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Old 10th August 2014, 09:17 AM   #4241
AndrewT is offline AndrewT  Scotland
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Quote:
turning the volume control above 9:00 or 10:00 was getting uncomfortably loud;
this tells you and us nothing.
We don't know what attenuation is being applied.
We don't know where in the clock max is, nor where min is.
Quote:
fully cw was 6:00 and fully ccw was about 7:30. So 12:00 was 12 steps down from full volume, and was actually less than half rotation.
this tells us where min and max are, but not the attenuation at your preferred setting.
Quote:
I usually have my DCB1 volume knob at or slightly above 12:00
your earlier post tells us nothing.
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Old 10th August 2014, 08:49 PM   #4242
nezbleu is online now nezbleu  Canada
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Quote:
Originally Posted by AndrewT View Post
this tells you and us nothing.
We don't know what attenuation is being applied.
We don't know where in the clock max is, nor where min is.this tells us where min and max are, but not the attenuation at your preferred setting.your earlier post tells us nothing.
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_pan...rols_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%	0.00
Do you feel any better informed?

Last edited by nezbleu; 10th August 2014 at 08:55 PM.
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Old 11th August 2014, 09:30 AM   #4243
AndrewT is offline AndrewT  Scotland
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Are you confirming that you listen @ -16dB
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Old 11th August 2014, 05:14 PM   #4244
nezbleu is online now nezbleu  Canada
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Depends on who else is in the room, but yes, that would be the "loud" end of the range where I listen.
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Old 12th August 2014, 09:19 AM   #4245
AndrewT is offline AndrewT  Scotland
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Quote:
I use self-powered Linkwitz Pluto speakers, and I usually have my DCB1 volume knob at or slightly above 12:00 (or let's say between 10:00 and 2:00). I consider this a good match.
Quote:
Originally Posted by AndrewT View Post
Are you confirming that you listen @ -16dB
Quote:
Originally Posted by nezbleu View Post
Depends on who else is in the room, but yes, that would be the "loud" end of the range where I listen.
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Old 12th August 2014, 06:05 PM   #4246
nezbleu is online now nezbleu  Canada
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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
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Old 13th August 2014, 09:57 AM   #4247
AndrewT is offline AndrewT  Scotland
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Originally Posted by nezbleu View Post
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
It does not matter. What does matter is the overall gain of the amplifier.

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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Last edited by AndrewT; 13th August 2014 at 10:00 AM.
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Old 19th August 2014, 05:08 PM   #4248
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In a balanced DCB1 build using the following schematic:

Click the image to open in full size.

will it be possible to accept unbalanced sources by shorting pins 1-3? Will it work?
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Old 19th August 2014, 05:19 PM   #4249
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Default Sjøstrøm Buffer

Would it be ok to add this buffer after the Dcb 1 and on the same supply ?
http://sjostromaudio.com/pages/index...r#.U_N4csV_vnd
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Old 19th August 2014, 05:29 PM   #4250
Salas is online now Salas  Greece
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What, two buffers in a row? Typically it should work although not sure if to the better.
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