line output transformer help

[milen007]

hi guys

i am planning to use the line output tranformer for my srpp linestage output to bring down the gain.

i search the benefit of using line stage but to no avail.

why in the beginning people use LOT on the line stage? is it because of more liquid sound that it provide?

can someone tell me the benefit or point me the article or link to it?

i need to attenuate around 10db, and my local manufacturer suggest 15K:7K5 and 15K:1K5, instead of the more popular 15K:600

suggestion?

or i better off rebuild my linestage that gives out lower gain, rather than using the LOT?

thanks in adv

erwin

[analog_sa]

There is absolutely no guarantee about the outcome if your local winder is not spectacularly good. Thus it's much safer to use transformers from recognised manufacturers.

You can expect subjective improvements such as increased dynamics and low level resolution but probably inferior bass. Before deciding upon transformer parameters you need to know: dc current through the primary if you don't parafeed, tube Rp which will determine the minimum primary inductance and how much gain you want to lose.

[SY]

i better off rebuild my linestage that gives out lower gain, rather than using the LOT?

Yes.

[grhughes]

unless it's a very exotic transmission line repeat coil...it's only advantage is driving a balanced line to get freedom from EFI and RF interferrence or converting passively from unbalanced to balanced and vice versa. If you don't live next door to a broadcasting station or HAM radio transmitter then an output transformer will only degrade the sound. Just run a 12k square wave through most any transformer and note that many will turn it into a sine wave.

[hesener]

Hi, I used a Lundahl 7902 as line output transformer for a SRPP line stage, and it worked beautifully for me. There was a notable improvement in the highs (less "grain"), and the line stage is a lot less susceptible to loading (e.g. long cables to connect to my monoblocks - I could even hook up a headphone and it sounds just sweet)
I have posted the full design elsewhere so if you search for my username you should be able to find it
any questions just get in touch

[dsavitsk]

Originally posted by milen007
why in the beginning people use LOT on the line stage? is it because of more liquid sound that it provide?

can someone tell me the benefit or point me the article or link to it?

It also lowers Zout and provides more current to drive difficult loads. There are active ways to do this, too, and with srpp you might not need it, but this is a real reason to use a transformer. Some of us prefer them to other solutions.

Originally posted by grhughes
Just run a 12k square wave through most any transformer and note that many will turn it into a sine wave.

Do you listen to a lot of 12k square waves? why do you care whether they can be transmitted accurately?

[HollowState]

Originally posted by dsavitsk
Do you listen to a lot of 12k square waves? why do you care whether they can be transmitted accurately?

I tend to agree. With the harmonics involved, a 2KHz square wave has been the accepted standard for useful evaluations of audio output transformers out to 20KHz. Higher fundamentals may only get you some bragging rights.

[milen007]

hi guys

thanks for all the mix inputs. but i might be encouraged to try it.

the local manufacturer is quite reputable locally. as importing from well-known transformer source is way too expensive for the total cost including the shipping and i am not prepare to that budget yet.

anyone has any schematic that show how to connect the line output transformer? that will really help.

anymore suggestions is really appreciated.

tia

erwin

[limono]

TESTING TRANSFORMERS WITH SQUARE WAVES

Jack Elliano
PROPER TESTING OF AUDIO DEVICES USING REACTIVE COMPONENTS

Ringing from square wave measurements has grown into a very negative response within the incorrectly informed audiophile group. The influential ones spreading this have probably measured an amplifier that has a flat frequency response from 100hz to 6000hz. This would show no ringing at all.

In order to slow down and hopefully stop a continuous barrage of incorrect technical statements used for influence and profit, it becomes necessary to confront them with facts. An example is: the measurement of speaker interconnects of its inherent capacity and inductance involved as featured in advertising. Realistically there is a problem with music that is played in the megahertz range. One statement heard to confront this is, “These advertised measurements are like being concerned about the aerodynamics of a golf cart.� This is the intent of this article. TRANSFORMERS THAT RING WHEN SQUARE WAVES ARE APPLIED

A square wave is composed of a leading edge with a rise time in the megahertz range (depending on quality of generator and frequency used) then to a given duration of a DC voltage across the top, then switched down (same speed as the rise time) in the megahertz range then to cross zero and repeat in the opposite polarity. Just to inject something here, we did have a transformer that will pass a DC voltage, it was shorted out.

This bipolar waveform, when measured with a Fourier series analysis, shows the square wave is composed of its fundamental frequency and an infinite number of odd harmonic frequencies. The even order content would have to be zero for a perfect square wave.

The use of a square wave to analyze an amplifier is shown in full in Tremaine’s Audio Cyclopedia, 2nd edition, Audio frequency measurements chapter, pg. 1521, as a means to test the transient response of an amplifier. If the amplifier has ringing at the top of the leading and falling edge, this shows an extremely good high frequency response from the transformer in use. Well, there it is folks!!

If one remembers the ignition system on the old engines, they used a set of points, generating a square wave of 12volts and applying this to a capacitor and spark coil (a very high ratio transformer for those who don‘t know). They rang to 15,000 volts or so. This is what a square wave will do to this combination of coils and capacitors.
AUDIO TRANSFORMER RINGING

A basic audio transformer with, lets say, a 10k primary and a 600 ohm secondary. We do know that the primary has many more turns than the secondary. Lets say that the total length of the primary wire is 1000 feet long and the secondary is 100 feet long. For this transformer to be perfectly coupled (little or no ringing), it would need to have the 100 foot secondary wire fully coupled next to the total of all the 1000 foot primary. How can this be done?? Well it can’t! End of statement. If one is to build a transformer with different primary to secondary ratios, like most of them are, then some portion of the primary is not coupled to the secondary, therefore ringing will occur due to what is called “leakage reactance�. This is the measured primary inductance left on the primary when the secondary/s is shorted. This reactance will react with the capacity within the coil to resonate. when a square wave is used and it is composed of the frequency (usually in or near the megahertz range, ringing can occur. When a transformer is in operation and loaded, the open winding or static inductance measurement is lower. Much higher though than the shorted “leakage reactance� indicated above. The ability to ring with a square wave is in play usually within a 10khz square wave.

An example is a class C operated RF amplifier, the output power, which is a pulse, going to the tuned tank circuit (coil and capacitor), tuned to resonance, will show a ringing waveform. The flywheel effect of the high Q resonant tank circuit, stores, combines and transfers this energy to the antenna as one frequency. By the way, this tank circuit is a transformer with a primary about 20,000+ ohms to a 50 ohm secondary, with no core. That’s another story.

The one audio transformer that will show little or no ringing is the bifilar wound (two equal lengths of wire wound together equally in turns); this is a 1:1 ratio type with total coupling of all wire involved. Try to design and build an amplifier with only 1:1 transformers. Smaller variations of this bifilar wound transformer are known as pulse transformers, usually used in radar and other pulse operated circuits. A pulse is a square wave of one polarity. Get the picture.

To sum it all up, a transformer is probably the most complicated device ever invented. Its many intricate designs and uses, then to have the few accepted, and common measurements made by those who never even built a transformer, evaluate them for all, is simply absurd.

Have you ever seen a wideband oscilloscope preamp circuit use a transformer? Those of you that have circuit experience will answer NO!!

To cap it off, those influential few who apply square waves to test and evaluate transformers could probably say “we played the clarinet by blowing into it backwards and it sounds very bad so in our opinion don’t buy one.�