Today I change my venerable 3009 trimpots on the biasing circuit by these : https://www.mouser.fr/ProductDetail/71-1280G-500-K ,I did not expect any change in sound and I can't tell there really are , or maybe in the subjective world , but it is way more easy to set the dc output , to 0.000 mv dc as I wished to , and just for that it worth it 
I set the I/V resistor at 50 ohms , it seems to me to be the sweet spot of it , here is the measurement :
trafo ratio is 1:18 , so chip output is 50 mv rms
the transparency of that DAC is amazing , voices and instruments plays like real , the stereo imaging is as wide as possible, tones are so subtils , the balance between low and high is perfect , nothing more nor less
it will be very hard to do any better in an passive setup as it is , with no filtering at all
it has been a great venture , thank's to John from EC-DESIGN in the first place who gave me the start with he's genius ideas , and all of those who cares
.
.
I set the I/V resistor at 50 ohms , it seems to me to be the sweet spot of it , here is the measurement :
trafo ratio is 1:18 , so chip output is 50 mv rms
the transparency of that DAC is amazing , voices and instruments plays like real , the stereo imaging is as wide as possible, tones are so subtils , the balance between low and high is perfect , nothing more nor less
it will be very hard to do any better in an passive setup as it is , with no filtering at all
it has been a great venture , thank's to John from EC-DESIGN in the first place who gave me the start with he's genius ideas , and all of those who cares
.
.
Last edited:
Looking at the harmonics profile on the MVLabs https://www.mvaudiolabs.com/digital/tda1541-iv-resistor-selection/
that 50 ohms looks very interesting, with H2,3,4 dominating; 60 Ohm looks even more interesting, with H7,9 well below the higher ones.
This is unlike 10 ohms which I was considering, where H3 dominates, then H2, and then H7,9, which looks quite ugly (on the plot at least).
With paralleled 1541A, 60R direct to the grid of 801A would give 4mA x 60R=240mV x 7.5 (gain of 801A) = 1.28Vrms, which could be sort of
enough for my power amp which has below 1Vrms sensitivity. But 240mA at the output that's about 10x than the datasheet quotes as the max
that 50 ohms looks very interesting, with H2,3,4 dominating; 60 Ohm looks even more interesting, with H7,9 well below the higher ones.
This is unlike 10 ohms which I was considering, where H3 dominates, then H2, and then H7,9, which looks quite ugly (on the plot at least).
With paralleled 1541A, 60R direct to the grid of 801A would give 4mA x 60R=240mV x 7.5 (gain of 801A) = 1.28Vrms, which could be sort of
enough for my power amp which has below 1Vrms sensitivity. But 240mA at the output that's about 10x than the datasheet quotes as the max
Last edited:
Took me a bit to realize my mistake: It is not the Ohms that matter but the output voltage. At 60R each chips' output is at the equivalent of 120R which is way too much. At Fabrice's 50 Ohms per chip, which looks like a sweet spot, my chain will generate (@lcsaszar I include the max/rms markings for you): 4mAmax x 24R=96mVmax x 7.5 = 0.5Vrms which is lowish. But adding the 1:8 tranny like I planned at the beginning and then attenuating at the TVC at the output should give the needed headroom to drive the amp and as a bonus increased current output of the preamp to drive my 6m interconnects. I actually happen to have 24R Z-foils, giving the equivalent of 48R for 2 chips.
Last edited: