trasformer coupling

[mik]

time ago in john brosky site I'have saw this curious configuration:



he say, trasformer doesn't see any DC current at his primary, then even ungapped trasformer can be used
http://www.tubecad.com/2010/03/blog0182.htm
and
http://www.tubecad.com/2010/03/blog0182.htm

is it possible to coupling an SRPP in this way with an ungapped trafo ?



what do you think ?

thank you.

Mik

 

[Kingston]

You are adding one more expensive capacitor (ignoring the pointless 1uF parallel cap) in comparison to standard single-cap-to-transformer-coupled SRPP circuit.

I guess your goal is avoiding caps in signal path if possible?

The floating base of the transformer between the caps is still "in signal path", somewhat similarly to a cathode bypass cap. Would be interesting to listen if there's some difference to be heard...

 

[mik]

You are adding one more expensive capacitor (ignoring the pointless 1uF parallel cap) in comparison to standard single-cap-to-transformer-coupled SRPP circuit.

yes I know.

I guess your goal is avoiding caps in signal path if possible?

Yes it is

The floating base of the transformer between the caps is still "in signal path", somewhat similarly to a cathode bypass cap. Would be interesting to listen if there's some difference to be heard...

yes capacitor is still in the path, but it seems to me a "not direct capacitor coupling" sorta thing
moreover, noise from PS should be cancelled because of the antiphase AC coupling
I think it is possible a differnt does exist..

Boskie used this coupling for his home Hi-Fi, he talk about a very open wide stereo perception, that is the same fenomena you could hear when dc servo coupling trasformer are used.


Mik.

 

[Kingston]

Interesting, it would seem this is also a good way to avoid the bass bump caused by transformer inductance acting with the coupling cap.

 

[desol]

Hmph. Neat.

 

[emrr]

Don't think I've seen that.  Worth comparing.

 

[zebra50]

It might be worth dropping John a message if you run into trouble. He was very friendly and helpful when I built a transformer coupled point-to-point Aikido preamp last year. (Actually I should take some photos of that sometime because it was a nice project.)

The kits are nice quality too.

Late night edit... My Aikido is pretty much the same as the circuit in the top post, but with a standard cap-coupled output tranny. I can easily rewire one channel and compare. I'll have a go and let you know.

 

[zebra50]

Interesting, it would seem this is also a good way to avoid the bass bump caused by transformer inductance acting with the coupling cap.

Hey Kingston,

Is that going to work? Can't quite get my head round it this late at night but doesn't the inductor/imnductance see the two (or four) caps that make up the voltage divider?

http://www.tubecad.com/2006/08/blog0074.htm

 

[gyraf]

transformer dosn't care which end the capacitor is connected at, and here in stead of capacitor in series with amplifier output, you have capacitor in series to ground (and some to supply, I ignore that for now)

I don't really see what benefit over standard circuit, other than maybe that (some of) current return path dosn't dump directly into ground.

Jakob E.

 

[Kingston]

Interesting, it would seem this is also a good way to avoid the bass bump caused by transformer inductance acting with the coupling cap.

Hey Kingston,

Is that going to work? Can't quite get my head round it this late at night but doesn't the inductor/imnductance see the two (or four) caps that make up the voltage divider?

http://www.tubecad.com/2006/08/blog0074.htm

I see. There's no free lunch.

cue Broskie:

Another point to ponder: Is this line amplifier really coupling-capacitor free? Are the two power supplies not working as coupling capacitors, although to ground, not the output? A good question. My take is the power supply capacitors are always in the signal path, if they ever see any of the AC signal current; so, yes they are acting as coupling capacitors, but they were in all the previous circuits as well. Hence the 1.5µF bypass capacitors across capacitors C1 and C2.

So taken further, any AC signal going to the very capacitive "ground" will act with the inductance of the transformer. Not sure if this is such a good idea after all. Double the capacitance needed for the caps and film caps get really expensive at around 10uF.

 

[mik]

As for what I have understud, signal doesn't pass "through" the capacitor before to meet the tranny,
this condition must have a different impact on sound.

let's wait for Zebra50 test.

M.

 

[MagnetoSound]

My experience with putting series caps in HV power supplies is that, unless you include bleed resistors (which act as a steady voltage divider while powered up), the voltage at the junction between the caps has a tendency to float around somewhat, sometimes quite dramatically.

Is the idea that the DC path through the transformer keeps this junction constantly biased at all times?

 

[Kingston]

Is the idea that the DC path through the transformer keeps this junction constantly biased at all times?

Yes indeed. Let it float, that's the point of the whole thing.

Also related,

As for what I have understud, signal doesn't pass "through" the capacitor before to meet the tranny,
this condition must have a different impact on sound.

It's not visually on the signal path, but the transformer has lots of DC present at the floating base. Transformer sees the DC path and this will act with the inductance of the primary. Quality of the cap will play just as important role as in any standard configuration. Bass bump will be there.

It's probably not any different from "coupling cap to ground in parallel with the transformer primary" configuration.

Anyone with an oscilloscope and some spare time, let us see what really happens.

My guess is that any distortion from the cap is still there, just summed to the audio signal inverted.

 

[zebra50]

Anyone with an oscilloscope and some spare time, let us see what really happens.

Well, I have an oscilloscope! Kinda busy at the moment, but might be able to find some time next week to reconfigure my Aikido.

My money is on not being able to measure / hear the difference. But I'll keep an open mind - We'll see!

 

[Kingston]

My money is on not being able to measure / hear the difference.

First measure just a single cap in series with some reasonably high voltage square wave. This way you'll know best what to look for visually.

 

[mik]

It's not visually on the signal path, but the transformer has lots of DC present at the floating base. Transformer sees the DC path and this will act with the inductance of the primary. Quality of the cap will play just as important role as in any standard configuration. Bass bump will be there.

It's probably not any different from "coupling cap to ground in parallel with the transformer primary" configuration.

Anyone with an oscilloscope and some spare time, let us see what really happens.

My guess is that any distortion from the cap is still there, just summed to the audio signal inverted.

trasformer see voltage, it is the current that act with inductace of the primary.
M.