Direct WM8816 to differential current output DAC

panson_hk · 27th June 2007, 01:14 AM

I want to make a DAC using TI DSD1792A and WM8816 as volume control. Is it possible to directly connect WM8816 input to DAC Iout+ and Iout- (one WM8816 per channel for balance control). Anyone tried before?

banana · 27th June 2007, 02:31 AM

Hi Panson,

There might be several possible methods to connect WM8816 with Iout DAC.

Connect Iout to LMO/RMO, and LFO/RFO to gnd, use the variable resistor as passive I/V. The ideal of passive I/V is where IC designers and diyers divided. DAC appnote aways oppose to passive I/V, but some diyers prefer it.

Connect Iout to LMO/RMO, use the external opamp as I/V and the variable feedback resistor as active volume control. This seems like more feasible way to go.

Since 1792 output a lot of current, u only need a few hundred ohms for full output. However, WM8816 datasheet didn't mention range of the internal feedback resistor. U might need to add resistor accross LFO/LMO (RFO/RMO) to bring down the output level.

panson_hk · 27th June 2007, 03:31 AM

Thanks for your suggestions!

I prefer active approach. However, your idea just uses part of the control. It seems there is a variable resistor at LIN/RIN. Do you think the control range affected? Zero crossing detector is bypassed too.

banana · 27th June 2007, 04:34 AM

I have no experience with WM8816. And you're right, bypassing the zero crossing detect would cause problem.

Maybe u could make it the other way, connect Iout to LFO/RFO and opamp output to LMO/RMO instead.

Gain range can be scaled by adding external resistor. But the scale might not be perfect logarithm anymore.

panson_hk · 27th June 2007, 05:03 AM

Thanks!

27th June 2007, 01:14 AM	#1
panson_hk :) diyAudio Member Join Date: Aug 2005 Blog Entries: 10	Direct WM8816 to differential current output DAC I want to make a DAC using TI DSD1792A and WM8816 as volume control. Is it possible to directly connect WM8816 input to DAC Iout+ and Iout- (one WM8816 per channel for balance control). Anyone tried before?

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27th June 2007, 02:31 AM	#2
banana diyAudio Member Join Date: Feb 2003 Location: Hong Kong	Hi Panson, There might be several possible methods to connect WM8816 with Iout DAC. Connect Iout to LMO/RMO, and LFO/RFO to gnd, use the variable resistor as passive I/V. The ideal of passive I/V is where IC designers and diyers divided. DAC appnote aways oppose to passive I/V, but some diyers prefer it. Connect Iout to LMO/RMO, use the external opamp as I/V and the variable feedback resistor as active volume control. This seems like more feasible way to go. Since 1792 output a lot of current, u only need a few hundred ohms for full output. However, WM8816 datasheet didn't mention range of the internal feedback resistor. U might need to add resistor accross LFO/LMO (RFO/RMO) to bring down the output level.

27th June 2007, 03:31 AM	#3
panson_hk :) diyAudio Member Join Date: Aug 2005 Blog Entries: 10	Thanks for your suggestions! I prefer active approach. However, your idea just uses part of the control. It seems there is a variable resistor at LIN/RIN. Do you think the control range affected? Zero crossing detector is bypassed too.

27th June 2007, 04:34 AM	#4
banana diyAudio Member Join Date: Feb 2003 Location: Hong Kong	I have no experience with WM8816. And you're right, bypassing the zero crossing detect would cause problem. Maybe u could make it the other way, connect Iout to LFO/RFO and opamp output to LMO/RMO instead. Gain range can be scaled by adding external resistor. But the scale might not be perfect logarithm anymore.

27th June 2007, 05:03 AM	#5
panson_hk :) diyAudio Member Join Date: Aug 2005 Blog Entries: 10	Thanks!

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