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PhiDAC hex kits with pre-built filters

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C

corzendonk

Member
Joined 2020
I built steps 1 and 2 on my PhiDeca and got the following test results using a 15V switching power supply and TP0 as the reference:


Power supply: 15.01V-15.02V



Step 1:
~~~~~~
TP1: 7.39V
TP2: 6.28V
TP3: 5.00V
TP4: 2.49V
TP9: 8.63V


Step 2:
~~~~~~
TP5: 6.23V
TP6: 1.87V <-- This is most concerning
TP7: 1.90V
TP8: 4.17V


Richard, I tested the LM317 and got the following results, per your message:


Pin 1: 7.39V
Pin 2: 8.64V
Pin 3: 15.01V (this pin is nearest to L1)


Please let me know what the next troubleshooting steps are. Thanks for your support!
 
abraxalito

abraxalito

Member
Joined 2007
Thinking out loud here - LM317 voltages indicate its likely working correctly as pin1 (ref) is 1.25V below pin2 (output). But pin1 voltage should be above 10V, created by the two zener diodes (D1,D2). Instead it seems to be the same voltage as TP1 which indicates D1 (4.3V) isn't passing any current to speak of (it should have 5mA running through it). And D2 voltage is way too high for a 6.8V zener (although we don't have a direct measurement of the voltage across it).

So to help me debug this further, please measure the voltage across D1 (4.3V). D2 (6.8V) and also across R10 (15R) and R9 (15R).

Let's not worry about getting step 2 voltages correct until we have step 1's voltages in the right ballpark.
 
C

corzendonk

Member
Joined 2020
abraxalito said:
No, by 'across' I meant put one probe on one side of the component and the other probe on the other side. When measuring across the resistors you may need a more sensitive range to be able to see something.
Click to expand...


Across R9: 0.1mV
Across R10: 79.3mV


The zener diodes are common cathode, yes? So the 2 pins on the same side are the anodes, the 3rd pin is the cathode? Measuring from each of the anodes to the cathode:


D1: 4.29V / 76.7mV
D2: 4.94V / 67.0mV
 
abraxalito

abraxalito

Member
Joined 2007
beardman said:
with the output cap 4.7uf how low is F3 frequency ---goes it down to 10hz or ??
Click to expand...

I calculate for a 10k input impedance the -3dB freq is about 3.4Hz. Almost all preamps will have >10k input impedance.

beardman said:
so if the input impedance is higher than 10k i can go a bit lower in cap calue ?
Click to expand...

Yes - for 22k you can go to 2.2uF, for 47k, 1uF.
 
Last edited:
abraxalito

abraxalito

Member
Joined 2007
corzendonk said:
Across R9: 0.1mV
Across R10: 79.3mV
Click to expand...

Ah thanks, so this tells me that about 5mA is passing through R10 but we don't know which way. Which side of R10 are you reading as the +ve one? The next resistors to measure across are R32 and R53, they're right next to the LT1028 opamps.

The zener diodes are common cathode, yes?
Click to expand...

I'm not sure of your meaning here. Normally 'common cathode' applies when there's more than one device in a package. But here only one zener per SOT-23 package.

So the 2 pins on the same side are the anodes, the 3rd pin is the cathode?
Click to expand...

Of the two pins on one side, only one is connected, the other is NC (no connection). The former pin has the more negative voltage in this circuit. NXP zener datasheet attached.
 

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C

corzendonk

Member
Joined 2020
Sorry for the confusion, I had assumed since it was a 3 pin package, that there were 2 zeners inside, without checking the datasheet.


abraxalito said:
Which side of R10 are you reading as the +ve one? The next resistors to measure across are R32 and R53, they're right next to the LT1028 opamps.
Click to expand...


For R10, I was reading the side closer to the center of the board as +ve and the side closer to the edge of the board as -.



Across R32: 0.00mV

Across R53: 79.0mV


I tried a few times to get a different reading from R32, voltage momentarily reads in the 10mV-50mV range, but drops to 0mV within 1 second, I assume that's just discharging static? Looks like that could be the problem area.
 
G

guglielmope

Member
Joined 2004
Good evening at the end I connected the 5th order filter of the PHYDAC on my dac with PCM1704 before the I / V. Before this DAC I have had both Buffalo III and Soekris but this PCM1704 is definitely superior. I didn't think I could improve it, but this happened.
Now the sound is cleaner, above all the soundstage has resized has become normal, before it was exaggerated not very real.
A big step forward, now I want to try the 7th order filter.
Thanks Richard
 

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C

corzendonk

Member
Joined 2020
abraxalito said:
Here my meaning for the voltages was the original test points. I'd like to see if removing this resistor has restored the TPs to their correct values, especially TP1 and TP2.
Click to expand...


All of the following are in reference to TP0:


R53 (terminal closest to board center): 0.367V

R53 (terminal closest to board edge): 6.88V


TP1: 6.94V
TP2: 9.96V
TP3: 5.00V
TP4: 2.49V
TP9: 12.43V
TP10: 11.18V


TP5: 10.11V
TP6: 1.87V
TP7: 3.63V
TP8: 11.69V



Looks like your experiment was correct! Step 1 voltages are close to expected values.
 
abraxalito

abraxalito

Member
Joined 2007
Ah now that's looking quite promising. There is a very slim possibility that the problem's with the capacitor (C22) rather than with the opamp. To separate out those two would you be able to solder back in R53 and lift pin3 of U16 from its pad? If R53 is lost or too badly damaged you could just use a wire in place of it for this experiment. If the voltages with pin3 lifted and R53 back in circuit remain unchanged from those in post #255 then we can safely conclude the fly in the ointment is U16 and not C22.
 
abraxalito

abraxalito

Member
Joined 2007
guglielmope said:
Good evening at the end I connected the 5th order filter of the PHYDAC on my dac with PCM1704 before the I / V. Before this DAC I have had both Buffalo III and Soekris but this PCM1704 is definitely superior. I didn't think I could improve it, but this happened.
Now the sound is cleaner, above all the soundstage has resized has become normal, before it was exaggerated not very real.
Click to expand...

From our past conversations, this PCM1704 DAC was using an OPA861 for the I/V stage. No feedback in I/V right? But now it has a 5th order LC filter between DAC chip and I/V with a matching resistor so that the filter gets the right termination impedance from the OPA861.
 
B

beardman

Member
Joined 2005
have first listen to the DAC ,,,and i can say, that i am a bit surprised ,over the sound

very positive ,,,,will now change output cap ,and see if i can get the best out of the output

i also have 3 different powersupply,,,

1..amb .org
2..salas supply (used in his preamp ) this i use now
3..salas shuntsupply

what will you use ??
 
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