Balanced Output Options

[gnnett]

Hi Guys

Hate myself for doing this (suggesting modifying a kit before it has fired a commercial shot in anger  ) but having balanced inputs on my amp, I am looking at options to get into DHT line stage at a lesser price than the BeePre.

I have a couple of options to use Smash and I was considering:

1/. resistor network at output as used on the BeePre, is this an option?
2/. add output transformers, B7? Cost implications obviously and not sure of results.
3/. use Existing TVC's as attenuators, at the output of the Smash and use resistors at inputs to match CD output to lower output from Phono stage, which should not overload the line stage direct, or if necessary could also be attenuated.

Option 1 is preferred, if it is feasible, and option 3 would allow me to use existing passive TVC as is, or at a later stage incorporate into the chassis. Option 2 would only be pursued if it was the best option in terms of sound quality and maybe would allow removal of the output capacitor?

Appreciate any thoughts you might have.

Kind Regards

Grant

[Paul Birkeland]

What is the input impedance of your amp?

The Smash will have high impedance with the network providing the balanced output.

The transformer is an option. Something like a 5K:600, but you'll lose a lot of gain and it won't sound as good.

Same with the TVC. 

When you consider the cost of the Smash and a pair of good nickel transformers, you'll be pretty close to BeePre in price.

It's also worth noting that a differential solid state amp won't benefit a whole lot from a balanced cable interface beyond rejecting noise picked up in the interconnects.

[Grainger49]

    .  .  .    It's also worth noting that a differential solid state amp won't benefit a whole lot from a balanced cable interface beyond rejecting noise picked up in the interconnects.

Paul,

"Balanced" comes up often.  What are the benefits over and above rejection of common mode noise?

I'm serious, that is all I know of.

[Paul Birkeland]

"Balanced" comes up often.  What are the benefits over and above rejection of common mode noise?

I'm serious, that is all I know of.

This is a topic of pretty serious debate on a lot of forums.

There was a thread on DIY audio where a builder made a long tail pair differential input stage with a current source under the tail.  He used half a 12AU7 and half a 12AT7, and the AC balance at the outputs was still phenomenal.  Despite this, there is still this dogma that a differential amplifier needs to see a differential signal at its input to perform well.  When you combine that with the incorrect assumption that a balanced cabling interface is the same as transmitting a differential signal, the conversation gets messy very quickly.

[Grainger49]

Got' cha!

[gnnett]

Hi Paul

Thanks for that. Just to be clear I do not have any philosophical or technical attachment to balanced cables, just that my journey has taken me through Atmasphere M60's and my current project of a particular set of active speakers (tube based) that just happen to have only balanced inputs.

I have a 0.4mV output cartridge, 20x suts, 41dB phono stage and amp/speakers with 100K input impedance, so gain and higher output impedance is probably not a major.

Will pick up a pair of B7's after playing with the TVC. Of course can use the unbalanced input on the M60's as well, but the actives are my current pursuit.

Kind Regards

Grantn

[Paul Birkeland]

The active speakers may well take an unbalanced feed, I'd double check the manual.

[Paul Joppa]

For more useful information, download the Jensen Transformers' white paper:

http://www.jensen-transformers.com/an/an003.pdf

Look at Fig 2.1 - an adapter cable that will connect an unbalanced preamp output to a balanced power amp input. This is probably all you need.

Fig. 2.4 is the approach in the BeePre; its only real advantage over Fig. 2.1 is better rejection of common-mode noise, which is usually only important in complex (typically studio) systems with long lines.

Figs. 2.2 and 2.3 are ways to use (Jensen!) transformers to achieve the same connections; note the use of 10K:10K transformers to maintain gain. Incidentally, few if any TVCs have a true balanced output.