Passive/Active

I see a lot of guys going through rounds of speakers, amps, preamps, dacs in the quest for the perfect sound. Or at least the sound they could finally be happy with.

But the sound they wanted could have been in front of them all the time.

The fact is, there is no perfect sound, we all hear, and seek different audio nirvana.

What I consider important to sound quality, you may dismiss in favour of some other aspect, and that is perfectly correct, audio is personally subjective.

There are many ways to voice a loudspeaker, from monitor quality, accurate frequency speakers for studio use to romanticly flavored midrange accentuated ear pleasers.

But no speaker will sound exactly as the designer intended in every room, or system.

There are so many variables that affect the sound,  that a speaker can sound vastly different from room to room,  and system to system.

One way to get closer to the sound that suits you is to actively drive the speakers individual drivers , thus providing some adjustment to tonal balance, with other important advantages.

I'll describe a couple of my own passive/active systems to explain.

Btw passive /active means the original passive crossovers are retained but split so they can be driven by a set of amps. So a two way speaker would have 4 amplifier channels, and a 3 way would have 6 channels.

Fully active means no passive crossover and crossover done by electronics, either digital or analogue.  This can give even more control over the sound, at some compromise.

I have an old set of AR-LST speakers , a legendary speakier that has a reputation for excellent sound, but difficult to drive and match to an amplifier.
It is a 3 way speaker, but with 9 drivers per speaker, and a rather complicated crossover.
In stock form it needs a very capable amp with lots of power , yet high quality as it is very revealing.
I could never get it to sound quite like I wanted, so decided to run it actively, to see if  I could manipulate the sound into shape.
I had to modify the crossover so that an amplifier could be connected to each of the bass, midrange and treble sections.

While I was there I replaced some of the older electrolytic caps for more reliable and accurate polyprop caps.

3 sets of amplifier connectors, split crossover sections.

Now that the load to each amp was now only a single section rather than the complete crossover,  it is much easier to drive, and I can even use low power tube amps for the mid and treble sections,  giving a much nicer and realistic sound.

But the real advantage is that now I can adjust the levels of each amp and the balance of the overall tone of the speaker.
It takes some time, and persistence, but there will come a result of each amps level adjustment that will result in the perfect combination of room and speaker , and your own taste, that will be very pleasing.

You will find that there is much more distinction between the bass ,mid and treble. They will have more entity and seperation, more openness,  you will simply hear more as you now have  amplifiers operating with specific and achievable functions.

I think this is one of the most rewarding ways to achieve good sound, you are actually making major changes to the speaker/room/taste equation, rather than wasting money on cables, equipment,  or another set of speakers.

You need a good preamp that can easily drive 3 sets of amps, a Supratek of course.

Digital or analogue active crossovers give even more control over the sound, with the ability to do room EQ , crossover frequencies and slopes. But apart for bass applications I'm not a fan of fully active systems, they always sound compromised to me, although maybe essential with a really difficult room/speaker.

Many speakers these days have jumpers on the crossover connections , especially 2 way speakers , so that they can be bi-amped, but it seems few take advantage of this excellent opportunity to customise the sound to your own ears.

Ive been building the Dual Cabernet preamp, with this specific purpose in mind, for years now, but sadly few seem to see the obvious advantages.

My Acoustat 2+2 electrostatic speakers have two panels per speaker , one bass and one treble.

Each panel is driven by a very high power amp, which stats need, so 2 amps for each channel.

I use a Dual Cabernet preamp which has a level control for the second preamp section , which is used for the bass amp.
The master volume control adjusts the overall volume and the level control for second preamp section adjusts the bass panel amplifier level.
The Acoustat is very sensitive to this adjustment and even fine adjustments can make a big difference to the tone and overall quality of sound.

Its hard to site a 7'10" tall speaker that needs to be a fair distance from rear wall, and this precise form of level control is very useful.

But any speaker that can be bi-amped will immediatly be transformed by using the Dual Cabernet and an extra set of amps.

I'd suggest you could spend a pile of money to get an expensive new pair of speakers , that still wont get you where you want to be, when going to bi or triamping will give you exactly what you want.

NOS 6SN7 Tubes

The 6SN7 and its derivatives 6H8C, ECC33, CV1988, CV181, VT-231, 5692 are excellent tubes and eagerly sought by tube enthusiasts after the "best" sound.

I've been buying 6SN7's for more than 30 years and have hundreds of them, with examples of all of the above.

So what is my personal preference , what is the Holy Grail of 6SN7's?

Well maybe surprisingly I'm not that keen on old NOS tubes, mostly because most of them are not NEW OLD STOCK.

The only way you can be sure that a tube from the period 1930- 1980 is a genuine NOS tube is if it comes in a sealed box that has not been opened .

Anything you buy from ebay is suspect, even genuine tube sellers really have no way of knowing if a tube has ever been used or not, or how many hours, and under what sort of operating conditions a tube has been used.

They like to assert quality by using a tube tester and give some vague measurement that really doesn't mean anything.

Quite often the tube tester is more than 50 years old and long past its use by date.

The only way to tell if a NOS tube will give optimum service is to actually measure it in the circuit it is being used in.

Gain and channel balance can be checked and if its a highly sophisticated circuit like the Supratek, the operating parameters can be adjusted for perfect performance. On the proviso that the tubes were in excellent condition to start with.

New production tubes aren't that exciting, the current Sovtek and Chinese 6SN7's aren't bad, but they aren't quite as good as the tubes made when cost cutting wasn't more important than quality.

The tubes I use in my preamps are Russian military NOS tubes with OTK certification.
I buy them in boxes of hundred , never used and they have what I value the most, near identical parameters and performance. They are constant and I know they will work as they are intended to.
You get the occasional bad one, but it would be less than 1 in a 100. And they are all checked in circuit to ensure the preamp has identical performance in each channel.

This is very important for phase response and resultant sound-staging.

Ever wondered where the imaging and sound-staging went with that pair of warm sounding NOS 6SN7 you bought off ebay?

Most likely the tubes are operating quite differently from each other and there is a mis-match between channels.

NOS 6SN7, particulary the early ones from 1930 on are usually microphonic, sometimes quite badly .

Some of the 6SN7 derivatives like the CV181 and the ECC33 aren't  really 6SN7s. They have different plate resistances and will give quite different electrical voltages in a circuit designed for 6SN7's.

This can result in different operating points and distortion figures , which might sound "warmer" or "romantic" .

Nothing wrong with that if it is pleasing to the ear, but it is not what the preamp was designed for.

So playing around with NOS 6SN7's can be a minefield, sometimes you'll get a blast you like, sometimes your shooting yourself in the foot.

Lyrics

Howard got it- Jane Siberry's "At the Beginning of Time"

An otherworldly , spiritual artist that really got to me a long time ago.
Not so much into her now, and I do wish her splendid works were better recorded, but I do still very much like this song.

Here's the complete song, I've never been much into classical poetry , but this is nice.

Tomorrow I'll talk about the NOS 6SN7 tubes I'm sending Howard.

At the beginning of time
Before there were waves
We'd sit in our boats
We'd float there all day

And there weren't any waves
'cause there wasn't any wind
'cause there wasn't any sun
We were waiting for the world to begin

We were waiting in the darkness

Each in our own boat
Each in our own thoughts
Sometimes you could hear people
Talking amongst themselves but...
(someone had a boat with wheels and I said
You're a bit early but I know how you feel)
But mostly it was just silence

And the silence only broken by
The absence of the clinking of the masts
And every now and then a bird would not fly by
And someone would look up and say
What wasn't that ?

We were waiting in the darkness

And one night (or was it day?)
I was awoken from a dream
I was dreaming of someplace like I'd never been
And I heard someone say
Someone's fallen in and they can't swim
So I leaned out and I pulled them in
And he was holding his head
And it was huge and shaped like a fish
And he slid down to the crook of the keel
And when I was sure he'd fallen asleep
I fell back to my reverie

We were waiting waiting waiting
Waiting in the darkness

And you know what I miss most about that time?
It was the quality of blackness
It was soft somehow
In the absence of fear
You could take it into your mouth
And send it out through your teeth
My dear

But the silence...
Oh, if I could go back to those times
I'd take that silence there
I'd take it into myself and bring it back to you
And this is what I'd say

Waiting in the darkness

At the beginning of time
Before there were waves
We'd sit in our boats
We'd float there all day
(or was it night?)

And there weren't any waves
'cause there wasn't any wind
'cause there wasn't any sun
We were waiting for the world to begin

We were waiting for the world to begin

Now?

No.

Songwriters: JANE SIBERRY

At The Beginning Of Time lyrics © Universal Music Publishing ARE YOU UP TO DATE WITH THE MOST AMAZI

And now for something completely different....

First person to name the song and Artist from these lyrics gets a pair of NOS 6SN7 tubes from my stash .
Email me at supra@supratek.com.au if you know the answer.


"And the silence was only broken by
The absence of the clinking of the masts
And every now and then a bird would not fly by
And someone would look up and say - what wasn't that?"

Preamp Gain

All the Supratek preamps have high , greater then 20dB, gain.
There's a pretty simple reason for this, it simply sounds very much more dynamic and realistic than a low gain preamp.
The 6SN7 triode tube is a dual triode, it has two separate sections, independent of each other, except for the heater.
In the Supratek preamps the two sections are cascaded, the first section is the input, the second section is the output.
This results in more gain than a single section, although the total gain is reduced by a step down output transformer, and the circuit design.
I've never heard a single section with the dynamics and ease of a cadcaded design.
The high gain can be a nuisance with many of todays power amps, as they often have high gain themselves,  a power amp should just convert gain into current , but too many power amps are designed more as integrated amps than dedicated power amps.
This is usually so they can be used directly with a CD player , and no preamp, just about the worst sound quality you can get.
So with a high gain power amp and a high gain power amp,  there will be a lot of gain, with the volume control at 9 o'clock or less.
There may also be a problem with noise as with such high gain the noise floor will be amplified.
I still would rather put up with a bit of noise (which you wont hear when the music is playing anyway) than listen to the dull and boring sound of a low gain preamp.
Obviously the best way is with a high gain preamp and a power amp with reasonable gain structure,  avoid those high gain power amps,  which are just integrated amps anyway!
Recent models of the Cortese preamp have  a gain control to fine tune the gain if necessary. It is switchable and can be completely switched out of circuit , but handy if you do need to use a high gain power amp.