Faulty TDA1541A?

[slav]

Hi slav,

TDA1541A full scale output current equals 4mA, so a 47R resistor and a single TDA1541A produces 0.004 * 47 = 188mVpp, with 2 x TDA1541A this amplitude doubles. Keep in mind that there is a limit to the ac voltage on the DAC output. In the datasheet it's specified as output compliance and it equals 50mVpp max. Exceeding this limit by a small margin doesn't lead to unacceptable THD, but above certain threshold the THD really starts to rise to unacceptable levels leading to distorted sine wave shape (clipping).

With 90R passive I/V resistor and a single TDA1541A, signal amplitude would be 0.004 * 90 = 360mVpp. I can guarantee you that this will introduce unacceptable high distortion. This can be easily verified by using a 1 KHz 0dB sine wave test track and observe the signal across the 90 Ohm passive I/V resistor.

Based on measurements I would recommend max. 33 Ohm passive I/V resistor value for a single TDA1541A.

Assuming your power amp would require 1V rms (2.82Vpp) for full power, tube amp gain would have to be 2.82 / 0.188 = 15x.

Grounded cathode tube amplifier is discussed here:

A little history and theory

I'm little confused , are we talking about total resistance between L and R outputs of TDA?
I have 47R connected between each output , it means Vpp from channel is 0.002x47=0.094V and to get 2.82Vpp on the output I would need 2.82/0.094=30x gain.Am I right?

 

[slav]

I'm thinking about re-designing output stage to suit my amp.
I have in a drawer pair of Amplimo's TM3 transformers , I could use them to increase voltage on the grid of Ecc88.
Using 20R i/v resistor would give me 0.002x20=0.04V , then 1:15 trafo it means on grid I have 0.6V, to achieve 2,82Vpp I need a tube stage with gain around x4.7.It could be done by using Vb=75V , Ra=1k , Rk=100 ohm.
Question is what to consider designing tube output stage , what values of Zin Zout are most suitable for DAC output?