Balanced phono cable

[Paul R]

In the general case with a phono cartridge it floats. Balanced inputs don't obviously offer any advantage.

In the ungeneral case, like a Decca, or some MMs that tie their bodies to '0v' and possibly then to earth via the arm, you're stuffed regardless.

Paul

 

[Julf]

No I'm not avoiding it al all I'm saying the opposite is true. Unbalanced is better than balanced.

Yes, that is what you keep repeating, but the only argument you have presented supporting that is "because balanced needs a lot more complexity" which I have shown not to be true.

By your "logic" a unicycle is better transport than a car as it requires only one wheel...

No, you are actually the one arguing extra circuitry is bad. What I am saying is that there is not much (or any, depending on the case) circuitry needed.

In any case, in your bicycle analogy it seems you are saying " there is no point in using a bicycle gear train made out of titanium if the whole bike isn't made out of titanium".

Differential and balanced are the same thing. It's just semantics.

A differential and balanced connection is the same, but a connection is not the same as circuitry.

If I was going to use balanced I would use completely balanced discrete circuitry from input to output and not bastardise it by repeatedly converting the signal from balanced to unbalanced and vice versa with op amps!

So connecting a balanced pickup to an unbalanced input is "bastardising"?

So now you agree that in a domestic setting unbalanced is fine. Good.

In most domestic settings, in most cases, you get by just fine even with unbalanced.

 

[Arkless Electronics]

In the general case with a phono cartridge it floats. Balanced inputs don't obviously offer any advantage.

In the ungeneral case, like a Decca, or some MMs that tie their bodies to '0v' and possibly then to earth via the arm, you're stuffed regardless.

Paul

If one believes balanced to be advantageous then a floating balanced source such as a cartridge is just fine and offers all the advantages of balanced.

Agreed to your second point. Early Rega arms were a problem in this respect.

 

[Arkless Electronics]

Yes, that is what you keep repeating, but the only argument you have presented supporting that is "because balanced needs a lot more complexity" which I have shown not to be true.



No, you are actually the one arguing extra circuitry is bad. What I am saying is that there is not much (or any, depending on the case) circuitry needed.

In any case, in your bicycle analogy it seems you are saying " there is no point in using a bicycle gear train made out of titanium if the whole bike isn't made out of titanium".



A differential and balanced connection is the same, but a connection is not the same as circuitry.



So connecting a balanced pickup to an unbalanced input is "bastardising"?



In most domestic settings, in most cases, you get by just fine even with unbalanced.

Repeating falsehoods does not eventually make them true and I've already proved everything you say above wrong...

 

[Julf]

Repeating falsehoods does not eventually make them true

I guess that is the part we both agree on.

I've already proved everything you say above wrong...

You seem to have an interesting definition for "proved" (sic). It might come as a surprise to you, but " because I think so" doesn't actually constitute proof. You don't actually address any of my arguments, you simply repeat the same claims over and over, so this has become rather pointless.

It all boils down to your absurd claim that very good (but not perfect) common mode rejection ratio is not (because it is not perfect) as good as having no common mode rejection ratio at all.

Calling Franz Kafka...

 

[Arkless Electronics]

Yes I'm saying that no common mode rejection is fine. The whole crux of the argument is that you believe balanced is a good thing and ALWAYS intrinsically superior to unbalanced. I very strongly disagree with this.

You're accusing me of precisely the same things I'm accusing you of so I suggest killing off the whole debate....

 

[Julf]

Yes I'm saying that no common mode rejection is fine.

That is not exactly what you were implying earlier. Are you also saying that no common mode rejection ratio is better than the common mode ratio achieved without adding extra components to an op-amp input?

The whole crux of the argument is that you believe balanced is a good thing and ALWAYS intrinsically superior to unbalanced. I very strongly disagree with this.

I can't think of a situation where balanced would be worse. There are lots of situations where the benefits are not important.

 

[Paul R]

Take a floating source like a typical cartridge. Impose a cm voltage. How would anybody know?

Now what would be interesting would be to phantom power the first stage of the phono amp and attach it to the back of the cartridge. Could get really advanced and put an ADC in there too.

Michael Fremer would love it.

Paul

 

[Arkless Electronics]

/\ oh dear....

 

[Julf]

Take a floating source like a typical cartridge. Impose a cm voltage. How would anybody know?

If that common mode voltage was between both cartridge terminals and ground/earth (remember, voltages are always between two points), a non-balanced/non-differential phono input would see that voltage directly between the " hot" pin and the ground/"cold" pin. A differential input would see the voltage attenuated by the common mode rejection ratio.

 

[Paul R]

But earth only turns up at the input to the phono stage. We aren't connecting two systems together both working to a notional 0v. The opportunity for coupling between the cart and 0v, such that currents flow and what started as cm ends up as a voltage on the signal, seem slim.

Is there a noise penalty to a balanced phono input?

Paul

 

[Julf]

But earth only turns up at the input to the phono stage. We aren't connecting two systems together both working to a notional 0v. The opportunity for coupling between the cart and 0v, such that currents flow and what started as cm ends up as a voltage on the signal, seem slim.

I answered the specific "impose a cm voltage" scenario that would require applying the cm voltage between the inputs and the earth. It does also become a real situation when the phono input stage earth connects to safety earth or turntable chassis.

Is there a noise penalty to a balanced phono input?

No - the dual inputs double the noise, but also the signal, so SNR stays the same.

 

[ChrisPa]

Like I said, point proved. I rest my case.

Chris. The first comment was aimed at Julf.... and yes of course you can deliberately "unbalance" the balanced input to give improved CMRR with a specific known input impedance. Not exactly ideal for a universal balanced input! The single op amp version is best kept for internal use in a piece of equipment where it can be driven from known low source impedances from a previous op amp stage.

The main argument was whether or not a single op amp balanced input was a good solution. I have proven that it is not.

You seem to think my previous post proves this point ^.
I can't see why you think that.

If so, you've seem to have ignored most of my post and picked on one small item which was included as a throwaway but technically accurate comment and not relevant to the real world maths
The engineering/maths is quite simple - balancing an input inherently provides CMRR (even if it's not perfectly balanced)

Refer back to the equations in Putzeys' document. The performance/CMRR of any balanced input connection is dependent on the balance of the input. It doesn't matter what this balanced device is - whether it's the input loading of an instrumentation circuit, an opamp, or a pair of transistors. Or even balancing the earth connection.
Balancing an unbalanced input is better for CMRR than leaving it unbalanced.

I prefer unbalanced to balanced in general for the reasons we started with... ie unless the circuitry itself is completely balanced it means adding op amps to the signal path.

As previously, you don't need to add opamps to get a balanced circuit.

Most so called balanced units are internally unbalanced. They then add op amps to the output to make it balanced just before it goes to the XLR socket. Usually the signal then goes through more op amps at the other end to convert it back to unbalanced where it then continues through unbalanced circuitry.

"Most" circuits doesn't mean it's the only way. Extra opamps are not needed.

No, you haven't. You have pointed out, and I agree, that it is not perfect. It is still much better than unbalanced. This is the fact you keep trying to avoid.

No I'm not avoiding it al all I'm saying the opposite is true. Unbalanced is better than balanced.

You're saying that no CMRR is better than having CMRR.

And as I have " proven" (to use your terminology), nothing needs to be added to a circuit that uses an opamp, and only the input transistor needs to be added to a discrete circuit. I even posted the circuit diagrams. Do I have to do it again?

You can post your circuits as many times as you like and will remain wrong as, apart from anything else, we are arguing different things.

Not wrong. A balanced impedance differential input is ... balanced.
If you take a circuit which has differential inputs and present the signal across the inputs with balanced impedances, then it is ... balanced

You are mixing up two separate things - fully balanced circuitry (that you seem to be talking about) and balanced/differential connections (that the OP is about). The latter only needs a differential input, not a fully balanced circuit all the way through the amp.

Differential and balanced are the same thing. It's just semantics.

It's important semantics. It's very easy to have an unbalanced differential circuit. Both are needed. Lots of circuit blocks are differential but aren't balanced.

If I was going to use balanced I would use completely balanced discrete circuitry from input to output and not bastardise it by repeatedly converting the signal from balanced to unbalanced and vice versa with op amps!

You're implying that deliberate conversion backwards and forwards between single ended and balanced is being advocated, and of course it's not. The point is that every time you can make the interconnection balanced (impedance) you improve CMRR, even if the circuit block is nominally single-ended.

If you haven't done so yet, please do go and read the Bruno Putzeys document. His balanced volume control stage is particularly interesting. And then come back and tell us what is wrong with the document.
(As Putzeys clearly states the (balanced) circuit included in the document is a proof of principle and not a production design, so let's stick to his maths and the balanced behaviour of the circuit.
There are quite a few of these preamps out in the wild)

 

[Arkless Electronics]

Wrong on many levels. Thread closed as far as I'm concerned.

 

[Julf]

Wrong on many levels. Thread closed as far as I'm concerned.

Your consistently fact- and evidence-based rational approach is admirable. Thank you for helping us understand your thinking.

Seems "tell us what is wrong with the document" is an useful magical incantation.

 

[ChrisPa]

Wrong on many levels. Thread closed as far as I'm concerned.

LOL
(well, it made me smile)

Unbelievable
But not unexpected.

I was hoping this could be handled as an exchange between equals, but if you can't do that, then please do go back and understand the science. It's laid out very clearly in Putzeys' document.