Impedance matching is critical. Much of the perceived differences between components is due to improper matching of impedance.
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Yes, thank you. I agree. But this does not answer my question. I am looking I guess for a technical response, such as too low an input impedance and the low frequency response degrades, or something to that effect.
The 10x thing (not sure who made that up) is easily met:
Input Z of amp: 22k
output Z of pre(se):300 ohms
ratio: 22,000/300 = ~73
But I cringe,a bit when i see the manufacturer's spec stating min z-load is 40k.
As well as a technical response, I am wondering of the audiogon members who have either ARC preamp, if they have worried about this or have used it with such amplifiers.
This impedance and capacitance form a single pole low pass filter. If the input impedance of the device you're driving falls much below 40K and/or the combined capacitance of the input and interconnect cable exceeds 1000pf (seems unlikely) you could end up with a 6 db/octave droop in the high frequency response of the combination.
The cutoff frequency of the low pass filter depends both on the impedance and capacitance. As long as your total capacitance is well below 1000pf your setup may work fine.
I suspect that the 40K/1000pf numbers were chosen by ARC to ensure that the cutoff frequency of this low pass filter would be significantly higher than 20khz under all normal configurations.
Ideally a preamp has very low output impedance, but the 300/600 ohm SE/Balanced value is typical for tubed output stages.
Consider dropping ARC tech support an email with this problem. In my experience they've been most helpful.
BTW, what are you going to drive with the preamp?
Driving an Aragon 8002
I have read that folks have driven, say a DNA 500 with 10K Z-in with Z-out(preamp) higher than 300, with great results.
Apart from moving the 3dB down point lower than 20kHz(knee of the curve), is there any concern about increased distortion now that the output section has to source more current? Or is there any concern about failure?
I will try ARC.
Thanks Ghost Rider 45.
How do you arrive at a LPF?
The ARC LS-15 tube outputs are connected in series to a 5uF cap. From an electrical perspective, if you look back into the output (from the rca jack) the impedance you see is in part pure resistance and capacitance. Since the the cap is in series with the output signal, and a cap's impedance is (1 / jwc), at freq = 0 Hz the cap has infinite resistance, and hence conducts no current. As frequency rises to infinity the cap approaches a short circuit.
Now looking into the input impedance of the amplifier, we again, see some pure resistance, say directly to ground. Whatever this stage is does not change the physical circuit of the preamp's composite output impedance (which is a function of frequency).
IME, of you examine the output stage of the ARC and the input stage of the amp you will see a HPF (high pass filter). As you go up in C, the 3dB point moves closer to 0 Hz. I ran a model in Matlab and varied the resistances from the output of the ARC model, as well as the input of the theoretical amp resistance.
What I see is that (with fixed ARC model parameters) if the input resistance is increased the 3dB point moves close to 0 Hz, but the delta b/t 22k And 100k, for instance is VERY subtle. Also the phase response is affected as well, but also very little difference b/t 22k and 100k.
I guess I had to prove this to myself.
Thanks for reading!