Budget passive preamp with stepped attenuator?

[Deleted member 58865]

Most likely ... yes but have no idea how this is done here.

I think you are complicating a simple thing. If I can't feel a tingle on the metal case and can't measure electric field around the metal case, then it is grounded to something.

In most cases, the ground is the outlet ground. I don't know what you exactly mean by safety ground. But, I know there is such a thing as outlet ground.

If something is not grounded, my EMF measuring device will pick up electric field around it. Simple.

ME3830B picks up 100V/m or more for floating circuits and =<2V/m for grounded circuits.

 

[Deleted member 58865]

3dB steps are kind of 'coarse' as a volume control but it will be fine for attenuating to a certain attenuation level.

For fine 1dB adjustments, I can use DAC volume. Then, application volume will kick in for per-application volume levels.

 

[solderdude]

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This one (RK27) is not connected to audio ground at all so there will be no 'tingling' feeling when touching the enclosure.
The stepped one also does not appear to have audio ground connected to the enclosure so here too you will not feel anything.

No idea what you will be measuring when the meter is close to the RCA cables and the volume knob and how reliable/accurate it is and what relevance it has.

 

[Deleted member 58865]

This one (RK27) is not connected to audio ground at all so there will be no 'tingling' feeling when touching the enclosure.
The stepped one also does not appear to have audio ground connected to the enclosure so here too you will not feel anything.

I don't know what you mean by audio ground. If I connect a metal case to a rod inserted into the ground of a rural barn that has no high EMF equipment nearby, does it qualify as audio ground?

I know for a fact that a high EMF equipment can contaminate areas of land around it.

 

[Deleted member 58865]

A passive pot or switched resistors only has 0 db gain at max volume.

In amir's review of Schiit Sys, 0dB gain was found at 3'o clock. Someone said AIYIMA A07 volume pot would have 0dB gain at 3'o clock, too.

 

[solderdude]

The enclosure is NOT connected to safety ground (the metal rod inserted deep into the ground).
Safety ground is NOT audio-ground. It ensures that when a voltage opposite neutral (which should be connected to safety ground locally) makes contact with the ground the voltage on it stays below safe limits till the fuse blows.

The attenuator box is not connected to anything so will only be capacitively coupled to 'physical ground' and will have the same voltage level when you touch it as yourself.
See the enclosure as class-II (double isolated) so safe to touch. At least up to several kV.
It will also have a capacitive coupling to the RCA common (audio ground) because of the PCB layout. That will only be RF though and not more than several pF.

I have done quite a few EMC measurements in the field and EMC lab.... contaminate ? You might mean RF fields being present ?

 

[Blumlein 88]

In amir's review of Schiit Sys, 0dB gain was found at 3'o clock. Someone said AIYIMA A07 volume pot would have 0dB gain at 3'o clock, too.

I'm sorry, you don't understand how these work, and I am unable to explain it to you. Passives never create gain. The review shows near +6 db at max level, but that can only be if a higher signal level was sent thru it. I'll bow out of this thread as I don't appear to be helping.

 

[solderdude]

In amir's review of Schiit Sys, 0dB gain was found at 3'o clock. Someone said AIYIMA A07 volume pot would have 0dB gain at 3'o clock, too.

At max. setting Amir seems to have measured +5.5dB but that is only compared to a set level for '0dB'.
At 3 o' clock Amir actually measured -5.5dB (or close to it) and was probably 1V or so (for 0dB he might have set 1V as reference) with about 2V in (which would be +6dB referenced to 1V)
0dB attenuation is reached at the max volume in an electrical sense.
If Amir had used the max. volume setting value as reference it would simply only have shown attenuation below 0dB. It is a 'reference level' thingy.

Passives pre's CAN create gain but use (auto)transformers which also change the impedance, are BW limited and are sensitive to source and load impedance.
Attenuators (the pots, relay ones and stepped ones) ONLY attenuate.

All (especially cheap) potmeters have a resistance track and near its end this becomes a normal conductive track (where the pins can connect to).
This means the 'ends' of those volpots show no variance.

The bigger the track (think RK27) the smaller this area. The smaller the pot the relatively bigger this 'no action' area and is one of the reasons the channel imbalance happens at the max. attenuation point.
Stepped and relay attenuators do not have this.

What Blumlein says is that there is quite a lot of production spread in those cheap used small potmeters. So it is a crapshoot near the extremes. Also these cheaper pots will start to scratch after a few years (depends on several external factors).
So what Amir measured is NOT representative for the one you might be buying or someone else owns.

 

[Deleted member 58865]

Okay, I just watched

Audio ground is the destination for audio signal. Earth ground is the destination for noise and anything that's not audio signal.

Balanced connections like XLR have a separate wire for earth ground. RCA has to carry earth ground, too. That' s why RCA can pick up EMF noise from the air or the house wires if you are not careful.

 

[solderdude]

Funny how you think you know what audio ground is and 'does'.

Audio ground is also known as 'common' or 'return' or 'reference'. It is what the audio signal is referenced to (signals are always between 2 points, those can be reference or, in case of balanced, the opposite voltage).
Shielding is also called 'ground' by many and may or may not be connected to 'reference' and/or safety ground.
Then we have 'floating' which is not connected to any ground (the enclosure of the mentioned attenuator and of class-II mains gear) so there can be no direct path to any ground.
Earth ground is physical ground you walk on and is not connected to safety ground directly but can form a capacitive path where 'signals' can find an (un)wanted path.
Safety ground is the metal rod in the ground that is there to ensure metal parts connected to it you can touch can never have lethal voltages on it when something inside such mains connected devices fails horribly. It does NOTHING for EMC/RF etc. as a wire is basically an inductor which is a high resistance for RF.

 

[Deleted member 58865]

What Blumlein says is that there is quite a lot of production spread in those cheap used small potmeters. So it is a crapshoot near the extremes.

So, it's best to keep a volume pot at a fixed position like 12'o clock or 3'o clock between extremes for minimal channel imbalance?

 

[solderdude]

the 3 o'clock is technically (for a log-type volume control) the 'worst' setting as the 'resistance' is highest there (1/2 the resistor track and 1/4 the track resistance when connected to a low impedance source). For a linear level control the -6dB setting is at 12 o' clock. For channel imbalance it is probably one of the 'best' settings (depends on build quality)

You set it to 3 o'clock, 12 o' clock or any other position when you need that attenuation.

Channel imbalance is worst near the maximum attenuation (near full counter clock wise setting) and is totally dependent on the mechanical construction of the device that does the attenuation.
So anything above 8 o'clock should be fine (when 7 o'clock is max anti-clock wise) but this is component dependent.

 

[Deleted member 58865]

I just read https://mynewmicrophone.com/what-is-amplifier-ground-where-to-ground-an-amplifier/

I now know what audio ground is. It is another name for signal ground. Signal ground can be connected to chassis ground and earth ground.

 

[Deleted member 58865]

the 3 o'clock is technically (for a log-type volume control) the 'worst' setting as the 'resistance' is highest there (1/2 the resistor track and 1/4 the track resistance when connected to a low impedance source). For a linear level control the -6dB setting is at 12 o' clock. For channel imbalance it is probably one of the 'best' settings (depends on build quality)

You set it to 3 o'clock, 12 o' clock or any other position when you need that attenuation.

Channel imbalance is worst near the maximum attenuation (near full counter clock wise setting) and is totally dependent on the mechanical construction of the device that does the attenuation.

So, where do you recommend keeping the amp volume pot at if I insert a stepped attenuator between DAC and amp?

 

[solderdude]

I prefer a usable range between 8 o'clock and 3 o'clock when using a decent pot as volume control where 3 is quite loud and 8 is soft sound (below background level)
To create that the correct gain of all devices is important as is the sensitivity of the used transducers.
My preference is not important though.

When using an extra attenuator to 'cure' channel imbalance of the 'regular volume control' or to 'cap' the maximum desired SPL you set the 'extra attenuator' so that the max. volume you need is reached at the 'max volume' setting.
Or the other way around... use the attenuator as volume control and set the 'volume control' of the amp to the max desired volume level.
That should also eliminate channel imbalance issues at the bottom side of the regular volume control range.
When it doesn't the volume control pot is a bad one and needs replacing with a better one.

 

[Deleted member 58865]

When it doesn't the volume control pot is a bad one and needs replacing with a better one.

I don't want to desolder a bad volume pot and solder a stepped attenuator in an amp. That can break my amp. That's also too much work that can be avoided by just inserting a stepped attenuator between DAC and amp.

I'd rather just attach a stepped attenuator between DAC and amp.

Really, amp manufacturers should start putting stepped attenuators in their amps and let customers use DAC volume for fine adjustments.

I hate volume potentiometers.

 

[solderdude]

Rather... manufacturers should put quality potmeters in amps (regardless if chip based or multiple gang), then there is no need for stepped volume controls.
Ladder potmeters and chip potmeters are easier to include remote control. A motor and drive on a regular volpot is much more expensive but possible.

Cheap amps will have cheap potmeters because... well... they are manufactured with cheap components.
The Ayima is a very cheap so that explains some of the things you ran into (leakage, enclosure connected to audio ground). You get what you paid for in essence. You can't sit front row for cheap in the world of electronics when it concerns quality. You can when it comes to more than decent technical performance but not for longevity and build quality. Something has got to give.

A solution could be to use an external volume control.
I think, when exploring this option, the best method is to go for 10k RK27 attenuator. It will outlive the Ayima and prevents possible costly errors that could occur when using a DAC and digital volume control.

Neither is 'better' but the external volume control is safer, has a better 'feel' when adjusting the volume and good adjustment range.

RK27 would be preferred over stepped as a volume control. Stepped would be preferred if you want to use the volume control on the Ayima.

 

[Zek]

10k RK27 attenuator

What is this actually, an Alps RK27 Potentiometer or a Stepped Ladder-Type Attenuator?

 

[Deleted member 58865]

RK27 would be preferred

It would have channel imbalance at low volume levels, would it not?

 

[Sokel]

It would have channel imbalance at low volume levels, would it not?

The four gang motorized one of those in my pre is as accurate as it gets,I know that for a fact cause I use it to set the electronic xover at 50-100mV level usually so I set unity gains,etc.
The most difference I have seen is down to 1mV and even that is rare.