Neve "clones"

[Federico]

Hi,
I'm deep into digital multitrack recording. I have a "portable" recording
studio and I record different projects in different places.
I record digital and mostly mix in the box.
I have been using different mic preamps during the years and I realized that
I am more on "colored" sounding ones.
So I'd like to have 24 channels of colored preamps.

Question 1:
I see that "colored" pres are very often single ended, class A with in and
out Xformes.
Are there other circuit typologies?

Question 2:
I am not rich and I can't afford 24 channels of Neve, Vintech and similars.
Even API and OSA are still expensive.
I am considering some "DIY" options like Seventh Circle Audio N72
http://www.seventhcirclestudios.com/SCA/SCA.htm or HamptoneHJFP2
http://www.hamptone.com/HJFP2.htm
Since one channel is around $300 the question is... Do they really sound
like a Neve 1073? Or they are missing something?
The price difference is it all on marketing and hype?

Thanks for your replies.
F.

[Ian Bell]

Federico wrote:
> Question 2:
> I am not rich and I can't afford 24 channels of Neve, Vintech and
> similars. Even API and OSA are still expensive.
> I am considering some "DIY" options like Seventh Circle Audio N72
> http://www.seventhcirclestudios.com/SCA/SCA.htm or HamptoneHJFP2
> http://www.hamptone.com/HJFP2.htm
> Since one channel is around $300 the question is... Do they really sound
> like a Neve 1073? Or they are missing something?


The big question is what makes a Neve sound the way it does? When they were
built, the idea was not to create a certain 'sound' but to provide
distortion free amplification as far as possible. I worked there in the 70s
and I can tell you transformers for instance were rigorously checked and
discarded if their distortion was too high (usually at low frequencies).
The simple three transistor class A preamps used are not the lowest
distortion possible by any means, but the topology does tend to produce
predominantly second harmonic (i.e. musical) distortion. The output stage
used a similar topology but with a bloody great 2n3055 in the output stage
and a huge transformer - much bigger than the ones in the references you
cited. Neve module typically used Tantalum bead interstage coupling
capacitors, supposedly frowned upon these days by audiophiles as they
create too much distortion.

Whether modern 'clones' fully emulate the Neve originals is hard to tell.
In the end, only your ears can tell.

Ian

[Scott Dorsey]

In article <44fc2ce9.0@entanet>, Ian Bell > wrote:
>
>The big question is what makes a Neve sound the way it does? When they were
>built, the idea was not to create a certain 'sound' but to provide
>distortion free amplification as far as possible. I worked there in the 70s
>and I can tell you transformers for instance were rigorously checked and
>discarded if their distortion was too high (usually at low frequencies).
>The simple three transistor class A preamps used are not the lowest
>distortion possible by any means, but the topology does tend to produce
>predominantly second harmonic (i.e. musical) distortion. The output stage
>used a similar topology but with a bloody great 2n3055 in the output stage
>and a huge transformer - much bigger than the ones in the references you
>cited. Neve module typically used Tantalum bead interstage coupling
>capacitors, supposedly frowned upon these days by audiophiles as they
>create too much distortion.

Most of the coloration in the old Neve consoles came from the transformers
in the front end (which were as uncolored as it was possible to get at the
time, but not as uncolored as it's possible to get a transformer today... and
even the best of transformers are colored) and from those tantalum caps.

I once recapped a channel strip on a studio Neve with film caps... it sounded
so much better... everybody else hated it... I almost got fired.

I'm not sure that the actual transistor stages make all that much of a
contribution to the sound (unless you overload them, which does seem to be
a depressingly fashionable thing to do). But the single-ended topology
means that there are a whole lot of coupling caps in the signal path.

>Whether modern 'clones' fully emulate the Neve originals is hard to tell.
>In the end, only your ears can tell.

And the other question is whether you want to emulate it precisely or not.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Federico]

> And the other question is whether you want to emulate it precisely or not.
> --scott

I don't really need to emulate any Neve preamp.
I just don't want to get stuck with some "fake-old-sounding" stuff.
Just like the "tube" preamps that are selling for $100/channel.

I'm wondering if a preamp that cost about $300/channel (plus the power
supply and case) can stand against a $1500/channel Neve 1272....
Or if there is something in its design that may not work properly.
As Ian Bell said in this thread:"huge transformer - much bigger than the
ones in the references you
cited" it gives me the idea of what the difference can be....
F.

P.S: Thanks Ian!

[Scott Dorsey]

Federico > wrote:
>
>> And the other question is whether you want to emulate it precisely or not.
>
>I don't really need to emulate any Neve preamp.
>I just don't want to get stuck with some "fake-old-sounding" stuff.
>Just like the "tube" preamps that are selling for $100/channel.

So listen before you buy. If you like how it sounds, buy it.

Even those fake tube preamps can occasionally be useful to dirty-up a
bass DI feed.

>I'm wondering if a preamp that cost about $300/channel (plus the power
>supply and case) can stand against a $1500/channel Neve 1272....
>Or if there is something in its design that may not work properly.
>As Ian Bell said in this thread:"huge transformer - much bigger than the
>ones in the references you
>cited" it gives me the idea of what the difference can be....

Well, the 1272 didn't used to be $1500/channel.... twenty years ago you
couldn't give those things away. Now they are fashionable and they sell
for a lot of money.

Look inside the $300/channel preamp and see what's in there. So much of
the sound is the transformer and the power supply. If it has a good
transformer and good power supply, it'll probably sound good.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Federico]

> Look inside the $300/channel preamp and see what's in there. So much of
> the sound is the transformer and the power supply. If it has a good
> transformer and good power supply, it'll probably sound good.
> --scott

That's a good thing to know. SCA power supply delivers 30V vs. 24V of the
Hamptone, so more headroom if I'm not wrong.
For the schematics... Here's the neve
http://members.nuvox.net/~zt.robgrow/circuits/neve/neveba283.html
And here's the SCA http://www.seventhcirclestudios.com/SCA/SCA.htm
I think that the word "similar" it's just an euphemism....
F.

[Federico]

Sorry, the right one for SCA is
http://www.seventhcirclestudios.com/SCA/N72/docs/n72_sch.pdf
F.

[Ian Bell]

Scott Dorsey wrote:
>
> Most of the coloration in the old Neve consoles came from the transformers
> in the front end (which were as uncolored as it was possible to get at the
> time, but not as uncolored as it's possible to get a transformer today...
> and even the best of transformers are colored)

What improvements have been made in transformers in the intervening 30
years?

Ian

[Ian Bell]

Federico wrote:

>
>> And the other question is whether you want to emulate it precisely or
>> not. --scott
>
> I don't really need to emulate any Neve preamp.
> I just don't want to get stuck with some "fake-old-sounding" stuff.
> Just like the "tube" preamps that are selling for $100/channel.
>
> I'm wondering if a preamp that cost about $300/channel (plus the power
> supply and case) can stand against a $1500/channel Neve 1272....
> Or if there is something in its design that may not work properly.
> As Ian Bell said in this thread:"huge transformer - much bigger than the
> ones in the references you
> cited" it gives me the idea of what the difference can be....
> F.
>
> P.S: Thanks Ian!

I think the answer is the only way to get the Neve sound is with a Neve
module. Other designs try to do the sort of things that Neve designs do in
the hope of recreating the sound. As I said, in the end only your ears can
judge. If anyone tries to sell you a preamp but won't let you audition it
then its time to walk away.

Ian

[Scott Dorsey]

In article <44fdf2cc.0@entanet>, Ian Bell > wrote:
>Scott Dorsey wrote:
>> Most of the coloration in the old Neve consoles came from the transformers
>> in the front end (which were as uncolored as it was possible to get at the
>> time, but not as uncolored as it's possible to get a transformer today...
>> and even the best of transformers are colored)
>
>What improvements have been made in transformers in the intervening 30
>years?

Depends on what you consider an improvement.

If you want a clean and uncolored transformer, a lot of things have been
improving. Better core designs, mostly the result of computer modelling
of magnetic fields. Better core materials, including mu-metal and amorphous
iron, neither of which was commercially viable thirty years ago. More
consistent wrapping (due to high speed machines designed for small motor
work, in part). In the case of larger transformers, square magnet wire
has been a recent innovation.

BUT, if you want colored transformers that sound just like classic ones,
that's a problem. And it's a problem because many of the older materials
that were once commodity items are gone. It's a problem because the market
for commodity transformers is gone or going away, so everything is now having
to be done in small batches without the economies of scale that we saw thirty
years ago.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Ian Bell]

Scott Dorsey wrote:

> In article <44fdf2cc.0@entanet>, Ian Bell >
> wrote:
>>Scott Dorsey wrote:
>>> Most of the coloration in the old Neve consoles came from the
>>> transformers in the front end (which were as uncolored as it was
>>> possible to get at the time, but not as uncolored as it's possible to
>>> get a transformer today... and even the best of transformers are
>>> colored)
>>
>>What improvements have been made in transformers in the intervening 30
>>years?
>
> Depends on what you consider an improvement.
>

Well I was responding to your comment about transformers being less coloured
today. I was hoping you would be able to say in what way there were so -
better frequency response, distrortion etc.

> If you want a clean and uncolored transformer, a lot of things have been
> improving. Better core designs, mostly the result of computer modelling
> of magnetic fields. Better core materials, including mu-metal and
> amorphous
> iron, neither of which was commercially viable thirty years ago.

I am certain mu-metal was around over 30 years ago.

> More
> consistent wrapping (due to high speed machines designed for small motor
> work, in part).

They were around too 30 years ago.

> In the case of larger transformers, square magnet wire
> has been a recent innovation.
>

Interesting, what improvement does that give?

> BUT, if you want colored transformers that sound just like classic ones,
> that's a problem. And it's a problem because many of the older materials
> that were once commodity items are gone.

Such as?

> It's a problem because the
> market for commodity transformers is gone or going away, so everything is
> now having to be done in small batches without the economies of scale that
> we saw thirty years ago.

I suspect the economies of scale were not huge even then. A typical Neve
desk had 3 per channel strip and and two per group so a 40 channel 16 group
desk would have about 150 transformers. I doubt we made one of those a week
so that's less than 10,000 a year. Even in those days there were a lot of
manufacturers doing essentially transformerless designs e.g. Cadac so I
suspect the total market was no more than 100,000 a year (in the UK that
is).

Ian

[Predrag Trpkov]

"Ian Bell" > wrote in message
news:44fe85e7.0@entanet...
> Scott Dorsey wrote:

> > It's a problem because the
> > market for commodity transformers is gone or going away, so everything
is
> > now having to be done in small batches without the economies of scale
that
> > we saw thirty years ago.
>
> I suspect the economies of scale were not huge even then. A typical Neve
> desk had 3 per channel strip and and two per group so a 40 channel 16
group
> desk would have about 150 transformers.


It's three transformers per channel amplifier module. There was at least
another transformer in the routing module. So it's at least four per channel
strip. Every output had line amp modules (1272, 3415) with two transformers
each - aux sends, 2-buss, talkback, pfl, oscillator etc. There were line amp
modules (3416) with two transformers each on the additional inputs - monitor
returns, 2-track returns etc. Such a desk would have well over 200
transformers.

Predrag

[Scott Dorsey]

In article <44fe85e7.0@entanet>, Ian Bell > wrote:
>Scott Dorsey wrote:
>
>Well I was responding to your comment about transformers being less coloured
>today. I was hoping you would be able to say in what way there were so -
>better frequency response, distrortion etc.

All of the above. You can get transformers today with better linearity,
wider frequency response, better impulse response, and you can get output
transformers today that are MUCH less sensitive to loading than the older
designs. The need for termination switches on the back panel is pretty
much gone.

>> If you want a clean and uncolored transformer, a lot of things have been
>> improving. Better core designs, mostly the result of computer modelling
>> of magnetic fields. Better core materials, including mu-metal and
>> amorphous
>> iron, neither of which was commercially viable thirty years ago.
>
>I am certain mu-metal was around over 30 years ago.

Mu-metal was a WWII development, but it's only been recently that cheap
mu-metal fabrication has been possible. The problem is that you need to
stamp out the stuff from sheets of alloy, then anneal it after stamping.
But when you anneal it, the size changes. If you machine it to size, you
need to reanneal it.

I'll point out that mu-metal has also improved tape head performance a
bit too. The modern Flux Magnetics heads have much better low end than
the old Ampex heads, for instance.

>> In the case of larger transformers, square magnet wire
>> has been a recent innovation.
>
>Interesting, what improvement does that give?

Tighter wraps with no gaps between wires. It's just solid metal all the
way down. So the winding actually takes up a smaller amount of space
and has less distributed capacitance as well. Take a look at the Manley
Labs output transformers, for instance.

Back in the sixties, Electrocube started making foil-wound transformers
for military applications and the military and aerospace guys were doing
square core stuff by the early seventies. But it didn't start becoming
available for the average audio equipment user until quite recently.

>> BUT, if you want colored transformers that sound just like classic ones,
>> that's a problem. And it's a problem because many of the older materials
>> that were once commodity items are gone.
>
>Such as?

All of the old core materials are gone. There used to be all kinds of soft
iron materials available, which nobody wants today except a few audio guys.
That's why none of the Pultec clones sound like actual Pultecs... it's a
real nightmare to try and replicate those inductors because the original
core material was the cheapest possible commodity junk in the fifties, and
today it's no longer made.

>> It's a problem because the
>> market for commodity transformers is gone or going away, so everything is
>> now having to be done in small batches without the economies of scale that
>> we saw thirty years ago.
>
>I suspect the economies of scale were not huge even then. A typical Neve
>desk had 3 per channel strip and and two per group so a 40 channel 16 group
>desk would have about 150 transformers. I doubt we made one of those a week
>so that's less than 10,000 a year. Even in those days there were a lot of
>manufacturers doing essentially transformerless designs e.g. Cadac so I
>suspect the total market was no more than 100,000 a year (in the UK that
>is).

Those Neve desks were built with transformers from Marinair, a company
that mostly made transformers for marine radio, intercom, and radar
systems. Neve was a small customer for them.

Back then, every table radio had an output transformer, and they had a bunch
of IF transformers. Every TV set had dozens and dozens of wideband
transformers and inductors in the sweep circuits. Intercoms, military radio
gear... everything was chock full of transformers. The audio folks were
a tiny fraction of the market and were basically piggybacking on top of
a much larger market for wideband transformers. That much larger market is
gone. Look inside a TV set today and the only magnet wire you'll see is
in the yoke and flyback... at best you might see a couple ferrite power
transformers.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Ian Bell]

Predrag Trpkov wrote:

>
> "Ian Bell" > wrote in message
> news:44fe85e7.0@entanet...
>> Scott Dorsey wrote:
>
>> > It's a problem because the
>> > market for commodity transformers is gone or going away, so everything
> is
>> > now having to be done in small batches without the economies of scale
> that
>> > we saw thirty years ago.
>>
>> I suspect the economies of scale were not huge even then. A typical Neve
>> desk had 3 per channel strip and and two per group so a 40 channel 16
> group
>> desk would have about 150 transformers.
>
>
> It's three transformers per channel amplifier module.

Well its 30 years since I worked there so memory could be faulty but IIRC
channel amps had two - one at the input and one at the insert point. The
routing module had one at its input which makes three per channel.

1272 line amps were for mixing so there was generally one per track with an
input (mixing bus) transformer and one at the output. That's two per group.

> There was at least
> another transformer in the routing module. So it's at least four per
> channel strip. Every output had line amp modules (1272, 3415) with two
> transformers each - aux sends, 2-buss, talkback, pfl, oscillator etc.
> There were line amp modules (3416) with two transformers each on the
> additional inputs - monitor returns, 2-track returns etc. Such a desk
> would have well over 200 transformers.

Actually I ignored auxes as I was only trying to get a rough idea, but you
may well be right, the figure is probably closer to 200. That's still only
about 10,000 a year at one console a week.

Ian
>
> Predrag

[Ian Bell]

Scott Dorsey wrote:

Major snippage of very interesting stuff which I have filed away for
reference.

>
> All of the old core materials are gone. There used to be all kinds of
> soft iron materials available, which nobody wants today except a few audio
> guys. That's why none of the Pultec clones sound like actual Pultecs...
> it's a real nightmare to try and replicate those inductors because the
> original core material was the cheapest possible commodity junk in the
> fifties, and today it's no longer made.
>

That's incredible - but surely soft iron cores are still available - used in
mains transformers for instance in wall warts etc?

>>> It's a problem because the
>>> market for commodity transformers is gone or going away, so everything
>>> is now having to be done in small batches without the economies of scale
>>> that we saw thirty years ago.
>>

Has it - the wall wart market seems pretty boyant to me.

>>I suspect the economies of scale were not huge even then. A typical Neve
>>desk had 3 per channel strip and and two per group so a 40 channel 16
>>group desk would have about 150 transformers. I doubt we made one of those
>>a week
>>so that's less than 10,000 a year. Even in those days there were a lot of
>>manufacturers doing essentially transformerless designs e.g. Cadac so I
>>suspect the total market was no more than 100,000 a year (in the UK that
>>is).
>
> Those Neve desks were built with transformers from Marinair, a company
> that mostly made transformers for marine radio, intercom, and radar
> systems. Neve was a small customer for them.
>

They also used St. Ives Windings (certainly when I was there).

> Back then, every table radio had an output transformer, and they had a
> bunch
> of IF transformers. Every TV set had dozens and dozens of wideband
> transformers and inductors in the sweep circuits. Intercoms, military
> radio
> gear... everything was chock full of transformers.

When I first got interested in electronics I joined the local radio club
(~1964). As a teenager I had little money for parts then one day the club
secretary invited me round his house because he had some scrap parts I
v=could have. We went into his back garden where there was a 10 ft pile of
old TV chassis. Bliss.

Ian

[Predrag Trpkov]

"Ian Bell" > wrote in message
news:44ff330e.0@entanet...
> Predrag Trpkov wrote:

> >
> > It's three transformers per channel amplifier module.
>
> Well its 30 years since I worked there so memory could be faulty but IIRC
> channel amps had two - one at the input and one at the insert point. The
> routing module had one at its input which makes three per channel.


There were separate mic and line level transformers at the input of the
channel amps.

Of course, I'm just nitpicking. Probably have too much time on my hands.



> 1272 line amps were for mixing so there was generally one per track with
an
> input (mixing bus) transformer and one at the output. That's two per
group.
>
> > There was at least
> > another transformer in the routing module. So it's at least four per
> > channel strip. Every output had line amp modules (1272, 3415) with two
> > transformers each - aux sends, 2-buss, talkback, pfl, oscillator etc.
> > There were line amp modules (3416) with two transformers each on the
> > additional inputs - monitor returns, 2-track returns etc. Such a desk
> > would have well over 200 transformers.
>
> Actually I ignored auxes as I was only trying to get a rough idea, but you
> may well be right, the figure is probably closer to 200. That's still only
> about 10,000 a year at one console a week.


Correct.

Predrag

[Ian Bell]

Predrag Trpkov wrote:

>
> "Ian Bell" > wrote in message
> news:44ff330e.0@entanet...
>> Predrag Trpkov wrote:
>
>> >
>> > It's three transformers per channel amplifier module.
>>
>> Well its 30 years since I worked there so memory could be faulty but IIRC
>> channel amps had two - one at the input and one at the insert point. The
>> routing module had one at its input which makes three per channel.
>
>
> There were separate mic and line level transformers at the input of the
> channel amps.
>
> Of course, I'm just nitpicking. Probably have too much time on my hands.
>

I had forgotten about them. ISTR not all modules had them especially on the
later in-line consoles but I could be wrong.

IAn

[Scott Dorsey]

In article <44ff357b.0@entanet>, Ian Bell > wrote:
>Scott Dorsey wrote:
>Major snippage of very interesting stuff which I have filed away for
>reference.
>
>>
>> All of the old core materials are gone. There used to be all kinds of
>> soft iron materials available, which nobody wants today except a few audio
>> guys. That's why none of the Pultec clones sound like actual Pultecs...
>> it's a real nightmare to try and replicate those inductors because the
>> original core material was the cheapest possible commodity junk in the
>> fifties, and today it's no longer made.
>
>That's incredible - but surely soft iron cores are still available - used in
>mains transformers for instance in wall warts etc?

Not the same types, though. Most of the crappy wall wart transformers today
actually use silicon steel types. The silicon steel alloys have lower
conductivity so there is less heating due to eddy currents running through
the core.

>>>> It's a problem because the
>>>> market for commodity transformers is gone or going away, so everything
>>>> is now having to be done in small batches without the economies of scale
>>>> that we saw thirty years ago.
>>>
>
>Has it - the wall wart market seems pretty boyant to me.

Those, sad to say, are not wideband transformers. And even the wall wart
market is slowly moving from power transformers to switching supplies with
ferrite transformers in them.

>When I first got interested in electronics I joined the local radio club
>(~1964). As a teenager I had little money for parts then one day the club
>secretary invited me round his house because he had some scrap parts I
>v=could have. We went into his back garden where there was a 10 ft pile of
>old TV chassis. Bliss.

Sadly most TV sets today have hardly anything inside them, but VGA monitors
are still great scrap for kids. Lots of film caps, wideband transistors,
power rectifiers. There's no sweep tube any more, but the sweep transistor
is still a one-transistor transmitter waiting to happen.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Fraser]

<<Well I was responding to your comment about transformers being less
coloured
today. I was hoping you would be able to say in what way there were so
-
better frequency response, distrortion etc. >>

Less phase lag, for one. Deane Jensen was quite adamant that his
transformers not exhibit noticeable phase lag until several octaves
above the audio band.

Scott Fraser

[Scott Dorsey]

Scott Fraser > wrote:
><<Well I was responding to your comment about transformers being less
>coloured
>today. I was hoping you would be able to say in what way there were so
>better frequency response, distrortion etc. >>
>
>Less phase lag, for one. Deane Jensen was quite adamant that his
>transformers not exhibit noticeable phase lag until several octaves
>above the audio band.

Since the transformer is pretty much minimum phase, the amplitude response
and phase response are tied together. If you want reasonable phase lag up
to one octave above the audio band, you need reasonable frequency response
up to two octaves above the audio band.

I'll say that the high ratio Jensen transformers like the JE-115KE do much
better in that regard than anyone else's high ratio transformers, but they
still have bigtime group delay in the top octave.

Also, of course, the really hard part is getting low group delay on the
bottom end, because with a given core material and a given level, the
size of the core grows exponentially as the bottom corner frequency
drops. (You could have a transformer that passes DC effectively if you
could have an infinitely large core on it). Modern core materials
with super high permeabilities reduce the required size a lot, but still
you need big transformers for good low end unless you can drop the level
very low.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Ian Bell]

Scott Dorsey wrote:

> In article <44ff357b.0@entanet>, Ian Bell >
>>That's incredible - but surely soft iron cores are still available - used
>>in mains transformers for instance in wall warts etc?
>
> Not the same types, though. Most of the crappy wall wart transformers
> today
> actually use silicon steel types. The silicon steel alloys have lower
> conductivity so there is less heating due to eddy currents running through
> the core.
>

Wouldn't that be good for audio transformers too?


Ian

[Scott Dorsey]

In article <45008aca.0@entanet>, Ian Bell > wrote:
>Scott Dorsey wrote:
>> In article <44ff357b.0@entanet>, Ian Bell >
>>>That's incredible - but surely soft iron cores are still available - used
>>>in mains transformers for instance in wall warts etc?
>>
>> Not the same types, though. Most of the crappy wall wart transformers
>> today
>> actually use silicon steel types. The silicon steel alloys have lower
>> conductivity so there is less heating due to eddy currents running through
>> the core.
>
>Wouldn't that be good for audio transformers too?

No. The linearity is very poor. With a power transformer, the line
distortion isn't all that important, but with an audio transformer it is.

That's why there are literally hundreds of core materials just listed in
the 1970 edition of the ITT Radio Engineer's Handbook. These days there
are far more than back then, too. Different tools for different jobs.

These days things are much more specialized than they used to be, with
lots of different materials for each different job and price range.
Try one of the Talema toroidal power transformers for instance. Because
of the core material they picked (and not because of the distributed
winding capacitance), the response of the transformer drops off very
abruptly around 100 Hz until it's down phenomenally at 1 KHz. Great
for keeping line noise out of the power supply. Bad for audio.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Ian Bell]

Scott Dorsey wrote:

> In article <45008aca.0@entanet>, Ian Bell >

>>
>>Wouldn't that be good for audio transformers too?
>
> No. The linearity is very poor. With a power transformer, the line
> distortion isn't all that important, but with an audio transformer it is.
>

snip

Thanks, useful info.

Ian

[Robert Orban]

In article >, says...
>
>
>Scott Fraser > wrote:
>><<Well I was responding to your comment about transformers being less
>>coloured
>>today. I was hoping you would be able to say in what way there were so
>>better frequency response, distrortion etc. >>
>>
>>Less phase lag, for one. Deane Jensen was quite adamant that his
>>transformers not exhibit noticeable phase lag until several octaves
>>above the audio band.
>
>Since the transformer is pretty much minimum phase, the amplitude response
>and phase response are tied together. If you want reasonable phase lag up
>to one octave above the audio band, you need reasonable frequency response
>up to two octaves above the audio band.
>
>I'll say that the high ratio Jensen transformers like the JE-115KE do much
>better in that regard than anyone else's high ratio transformers, but they
>still have bigtime group delay in the top octave.
>
>Also, of course, the really hard part is getting low group delay on the
>bottom end, because with a given core material and a given level, the
>size of the core grows exponentially as the bottom corner frequency
>drops. (You could have a transformer that passes DC effectively if you
>could have an infinitely large core on it). Modern core materials
>with super high permeabilities reduce the required size a lot, but still
>you need big transformers for good low end unless you can drop the level
>very low.

The Jensen JT-123-BLCF is 3 dB down at 0.03 Hz and up about 0.1 dB at 200
kHz. We sell a box using this transformer to pass FM stereo composite
baseband, breaking ground loops and getting rid of noise when all else
fails.

[Scott Dorsey]

Robert Orban > wrote:
Scott Dorsey writes:

>>Also, of course, the really hard part is getting low group delay on the
>>bottom end, because with a given core material and a given level, the
>>size of the core grows exponentially as the bottom corner frequency
>>drops. (You could have a transformer that passes DC effectively if you
>>could have an infinitely large core on it). Modern core materials
>>with super high permeabilities reduce the required size a lot, but still
>>you need big transformers for good low end unless you can drop the level
>>very low.
>
>The Jensen JT-123-BLCF is 3 dB down at 0.03 Hz and up about 0.1 dB at 200
>kHz. We sell a box using this transformer to pass FM stereo composite
>baseband, breaking ground loops and getting rid of noise when all else
>fails.

Those are great transformers and I have them on the outputs of my ATR-100;
they are much cleaner sounding than the original transformers.

But, they are comparatively large, and they are much higher loss than
typical designs. The high loss is just fine for an output transformer
where you can afford to throw some power away, but very bad for an
input transformer where S/N is paramount.

I also question that low frequency figure; as with all transformers, the
low end drops off as the operating level goes up and whatever nominal
level Jensen did the plot on the data sheet at, it's lower than the level
I run them at.

Still, this is a great example of how modern core materials and winding
techniques can allow design engineers to optimize a transformer for a given
application and get much better performance than was possible twenty years ago.

Even scarier are the Allen Avionics transformers that can pass full bandwidth
NTSC video without screwing up the synch!
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."