Budget passive preamp with stepped attenuator?

[solderdude]

Upon further contemplation, I realized increasing SNR by 3~4dB with an expensive power supply is foolish.

Is there a (stepped) attenuator for amplifier output? Even a fixed 20dB attenuation at the amp output can be good.

No it does not exist for speakers but does exist for (sensitive) headphones.

I have probably lost about 40~60dB of dynamic range because the amp's gain is too high.

Nope.

 

[solderdude]

I listen at low volumes. At 9'o clock, I still need to set DAC volume to -20dB. Below 9'o clock, I have channel imbalance.

If the volume pot is at max position, I find myself setting DAC volume to something like -60dB.

Buy a cheap stepped attenuator or potentiometer attenuator. No need to worry about channel imbalance or noise issues.
or another amp. Could be a 2nd hand integrated one given the fact you do not play loud it could be 2x 30W to 2x60W or so.

 

[Deleted member 58865]

What is the unit of THD+N? Voltage? Power? THD+N of 0.001% usually pops up as the maximum inaudible level of THD+N.

What is SINAD in decibel for THD+N of 0.001%? 60dB? 30dB? I am not sure.

 

[mdsimon2]

What is the unit of THD+N? Voltage? Power? THD+N of 0.001% usually pops up as the maximum inaudible level of THD+N.

What is SINAD in decibel for THD+N of 0.001%? 60dB? 30dB? I am not sure.

0.001% = 20 x log (0.001/100) = -100 dB

Very important to note that audibility of THD and N are different.

Michael

 

[Deleted member 58865]

I'm not limited by the amp's SINAD. I'm limited by -40dB ~ -70dB of attenuation. With -40dB of attenuation from an attenuator and DAC volume and application volume, I get SINAD of 124(thermal noise)-40 = 84dB. With -70dB of total attenuation, I get SINAD of 44dB.

If I can just knock down the gain by 20dB, I would still get SINAD of 64dB in the worst case. Actually, I want no gain.

What do I want as minimum SNR and minimum SINAD?

 

[Zek]

Attenuate the output of an amplifier.

How do you think you do that?

 

[Zek]

I will buy one with a low gain, no gain, adjustable gains, or a volume knob that adjusts the gain level.

Obviously you didn't understand something well!!!
An amplifier cannot be without gain.
Most speaker amplifiers have a fixed gain.
The volume knob does not adjust the gain level.

 

[solderdude]

I'm not limited by the amp's SINAD. I'm limited by -40dB ~ -70dB of attenuation. With -40dB of attenuation from an attenuator and DAC volume and application volume, I get SINAD of 124(thermal noise)-40 = 84dB. With -70dB of total attenuation, I get SINAD of 44dB.

If I can just knock down the gain by 20dB, I would still get SINAD of 64dB in the worst case. Actually, I want no gain.

What do I want as minimum SNR and minimum SINAD?

Power amps with 0dB gain (1x) do not exist. They would be buffers. Besides... 2V into a 4 ohm speaker = 1W. That won't sound very loud and is just enough for 'all day listening volume' and would be the maximum you would get out of it. In such a case the new Schiit super low noise desktop power amps would have been a better choice.

You should forget the whole -124dB. Even if you had no signal at all the amp would be much much noisier than that.
The DAC is about -115dB
It is dwarfed by the distortion and noise of the Aiyima.
The limiting factor is the amp (distortion and noise) not its input voltage.

 

[Jimbob54]

I might have missed it, but 9 pages in (plus myriad other musings on similar threads) and I dont think anyone has asked or stated what the speakers are.

 

[Deleted member 58865]

Obviously you didn't understand something well!!!
An amplifier cannot be without gain.
Most speaker amplifiers have a fixed gain.
The volume knob does not adjust the gain level.

Paul McGowan of PS Audio said some of their amplifiers let users adjust gain with the volume knob on the amps. The amps don't attenuate signals with the volume knobs.

Some amps have gain switches. It's said that some amps like AIYIMA A04 have low gains.

No gain. No pain.

That won't sound very loud and is just enough for 'all day listening volume' and would be the maximum you would get out of it. In such a case the new Schiit super low noise desktop power amps would have been a better choice.

I will look into new Schiit amps. Schiit!

You should forget the whole -124dB. Even if you had no signal at all the amp would be much much noisier than that.
The DAC is about -115dB
It is dwarfed by the distortion and noise of the Aiyima.
The limiting factor is the amp (distortion and noise) not its input voltage.

SINAD of AIYIMA A07 is 83dB. -40dB ~ -70dB attenuation from the thermal noise(124dB) is lower than 83dB. With -70dB total attenuation, what is the entire audio system's SINAD? You tell me. Since a passive attenuator is used to attenuate DAC output a lot, I think thermal noise should be considered for the input signal to the amplifier.

I might have missed it, but 9 pages in (plus myriad other musings on similar threads) and I dont think anyone has asked or stated what the speakers are.

My speakers are Eltax Monitor 3.

MONITOR III | Eltax

It is one of the most talented compact speakers of its generation. Awarded the famous 5-star label What Hi-Fi, the Eltax Monitor III shines with a thousand qualities. The serious product is prodigious considering its small size. Two speakers drive this compact speaker, one 13 cm bass midrange...

en.eltax.com

System: 2 way Bass-reflex
Power consumption: 90 W
Woofer: 130 mm, insulated
Tweeter: 25 mm soft dome
Frequency response (±4dB): 50 Hz - 22 kHz
Sensitivity: 89dB
Impedance: 4-8 Ohms
Dimensions (W x H x D): 195 x 300 x 230 mm
Weight: 5 kg
Finishes: Black, white, calvados, walnut

 

[Deleted member 58865]

https://www.schiit.com/products/rekkr has 12dB of gain, and this turns out to be a pure power amplifier without a volume knob.
Thus, I will definitely want my new stepped attenuator.

Power Output:

Stereo, 8 Ohms: 2W RMS per channel
Stereo, 4 Ohms: 3W RMS per channel
Mono, 8 ohms: 4W RMS

Frequency Response: 20Hz-20Khz, +/-0.01db, 3Hz-500KHz, +/-3dB

THD: <0.001%, 20Hz-20KHz, at 1V RMS into 8 ohms

IMD: <0.001%, CCIR, at 1V RMS into 8 ohms

SNR: >120dB, A-weighted, referenced to full output

Damping Factor: >100 into 8 ohms, 20-20kHz

Gain: 4 (12dB)

Input Sensitivity: AKA Rated Output (Vrms)/Rated Gain. Or, 4/4. You do the math.

Input Impedance: 20k ohms SE

Crosstalk: >80dB, 20-20kHz

Inputs: L/R RCA jacks for stereo input, switch for mono input on R jack

Topology: fully discrete, fully complementary current feedback, no capacitors in the signal path

Oversight: over-current and over-temperature sensors with relay shut-down for faults

Power Supply: 6VAC, 2A wall-wart, 12,000uF filter capacitance, plus boosted, regulated supply to input, voltage gain and driver stages

Power Consumption: 12W maximum

Size: 5” x 3.5” x 1.25”

Weight: 1 lbs

I'm not sure that 12dB of gain is the lowest I can get, but it is better than 21.5dB of gain. Can I go lower? I think AIYIMA A04 would be another choice if I want low gain, but AIYIMA doesn't document the gain of AIYIMA A04.

 

[mdsimon2]

SINAD of AIYIMA A07 is 83dB.

Do you understand that the "S" in SINAD stands for signal, therefore SINAD is dependent on level. If you have no output from your amplifier you effectively have 0 SINAD. As such quoting SINAD without referencing level is meaningless.

With -70dB total attenuation, what is the entire audio system's SINAD? You tell me.

You've been shown how to do the calculations, why don't you do it? It will depend on the position of the AIYIMA volume knob as that will determine the level of the output. IIRC the AIYIMA has a max gain of about 32 dB.

Starting from 86 dB SNR for 5 W in to 4 ohm and assuming noise dominates SINAD here is system SINAD assuming a perfect 2 V output DAC with a perfect analog volume control resulting in 70 dB of attenuation. For reference residual noise is 224 uV from the amp alone.

32 dB gain
amp output = 0.025 V
SINAD = 41 dB

26 dB gain
amp output = 0.013 V
SINAD = 35 dB

20 dB gain
amp output = 0.006 V
SINAD = 29 dB

A fun exercise which I will leave for you is how much worse will SINAD be using a real DAC with digital volume control?

Michael

 

[Deleted member 58865]

Right, SINAD is dominated by attenuation. That's why I want to remove the damn gain. Can I connnect DAC directly with speakers without an amplifier between them?

Or, can I insert a stepped attenuator between DAC and speakers?

 

[JustJones]

Right, SINAD is dominated by attenuation. That's why I want to remove the damn gain. Can I connnect DAC directly with speakers without an amplifier between them?

Or, can I insert a stepped attenuator between DAC and speakers?

Sure

 

[mdsimon2]

Right, SINAD is dominated by attenuation. That's why I want to remove the damn gain. Can I connnect DAC directly with speakers without an amplifier between them?

Not really, more like if you solve the noise issue upstream of the amplifier (either via a very low noise DAC or a good analog volume control) you will still be limited by the residual noise of the amp.

Michael

 

[Deleted member 58865]

Not really, more like if you solve the noise issue upstream of the amplifier (either via a very low noise DAC or a good analog volume control) you will still be limited by the residual noise of the amp.

You mean SINAD and SNR at 5W of amplifier output and the absolute amount of noise injected by the amplifier are what really matters?

In retrospect, I realize that SINAD of attenuated analog signals doesn't really change the thermal noise and the absolute amount of noise injected by amplifier.

At 5W, most speakers reach about 96dB. That's 16-bit audio. At least, Eltax Monitor 3 reaches 96dB at 5W.

 

[Deleted member 58865]

Anyway, I think a stepped amplifier that includes a stepped attenuator is going to be a lot cleaner than existing fixed-gain amps.
A stepped amplifier would have a volume knob that looks like this.

At 0dB, the amplifier gain is 0dB. Above 0dB, you can adjust the amplifier gain in steps.
Below 0dB, there is no gain, but the built-in stepped attenuator kicks in.

If the volume knob has 61 steps, then you can adjust the volume in 1dB steps. This amp is not going to need a separate attenuator. You only need to adjust DAC volume a little bit.

Even a stepped amplifier without a built-in stepped attenuator is quite good when it's combined with a (stepped) attenuator.

If there is no such thing as a budget stepped amplifier, then Schiit Rekkr could be a good alternative as it has lower noise and lower gain.

 

[solderdude]

Since a passive attenuator is used to attenuate DAC output a lot, I think thermal noise should be considered for the input signal to the amplifier.

No because it is NOT the thermal noise that will ever be the issue with the Aiyima because the selfnoise + THD + IM will always be much, much higher than the noise level at the input so that's all moot. The noise at the input of the amp is NOT determining the system noise level. So you can forget all the calculations you are doing.
The noise floor will always be determined by the Aiyima and will only be worse than that because of IM and HD when music is playing which will mask selfnoise of the Aiyima.

As long as you do not hear any noise all of that is below audible levels and noise numbers are then irrelevant.

I suggest you play a white noise recording and then attenuate till you don't hear that noise and then you know what level of noise matters and what 'dynamic range' you got.
The dynamic range is the level difference between peaks (2V from the DAC) and the softest sound you can hear.
For that you play a 4kHz tone (that switches on and off every second or so) and start to play this at -50dB and then lower the level till you cannot hear it.
You cannot hear/perceive below the hearing threshold.

You continue to believe that the DAC and amp input matters which they don't in your case.

 

[Deleted member 58865]

No because it is NOT the thermal noise that will ever be the issue with the Aiyima because the selfnoise + THD + IM will always be much, much higher than the noise level at the input so that's all moot.

Okay. But, the stepped amplifier idea is cool. I think stepped amplifiers should be widespread.

I ordered GST60A24-P1J in the hope of maybe increasing the dynamic range by 1 or 2 dB.

 

[Deleted member 58865]

I suggest you play a white noise recording and then attenuate till you don't hear that noise and then you know what level of noise matters and what 'dynamic range' you got.
The dynamic range is the level difference between peaks (2V from the DAC) and the softest sound you can hear.
For that you play a 4kHz tone (that switches on and off every second or so) and start to play this at -50dB and then lower the level till you cannot hear it.
You cannot hear/perceive below the hearing threshold.

I will try.