Help to comment this simple I/V
I am building a pcm1794 based DAC, which has a bias of 6.2mA.
I ever tried to build a I/V similiar to à la AD844, but failed with a really high THD, partly due to bad matching of BJTs.
Can you help to comment this simple, low THD but no PSRR I/V?
I just dont clear whether try this simple I/V or give à la AD844 another try.
I am building a pcm1794 based DAC, which has a bias of 6.2mA.
I ever tried to build a I/V similiar to à la AD844, but failed with a really high THD, partly due to bad matching of BJTs.
Can you help to comment this simple, low THD but no PSRR I/V?
I just dont clear whether try this simple I/V or give à la AD844 another try.
Attachments
This is essentially the same as the one from Jan from 1989 :
Simple, high-quality I/V converter | Linear Audio NL
You are putting a lot of power through those SMD transistors.
So I would at least consider BC327 instead.
And you are relying on Q2/Q3 to keep the input at Gnd level, but they have a much lower bias than Q1/Q8.
So the input is not at 0V, but some 50mV.
There is no means of adjustment in your ciruit.
And as you say, no PSRR.
Also high Zout (=Riv), output coupling caps, etc.
But it is simple enough to make a quick build and see if it works for you ?
You will need well matched (hfe & Vbc) transistors to get optimum results.
Patrick
Simple, high-quality I/V converter | Linear Audio NL
You are putting a lot of power through those SMD transistors.
So I would at least consider BC327 instead.
And you are relying on Q2/Q3 to keep the input at Gnd level, but they have a much lower bias than Q1/Q8.
So the input is not at 0V, but some 50mV.
There is no means of adjustment in your ciruit.
And as you say, no PSRR.
Also high Zout (=Riv), output coupling caps, etc.
But it is simple enough to make a quick build and see if it works for you ?
You will need well matched (hfe & Vbc) transistors to get optimum results.
Patrick
Someone asked by PM how to use the CM IV with TDA1545.
Please ask your questions here, not by PM.
I have no experience with TDA1545.
So I can only tell you from information in the datasheet.
The TDA1545 has a DC bias current of ~ 0.72mA.
But it also specifies that the output should be at minimum 2V DC.
The CM IV expects to see 0V at its current input pin.
There is no easy way to change this to 2V without affecting performance.
(e.g. raise the Gnd level of the entire CM IV to 2V and use output coupling caps.)
But Mr. Juaneda seems to know a lot more about TDA1545 than me :
Junilabs - Jundac Five, NOS DAC kit with TDA1545A up to 192KHz
Maybe he can give you some advice from his hands-on experience.
To me, using a costly discrete IV with a 5€ DAC chip somehow does not seem to be in proportion.
Maybe just a passive IV is a better choice, like the TDA1543.
http://www.diyparadise.com/cs8412-tda1545.gif
Sorry I am not able to be of more help,
Patrick
Please ask your questions here, not by PM.
I have no experience with TDA1545.
So I can only tell you from information in the datasheet.
The TDA1545 has a DC bias current of ~ 0.72mA.
But it also specifies that the output should be at minimum 2V DC.
The CM IV expects to see 0V at its current input pin.
There is no easy way to change this to 2V without affecting performance.
(e.g. raise the Gnd level of the entire CM IV to 2V and use output coupling caps.)
But Mr. Juaneda seems to know a lot more about TDA1545 than me :
Junilabs - Jundac Five, NOS DAC kit with TDA1545A up to 192KHz
Maybe he can give you some advice from his hands-on experience.
To me, using a costly discrete IV with a 5€ DAC chip somehow does not seem to be in proportion.
Maybe just a passive IV is a better choice, like the TDA1543.
http://www.diyparadise.com/cs8412-tda1545.gif
Sorry I am not able to be of more help,
Patrick
Hi guys.
Regarding a psu for these boards....
I am creating 4 rails, so 2 pos and 2 neg but using 4 times LT3042, so obviously each will have its own winding and rectifier.
Regarding transformers that I wish to order, I though about using small 'blue' encapsulated trafos. Maybe 6va so 3va per regulator. Is that enough or should I be upping the power rating.?
Regarding a psu for these boards....
I am creating 4 rails, so 2 pos and 2 neg but using 4 times LT3042, so obviously each will have its own winding and rectifier.
Regarding transformers that I wish to order, I though about using small 'blue' encapsulated trafos. Maybe 6va so 3va per regulator. Is that enough or should I be upping the power rating.?
Nice copy.
But this is already superceded by something else :
https://www.diyaudio.com/community/...st-tht-i2s-input-nos-r-2r.354078/post-7025945
https://www.diyaudio.com/community/...st-tht-i2s-input-nos-r-2r.354078/post-7026473
https://www.diyaudio.com/community/...st-tht-i2s-input-nos-r-2r.354078/post-7035939
Patrick
But this is already superceded by something else :
https://www.diyaudio.com/community/...st-tht-i2s-input-nos-r-2r.354078/post-7025945
https://www.diyaudio.com/community/...st-tht-i2s-input-nos-r-2r.354078/post-7026473
https://www.diyaudio.com/community/...st-tht-i2s-input-nos-r-2r.354078/post-7035939
Patrick
