Oomph or pressure?

I had this same perceived problem with autoformers and the Lightspeed. A transformer based passive did the trick for me. Some examples off the top of my head are Music First, Electra Fidelity, Silvercore, older Bent Audio units.

is that normal for a passive?

It is a common complaint.

Passive systems, which include transformer volume controls, are a bit too simple to do their job perfectly. That is why you see so many threads about this topic.

If all the parameters surrounding the control are right, it will work pretty good. But getting them right can be a bit of a trick- it depends on the other gear in your system including the cables.

Transformer type controls are different from passive volume controls in that a transformer is used to do the job of volume control- you use different taps to affect the output voltage. The problem is that transformers have to be properly loaded in order to do their job of impedance transformation. The thing is, you're looking for voltage conversion, not so much impedance conversion, and the impedances on either side of the control (source and power amp) are not changing, so its job is made a lot more difficult!

When a transformer is not loaded correctly, it can ring (distort), it may not express its turns ratio correctly and may instead express some of its internal capacitance (which results in non-linear frequency response) and/or it can be rolled off if its load is below what is called 'critical damping'.

For this reason the transformer will need extra switch decks to switch in different value resistors as part of the loading scheme (the source and power amp being the other part of that, and as you might have guessed, its a bit of an uncontrolled variable as amplifier input impedances vary by about 10:1 depending on the amp).

The other part of this is that most people don't realize (including many designers) that the job of an active line stage has four aspects:
1) volume control
2) input switching
3) provide any needed gain
4) control the interconnect cable to minimize its effects on the sound of the system.

It is that last bit that is most widely misunderstood. Most passive systems don't provide any cable control until the volume is turned up (and then the impedance of the source is what is providing the control), which is why you hear a lack of 'oomph' at lower volumes.

IOW, it is quite possible that you can get less coloration with a well designed active line stage.

I have an Intact Audio autoformer that uses the same autoformer as your Emia (assuming you have the copper version, not the silver).  And I also have an Emotive Audio Epifania linestage (modified) which uses a single 12B4 tube per channel.  Coincidentally I have been comparing the two over the past few days for the first time since I got the autoformer last fall. 

In my case, the autoformer and the active linestage sound very, very similar with regard to tonal balance, detail and dynamics.  In terms of tonal balance, the autoformer has a little more weight in the bass and the upper midrange is a bit dark sounding; to my ears the Emotive is just about perfect in tonal balance.  The Emotive has somewhat more refinement and delicate detail in the highs, and it has a more involving, propulsive sound.  The autoformer has a lower noise floor (as in next to no noise).  These specifics aside, on an overall basis the active and passive sound remarkably similar.  

In particular I have not noticed any lack of dynamic "oomph" at lower volumes.  That makes me question whether your source is able to drive the autoformer properly.  I have much experience over the years with resistive passive attenuators and they do have the dynamic reticence that Ralph describes above.  The Emia autoformer does not suffer from that problem.

All of the above is In My Opinion and In My System of course.

Hi Sal,
Thanks for the descriptive comparison of high quality passive and active preamplifiers in your system. Based on your descriptions of sonic characteristics I’d choose the active Epifania (if I could only have one or the other). You found it "more involving " than the passive. Musically and emotionally involvement are critical for my long term enjoyment, this is a must have quality for me.

In my opinion when ever comparing audio components the one that allows/permits more involvement in listening to music is the better component. It seems that the "Emotive Audio" is inappropriately named 😊.
Charles

Charles, I think you got the names confused.  The active preamp is the Emotive Audio Epifania so nothing inappropriate in its name.

I should emphasize that the Emia autofromer is very good by any standard.  I am somewhat splitting hairs by focusing on the differences. 

One final point.  It will take a very good active linestage to surpass the Emia/Intact Audio autoformer.  In my case, the Emotive Epifania started out as an excellent sounding preamp, but I have tweaked it to death over the past 10 years by swapping out different resistors, capacitors, chokes, and wire to find the best sounding combination.  I also eliminated the switching so it is a dedicated single-input linestage.  When I got the autoformer I followed the same approach---no switching, just a single input, and the same wires that I settled on with the Emotive preamp.  So they each have some advantage over your typical commercial products.

52tiger
Emia autoformer as my preamp. It sounds fantastic but one thing I noticed is I have to turn the volume up quite a bit to get any oomph out of it. thanks, Scott

Nothing wrong with having to do that, as Nelson Pass explains below.
Scott, passives rule!!, they are the most transparent/dynamic way of getting the source signal to the amp with control over the volume. Only better is direct source to amp (but you need a level control in the source) 

Nelson Pass,

"We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.

Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.

Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.

What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.

And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp."

Cheers George

And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp.

Precisely the complaint of this thread. Nelson goes on to say:

I suppose if I had to floor the accelerator to drive 55 mph, maybe I’d think the life was being sucked out of my driving. Then again, maybe I like 55. Nice and safe, good gas mileage…

Is impedance matching an issue? Passive volume controls do have to make a trade-off between input impedance and output impedance. If the input impedance is high, making the input to the volume control easy for the source to drive, then the output impedance is also high, possibly creating difficulty with the input impedance of the power amplifier. And vice versa: If your amplifier prefers low source impedance, then your signal source might have to look at low impedance in the volume control.

This suggests the possibility of using a high quality buffer in conjunction with a volume control. A buffer is still an active circuit using tubes or transistors, but it has no voltage gain – it only interposes itself to make a low impedance into a high impedance, or vice versa.

- essentially pointing out the same problems I did earlier in this thread.

Since all digital sources make way too much voltage to clip any amp made, a buffered control is a good idea, as it isolates the volume control from the output, and the buffer circuit helps to control the interconnect cable. Note that Nelson is careful to point out that this is an active circuit. We build similar circuits for customers that don't need the gain (but using tubes with a direct-coupled output).

Yes he does, for amps with low input impedance (<20khoms) that aren’t passive friendly, you need a unity gain buffer (no gain as he infers) and those amps thankfully are very not common place, and are around 5% of the market share. some Class-D and some First Watt, Pass Labs

Any amp that is 33kohm or "industry standard input of >47kohm" or higher is fine for any passive pre without the need for a unity gain buffer.

As for active preamps with gain they are not needed in this world any more, and are a left over from phono days when a preamp needed gain.

Even Pass Labs now has lowered the gain of many of their amps from the common 28-34db, down to the low 20’s, just so his and other high gain preamps can be used with most of the volume range they have, instead of being at 9 o’clock for loud!!

Since all digital sources make way too much voltage to clip any amp made

Not just digital even analogue sources, tuners, phono stages etc etc. Have more than enough voltage to clip just about any poweramp.

Cheers George

Sal,
Autospell got me again! I surely meant appropriately named in referring to the Emotive Audio Epifania. I believe that my post however made it clear that I’m complementing the Epifania and its heightened level of involvement you cited.
Charles 

Hello Ralph, 
I've heard your MP-1 preamplifier with several different amplifiers including my own and find it to be an excellent component.  Could one be ordered by a customer with either no gain or say low gain (10db and less) ?  Just curious. 
Charles 

@charles1dad ,
Are you a manufacturer/designer?
Bob

 I went through a period where I was very interested in passive but ultimately found an active gave me better involvement with the music. I found the passive to lack dynamics and drive in the music basically the same as the complaint in this thread. 
 I do think a passive with the unity gain buffer may be a good compromise as  it's true what atmosphere is saying, there are impedance issues but we do have plenty of game in our systems.

Hi gdnrbob,
I'm not involved in the audio product industry,  just a nappy music lover. I  heard a friend's MP-1 preamp with my 300b SET amplifier and the combination was quite impressive. If I didn't own the superb Coincident Line Stage I could be "very" satisfied with the MP-1.
Charles 

The term “passive” is an unfortunate one since it includes both resistor-based attenuators and magnetics such as transformers and autoformers.  The complaints often leveled against “passives” relate to problems with dynamics and drive, as others have mentioned, but those complaints pertain to resistor-based passives, not magnetics.  At least that has been my experience.

The OP, however, raised similar complaints about his autoformer, something I have not experienced with mine or heard about from other users.  That’s why I questioned whether he may have a problem with inadequate drive from his source.

I don’t think that’s the issue, it does seem like I have to turn the volume up to around 2 or 3 to get it to have that fullness or pressure in the room.

I will say this is by far the best passive I have had and I have tried a few.

i actually went to a passive because of my system and only. Being able to barely turn the volume knob with the active preamps I have had.

my amp is different now in that it has a volume knob so some gain can be thrown away at the amp end.
 
My question was mainly if with the right setup can I get room filling pressure at a lower volume.

but this Emia is quite something to hear, may just keep it and try some other options

The complaints often leveled against “passives” relate to problems with dynamics and drive, as others have mentioned, but those complaints pertain to resistor-based passives, not magnetics.

I have resistive, opto-coupler, photo cell, transformer, autoformer, and potentiometer passives. While I admit paying attention to impedance matching is important to maintain dynamics and drive, you can have those issues with any of the passive topologies, singling out resistive passives as a problem child is just plain silly. FWIW I also have Atmasphere MP-3 and Beveridge RM-1/RM-2 active preamps. My passives give up very little to nothing against them.

52tiger - I was curious about your question and if it is sufficient volume level to load the room then just turn it up. I operate my passives anywhere from 1 to 3 o'clock on the control. Slage's autoformers are well made. I have a set and they measured very well. Enjoy your Emia.

Clio09 - You have more experience so maybe my generalization was wrong.  The Emia/Intact Audio autoformer is the only magnetic attenuator I have tried.