About stepped attenuators (i.e. am i hearing things ?)

[restorer-john]

the overall point is that the SNR of active preamps typically drops 1:1 as you reduce the volume

Plenty of preamps where the volume control sits up front of the flat gain/tone/filter/buffer stages, sure.

But there's also a lot of better vintage preamps that used active buffered inputs and low value (~<10k) dual ganged volume pots, where both the input gain stage and the final stage buffer are controlled by the volume. They better maximised the S/N over the full range of volume settings.

I'm not aware of many (or any) new offerings using similar tactics. Mainly due to the proliferation of balanced IPs, which would double the number of gangs required from 2-4-8 for such a setup.

 

[restorer-john]

Even worse, preamp SNR is generally specified referred to maximum output, which more often than not is 6 to 9 Vrms.

Signal to noise is referenced to rated output, not maximum output. Most preamps of the past were between 1.0V and 2.0V for rated outputs from 150mV line input (single ended).

I have never seen SNR on a preamp spec sheet referenced to maximum output, where that output is derived from driving the inputs way in excess of their rated sensitivity in order to clip the output stage on the rails. That would be a max dynamic range spec, not a S/N spec.

 

[LSPhil]

I'm lazy by nature and therefore love computers and electronics, so I asked AI and got a well-formulated answer. I couldn't have explained it better:

"The signal-to-noise ratio (S/N) is better when the signal is strong relative to the noise. In an amplifier this means that the ratio between the amplified signal and the noise should be as large as possible.

In general, however, it is important to note that the signal-to-noise ratio depends not only on the setting of the amplifier, but also on the quality of the signal itself, the quality of the amplifier and other external factors.

Regarding the preamplifier and the power amplifier, a good preamplifier with adequate gain can help amplify the input signal to be well above the noise, resulting in a better signal-to-noise ratio. The power amplifier should then amplify this signal without introducing additional noise to maintain the optimal signal-to-noise ratio.

In short, the signal quality, the amplifier settings, and the quality of the amplifier itself are all important factors that can affect the signal-to-noise ratio."

In other words, if it regulates the signal level at the preamplifier input, it is much worse than if it regulates its level at the preamplifier output. for example, if the smartphone is a signal source and I set it to half the volume and the amplifier has to adapt the signal to the amplifier, it generates a lot of noise

 

[gino1961]

Mine are series-types in 5k Ohms, as in the circuit shown in the Stepped Volume Control paper by W.Marshall Leach Jr. I used Susumu RR, 0.5% 25ppm, surface mount 0805 packages, because they are practical. At low volumes, the noise is the equivalent of a 4950 Ohm resistor in the signal path. This value reduces as the volume control is rotated clockwise. It’s not a problem. It is transparent and absolutely silent.
In fact, I couldn’t distinguish it from the noise floor of the analyzer, ie 5-digits right of the decimal.

Hi very impressive Did you built the attenuator yourself ? smd is beyond my ability I like them but Suisse precision is needed

About the “noise of the resistors sum up”:
Even if a non-series type stepped attenuator is used, it still has the same noise level if it’s the same value. This is because it has to use the same resistance values for equivalent attenuation. Whether it be one or 50 resistors makes no difference in this regard. Many high voltage test probes use resistors in series rather than a single, and this does not degrade them.

very interesting and thank you for the explanation if i understand well 2 50 ohm resistors in series will have the same noise of 1 100ohm resistor of the same grade Very good to know In some kits i see very often used Dale resistors Maybe they are only Dale looking resistors
Vishay are more expensive

 

[gino1961]

Plenty of preamps where the volume control sits up front of the flat gain/tone/filter/buffer stages, sure.

But there's also a lot of better vintage preamps that used active buffered inputs and low value (~<10k) dual ganged volume pots, where both the input gain stage and the final stage buffer are controlled by the volume. They better maximised the S/N over the full range of volume settings.

I'm not aware of many (or any) new offerings using similar tactics. Mainly due to the proliferation of balanced IPs, which would double the number of gangs required from 2-4-8 for such a setup.

hi very interesting
to try to keep the circuit as simple ad possible which option could provide better performance in your opinion ?
option 1) buffer/preamp stage followed by the 10K pot
option 2) 10k pot followed by buffer/preamp stage

option 2 seems more popular

 

[restorer-john]

Basically, the levels are increased/decreased in order to maintain the S/N. It's kind of like keeping an A/D converter in its "sweet spot" by either attenuating and amplifying or amplifying and attenuating or just one or the other.

Audio analysers like the Audio Precision and others do the same thing with their ranging. They attempt to keep the applied signal in a range where the A/D offers the best signal to noise and distortion.

 

[gino1961]

Basically, the levels are increased/decreased in order to maintain the S/N. It's kind of like keeping an A/D converter in its "sweet spot" by either attenuating and amplifying or amplifying and attenuating or just one or the other.

Audio analysers like the Audio Precision and others do the same thing with their ranging. They attempt to keep the applied signal in a range where the A/D offers the best signal to noise and distortion.

thank you very much for the kind reply So if i catch it right better the put the buffer at the input and attenuate a stronger signal

 

[MRC01]

...
In other words, if it regulates the signal level at the preamplifier input, it is much worse than if it regulates its level at the preamplifier output. for example, if the smartphone is a signal source and I set it to half the volume and the amplifier has to adapt the signal to the amplifier, it generates a lot of noise

Sure, but it's better yet to take the preamp out of the picture entirely. Put the passive attenuator between your source and the power amp without any preamp at all. This is assuming the gain and impedance matches well enough, which it usually does.

If one wants to keep the preamp, but it has too much gain, then put a simple voltage divider on the preamp outputs. -6 or -12 dB often works well. That's like a ladder attenuator with a single position, no knob, just 2 resistors, like this.

 

[MRC01]

Plenty of preamps where the volume control sits up front of the flat gain/tone/filter/buffer stages, sure.

But there's also a lot of better vintage preamps that used active buffered inputs and low value (~<10k) dual ganged volume pots, where both the input gain stage and the final stage buffer are controlled by the volume. They better maximised the S/N over the full range of volume settings.

I'm not aware of many (or any) new offerings using similar tactics. Mainly due to the proliferation of balanced IPs, which would double the number of gangs required from 2-4-8 for such a setup.

To optimize SNR at all volume settings, it would seem ideal for preamps to have a discrete volume control that changes the resistors in the gain-feedback loop. The volume knob simply changes the gain ratio. It would have to be inverting in order to have gain ratios < 1, but that shouldn't be a problem, you can leave it inverting or have another downstream inverting unity stage at the outputs. I wonder why this is not more common. I suppose it's due to design complexity & expense, but I don't really know.

 

[egellings]

I only used a quality Japanese brand that cost like less than a dollar each. That is all that is required. Capacitive reactance is not better or changed by more expensive snazzy caps.

Once dissipation factor, ESR, ESL and dielectric absorption of a cowpasiture are under control and the value is in tolerance, I'm good to go. A nice thing about stepped attenuators is that at low volume settings, resistor matching between channels becomes important, so that adjustment of volume does not make the channel balance wander as adjustment is made. With stepped attenuators, that's easy to get using resistors of 1% or better. That is hard to get with a carbon or cermet track with slider type attenuator, AKA potentiometer.

 

[KSTR]

The Baxandall Volume Control is pretty much ideal wrt SNR, but restricted to at least 3x max gain to be effective (especially with a linear pot). Balanced output is for free.

 

[MRC01]

To optimize SNR at all volume settings, it would seem ideal for preamps to have a discrete volume control that changes the resistors in the gain-feedback loop. The volume knob simply changes the gain ratio. It would have to be inverting in order to have gain ratios < 1, but that shouldn't be a problem, you can leave it inverting or have another downstream inverting unity stage at the outputs. I wonder why this is not more common. I suppose it's due to design complexity & expense, but I don't really know.

BTW, some DACs and preamps do some variation of this. For example the RME ADI-2 has the "Ref Level" setting, which sets 4 volume levels each 6 dB apart based on gain-feedback, then between those levels uses digital attenuation. The Tascam DA-3000 does the same having 5 reference levels 2-5 dB apart. A pure analog preamp could have 64 reference levels as the volume control.

 

[pma]

So I was thinking about a DACT but they aren't cheap

You will get nothing wrong with the DAC. This is my implementation (10k)

 

[gino1961]

You will get nothing wrong with the DAC. This is my implementation (10k)

View attachment 361591

hi very beautiful indeed I looked at your audio pages but did not find this project
Dact attenuators have the useful benefit of a very compact size I have to check their prices
Speaking of buffer/preamps lately i converted to opamps
I am a Goldmund fan. I had the opportunity to listen to their old Mimesis 27 preamp and i heard the perfection Price was very high however
When I see that they have abandoned discrete circuits to switch to operational amplifiers in the latest models no more doubts
Usually the new designs should improve on the older ones.
OA are very convenient and there are an endless variety of them. Unfortunately the latest models are smd. They should do giant ones.
The main problem for me is to do something without using capacitors on the signal path
Some years I had made a humble line pre with an ad797 per channel and it sounded quite clean
but it had a capacitor at the input and one at the output
so not superclean like the Goldmund

 

[MRC01]

You will get nothing wrong with the DAC. This is my implementation (10k)
...

That's quite nice, looks as clean as the best professional gear. Here's the one I built using dual mono Goldpoint attenuator switches and Vishay/Dale resistors:

 

[mhardy6647]

i am not sure to understand what i mean is that there is a lot of discussion about the best coupling caps but almost never i see lab tests
parts like Mundorf Jensen Audyn Solen etc. I would love to see measurements

If I were smart, I wouldn't mention this at all -- but I am not smart. Ample evidence for that.
DISCLAIMER: Nope, no measurements. Not a one. No lab. Lots of words. Lots of capacitors "tested", though!
and that's why I mention it!

Humble Homemade Hifi - Cap Test

Humble Homemade Hifi - Very high quality loudspeaker kits, components, upgrades, modifications and custom solutions.

www.humblehomemadehifi.com

You have been warned.

 

[gino1961]

That's quite nice, looks as clean as the best professional gear. Here's the one I built using dual mono Goldpoint attenuator switches and Vishay/Dale resistors:

very very nice I guess they must sound pretty great I see often Dale resistors on ebay coming from China I am a little worried by the fake industry
Sometimes seem too cheap to be original

 

[gino1961]

If I were smart, I wouldn't mention this at all -- but I am not smart. Ample evidence for that.
DISCLAIMER: Nope, no measurements. Not a one. No lab. Lots of words. Lots of capacitors "tested", though!
and that's why I mention it!

Humble Homemade Hifi - Cap Test

Humble Homemade Hifi - Very high quality loudspeaker kits, components, upgrades, modifications and custom solutions.

www.humblehomemadehifi.com

You have been warned.

wow thank you very much This must be the Bible of caps
lately i have become more techy
I tend to prefer lab measurements to prose

 

[mhardy6647]

This must be the Bible of caps

For better or for worse.

 

[juliusskinner]

I decided to jazz up my audio setup by adding a DIY attenuator, and man, what a game-changer! It's like going from squinting at a tiny screen to being smack dab in the middle of an IMAX theater – the sound just got way more vibrant and immersive.