Hello everybody,
Im intending to build an analog tube stage for an ES9038 dac, inspired by Lukasz Fikus circuits. It seems to be differential output dacs, and the board uses two 9038 chips. I saw that left and right negative outputs come together (paralleled?) before entering the opamps, as well as the positive ones.
Since I want the dac negative outputs to send the signal to the tubes grid, I took the signal right before the first resistor, where the left and right negatives are already together. Did it on both 9038 chips, so I understand that I will have stereo output with separate left and right channels, is that right?
All comments will be really appreciated.
Tks all!!
Im intending to build an analog tube stage for an ES9038 dac, inspired by Lukasz Fikus circuits. It seems to be differential output dacs, and the board uses two 9038 chips. I saw that left and right negative outputs come together (paralleled?) before entering the opamps, as well as the positive ones.
Since I want the dac negative outputs to send the signal to the tubes grid, I took the signal right before the first resistor, where the left and right negatives are already together. Did it on both 9038 chips, so I understand that I will have stereo output with separate left and right channels, is that right?
All comments will be really appreciated.
Tks all!!
Normally if there are two dac chips, then one is for each audio channel. The two channels of one dac chip operating in mono mode could then be paralleled. Not hard to ring out the circuit with a DVM and needle probes to verify how its hooked up. Then if you want to operate the dacs in voltage output mode, you could simply take the parallel output signals for one phase of each dac, add a DC blocking cap, and look with a scope to verify you have the audio without the DC offset. Right?
Of course, this thing is likely to sound pretty awful and a tube output stage isn't really going to fix it. Maybe you will like it better though.
Of course, this thing is likely to sound pretty awful and a tube output stage isn't really going to fix it. Maybe you will like it better though.
Hi Markw4,
Tks for the comments. So, do you think that an analogue tube stage does not work with this Dac? It is not a normal voltage output dac?
Someone told me that "they are designed to feed into a 'virtual ground' which is provided by an opamp transimpedance amplifier". If it is right, the opamps cannot be replaced by the tubes?
Thank you!
Tks for the comments. So, do you think that an analogue tube stage does not work with this Dac? It is not a normal voltage output dac?
Someone told me that "they are designed to feed into a 'virtual ground' which is provided by an opamp transimpedance amplifier". If it is right, the opamps cannot be replaced by the tubes?
Thank you!
ESS dacs can be operated in voltage out mode or in current out mode. Distortion is less in current output mode. However, distortion is lowest if the I/V converter holds the dac output at a very solid ground (or offset ground) level. To whatever extent the virtual ground (or virtual offset ground) voltage is allowed to vary, then distortion is increased. To keep the I/V converter input solidly held at a fixed level requires lots of feedback, along with good immunity to RF at the I/V converter inputs.
Normally with tube amps there isn't enough loop gain to hold the grid (or maybe the cathode) of a tube at a very solid fixed level. Thus distortion will be increased.
IMHO, rather than struggle with a dac chip with such requirements it might be nicer to use a type of dac that is inherently more linear and thus in less need of a very precise virtual ground. IME, switched resistor discrete dacs can sound better and do so with less challenging I/V conditions (or no I/V at all). That said, getting the best, most hi-fi sound I have heard is not all that low cost to do. IMHO one of the more costly problems is the need for good clocking (which is the time reference for conversion of digital to analog). The other crucial reference needed by dacs is called by various names (AVCC, Vref, etc.). It is the voltage reference for conversion of digital to analog.
Then there is all the other stuff having to do with layout, bypassing, capacitor types depending on application, etc.
Anyway if it were me, I might be willing to go for a fairly linear tube stage so long as I have type of dac that is tolerant to such while still being able to produce very likeable sound quality.
There is a lot more that could be said, but perhaps some of the above could be of possible interest.
Normally with tube amps there isn't enough loop gain to hold the grid (or maybe the cathode) of a tube at a very solid fixed level. Thus distortion will be increased.
IMHO, rather than struggle with a dac chip with such requirements it might be nicer to use a type of dac that is inherently more linear and thus in less need of a very precise virtual ground. IME, switched resistor discrete dacs can sound better and do so with less challenging I/V conditions (or no I/V at all). That said, getting the best, most hi-fi sound I have heard is not all that low cost to do. IMHO one of the more costly problems is the need for good clocking (which is the time reference for conversion of digital to analog). The other crucial reference needed by dacs is called by various names (AVCC, Vref, etc.). It is the voltage reference for conversion of digital to analog.
Then there is all the other stuff having to do with layout, bypassing, capacitor types depending on application, etc.
Anyway if it were me, I might be willing to go for a fairly linear tube stage so long as I have type of dac that is tolerant to such while still being able to produce very likeable sound quality.
There is a lot more that could be said, but perhaps some of the above could be of possible interest.
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