low noise Pre-Amp / DAC power supply MJE15034 TL072 Regulator based on STUDER 900

Yes, that's the problem.

... so that 'side' of the PSU is not able to supply the 0.9A required by the ApplePi DAC... The 'STUDER' copy PSU claims a 2A output current which is very likely the SUM of the TWO PSUs on the board i.e. 1A + 1A. This means that the DAC current requirement pushes the PSU to its limit... Is the same thing happening if you connect the DAC to the other PSU? If the answer is YES than there are two possibilities: - both the DAC and the the 'STUDER' are over-stepping the published current requirements ( the DAC requires more than 900mA and the PSU can supply less than 1000mA on each of its two PSU) - one of the two devices is out-of-spec by quite a margin Also when the 'STUDER' PSU is connected via the X6 microUSB on the DAC there should be no 'jumper' on the J2 connector DAC-side (used only when the DAC is supplied 5V from the RPi) If you have a 5V PSU that safely works with your DAC DIRECTLY (not via RPi with the DAC-side J2 'jumpered') you could measure the actual current flowing between the PSU and the DAC with a multimeter and draw a conclusion from this test.
 
agree with you, hardly possible... but a 'request' for anything over 1A will either activate the shortcircuit protection or the stated 5V output may go down to an unseable 4.x Volts.. (unless I've missed this info) We only know that the DAC does not work with one of the PSUs.. We don't know what are the output voltages with the DAC connected or not connected... Is there a nice and steady 5V with the KALI connected?
 
We don't know what are the output voltages with the DAC connected or not connected... Is there a nice and steady 5V with the KALI connected?

Yes with the Kali there's a steady 5V. With the DAC connected the 5V drops below 2V. Using another power supply I measured the DAC current to be 600mA. There is no J2 jumper on my DAC: It's one of the early review versions. I'm supplying it separately via the GPIO pins, and have removed the 0 Ohm resistor from the Kali in order to do that.
 
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...that means that the 'STUDER' copy is seriously overrated or there's a component choice that went wrong... that is IF BOTH PSUs are behaving in the same manner... I admit that the cost of the so-called STUDER is pretty low and one cannot have a high expectancy of top quality... at least you've found a notable sound improvement in feeding 5V to the KALI. The 'single' PSU in the link proposed by FauxFrench seems to be similar to your double-decker and the bonus is that it contains a schematic diagram... that is if you want to spend some time to narrow down the problem.
 
This circuit uses a current limiter set to some 1.5A (set by 0.4R). Perhaps your board has got a similar current limiter.
Can you see if pin 3 (the right-most pin) on the MJE15034 is connected to a resistor wit a value below 2.2 Ohm? That may be the resistor setting the current limit.

The current limiting resistors on my board are 2.2 Ohm. The value marked on the board where they are mounted is 0.1 Ohm! I guess it would be worth experimenting with lower value resistors here?
 
Yep!
A very used way of implementing a current limiter is with a power transistor emitter resistor turning the current into a voltage, then using this voltage to control another transistor (base to emitter) that will pinch-off the power transistor when the voltage becomes too high. In other words, when the voltage across the 2.2 Ohm reaches 0.65V, the current limiter becomes active.

2.2 Ohm corresponds to 0.3A. Had it been 0.1 Ohm it would have been 6.5A. None of these values are useful for your needs. I suggest 0.56 Ohm that should result in a current limit of good 1.1A. You will need a 1W resistor. Alternatively use two 1R2 in parallel with a power rating of 0.5W each. Check if the heatsink becomes too hot.
 
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TL072 Regulated Power Supply DIY Kits based on STUDER900 For Pre AMP DAC | eBay
s-l1600.jpg
 
I found some 0.5R resistors locally and fitted one in place of the 2.2R. The reg now feeds a steady 5v to the DAC and all seems well. The heatsink temp stabilises at about 55 degC in its hottest area.
Thanks again for the help guys. :)

What's your input voltage to the reg?

Tr1 & 2 provide a very basic regulator to power the TLO72 at approx 10V (referenced to VCC), which is the datasheet minimum. With an input voltage < about 11V the circuit may not work properly.

0.5R will give you a current limit of about 1.2A (VBE/0.5).

The Ebay board follows the Studer schematic fairly closely except the reference voltage is derived from an LED instead of the original zener. They also added an extra decoupling cap or two and simpliified the pot chain a bit. The pcb layout is rather poor and the schematic (as above) could be a lot more logically drawn!
 
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Hi all,

Let me explain a little further what my plan is. I ordered two of these power supplies Regulated linear supply Module OP TL072 MJE15034 28V - Audiophonics. I want to use them for powering two NUC pc’s as audio server and audio endpoint. I seems that with computer audio that the better the power supply the better the sound will be. The better power supplies use dual regulated rails like Paul Hynes. So I got the idea to use these two independent studer 900 rails in series to create a even lower noise floor.
This is just an experiment . It may take a while for the verdict as I am still waiting for parts and building nuc fanless cases.
 
@The traveller

If you've read the thread you'll be aware that, depending on your current requirement, you may have to change the value of the current limiting resistors.
Having done that I'm happy with mine, supplying two +5V rails and +/- 15V rails to my Katana DAC.
 
Hello,

for whoever is interested, I built a spice model with Tina TI of this regulator (file .TSC inside the .zip file in attachment). It is based on the board I bought from Audiophonics. The schematic matches the one of post #31 and it is quite close to the original Studer900 (see pdf file) even though there are some differences.
From the simulation with 15VAC in and 15VDC out, it looks like the ripple is in the few uV range. It would be interesting to make some real meaurements, but I do not have the equipement.
 

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