to be soldered to components for easy access for hooking up the alligator clips to the resistors, or is it easier to just solder the resistor in place and then de-solder if necessary. This is why I asked in the post above #1621 about a value for the current (I) so R can be calculated.

As always, any help is appreciated.
 
Founder of XSA-Labs
Joined 2012
Paid Member
Hi Myles,
Sorry I didn’t see this earlier. By thread activity notification for this thread isn’t working for some reason.

The Hakuin draws about 78mA total per channel. 70mA in the main output BJT and 8mA for the JFET input.

Using Ohms law, if you need a 4v drop in your PSU, R=V/I so R = 4v/0.078A or about 51ohms. Anything close like 47R to 56R can work. It will dissipate some heat though.

Power = i^2*R or 0.078^2*51= 310mW. So use at least 0.5w resistors and preferably 1W. You can do this in two stages for a CRCRC and 25R each for example.

Hope that helps. Schematic from Etsy shop.

IMG_7792.jpeg