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Old 11th June 2013, 02:10 AM   #21
wa2ise is offline wa2ise  United States
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Originally Posted by billbo View Post
,,, The DAC is actually 8xTDA1543's. I/V resistor is about 2.2k/8 = 275Ohms (I used 270 ohms) and the VRef resistor is 1.5k/8 = 187.5 ( I used 180 ohms)....
I've played with that DAC chip myself, but just with one at a time.
Click the image to open in full size. Note that the diagrams only show one of the two analog output channels.
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Old 11th June 2013, 09:39 AM   #22
billbo is offline billbo  Australia
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Circuit can be improved? Yes indeed. implaced 50k pot with fixed resistor once you have the desired gain that you want. LM317 reg instead etc. Can you draw up the sin c compensation that needs to go on the passive I/V output?
It would be much appreciated.
Billy D...
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Old 14th June 2013, 08:27 AM   #23
billbo is offline billbo  Australia
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Default Update on NOS DAC

I found out why the highs are slightly rolled off and it was not the tube buffer which I had installed. The existing output of the dac had a 2.2nF cap to ground before entering into op amps which had a low pass effect on the output. This bought back the highs at the top end. Due to limitted test equipment that I have I made a CD with a series of test tones. 100hz, 1Khz 10Khz, 15Khz and 20khz at -6dB and -3dB levels. I used Cool Edit pro which you can generate tones of any waceform you want. I burnt them on a CD and played it back on my CD player. I hooked up my CRO and yes I did see the roll off at 10khzm 15Khz and 20Khz. After I removed the 2.2nF cap the amplitude on all frequencies was the same. 100hz all the way up to 20Khz. There was slight artifacts on the 15Khz and 20Khz waveforms which is due to the nature of NOS dacs (or maybe the quality of the cct or my CRO).
P.S. I upgaded the output coupling caps from .33uf to 10uf which improved the bass respose slightly.
Billy D...
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Last edited by billbo; 14th June 2013 at 08:29 AM.
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