Hi Patrick, Nic
Patrick- thank's for taking the trouble to explain- again. I now, I hope, understand all aspects of the circuit!
BTW, in Twisted Pear's implementation of the ESS9018- the Buffalo, that Nic and I own- four paralleled DACs are used per channel, so the output impedance is 4 x lower than in your simulation. And I've chosen to use 330 R IV resistors. So I've ~1/8 of nothing to worry about- which I won't worry about
Nic- I'll get on with it!
Best wishes
Paul
Patrick- thank's for taking the trouble to explain- again. I now, I hope, understand all aspects of the circuit!
BTW, in Twisted Pear's implementation of the ESS9018- the Buffalo, that Nic and I own- four paralleled DACs are used per channel, so the output impedance is 4 x lower than in your simulation. And I've chosen to use 330 R IV resistors. So I've ~1/8 of nothing to worry about- which I won't worry about
Nic- I'll get on with it!
Best wishes
Paul
Hi Patrick
with 4 paralleled DACs per channel the ESS9018, at 0 dBFS, outputs about 5.7 mA rms- so 1.87 V across a 330 R load. In fact, 150 R might have been a better fit in my system (my present Legato IV stage uses this value). 680 R gives close to standard balanced output level but I don't need this much.
And, of course, SEN doesn't care!
Best
Paul
with 4 paralleled DACs per channel the ESS9018, at 0 dBFS, outputs about 5.7 mA rms- so 1.87 V across a 330 R load. In fact, 150 R might have been a better fit in my system (my present Legato IV stage uses this value). 680 R gives close to standard balanced output level but I don't need this much.
And, of course, SEN doesn't care!
Best
Paul
Hi Patrick
The calculation in my last post is- I think- out by a factor of two. An IV R of 330R gives ~ 3.5 V rms maximum out. As I'm converting the balanced signal to single ended, an IV R of 150 R would have been a better choice, giving me 1.65 V rms out
The crucial thing is that the DAC as Buffalo uses it parallels four outputs per channel, so the DAC's output Z is reduced to 195 R. From the TP website, and the ESS9018 datasheet-
"Each analog output at 0DBFS is equivalent to a voltage of approximately 92.4% of AVCC in series with 195 R. So given 3.3VDC AVCC it will be about 3.05Vpp across 195 R"
I checked using your LT Spice SEN/9018 simulation. I made R1 195 R, and played with the value of the IV resistor (R5). BTW, with 680R and 4 paralleled outputs, the output clips severely. I think Nic uses 500 R, which is a bit marginal.
Though given my recent track record, I’ve probably got this all wrong! I’d like to be certain, as in a fit of madness- and in tribute to my belief in Nic’s assessments- I bought 4 x 330 R Vishay naked foil (Charcroft) resistors for IV duties! I could probably still swap them for 150 R- perhaps I ought to try some cheaper resistors first
Paul N
The calculation in my last post is- I think- out by a factor of two. An IV R of 330R gives ~ 3.5 V rms maximum out. As I'm converting the balanced signal to single ended, an IV R of 150 R would have been a better choice, giving me 1.65 V rms out
The crucial thing is that the DAC as Buffalo uses it parallels four outputs per channel, so the DAC's output Z is reduced to 195 R. From the TP website, and the ESS9018 datasheet-
"Each analog output at 0DBFS is equivalent to a voltage of approximately 92.4% of AVCC in series with 195 R. So given 3.3VDC AVCC it will be about 3.05Vpp across 195 R"
I checked using your LT Spice SEN/9018 simulation. I made R1 195 R, and played with the value of the IV resistor (R5). BTW, with 680R and 4 paralleled outputs, the output clips severely. I think Nic uses 500 R, which is a bit marginal.
Though given my recent track record, I’ve probably got this all wrong! I’d like to be certain, as in a fit of madness- and in tribute to my belief in Nic’s assessments- I bought 4 x 330 R Vishay naked foil (Charcroft) resistors for IV duties! I could probably still swap them for 150 R- perhaps I ought to try some cheaper resistors first
Paul N
In practice, with ES9018 and the SEN, I went from 2x 9V NiMH batteries (18V nominal) to 3x 9V NiMH batteries (27V nominal) without bothering to change R1/R2 (chosen for 16V) and the change in DC offset on the output was <5 mA (as far as I recall).
I am now running at 22.5V (regulated) and the output DC offset is stable, below 1 mV, and I still did not change R1/R2. It may be as much as 6-7 mV at cold start, but it settles in a couple of minutes (I guess when the FETs reach equilibrium temp).
I will eventually change R1/R2 to their correct values, but for the moment I'm just enjoying the music
Cheers,
Nic
Did you notice any difference in sound when increasing the voltage?
Paul,
I am interested in your findings.
With the recommended 680R the gain is quite a bit to high for my system. It is very clearly higher than with Legato (with stock resistor values). As I am using attenuation in the digital domain I am unlikely to have noticed clipping as I am generally listening to low levels. I assume you are doing the attenuation in your tube-pre and getting the I/V-resistor right is more critical for you.
I did not bother to "adjust" the I/V resistor to achieve a better gain structure in my system yet as my downstream amplification is going to undergo some major upgrades in the near future
I will be using Vishay naked foil resistors for the voltage divider and I/V in my SEN "Mk2", which is slowly in the works. Same circuit but hopefully with a mezzanine adaptor PCB for BII to accomodate the voltage divider circuit, Avcc regulators and to interface with the SEN PCBs. It is a bit messy the way I have done it at the moment and complicated to tweak. There is still quite some discussions on which is the better way to regulate Avcc (some people, which ears I trust, seem to prefer series regulators with large caps) and as this regulator is now also setting the SEN Vref this is an area where I might want to experiment in the future. At the moment just enjoying
Cheers,
Nic
I am interested in your findings.
With the recommended 680R the gain is quite a bit to high for my system. It is very clearly higher than with Legato (with stock resistor values). As I am using attenuation in the digital domain I am unlikely to have noticed clipping as I am generally listening to low levels. I assume you are doing the attenuation in your tube-pre and getting the I/V-resistor right is more critical for you.
I did not bother to "adjust" the I/V resistor to achieve a better gain structure in my system yet as my downstream amplification is going to undergo some major upgrades in the near future
I will be using Vishay naked foil resistors for the voltage divider and I/V in my SEN "Mk2", which is slowly in the works. Same circuit but hopefully with a mezzanine adaptor PCB for BII to accomodate the voltage divider circuit, Avcc regulators and to interface with the SEN PCBs. It is a bit messy the way I have done it at the moment and complicated to tweak. There is still quite some discussions on which is the better way to regulate Avcc (some people, which ears I trust, seem to prefer series regulators with large caps) and as this regulator is now also setting the SEN Vref this is an area where I might want to experiment in the future. At the moment just enjoying
Cheers,
Nic
Nothing that I noticed, but as I never went back it is difficult to say.
The FET sinks got more hot than I was comfortable with @27V so I settled for the regulated 22.5V intermediate. I will try FETs with higher Idss, but as the circuit sound so very well in "stock" configuration I find it difficult to believe that I will obtain any objective improvement. I should also note here that I did not notice any major improvement using regulated supplies, but as it did not sound worse I left it in.
Being professionally very familiar with the potency of the placebo effect I will continue to tweak (preferably with expensive components
) as this can only bring about subjective improvement - which are very realCheers,
Nic
Nothing that I noticed, but as I never went back it is difficult to say.
The FET sinks got more hot than I was comfortable with @27V so I settled for the regulated 22.5V intermediate. I will try FETs with higher Idss, but as the circuit sound so very well in "stock" configuration I find it difficult to believe that I will obtain any objective improvement. I should also note here that I did not notice any major improvement using regulated supplies, but as it did not sound worse I left it in.
Being professionally very familiar with the potency of the placebo effect I will continue to tweak (preferably with expensive components
Cheers,
Nic
Ok, thanks.
A very naive and basic question: with the SEN9018 I am doing the I/V-conversion using resistors connected on the XLR output pins.
Why not do it on the pre-amp input, or even in the power amp if the pre-amp is a current amplifier?
Is current coupled signal transmission more prone to interference than potential coupled?
Forgive me my ignorance and sorry for the OT - just trying to learn here
Cheers,
Nic
Why not do it on the pre-amp input, or even in the power amp if the pre-amp is a current amplifier?
Is current coupled signal transmission more prone to interference than potential coupled?
Forgive me my ignorance and sorry for the OT - just trying to learn here
Cheers,
Nic