Gee, I thought I told you exactly what I wanted to tell you. I told you that in both cases I was using a "standard" log taper pot. I know that there are many "log tapers", but they tend to share some characteristics. Take a look at this PDF from Bourns, for example: http://www.bourns.com/pdfs/gapno_panel_controls_taper.pdf Most audio-taper pots are similar (Alps have a very similar document), and have about 90% voltage attenuation at 50% rotation.
Further, I told you that with the DCB1 I am able to use a larger part of the available rotation of the volume control, and I like that.
Since you seem top want some more details, I measured the resistance of both pots. I measured them in-circuit, but of course with power off. The readings will be slightly off because of other elements in the circuit, but still should give you a good idea. The Arcam Delta 290 integrated amplifier uses a motorized 10K "A" taper pot. There are "index" marks around the volume knob, so I measured at each of those marks, although there are no detents. The DCB1 uses a 20K 21-step attenuator. I measured one channel in each case. Here are the results (R is resistance from input to wiper in kilohms, the rest should be self-explanatory):
Code:
Arcam
R V ratio % att dB
ccw 9.9 0 100.0% -inf
9.87 0.003 99.7% -50.37
9.79 0.011 98.9% -39.08
9.72 0.018 98.2% -34.81
9.61 0.029 97.1% -30.66
9.53 0.037 96.3% -28.55
9.35 0.056 94.4% -25.11
9.07 0.084 91.6% -21.53
8.76 0.115 88.5% -18.77
50% rot 8.4 0.152 84.8% -16.39
8.11 0.181 81.9% -14.86
7.75 0.217 78.3% -13.26
7.34 0.259 74.1% -11.75
6.37 0.357 64.3% -8.96
5.24 0.471 52.9% -6.54
4.13 0.583 41.7% -4.69
2.68 0.729 27.1% -2.74
0.54 0.945 5.5% -0.49
cw 0.05 0.995 0.5% -0.04
Code:
DCB1
ccw 19.63 0.000 100.0% -inf
19.61 0.001 99.9% -59.84
19.57 0.003 99.7% -50.30
19.50 0.007 99.3% -43.58
19.40 0.012 98.8% -38.62
19.27 0.018 98.2% -34.73
19.12 0.026 97.4% -31.71
18.91 0.037 96.3% -28.71
18.64 0.050 95.0% -25.95
18.32 0.067 93.3% -23.51
50% rot 17.91 0.088 91.2% -21.15
17.40 0.114 88.6% -18.89
16.74 0.147 85.3% -16.64
15.92 0.189 81.1% -14.47
14.92 0.240 76.0% -12.40
13.62 0.306 69.4% -10.28
12.00 0.389 61.1% -8.21
10.00 0.491 50.9% -6.19
7.38 0.624 37.6% -4.10
4.13 0.790 21.0% -2.05
cw 0.00 1.000 0.0% 0.00Do you feel any better informed?
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It does not matter. What does matter is the overall gain of the amplifier.Yes, so now since we know I used the Arcam with the volume control in the 8:00-11:00 range, it is left as an exercise for the reader to determine the voltage gain of the Arcam preamp stage
In the other case your amp would have a gain, let's assume it is +28dB
and assume you have an RF filter fitted as well that loses another 1dB.
The preferred vol pot setting you listen at is -16dB.
The gain from the Source to the Speakers is (+28 -1 -16) = +11dB
i.e. the Speaker voltage is ~3.6 times the Source voltage.
You can measure this with a test signal and a voltmeter.
You could also check the Source to Speaker voltage ratio of the Arcam at your preferred listening level.
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Sjøstrøm Buffer
Would it be ok to add this buffer after the Dcb 1 and on the same supply ?
http://sjostromaudio.com/pages/index.php/hifi-projects/126-qrv05-diamond-buffer#.U_N4csV_vnd
Would it be ok to add this buffer after the Dcb 1 and on the same supply ?
http://sjostromaudio.com/pages/index.php/hifi-projects/126-qrv05-diamond-buffer#.U_N4csV_vnd
the DCB1 has limited output current.
If you need/want more output current than what the DCB1 can provide then build a different Buffer that suits your needs.
The DCB1 has a vol pot followed by a Buffer (with it's own AC to DC PSU). It's all integrated on the PCB.
If you want a Buffer before the vol pot then the DCB1 is not what you need.
Sort out what your requirements are and then select suitable Buffers to fit that.
A DCB1 plus another higher current Buffer afterwards is nonsense.
With power i mean more A. But more voltage sving would be nice to.
So a new design with higher voltage and more I max would be nice.
It not that I consider it bad. I just want more