MAINLINE with high impedance tube output DAC

[minionas]

Hi,

Im thinking of building a Mainline and use it with my HD650 and later planned HD800S headphones.
I would pair it with diy dac with tube output. Im not sure about its output impedance, but it must be within 20-30k range.. Would this cause any problems with Mainline of 25K input impedance?

Thanks in advance for advice.

Robertas

[Paul Birkeland]

I would pair it with diy dac with tube output. Im not sure about its output impedance, but it must be within 20-30k range.. Would this cause any problems with Mainline of 25K input impedance?

20,000-30,000 Ohms of output impedance is extremely high, and you would be needing to worry about treble rolloff from cable capacitance regardless of the headphone amp you used.  What is the actual DAC you plan to use?  It may be possible to estimate the output impedance of none is available. 

[minionas]

Hi,

It is ESS9018 DAC with russian 6n16p subminiature balanced output stage. Please see its scheme (cathode resistors "?" are of 390R and 390k).

Im using this dac with SS amp with 47k input.

[Paul Birkeland]

Are you sure there isn't more circuitry beyond what's shown there?  This just looks like a push-pull IV stage.  That arrangement would provide a balanced output with something around 45,000 Ohms of output impedance, but there should be a lot going on after that stage.  Perhaps you might want to contact the manufacturer? 

[minionas]

Its a diy dac. Nothing after. Just 1uf PIO output caps. And phases +- to SE "hot" pins with 250k resistor to shield. Its a output IV recommended by famous Mr. "Lampizator" sold to me as assembled kit for my mentioned dac.

[Paul Birkeland]

I think that the answer to your inquiry has been adequately addressed by this dialog, and I'm not sure that we can offer any additional assistance without completely redesigning our product to suit someone else's kit, or redesigning said kit to have different performance parameters.

[minionas]

So should i trash all this IV ..? It has 2 very stable choke filtered electrolyteless ~50ma 230V tube power supplies.. would be a shame..
I would rather redesign it. As im planning to put a Luhndal LL1941 1:32 step up transformer, to pull my dac to "current mode" which has better perfomance and to make some better tube buffer..

Thanks for any tips.

[Doc B.]

I'm going to back up PB here. What you need for Mainline is a source with a lower output impedance, maybe around 5K max or even lower would be better. The Mainline's input impedance has been chosen to work well with the 6C45pi tubes.

[Paul Birkeland]

I would rather redesign it. As im planning to put a Luhndal LL1941 1:32 step up transformer, to pull my dac to "current mode" which has better perfomance and to make some better tube buffer..

I think that is a good choice.  The issues that you have now will be an issue with just about any component being fed by your DAC.

The SUT's are a good idea, I would do that and use a single 5687 per channel.  You have 230V of B+, and I would run as much current through the 5687's as you have available (to a point).  C4S loading would also be a nice idea, but not completely necessary to start.

Your output impdeance will drop to under 3K with this effort, and without putting pencil to paper, I would expect and order of magnitude less THD at the same time.

[minionas]

No need to back up, as no pressure intended:) The opposite - im glad get any advises and to rework my dac's output and to take its analog side to corresponding level with digital side, which i think is very good (only few ideas for future upgrade).

I'm going to back up PB here. What you need for Mainline is a source with a lower output impedance, maybe around 5K max or even lower would be better. The Mainline's input impedance has been chosen to work well with the 6C45pi tubes.

[minionas]

Thanks for those ideas! I really appreciate it as my experience with tubes is still very limited, but i like it a lot:/
Would you recommend ~same balanced push-pull scheme? Or maybe i could do BAL/SE conversion in SUP and then some SE scheme?
I would definitely would like to load anodes with your C4S right from the start.

The SUT's are a good idea, I would do that and use a single 5687 per channel.  You have 230V of B+, and I would run as much current through the 5687's as you have available (to a point).  C4S loading would also be a nice idea, but not completely necessary to start.

Your output impdeance will drop to under 3K with this effort, and without putting pencil to paper, I would expect and order of magnitude less THD at the same time.

[Bonzo]

I know it's not the simplest way, but what about adding a simple ss buffer between your dac and mainline? Maybe something similar to Nelson Pass B1?

Just my 2c.
Ciao!

[Paul Birkeland]

If you use an IV step-up transformer, that is your differential to single ended converter.

-PB

[2wo]

Before I got my Bottlehead DAC, I was using a pair of Mike transformers on a DIY DAC with some success...John