John Curl's Blowtorch preamplifier part II

Status
Not open for further replies.
Jump to Latest
#47,881
What about Chris comments

http://www.diyaudio.com/forums/loun...ch-preamplifier-part-ii-4784.html#post3803340


jan.didden said:
Most likely the first graph looks the same in shape as the second one if it was only for the noise. The rise of THD+N in the 1st graph towards lower levels is noise that rises above the THD which is no longer visible.
In the second graph the THD is so large that it rises above the noise so the noise is no longer visible.

You can only meaningfully compare the two graphs if they would show THD only, not THD+N.

Edit: I was shooting from the hip - I now see that others have made a similar comment. Anyway, the plot is clear 🙂

Jan
Click to expand...
 
#47,882
Chris Hornbeck said:
And your point about crossover distortion is not amiss: -93dB 3rd harmonic from a +25dBW output signal is -68dB ref 1 watt, a reasonably typical listening level with typical speakers of say 88dB SPL/1W/1M.
Click to expand...

At one watt, the measurements show something like 0.002% THD+N, noise dominated. Where did you get the idea that the distortion amplitude was constant with level?
 
#47,887
a.wayne said:
Ok,

1. How are you determining noise from thd ?
2. Why do thd+N ?
3. At mW outputs where noise dominates( based on thd+N) then wouldnt this be part of its distortion spectra.
Click to expand...

I don't know what you are questioning but imo THD and N not only have different measures but also different perceived sounds. Noise is not fatiguing or problematic but it masks detail and (from simulation it seems) bass performance.
 
#47,889
a.wayne said:
1. How are you determining noise from thd ?
2. Why do thd+N ?
3. At mW outputs where noise dominates( based on thd+N) then wouldnt this be part of its distortion spectra.
Click to expand...

1. Shape of the curve, along with actual reported noise measurement.
2. Ask John Atkinson.
3. No, it's part of the spectra (floor), but it's noise, not distortion.

Compare and contrast to, say, the big Parasound amp.
 
#47,891
merlin el mago said:
How to calculate the cap value?
About the resistor value 100-300 ohms don't change if the loudspeaker have 4 ohms?
TIA & sorry in advance for these newbie wuestions.
Click to expand...

The resistor should be the cable's impedance. It's nothing to do with the speaker nominal impedance.

If you use a very low impedance cable, like 8 ohms, then the resistor will be too much of a load and will get hot. Since the reason for the resistor is to quash high frequency effects outside of hearing, you can just model it as a hf crossover, with the break frequency above 20 Khz.

Triodethom said:
Why is the autotransformer not a sub class of transformers ( having only one coil) but rather a different class all together ?
Click to expand...
Because it does essentially does what a transformer does. The core will be the same, but the primary and secondary share a portion of the wind.

jn
 
#47,898
Jay said:
😀

I believe/guess that the absence of galvanic isolation as Hoyt mentioned is more towards the beneficial side for autoformer. I'm familiar with transformer sound but not autoformer but I guess there is not many issues with autoformer as it is commonly used in speaker crossover with unnoticeable problems.
Click to expand...

Yep nothing wrong with miles of copper before speakers
 
Status
Not open for further replies.
Top Bottom