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dam1941 - Next Gen Discrete R-2R Sign Magnitude 24 bit 384 Khz DAC module

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S

Staticx

Member
Joined 2015
Hi Soren and all,

I want connect to 1941 output directly (via gridstopper and grid leakage R) 6c45pi tube and i want producing a spud power amp with only one tube. My question is, how big is the output resistance not impedance of DAC, or the output impedance is clear resistance character? I want run the 6c45 near zero grid voltage and therefore a small grid current will flow. Therefore i interest about output resistance of DAC. If is output resistance of dac only 600Ohm (or 300 in parallel) i dont need use the grid choke for tube - grid current flow trought output resistance to ground. Or you recommended chrid choke despite the low output resistance of dac? Can grid current negatively affect the dac output circuit?

Thank you

Jan
 
S

Staticx

Member
Joined 2015
euro21: you wrote about reverse grid current, which flow from grid to ground in common cathode connection. This curent is about 0,3uA and flow always. I am not afraid of this current, because it will be lifted to the ground through the output resistance of DAC, because output resistance is quite low.

analog_sa: you wrote about grid current which flow when is the grid positive or near zero. This is the current I'm afraid of. I dont go with Ug positive but only near zero (-0,1V is maximum). My operating point is on Ug=-1.9V. If is Ug near zero i don know grid current which flow to grid. If it is 0,3 mA (this is normal value of grid current near zero of another tubes) and output voltage from DAC is 1,8V (maximum Vp), then input impedance of tube in mid frequency range is 6KOhm. What is OK, when is output impedance of DAC 600Ohm. If is grid current greater as 0,3mA i have problem. Maybe i move the operating point away from zero Ug.
 
S

Staticx

Member
Joined 2015
Power Supply

Hi all,

I have question about power supplies for this dam. I want make positive and negative supply with lt3045 and 3094. For positive i need two separate supplies or i can supplied booth digital and analog section with one positive supply? Or can you recommend me some other linear regulated supply?

Thanks
 
Last edited:
L

lwr

Member
Joined 2003
Paid Member
My input auto-select function has stopped responding to BNC and RCA inputs. I have verified that the signal to those inputs is good by substituting another DAC in the chain.

I have vague recollections of there having once been a way to use u-manager to override the auto-select function and manually assign an input, in this case either BNC or RCA. I would appreciate it if someone would direct me the command that u-manager is looking for to get this done.

Thanks
 
TNT

TNT

Member
Joined 2003
Paid Member
I found this in the manual....

Command Messages
Ix Input select mode, 7 = Auto, 0 = USB, 1 = AES/EBU, 2 = BNC, 3 = RCA, 4 = Toslink, 5 = I2S.
Fx Filter Type, 4 = linear, 5 = mixed, 6 = minimum, 7 = soft
Vxxx Volume, -90 to +10
Px Phase, N = Normal, I = Inverted
Xx Crossfeed Mode 0..3, 0 = off, 3 = max, only valid when headphones are selected


I think one enters (out of the promt mode i.e. not in the uManager - if you are there enter: Exit..) e.g.:

I4

Which should make the DAM listen to the Toslink input. But how to really use this is not described in the manual in a user friendly or pedagogic manner.

//
 
L

lwr

Member
Joined 2003
Paid Member
2020-10-28 17_03_21-Window.jpg

Now able to run command line to activate Inputs but only able to get sound from Toslink (I4) and USB (I0). No sound from AES/EBU (I1), BNC (I2), or RCA (I3).

I confirmed that the signal to the AES/EBU, BNC, and RCA are good by substituting another DAC that also has these input options. I also measured the input impedences of each of the types of inputs on both DACs, and they were consistent from one to the other.


I thought that a firmware refresh or update for the dam1941 might solve the problem, so I ran uManager and found that the installed firmware is dam1941 uManager Rev 1.23 20190311 FPGA Rev 1.23

I downloaded and programmed the latest firmware (1541_full121.skr) from soekris.dk, but when I went to install it, I got an error message saying "Incorrect Image."

Can someone please direct me to the latest firmware for the dam1941? Thanks
 
L

lwr

Member
Joined 2003
Paid Member
Thanks for the help guys.

I downloaded and reinstalled a fresh copy of the latest firmware for the dam1941, and I used the command line to verify that the various inputs were in fact being selected (eg USB (I0), AES/EBU (I1), BNC (I2), or RCA (I3), Toslink (I4), I2S (I5), and Auto (I0).

I still find that the AES/EBU (I1), BNC (I2), and RCA (I3) inputs are not working (eg dead quiet when supplied with known good signal). The USB (I0) and Toslink (I4) inputs work properly, whether selected individually by command line, or from the Auto select mode (I7).

I had already substituted another DAC with the same input configuration (a Soekris dac1541) and verified that all of the various input sources and cabling connections are good).

I had already checked the dam1941 board installation in the chassis to verify that it is completely isolated from the chassis, and then removed it from the chassis and visually inspected it for possible instances of obvious shorts or open circuits.

I then checked the impedance of each of the inputs on the dam1941 against the same inputs on the dac1541, and found that they all matched. I have not tried or measured the I2S (I5) input headers on either the dam1941 or the dac1541, as they are only accessible from board headers and I would have to make a header to HDMI socket adapter to do so.

Can you recommend additional troubleshooting steps for me to try?

By the way, the power supplies for the dam1941 consist of two MPAudio split supplies +/- 5VDC in series, and one Uptone Audio LPS-1.2 @ 5VDC.

Thanks
 
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