Designing a versatile pre with balanced and unbalanced in/out

[Nikon1975]

I made some diagrams:
1) Yellow and green boxes represent two different chassis.
2) The thick connection are balanced signals the thin are SE
3) The dotted are external cables.

The last picture contain a question, whose answer I am not sure, most probably depends on the implementation.

Commenting on Thorsten suggestion, the only thing I do not like is that for SE signals that go to SE amps, you have double conversion back and forward. I was trying to minimize the signal manipulation, but mine could just be a misconception of how things work.

The proposed solutions allows great flexibility, beside the fact that I already have the SE amp, and the converter.

I like them all for different reasons:
Option 1 because the two devices are by themselves kind of flexible.
Option 2 because all the cabling is balanced. In reality I do not have big issues with ground loops, so...
Option 3 one power connection less in the rack.

All minor things.

Thanks,

Davide

[NicMac]

Ciao Davide,
Thank you for the diagrams. I was hoping to avoid two volume controls even if I understand that two conversions will be required when using SE source and SE amp in this case. I have attached a diagram of what I have in mind.
Cheers,
Nic

[ThorstenL]

Davide,

Originally Posted by Nikon1975

Commenting on Thorsten suggestion, the only thing I do not like is that for SE signals that go to SE amps, you have double conversion back and forward.

First, I must say that I generally come from an "SE" viewpoint towards things. While fully differential circuits have some advantages (and disadvantages) compared to single ended circuits I would say that the implementation is by far more critical than anything else.

Being basically also a "fan" of transformers my personal solution to mixing SE and Balanced freely would of course be a TVC "passive preamp", possibly pre-buffered with a balanced DCB1 section or similar and a transformer designed to give more "gain" as option.

If I already had an SE Preamp I really liked would probably keep it and just add an input transformer in front of the volume control and add balanced ins and use balanced input switching ahead of the transformer (and operate the SE Inputs also as "floating balanced". You can see this style of inputs in various of Sy's preamp designs, including the Impasse.

You now have a SE Preamp which has transformer coupled SE and Balanced inputs that are being treated equally.

You can keep the SE outputs as is, for balanced outputs just add an output transformer, or again, use the output transformer to drive both SE and balanced outputs with full isolation optional (this will help even for SE).

Note that as such there is no BAL/SE or SE/BAL conversion ongoing, just transformers. Transformers don't "know" if the source or load is balanced or not, they simply react to voltage/current between two points and output voltage/current between two other points.

Of course you may feel that the two transformers hopelessly compromise fidelity, then maybe you have to such a kludge as you have shown.

In this case my gut feeling would be to make an preamp with a true balanced input (in other words it always reacts to the difference between two points, one of which may be ground) so it accepts balanced and single-ended sources equally and to accept that the SE output is one phase of the balanced output signal.

Ciao T

[Nikon1975]

I like the "democratic" approach of transformers, that does not really differentiate between SE and balanced .

I am listening not to the ESS9018 with the transformer, not bad at all. I am trying to make my own opinion about the use of transformer. Here in Japan there is a good production of audio transformers, but the prices are over the sky. You can easily pay 700 $ for two input transformers, while the Jensen are just 200 $.

D.

[dimkasta]

Hello guys. This thread was a very nice read

I came here trying to find a way to connect my Audio Research PH3 and EAR 834p phonos to a passive dact and then to my balanced only input Electrocompaniet AW120DMB

I was planning to work something with the JT-11p-1 according to the as060 application note from Jensen.



Probably what Nikon did on the wooden box of his son right?

Sorry to jump in the middle like that, but could you please help me to better understand that part of phase splitting and how it would affect the impedance matching? What resistors should I use to better match input and output?

Thanks a lot

[Speedskater]

What is a "passive dact" ?

[dimkasta]

Originally Posted by Speedskater

What is a "passive dact" ?

I was thinking of a passive volume control. An attenuator for example like the one made from dact

[ThorstenL]

Hi,

Originally Posted by dimkasta

I came here trying to find a way to connect my Audio Research PH3 and EAR 834p phonos to a passive dact and then to my balanced only input Electrocompaniet AW120DMB

Some notes first, the EAR 834P does not do well with low impedance loads, it should be used with a 100K Attenuator or Pot.

Using such you stand absolutely zero chance of driving a transformer, unless you add a buffer.

So I would suggest a 100K attenuator combined with the DCB1 Buffer and then a line output transformer from Jensen, JT-11-BMCF would be good. This would be quite close in concept and mostly parts to the Steve McCormack "Virtual Reality Engine" preamplifier that sells for a lot of money, if possibly not quite to the same level.

If balanced inputs are needed as well then adding a Jensen JT-11P-1 to handle this will do splendidly.

So for SE Inputs the circuit would be:

RCA Input ->
Input Selector ->
DACT 100K Attenuator ->
DCB1 Buffer PCB ->
Jensen JT-11-BMCF ->
XLR & RCA Outputs

For Balanced Inputs the circuit would be:

XLR Input ->
Jensen JT-11-P1 ->
Input Selector ->
DACT 100K Attenuator ->
DCB1 Buffer PCB ->
Jensen JT-11-BMCF ->
XLR & RCA Outputs

Outputs from the Jensen JT-11-BMCF can be SE or Balanced but not SE & Balanced mixed.

Ciao T

[dimkasta]

What if we keep the internals in balanced topology?

I mean for RCA inputs:
RCA input ->
Jensen JT-11-P1 (1:1+1) ->
Input Selector ->
Attenuator ->
Jensen JT-11-BMCF ->
XLR & RCA Outputs

and for Balanced inputs it would be
XLR Input ->
Input Selector ->
Attenuator ->
Jensen JT-11-BMCF ->
XLR & RCA Outputs

For attenuator I am thinking of building a custom one in Balanced T (H) topology to preserve input and output impedance.

[Nikon1975]

Thorsten,

as far as I know the for DCB1 25k is the maximum value for pot recommended.

Dimkasta, the evil is in the details. Without the buffer you will have troubles in driving the transformers, depending on your source.

D.