I am going to make discrete opamp Sections that are semi symmetrical . Input will be LTP, second stage is an current mirror, followed by an buffer. This Way it will only have "single gain stage".
I could make it symmetrical but complexity will grow a lot.
But more will follow tomorrow morning
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The attached opamp design is the one i will use for the discrete output shield.
As we only have 100mA i total to the outputstage we will have an maximum of 15 - 20mA per opamp to be on the safe side.
This opamp will rest at around 14mA.
I have chosen npn bjt in the input stage as the source impedance's are relatively low, and with bjt we will get a lower offset than with JFET which for 2sk2145-BL is around 20mV. For BJT we can get down to 1/10 of that. And because of the symmetrical loading of the opamp, there is no extra offset build up by the mismatch of source impedance's.
2 opamps will be used for balanced and 1 for balanced to singleended conversion on the output per channel.
BR
Sonny
As we only have 100mA i total to the outputstage we will have an maximum of 15 - 20mA per opamp to be on the safe side.
This opamp will rest at around 14mA.
I have chosen npn bjt in the input stage as the source impedance's are relatively low, and with bjt we will get a lower offset than with JFET which for 2sk2145-BL is around 20mV. For BJT we can get down to 1/10 of that. And because of the symmetrical loading of the opamp, there is no extra offset build up by the mismatch of source impedance's.
2 opamps will be used for balanced and 1 for balanced to singleended conversion on the output per channel.
BR
Sonny
Thanks Sonny!
This is also what I use, Pi 2 with volumio 1.55
Will start working on it soon. I'm at the Montreal Grand Prix this weekend so I put music on the side for a few days.
I will be using Sigma 22 and Sigma 11 from AMB for powering the DAC.
Ciao!
Do
This is also what I use, Pi 2 with volumio 1.55
Will start working on it soon. I'm at the Montreal Grand Prix this weekend so I put music on the side for a few days.
I will be using Sigma 22 and Sigma 11 from AMB for powering the DAC.
Ciao!
Do
I have found a solution for changing filter. The frontpanel makes it possible. The USB DAC reads the selected filter from the front panel as well as sending the type of data stream that it receives.
We have have test an OLED display in december with 64x256 pixels.
This frontpanel has IR receiver. and will be the same used for the preamp.
We will make a brown colored Plexiglas front for it..
BR Sonny
We have have test an OLED display in december with 64x256 pixels.
This frontpanel has IR receiver. and will be the same used for the preamp.
We will make a brown colored Plexiglas front for it..
BR Sonny
Amazing, these ideas make us more convenient. Thanks a lot.
Please use codes for Apple remote.
Hi Sonny, Looks really neat 🙂 I am eagerly looking forward to hearing it (that's was huge understatement! 😉 Very grateful to you for assembling it for me when I couldn't do it myself due to health. THANKS a lot and all the best, Per
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For the preamp designs i will use my jfet discrete opamp i designed In april 2013. It is still State of art regarding size and Performance
For the preamp designs i will use my jfet discrete opamp i designed In april 2013. It is still State of art regarding size and Performance
The match the layout of dip8 single opamps.
I stumbled over this post from Sonny in the TSSA 1.7 thread. These must be the discrete opamps that are used in the output board for the balanced version of the DAC. Very impressive work. These fellows are tiny...
Great, are they still available? Can you plug them right into your output shield? and what are the power requirements? +/- 15v ?
Yes they are still available. They cost 30€ and is available in two variants. One with JFET and one with Bipolar transistor inputs.
Jfet has higher input impedance and "zero" offset current on the inputs, but as much as 20mV offset.
The bipolar version has about 6uA input bias offset. It works best with low impedances. Voltage Offset is around 5mV.
Jfet has higher input impedance and "zero" offset current on the inputs, but as much as 20mV offset.
The bipolar version has about 6uA input bias offset. It works best with low impedances. Voltage Offset is around 5mV.