I built the OPA660 IV circuit for TDA1545a as per Kuei's schematic a while back and found output from TDA1545 was too low for the circuit to work. Resistors to vref pin 7 were 11K & 11K with 3.3V vref taken after first 11K res.
I thought I had blown my 1545 Dac as when I tested output from dac it was only 0.7V accross 1K IV resistor. I ordered more and tested them before installation in circuit (using 1K IV res as before). Same result 0.7V.
I have confirmed this with another inmate who opened his working Marantz CD4000 and rerouted output through 1k IV res - same result.
What gives? Is the 1545a current output at digital silence not 2.5mA ? Bias current in datasheet states (Ibias) typically 0.7mA and full scale current (Ifs) 2mA (when using 11K + 11K res as above). Where does Kuei get the 2.5mA current at digital silence from?
Can anybody help? I would love to hear this circuit working as I intend to compare it to R Broertjes jfet looped cascode output stage which sounds excellent.
Re: TDA1545 question
Because with only 0.7V across 1k this indicates 0.7mA current which would not leave enough room for the DAC to swing +/-1mA....
Did you play music and get ANY signal (on the 'scope) for the 1k I/V resistor? Did you try raising this resistor to 2k?
thank you for replying and sorry for taking up your time on such trivial issues -
Should Ibias go up to 1.4V when 11K + 11K resistors on Vref are used
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