AN DacKit 1.2 Upgrade Ideas

[Bryan]

Hey All,

I want to upgrade my dac. I have the Audio note DacKit1.2 with the AN upgrades (bg decoupling, Copper PIO coupling, tants).

Firstly, looking at the schematics, I think the output stage would be a good place to start. Currently, the PS consists of a 6X4-CLC-VR-R supply which feeds both output tubes from the same point.

I'm thinking it would be good to get a little seperation between the two 6922's, and not load them both with the same resistor. If I wanted to try choke loading the 6922's, how would I decide on a good candidate? Does this seem like a good thing to do, and if so, where should I split the PS? The 6922's are both currently fed with one 2K resistor directly from the VR tubes.

Any input is appreciated.

Thanks,

Bryan

PS. I have the schematics, but I am not sure if it is ok to post...?

[fdegrove]

Hi,

Bryan,

For choke loading the 6922s you're probably going to have to burn off alot of volts.

BTW, I'm not sure it's O.K. to post the DAC 1.2 circuit but if you like I can send you the one for the DAC 2.0.
If you want you can send the one for the DAC 1.2 as it seems to be quite different from 1.1 that I've seen before.

In that way we can perhaps both learn from each other...

Cheers,

[Little_Eddy]

Bryan,

I am a couple of steps behind you. I have just bought a 1.2 kit with the PIO decoupling caps and output tube upgrades but I am interested in what you have done regarding the "bg decoupling" and "tants".

Could you please enlighten me with details of these basic upgrades you have done, especially since I am lead to belive the BGs may not be available for too much longer.

Many thanks in advance,

Little_Eddy.

[TJ]

What the dif between the dac kit 1.2 and the AN2.1x and 3.1x ? (the digital circuit )??

[Little_Eddy]

TJ,

My understanding is that the 1.1 and 1.2 kits are very similar to the AN-built 1.1x and 2.1x. I have seen a few posts on the audio asylum - there is a dedicated AN Kits section where I suggest you look for more information. 1.1 kits are still available through http://audionotekits.espyderweb.net/dac.htm, for which you will find a lot of very positive reviews on the web.

In terms of the specifications of the various AN-built models, refer to http://www.audionote.co.uk//dacs/dac_intro.html for more info.

Little_Eddy

[ThorstenL]

Konnichiwa,

Originally posted by Bryan
Firstly, looking at the schematics, I think the output stage would be a good place to start. Currently, the PS consists of a 6X4-CLC-VR-R supply which feeds both output tubes from the same point.

I'm thinking it would be good to get a little seperation between the two 6922's, and not load them both with the same resistor.

Hmm, the VR Regulated supply presents a pretty low impedance, in effect doubling up the VR Valves and splitting the supply into two may give some improvements, but I suspect nothing world shaking.

Originally posted by Bryan
If I wanted to try choke loading the 6922's, how would I decide on a good candidate?

You mean a good choke candidate? It needs to be designed for audio and have loads of Henry. You can get suitable devices from Tango (TC160-15W) and Magnequest (EXO-01), Stevens & Billington has/had sporadically an anode load choke available I had them develope for my own use, I measured around 160H at 50Hz with 12mA DC, this used 40% Nickel in the core.

Any of them I'd think would be a good candidate.

You may have to change the VR Valve to one with lower Voltage and change some other parts in the PSU to adapt the circuit.

Originally posted by Bryan
Does this seem like a good thing to do,

Using chokes as anode loads for the Output valve is a good idea, if done well.

Originally posted by Bryan
where should I split the PS? The 6922's are both currently fed with one 2K resistor directly from the VR tubes.

I see, you are actually NOT talking about "choke loading" the output valves at all. You want to split the supply into two channels.

Easiest is to add a second VR Valve and to use two seperate 3K9 Resistors, this keeps all as before but splits up the supply, though I doubt there will be any significant improvement as a result.

Originally posted by Bryan
Any input is appreciated.

In my personal view, the biggest improvement you can make is getting rid of the current lowpass filter used and to replace the whole I/V circutry with one offering a less steep lowpass (as also applied to more recent AN UK DAC's) and to then add in my suggested "Anti-SinC" correction Filter (1R, 1C & 1L per channel, easily bypassable).

The second biggest would be the right ECC88 (not sure which one will suit you best though).

Sayonara