Hi all!
After exploring the magic of TDA1541 dac chip with this project:
https://jelabs.blogspot.com/2020/04/tda1541-nos-dac.html
...and needing another dac, I have the insane idea of applying a Papa's D1 stage to a 1521 board thanks to the PCBs made by His Mightyness ZM:
https://www.diyaudio.com/community/...0400a-who-have-heard-both.347298/post-6872371
Bad or good idea?
I do love that chip and there're lots of boards for it...
Thanks in advance.
After exploring the magic of TDA1541 dac chip with this project:
https://jelabs.blogspot.com/2020/04/tda1541-nos-dac.html
...and needing another dac, I have the insane idea of applying a Papa's D1 stage to a 1521 board thanks to the PCBs made by His Mightyness ZM:
https://www.diyaudio.com/community/...0400a-who-have-heard-both.347298/post-6872371
Bad or good idea?
I do love that chip and there're lots of boards for it...
Thanks in advance.
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I'd like to go for single endedI have some zen IV boards I made for the AD1862 project Paddy mentioned above. Sounds great. Let me know if you want gerbers
Yup, I know it's a common gate, but what's the impedance seen by dac chip?
DAC chip output, being current source, regarding resulting THD, best load is 0 Ohms
but, resulting voltage swing - product of chip current swing across loading impedance, then is 0V, and we still want some voltage there, because without voltage there is no music
so, instead of using resistor of some moderate value, compromise between THD and voltage swing, we are feeding chip current in a middle of constant current source , point having low input impedance, while still conducting entire current swing of DAC chip
see where input point of D1 is, source of mosfet ; observe INR point
if you have 5mA (arbitrary figure, lazy to check 1541 data) of current swing out of DAC chip, it is entirely transferred up through D1 current path; said current path is R4,Q1,R5,R6,R7,R8
so , when your measly 5mA of current swing do its thing across R4, there is suddenly 5mA * 1K5 = 8Vpp (2V82rms) of voltage swing, which is sent to gate of Q2 source follower, then meeting outer world with low Rout, at OUTR point
Papa's words (tnx to Ben) , xconductance of IRF510 is in range of 0.5-1S (lazy to search datasheet showing xconductance at small currents; same always declared at damn manly levels)
which means Rin at its source is 1/S ...... few Ohms max
output at TDA1541 loaded with few Ohms max of normal resistor should be of decent quality, but no damn voltage swing
with decent I/V stage - practically - you're loading I output chip heavily (proper way) without robing it of possible current swing
As you said, the TDA1541A actually wants see a low impedance load for best performance.
The data sheet (page 7) says, "To ensure no performance losses, permitted output voltage compliance is ±25 mV maximum."
The current output of the chip is +/-2mA, with an offset of -2mA.
So for +/-25mV, maximum, the chip wants to see about 12 Ohm maximum. I'm sure that is why peppennino is interested in the D1's input impedance.
But then I load my dac with about 70R IV resistor and enjoy its sound. diyAudio member ecdesigns (John Brown), who has done a lot of work with the TDA1541A, has suggested that up to 150R may be used for IV.
ecdesigns IV resistor
But the D1 circuit is cool. The input mosfet is a current buffer.
I may try it but use a lower value for R4 since I don't need 3Vp output.
The data sheet (page 7) says, "To ensure no performance losses, permitted output voltage compliance is ±25 mV maximum."
The current output of the chip is +/-2mA, with an offset of -2mA.
So for +/-25mV, maximum, the chip wants to see about 12 Ohm maximum. I'm sure that is why peppennino is interested in the D1's input impedance.
But then I load my dac with about 70R IV resistor and enjoy its sound. diyAudio member ecdesigns (John Brown), who has done a lot of work with the TDA1541A, has suggested that up to 150R may be used for IV.
ecdesigns IV resistor
But the D1 circuit is cool. The input mosfet is a current buffer.
I may try it but use a lower value for R4 since I don't need 3Vp output.
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Thank you for the detailed D1 circuit explanation ZM
My application is slightly different than Peppennino's TDA1541A but from your comments, R4 should be doubled for a dac chip with Iout of +/-1mA and no offset. Would there be any other modifications?
Perfect timing with this thread Peppennino, Good luck with your TDA1541A dac project. (I'm using an AD1862)
(I should add: PCM63 Iout is +/-2mA)
My application is slightly different than Peppennino's TDA1541A but from your comments, R4 should be doubled for a dac chip with Iout of +/-1mA and no offset. Would there be any other modifications?
Perfect timing with this thread Peppennino, Good luck with your TDA1541A dac project. (I'm using an AD1862)
(I should add: PCM63 Iout is +/-2mA)
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Vunce, in case of needing different circuit gain, I would go with circuit optimization - most likely change of positive rail, to retain same operating values ( Iq, voltage levels) for both input and follower mosfets
what Ben said, 1541 2mA sinking, with D1 stage - taken care of with proper setting of PR/PL, no need for small additional CCS
what Ben said, 1541 2mA sinking, with D1 stage - taken care of with proper setting of PR/PL, no need for small additional CCS
Great explanation, ZM! Thanks. I'll ask somewhere in China for a little batch of PCBs. I'll try before installing the dac board on its definitive cabinet!...
with decent I/V stage - practically - you're loading I output chip heavily (proper way) without robing it of possible current swing
looking forward to your progress.Great explanation, ZM! Thanks. I'll ask somewhere in China for a little batch of PCBs. I'll try before installing the dac board on its definitive cabinet!
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