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Budget passive preamp with stepped attenuator?

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Deleted member 58865

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Is there any? I just want volume control for RCA cables without channel imbalance.
 
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kenji said:
I just want volume control for RCA cables without channel imbalance.
Click to expand...
Not perfect... but very cheap;
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JSmith
 
As far as I know, all potentiometers degrade over time, and nearly all of them have noticeable channel imbalance.

Stepped attenuators are the way of the past, the present, and the future.
 
I'd strongly suggest you make the steps no more than 1 db. That is so close to continuously variable there is no need for smaller. 1.25 db might almost be good enough, but just make it 1 db per step and you'll be happy. 1.5 db is nearly enough, but is not quite small enough.
 
I built my bargain basement passive attenuator with two pots - left and right.

Since it sat in the middle between the two speakers, it was simple to adjust by ear.
 
mdsimon2 said:
a high dynamic range DAC with digital volume control
Click to expand...
I don't know how expensive it would be. Topping D10s has 112dB of dynamic range. So, with the DAC volume currently at -16dB, I get 96dB of dynamic range.

With the DAC volume at -16dB, application volume at 100% is loud enough to disturb me and people around me. I keep application volume at 25~70%.

It seems 121dB is the best dynamic range you can get from DAC.

My AIYIMA A07 amplifier doesn't have 96dB of dynamic range because the AC/DC power adapter is not clean enough. If I buy a better power supply, I may get more dynamic range from the amp.

Really, AIYIMA should step up its game and put stepped attenuators in their amplifiers. I would buy AIYIMA A07 with a stepped attenuator instead of potentiometer as long as the gain structure of the stepped attenuator is correct.
 
Last edited by a moderator:
2023-03-30 18:49:05.png

I just saw this comment on
However, reducing DAC volume still reduces DAC's dynamic range.
 
Can a passive preamp raise noise floor? It seems all phono preamps reviewed on this forum have SINAD below 91.
 
kenji said:
However, reducing DAC volume still reduces DAC's dynamic range.
Click to expand...

Reducing the volume = reducing the dynamic range.
Reason is simple. The max amplitude is lower so lower volume signals will fall below the hearing threshold limiting the 'dynamic range'.
Yes, electrically the dynamic range may still be the same high level but what is below the hearing threshold you simple cannot hear.

The dynamic range of your hearing is about 70dB at any 'average' level so music at 120dB level means you won't be hearing any sounds at 50dB SPL at that moment (you can later on when the music is silent).
This means hiss will become audible (when high enough) when there is silence (or music playing at low levels)
When listening to music at 80dB SPL you won't be hearing things at 10dB SPL at the same time.


Yes, a passive amp can raise the noise floor (very slightly) depending on the input stage of the amp.
Selecting a lower resistance is always the best. (10k or lower)
 
solderdude said:
The dynamic range of your hearing is about 70dB at any 'average' level so music at 120dB level means you won't be hearing any sounds at 50dB SPL at that moment (you can later on when the music is silent).
Click to expand...
You mean reducing DAC volume is just as good as setting it at 0dB and reducing the volume on stepped attenuator?

Topping D10s has SINAD of 112dB. If the total digital attenuation from application volume and DAC volume is -42dB, then the dynamic range would be 70dB.
-42dB of digital attenuation is probably going to be more than enough. I don't know whether my ear's dynamic range is larger than 70dB at quieter volume levels.

I often listen to video and music at low volume levels in order to protect my hearing and to not disturb people around me.
 
kenji said:
I don't know how expensive it would be. Topping D10s has 112dB of dynamic range. So, with the DAC volume currently at -16dB, I get 96dB of dynamic range.

With the DAC volume at -16dB, application volume at 100% is loud enough to disturb me and people around me. I keep application volume at 25~70%.

It seems 121dB is the best dynamic range you can get from DAC.

My AIYIMA A07 amplifier doesn't have 96dB of dynamic range because the AC/DC power adapter is not clean enough. If I buy a better power supply, I may get more dynamic range from the amp.

Really, AIYIMA should step up its game and put stepped attenuators in their amplifiers. I would buy AIYIMA A07 with a stepped attenuator instead of potentiometer as long as the gain structure of the stepped attenuator is correct.
Click to expand...

You are simplifying this too much. You need to look at residual noise at the amplifier output as a function of volume control position considering residual noise and gain from the amplifier as well as residual noise inherent in your source.

If you don't have issues with audible hiss currently, adding an analog volume control is not going to help you.

Based on PMA's measurements -> https://www.audiosciencereview.com/...s-power-supply-measurements.19507/post-642669 A07 residul noise is 10^(-75.2/20) = 174 uV residual noise from the A07 with an improved power supply. For reference this is a 5 W in to 4 ohm dynamic range of 20 x log[sqrt(5 x 4) x 10^6 / 174] = 88 dB.

Actual system noise performance will depend on the volume control position of the A07, lower gain = lower amplification of upstream noise but this comes with a channel imbalance penalty. For this analysis let's assume 29 dB gain like the ASR review.

Residual noise from D10S = 2 x 10^(-112/20) = 5 uV
Amplified residual noise from D10S = 5 x 10^(29/20) = 142 uV
Total residual noise from amplified DAC output and amplifier = sqrt (142^2 + 174^2) = 225 uV

225 uV residual noise is pretty good and is likely not audible depending on speaker sensitivity, hearing and listening position.

Now let's say you typically listen at -20 dB, that will reduce your output signal but noise remains constant with digital volume control.

Voltage at DAC output at -20 dB = 2 x 10^(-20/20) = 0.2 V
Voltage at amplifier output at -20 dB = 0.2 x 10^(29/20) = 5.6 V
Dynamic range at amplifier output at -20 dB = 20 x log(5.6 x 10^6 / 225) = 88 dB

Now let's look at the case of perfect analog volume control. In this case both upstream signal and noise are attenuated.

Attenuated residual noise from DAC output at -20 dB (analog) = 5 x 10^(-20/20) = 0.5 uV
Amplified residual noise from DAC output at -20 dB (analog) = 0.5 x 10^(29/20) = 14 uV
Total residual noise at -20 dB (analog) = sqrt (14^2 + 174^2) = 175 uV

Now noise is dominated by your amplifier where as before it was roughly equal parts DAC and amplifier.

Dynamic range at amplifier output at -20 dB (analog) = 20 x log(5.6 x 10^6 / 175) = 90 dB

You've gained 2 dB dynamic range at -20 dB volume position with a perfect analog volume control. Without a lower noise / lower gain amplifier you will not be gaining much from using a higher dynamic range DAC or an analog volume control.

Michael
 
Anyway, noise floor is different from dynamic range.
 
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