Hi,
returning to the Abraxas.
The simulation schematic shows a stepping of the Ry resistors that define the current distribution between the CFPs Master- and Slave-transistors.
It is chosen ~71R for equal current values.
The resistor in the Master´s collector path adds a bit noise, so a small enough resistor value is wished for.
If one makes the resistor larger on the other hand, the current distribution becomes such, that less current is routed through the Master and more through the Slave, which is positive for THD.
My own sims showed that increasing Ry to 330R lead to THD-values of more than an order lower with an noise penalty of less than 1dB.
Simmed with 1mV @1kHz input voltage the difference is not that obvious, but at higher input voltages (10mV), which occur due to the raising RIAA-response towards the upper audio range.
The smaller the current setting resistor of a CFP, hence the lower the slave´s current, the less CFPish it looks, and the more it looks like a single transistor.
Was there any not yet mentioned reason to choose the Ry so low?
jauu
Calvin
ps. will we meet at HE in MUC in a month?
pps. You may have noticed the addition of a DC-Servo to the Calvin-Buffer in the Preamp-Buffers Thread
returning to the Abraxas.
The simulation schematic shows a stepping of the Ry resistors that define the current distribution between the CFPs Master- and Slave-transistors.
It is chosen ~71R for equal current values.
The resistor in the Master´s collector path adds a bit noise, so a small enough resistor value is wished for.
If one makes the resistor larger on the other hand, the current distribution becomes such, that less current is routed through the Master and more through the Slave, which is positive for THD.
My own sims showed that increasing Ry to 330R lead to THD-values of more than an order lower with an noise penalty of less than 1dB.
Simmed with 1mV @1kHz input voltage the difference is not that obvious, but at higher input voltages (10mV), which occur due to the raising RIAA-response towards the upper audio range.
The smaller the current setting resistor of a CFP, hence the lower the slave´s current, the less CFPish it looks, and the more it looks like a single transistor.
Was there any not yet mentioned reason to choose the Ry so low?
jauu
Calvin
ps. will we meet at HE in MUC in a month?
pps. You may have noticed the addition of a DC-Servo to the Calvin-Buffer in the Preamp-Buffers Thread
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Yes, that was equal current distribution.
As far as i can tell the circuit simulated with very low distortion but we did not try to make Ry as high as you did plus i can not remember at what maximum voltage we simed.
Do you mind if you publish the version that you like best ?
I have a prototype working of the Abraxas and i could compare your version with what i have.
I have looked up the Simple Ideas thread from time to time. I will look it up again.
As far as i can tell the circuit simulated with very low distortion but we did not try to make Ry as high as you did plus i can not remember at what maximum voltage we simed.
Do you mind if you publish the version that you like best ?
I have a prototype working of the Abraxas and i could compare your version with what i have.
I have looked up the Simple Ideas thread from time to time. I will look it up again.
Yes, i am in Munich. Some of my stuff is on the BFly Audio booth and i am walking around as always.
In an MC stage like the Abraxas i like the input transistors to run on substantial iddle because of lowest voltage noise.
My Lyra Atlas has only 4.4 Ohm and a allows a signal-noise of over 80db theoretical.
I do not like to throw that baby out of the water.
My Lyra Atlas has only 4.4 Ohm and a allows a signal-noise of over 80db theoretical.
I do not like to throw that baby out of the water.
One could of cause crank up the constant current sources a bit. Then the masters could run on the same idle as now and the slaves could have some more.
You can look at my Kmultiplier page for descriptions about how Ry affects CFP behavior. It speaks from a perspective of output impedance behavior. Since this output impedance is nonlinear and in series with the gain resistors, it directly contributes to distortion. The basic idea is, with low Ry the output impedance is like that of 2 diodes in series (120mV/decade). With high Ry the output impedance is like that of just one diode (60mV/decade). The latter case is more linear, although the CFP transconductance is actually smaller due to absolute bias. There are a number of ways to compromise with the CFP.
I expect the optimal points for noise and distortion will not be the same.
I expect the optimal points for noise and distortion will not be the same.
Yes, we went for lowest noise. Still distortion from this stage is low.
It will likely not see more then 20mV at the input. OK, some dirt and blemishes on the record will create some steep pulses. I keep my records clean though.
It will likely not see more then 20mV at the input. OK, some dirt and blemishes on the record will create some steep pulses. I keep my records clean though.
This is interesting, current is then a migration of charge, not a migration of cf charged particles, a bit like this Toy where energy is transferred by elasticity of the equal mass balls
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Interesting circuit in #9772, maybe you can use 8 parallel BF862 in the input jfet as Syn08 use on his HPS 5.1 Mc amplifier.
Syn08 claims less than 0.3nv/rtHz for his amplifier.
In BF862 datasheet it indicates that the equivalent noise input voltage is only 0.8nv/rtHz.
Low Noise Design Schematics
Syn08 claims less than 0.3nv/rtHz for his amplifier.
In BF862 datasheet it indicates that the equivalent noise input voltage is only 0.8nv/rtHz.
Low Noise Design Schematics
AS Audio came up with that variety. It should work and the paralleling of J-Fets at the input works too. Unfortunately i do not find enough time to build it right now.
Quite the way to go...
Any chance to see that in public (my frickelfestforum account has been defeated)?
Rüdiger
Yes, it´s real.
We are still working on the algorithms and the analog volume control but in principle it works.
Nice to see you back. Where habe you being ?
We are still working on the algorithms and the analog volume control but in principle it works.
Nice to see you back. Where habe you being ?
busy doing things...
I do not spend time for diy at the moment and my work bench is collecting dust, but my passion for music is still alive (of course) and I'm using my gear.
And lurking around here from time to time...
That A/D-D/A-phono is something I'd really like to listen to.
Rüdiger
I do not spend time for diy at the moment and my work bench is collecting dust, but my passion for music is still alive (of course) and I'm using my gear.
And lurking around here from time to time...
That A/D-D/A-phono is something I'd really like to listen to.
Rüdiger