Hi,
I have a USB Dac based on the PCM1794 chipset. There is no volume control and I'm feeding it into active speakers (also with no volume control).
The active speakers have an impedence of 47k. The volume is high enough at present so I'm only looking at a reduction.
What would you recommend? At first I tried a 10k sliding potentiometer but the quality of the output suffers and it has almost no control.
Regards, Andrew
I have a USB Dac based on the PCM1794 chipset. There is no volume control and I'm feeding it into active speakers (also with no volume control).
The active speakers have an impedence of 47k. The volume is high enough at present so I'm only looking at a reduction.
What would you recommend? At first I tried a 10k sliding potentiometer but the quality of the output suffers and it has almost no control.
Regards, Andrew
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It should be possible to use a potentiometer at the output of the DAC. If the DAC output (the filter output) cannot pull 10K then try with a 47K potentiometer.
This switched resistor pot should work fine. Choose the 10k option.
DACT Type SMD Stepped Attenuator 21 step volume control pot D Shape Shaft | eBay
So I have a 10k slider potentiometer from the output to ground. At anything above about 500 ohm it's at full volume.
You have a linear slide pot, so it's no good for a volume control in this application.
A volume control that you need has a log taper, like the one linked in post #3.
Potentiometer taper - audio taper >> Resistor Guide
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Doh! - ok.
Couple things:
1. Why a stepped pot?
2. I noticed with an inline 10k resistor the sound from the Beolab 1 speakers I'm driving is very poor (most top end is gone and the bass is wooly/boomy.
If using a log pot wouldn't say 500ohm / 9500 ohm have the same affect?
Couple things:
1. Why a stepped pot?
2. I noticed with an inline 10k resistor the sound from the Beolab 1 speakers I'm driving is very poor (most top end is gone and the bass is wooly/boomy.
If using a log pot wouldn't say 500ohm / 9500 ohm have the same affect?
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It would, you would just turn the knob further clockwise before reaching 500 ohm/9500 ohm.
<500 Ohms across the output "near-shorts" the output, making it work too hard and distort more.
10K in series "strangles" the signal to the amplifier. In this case the amp input is not a pure 47K, but apparently lower in the treble, lost highs.
THE answer is a combination. As said, 10K across the amplifier (light load) and take a TAP from a selectable position along the 10K to go to the amplifier. If you tap in the middle you get half the signal(*); tap at 1K up you get 1/10th signal.
With a 10K potentiometer the maximum impedance at the wiper is 2.5K, which the amplifier should not mind. (Long cables can matter.)
A true Linear potentiometer is good for making small changes around 25%-75% of max. The way we usually run audio systems we need good control down below 5%. An "Audio" taper stretches-out the lower levels so you do not have to dial-in 0.07 on a 0-10 scale.
(*) These ratios are affected by pot loading; half-scale on 10K feeding 50K is really 48%. This is no big deal.
Any DAC which will not drive 10K (8K full-up) must be very strange. The observed DAC output is near 500r, so 10K-8K is a light load and it will be happy.
10K in series "strangles" the signal to the amplifier. In this case the amp input is not a pure 47K, but apparently lower in the treble, lost highs.
THE answer is a combination. As said, 10K across the amplifier (light load) and take a TAP from a selectable position along the 10K to go to the amplifier. If you tap in the middle you get half the signal(*); tap at 1K up you get 1/10th signal.
With a 10K potentiometer the maximum impedance at the wiper is 2.5K, which the amplifier should not mind. (Long cables can matter.)
A true Linear potentiometer is good for making small changes around 25%-75% of max. The way we usually run audio systems we need good control down below 5%. An "Audio" taper stretches-out the lower levels so you do not have to dial-in 0.07 on a 0-10 scale.
(*) These ratios are affected by pot loading; half-scale on 10K feeding 50K is really 48%. This is no big deal.
Any DAC which will not drive 10K (8K full-up) must be very strange. The observed DAC output is near 500r, so 10K-8K is a light load and it will be happy.
Nearly sorted, the pot's I was using were wired incorrectly.
How about this? Is there a reason for using SMD steps instead of the more traditional carbon rail?
10K Logarithmic Slide Potentiometer Log Slide Pot Potentiometer Module Dual Output For Arduino AVR Electronic Block Red on Aliexpress.com | Alibaba Group
How about this? Is there a reason for using SMD steps instead of the more traditional carbon rail?
10K Logarithmic Slide Potentiometer Log Slide Pot Potentiometer Module Dual Output For Arduino AVR Electronic Block Red on Aliexpress.com | Alibaba Group
Slide pots (correctly wired) have been a mainstay of audio for decades.
Those appear to be wired correctly for an audio Volume control.
You don't actually need the PCB that comes with it; but for 2 bucks total, who cares?
And for 2 bucks, you have to wonder about "quality". They may "scratch" as you slide them. They may wear-out in a few years. But they are probably comparable to the slide pots on most of the Japanese gear of the 1980s-1990s. And again, for 2 bucks, you can buy a dozen, find a few good ones, replace as they wear out. (I bought $13 meters, made a custom box, one had a bad back-light, I just bought a few extras so I can replace them as needed.)
I have NO idea why that slide-pot says "Arduino". While you "could" use it to input analog voltage to a digital computer, why lot-taper? why dual? I think the vendor does not know what he is selling, just sprinkles hot buzz-words in the description.
Those appear to be wired correctly for an audio Volume control.
You don't actually need the PCB that comes with it; but for 2 bucks total, who cares?
And for 2 bucks, you have to wonder about "quality". They may "scratch" as you slide them. They may wear-out in a few years. But they are probably comparable to the slide pots on most of the Japanese gear of the 1980s-1990s. And again, for 2 bucks, you can buy a dozen, find a few good ones, replace as they wear out. (I bought $13 meters, made a custom box, one had a bad back-light, I just bought a few extras so I can replace them as needed.)
I have NO idea why that slide-pot says "Arduino". While you "could" use it to input analog voltage to a digital computer, why lot-taper? why dual? I think the vendor does not know what he is selling, just sprinkles hot buzz-words in the description.
Please resist buying cheap junk, good audio volume controls are more than $2.
The switched resistor control posted as an example is, by far, the best low cost
control available, quiet with near perfect tracking.
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