john curl said:
Yes, Les Tyler is a great guy.
Good suggestion wrt adding balanced to my design. I'll give it a shot.
Bob
Steve, I have a signal transformer with shield between primary and secondary winding. I can measure HF noise pickup and increase, though. Much worse compared to properly done direct coupling.
P.S.: I hope you do not start to recommend me where to connect the shield 😀 😀 😀
P.S.: I hope you do not start to recommend me where to connect the shield 😀 😀 😀
PMA said:
Would you mind describing your test setup and methodology so I could perhaps try it here?
Don't be a wimp! Just bend over and do it! It doesn't hurt much. 😱
Steve,
I always measure noise of the whole audio chain, i.e. player, preamp, power amp, speakers. At every interface/connector, binding post point.
a) LF by FFT, 20Hz - 23.5kHz
b) HF by oscilloscope with 1mV/div sensitivity.
By (b), I measure HF noise pickup/increase in case of signal transformer inserted between preamp and power amp. With shield (properly connected). Just try and please do not ask me to study Jensen application notes etc., I have already done it years ago.
Also, I had to use impulse transformers sometimes in my professional praxis. They have some advantages, but they have issues. Optical fibre is the solution.
I guess that transformer itself picks up the HF noise. Similar to unshielded piece of wire.
Last and not least, there is a considerable increase of distortion at low frequencies (below 100Hz) and higher amplitudes (above 1Vrms) with signal transformers.
I always measure noise of the whole audio chain, i.e. player, preamp, power amp, speakers. At every interface/connector, binding post point.
a) LF by FFT, 20Hz - 23.5kHz
b) HF by oscilloscope with 1mV/div sensitivity.
By (b), I measure HF noise pickup/increase in case of signal transformer inserted between preamp and power amp. With shield (properly connected). Just try and please do not ask me to study Jensen application notes etc., I have already done it years ago.
Also, I had to use impulse transformers sometimes in my professional praxis. They have some advantages, but they have issues. Optical fibre is the solution.
I guess that transformer itself picks up the HF noise. Similar to unshielded piece of wire.
Last and not least, there is a considerable increase of distortion at low frequencies (below 100Hz) and higher amplitudes (above 1Vrms) with signal transformers.
PMA said:
Thanks, Pavel.
So you haven't done any comparative measurements where the transformers are built into the component, i.e. a preamp or power amp? Just with the transformers situated between two components strung together across two pairs of interconnects?
Also, when you do the measurement without the transformers, are you using just one pair of interconnects or two? If two, how are you connecting them at the point where the transformers would have otherwise been?
Well, if the transformer is well shielded, and the interconnects going into and out of it are well shielded, I don't see why the transformer would necessarily pick up so much RF as you're saying they do.
Well yes, the lowest frequencies and the highest amplitudes are the transformer's weak point. But unless you're just playing purely a number's game, with proper design, I haven't found this to be problematic.
se
Steve Eddy said:
Hi Steve,
no, I have not done any comparative measurements where the transformers are built into the component, I do not have such a component or a chance to borrow it.
I measure the whole audio chain, i.e. both left and right interconnect cables connected. Both from CD to preamp and from preamp to power amp. And speakers connected as well. I substitute one inteconnecting pair of cables by transformer box.
I agree that if a transformer is well shielded, and especially inserted into metal box that shields the connecting wires as well, and shield continuity is nowhere interrupted, the result might and should be better. This was not my case, manufacturer used plastic box, so the wires from transformers to XLRs are unshielded.
john curl said:
Elaborate please? Maybe it's your circuit configuration. I think I sent you plots a long time ago of a real cartrige (sans stylus) used as a source resistor for noise measurements. Quite telling.
Hi Scott, surely someone has told you about the new article in 'Audio Express' of a phono stage, using your 797. He elected to put a 2sk170 in front to reduce the noise current contribution at 10KHz with a fairly high inductance moving magnet cartridge.
PMA said:
Haven't you made any of your own preamps or power amps? Or have a preamp or power amp that you could build a pair of transformers into?
Ok.
How exactly are you accessing hot and ground in the case of an RCA or + and - in the case of an XLR in order to make your measurements? Are you opening up the equipment chassis to get access?
Ok. That's what I thought.
Yes, one would think.
I don't see how you can come to any meaningful conclusions about the transformers themselves given this situation.
I mean, you're comparing a single length of interconnect where the shielding remains continuous along the entire length to two lengths of interconnects with an unshielded portion between them.
If all you did was take a plastic box and mount some connectors to it with the connectors hardwired straight from one to the other, and hooked this up between two lengths of interconnects, I'd think one could expect to see more RF compared to a single run of shielded interconnect.
se
Steve,
this product was bought. Many, even well known manufacturers, do it same way. I know one who uses wooden box to shield the wires.
this product was bought. Many, even well known manufacturers, do it same way. I know one who uses wooden box to shield the wires.
Hi,
The Cinemag, I bought through the GB has a screening can around it.
The wires are unscreened.
How should this be done to minimise interference.
I plan to use them at the receive end (power amp) at the other end of the room from the source.
Presumably they go adjacent to the input stage with the output wires direct to the PCB.
What about the input wires?
Any twisting recommended?
The Cinemag, I bought through the GB has a screening can around it.
The wires are unscreened.
How should this be done to minimise interference.
I plan to use them at the receive end (power amp) at the other end of the room from the source.
Presumably they go adjacent to the input stage with the output wires direct to the PCB.
What about the input wires?
Any twisting recommended?
PMA said:
I think you're missing the point here.
You made a rather blanket statement that you found that RF was increased by signal transformers.
When I dig a little deeper, I find that the circumstance with which you'd made your measurements is one in which one would expect to see increased RF even if there were no transformers involved at all.
And while transformers can be had in separate boxes, some of them not shielded, this isn't the only way in which transformers can be employed. In fact the context in which I was bringing them up here was their being built into the component in question, not stuck in boxes and strung between components.
se
AndrewT said:
Ideally they should be mounted inside the amplifier chassis close to the input stage. Twisting the lead wires is a recommended. You can also mount the can externally on the chassis itself if you have the room though this would require drilling holes in the chassis.
se
Steve,
a communication with you would be a never ending story, that is why I have not reflected to another points you have made. I am a professional in a field of measurement and I do not feel like to defend my measurement techniques.
The only valid point you have stated concerned the trafo box. Yes, it was not optimal and it was like it was. BTW, the shield was interconnected trough the box. Anyway, I do not prefer signal transformers for home use. I can suppress noise and interference another way. For me, the transformer is best to avoid. Howgh.
BTW, try once to measure transfer function of your transformers up to hundreds of MHz, that is the environment we live in. You will be surprised.
a communication with you would be a never ending story, that is why I have not reflected to another points you have made. I am a professional in a field of measurement and I do not feel like to defend my measurement techniques.
The only valid point you have stated concerned the trafo box. Yes, it was not optimal and it was like it was. BTW, the shield was interconnected trough the box. Anyway, I do not prefer signal transformers for home use. I can suppress noise and interference another way. For me, the transformer is best to avoid. Howgh.
BTW, try once to measure transfer function of your transformers up to hundreds of MHz, that is the environment we live in. You will be surprised.
PMA said:
Well, when you make the blanket statement that signal transformers increase RF, and the only measurements you've made in this regard involve a situation where one would expect to see more RF even without the transformers involved, whether you feel like defending your measurement techniques or not I think there's certainly enough to question here.
Yet it was measurements made with this sub-optimal situation that you used to substantiate your original statement.
Not sure exactly what you mean by this. Do you simply mean that the pin 1s on the XLRs were tied together?
Fine. No skin off my nose.
I don't recall ever recommending transformers for the primary purpose of suppressing RF noise and interference so I don't see what the relevance is here.
Fine. Again, no skin off my nose.
Ok. But when have you made such a measurement?
se
There used to be a member of the local brewing club who was addicted, for lack of a better word, to hops. Everything he brewed was hopped to the max, whether it was true to the beer style or not. And he would argue endlessly about it, claiming that something like a barley wine, in which the malt taste should predominate, should be predominately hoppy. Hops were damned near a religion to him. Probably had them on his breakfast cereal. Intravenous injections of lupulins to keep him going in the afternoons. Centennial flowers for snacks. The works.
I think of him every time I see Steve posting about transformers.
Grey
I think of him every time I see Steve posting about transformers.
Grey
GRollins said:
In other words, you've nothing to add to the subject so you just figured you'd just take a cheap shot at me instead. Yes?
se
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