Soekris Dam Dac

[nige2000]

id be inclined to think the stm32 might be ok once its blinking on startup
it is blinking aint it?

i think v+00 is vol level

is there a short on the 3.3v rail on the dam

Yes, it blinks on power up and is solid when playing music

yes, I too think v+00 is volume level and it should be v+99

I've just put the meter on the 3.3v, measures 3.8kOhm to earth?

Val

no i think v+00 should be right if you look at this old dimdim screenshot



cant remember but 3.8k does not sound odd

check v ref voltage and check for signal on the fpga to shift register caps

[jkeny]

OK, thanks but I'm not sure what this is a graph of (or many graphs overlaid)? I presume you changed all out-of-spec resistors & you are getting no reduction in harmonics but rather random increases in different harmonics?

so matching the resistors doesnt resolve or stablise?

thanks for replying,

1. initially i have experimented a lot with changing of different resistors(to much worse values) and saw significant decreasing of harmonics. So the logic works in reverse side.

2. but when i have started to correct to the better values from mathematical calculation, i didn't received the explicit results. I received the strange behavior of harmonics based on random.

3. possibly i didn't understand how r2r matrix works to the end. so i asking you to help to find out.

A couple of things:
- I now know what the resistor structure for the 0,1 & 2 bits is doing - it's a Unary DAC as opposed to R2R DAC. This is a common approach now in modern DACs where usually the 6 MSBs are handled in this way. The advantages of doing this is that it lessens the accuracy requirements needed for the resistors used for the MSBs. A good post about it here http://www.whatsbestforum.com/showthrea ... 8-DACs-101

I still don't understand why correct the resistor values makes for random harmonic increases - we must be missing something? What resistor types are you using as replacements?

[nige2000]

OK, thanks but I'm not sure what this is a graph of (or many graphs overlaid)? I presume you changed all out-of-spec resistors & you are getting no reduction in harmonics but rather random increases in different harmonics?

so matching the resistors doesnt resolve or stablise?

thanks for replying,

1. initially i have experimented a lot with changing of different resistors(to much worse values) and saw significant decreasing of harmonics. So the logic works in reverse side.

2. but when i have started to correct to the better values from mathematical calculation, i didn't received the explicit results. I received the strange behavior of harmonics based on random.

3. possibly i didn't understand how r2r matrix works to the end. so i asking you to help to find out.

jkeny has more knowledge of r2r
i know this because i know nearly nothing

oh i see hes here now

a bit of thinking out aloud (i don't recommend the practice btw)
from your results i can only guess that the resistor matching is a problem that needs attention
but the random results suggest there is another larger issue not directly related to r value or the resistors themselves
all thats left is the ps of vref, the shift registers noise handling and possible jitter from fpga?

this is probably not thee r2r dac were looking for but been discrete gives us more to play with

[Val33]

cant remember but 3.8k does not sound odd

check v ref voltage and check for signal on the fpga to shift register caps

All the voltages check ok and there is voltage (changing) on the shift register caps. Cant check for signal as although I have a scope, I've yet to actually learn how to use one!

Stumped

Val

[nige2000]

cant remember but 3.8k does not sound odd

check v ref voltage and check for signal on the fpga to shift register caps

All the voltages check ok and there is voltage (changing) on the shift register caps. Cant check for signal as although I have a scope, I've yet to actually learn how to use one!

Stumped

Val

damn buggered up the page with that screenshot

hope you havnt forgot to turn the amps on?
continuity/resistance between se output and gnd?

[Val33]

damn buggered up the page with that screenshot

hope you havnt forgot to turn the amps on?
continuity/resistance between se output and gnd?

Definitely turned on, also tried connecting a nasty cheap headphone to the output, definitely nothing there.

8.8 Ohm

Worked out why I had a problem without the isolators, the grounds on the Dam and the Rpi vary by 8v, oops.

I'm sure that the lack of output must be related to the missing uManager, have ordered the ST-Link and see how I get on when it gets here., Like you, I think that the STM32 and FPGA are probably ok, just something corrupted I hope.

Val

[nige2000]

8.8 Ohm

can't be right surely
disconnect interconnects and test again

[Val33]

That is with the leads disconnected, DAC off

with the power on and signal in, 0.64 kOhm

Val

[nige2000]

which revision is it?
I had to remove a sot from a r3 to get sound just before se output

[Val33]

Its an R3 board.