I've replaced the headers successfully and I'm listening to the RTZ DAC again - sounding as good as I remember from last weekend - currently enjoying Vivaldi's Four Seasons from a Native DSD256 recording via my Noir HPA.
Replacing the headers has ceraintly made the connections between the boards a lot more consistent, if not guaranteed (I still needed to twist the filter board back and forth a little to get sound out of it but I think some additional stand-offs to clamp the boards together would solve that - as it is there is only one stand-off to clamp the boards together).
When installing the new headers I did a bit of tidying up of the hook-up wiring and the whole thing is now screwed down to a piece of MDF.
Marcel, one thing that worried me about the header rework was how much heat was required for solder connections to the ground plane on the DAC board?
Replacing the headers has ceraintly made the connections between the boards a lot more consistent, if not guaranteed (I still needed to twist the filter board back and forth a little to get sound out of it but I think some additional stand-offs to clamp the boards together would solve that - as it is there is only one stand-off to clamp the boards together).
When installing the new headers I did a bit of tidying up of the hook-up wiring and the whole thing is now screwed down to a piece of MDF.
Marcel, one thing that worried me about the header rework was how much heat was required for solder connections to the ground plane on the DAC board?
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Yes, I thought you had similar problems Marcel...
Unfortunately I've only got the JLSounds 12soverUSB version 2 and that is limited to DSD256 but DSD64, DSD128 and DSD256 (at both 44.1KHz and 48KHz family rates) all work fine. I do have a V3 but it is installed in the Valve DAC and it would be a lot of work to extract it and that project will be shipping out to its owner soon so I'll resist the temptation.
I do like the sound Marcel, I'm still listening and exploring my library again (and exploring different settings in HQ Player). It does seem to improve in sound over the first 30-60mins, it seems to get a little smoother and becomes very easy to listen to. It sounds very clean but without being clinical.
I started to put one of these output stages together today to try with the RTZ DAC, including Marcel's suggested amendment to make it compatible. I would like to try it before returning the RTZ to Marcel so I'm looking to quickly put together a suitable B+ supply - I think I have everything else to hand.
Marcel, a slight change of plan; because I have more of the parts available I propose implementing the version of the 'CD Enhancer' circuit shown below (except I will use 6SN7 tubes instead of 5687s) - it's a little different to the 3A5 version with respect to the cathode to ground arrangement - thoughts?
Attachments
I use a rather old version of KiCAD, version 4.0.5+dfsg1-4~bpo8+1 from 2015. Using a search engine with search term sym-lib-table, it looks like those were only introduced in 2017. I don't know about the fp-lib-table.
Compared to the earlier circuit, the 1800 pF filter capacitors are missing. I think you will need them, possibly with a grid stopper after them if needed for stability.
The voltage drop across the 1 kohm cathode resistors at the indicated current of 12 mA would be 12 V, but according to http://www.r-type.org/pdfs/5687.pdf , a triode from a 5687 needs about -8 V grid voltage for 12 mA anode current at 168 V anode-cathode voltage. That is, either the circuit expects a 4 V common-mode voltage or the current will be a bit less than indicated. I expect it will be about 10 mA with the 1.25 V output common-mode voltage of my DAC. That shouldn't make much of a difference.
Edit: sorry, about 6 mA, as you use 6SN7, http://www.r-type.org/pdfs/6sn7gt-2.pdf
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I've just returned from a gathering of UK-based audio DIYers, organised via the Audio-Talk forum. I took both the Valve DAC and RTZ DAC and demo'ed them via my Noir headphone amp and BeyerDynamic DT-880 headphones. Source was a laptop running a demo version of HQPlayer and media was a selection of .dsf recordings, played back via direct DSD mode.
The response of those who listened was universally positive about the sound quality of both DACs with the Valve DAC being preferred, but only by a very small margin.
I also had an opportunity to demonstrate the Valve DAC through some high-end amplifiers and a pair of beautiful looking acryliic open-baffles speakers, which were a fantastic sounding combination. Feedback was that the Valve DAC outperformed a high-end vinyl front end that was used just before (though to be fair it had to be used on a less than optimal table).
I think the RTZ is a fantastic DAC that is somewhat simpler and more affordable than the Valve DAC and I would certainly want to build one.
The response of those who listened was universally positive about the sound quality of both DACs with the Valve DAC being preferred, but only by a very small margin.
I also had an opportunity to demonstrate the Valve DAC through some high-end amplifiers and a pair of beautiful looking acryliic open-baffles speakers, which were a fantastic sounding combination. Feedback was that the Valve DAC outperformed a high-end vinyl front end that was used just before (though to be fair it had to be used on a less than optimal table).
I think the RTZ is a fantastic DAC that is somewhat simpler and more affordable than the Valve DAC and I would certainly want to build one.
There are a couple of comments about the DACs on Audio-Talk here;
https://www.audio-talk.co.uk/phpBB3/viewtopic.php?p=199863#p199863
but the general sentiment was that the RTZ gives very little away to the Valve DAC, which is impressive given that is is still a prototype. An advantage that the RTZ has over the Valve DAC is that there is no tweaking required to set it up or as the valves age - that has become obvious to me over the last couple of weeks!
There was interest in having the option of a simple valve-based filter/output stage based on me attempting to put together one based on the 'CD Enhancer' schematic - perhaps if you could design an optimised stage along those lines...
Another option I would like to suggest is a version of the RTZ board with a header that allows a JLSounds i2soverUSB board to be plugged straight on - in my experience the JLSounds board is better than the Amanero and also includes galvanic isolation. At present I have to use an adaptor PCB to connect my JLSounds modules to Amanero style headers.
I mentioned a few other suggestions a few posts back.
And some pictures;
https://www.audio-talk.co.uk/phpBB3/viewtopic.php?p=199887#p199887
Sorry the Valve and RTZ DACs are getting referenced across the two threads.
https://www.audio-talk.co.uk/phpBB3/viewtopic.php?p=199887#p199887
Sorry the Valve and RTZ DACs are getting referenced across the two threads.
After the DIYer event yesterday I've been motivated to get on with a valve stage for the RTZ DAC. As it happens when I checked I found i don't have a transformer suitable for the 6SN7 power supply to hand so I've reverted to the 3A5 circuit and have assembled and tested power supplies for the B+ and filaments.
The filament supply is an LT1085 based regulator and is set to 2.8VDC delivering 500mA to a dummy load.
The B+ supply is a Maida regulated supply delivering 125VDC delivering 50mA to a dummy load. 125V is a little higher than specified on the 3A5 schematic but is 10V under the max plate voltage so should be OK. I could change some components on the reguulator board to lower the voltage but i would prefer to avoid messing with it.
I've started putting the 3A5 circuit together on some vero type PCB and have ordered the 1800pF caps I need.
The 3A5 is a DHT so if the breadboard shows promise I'll look to swap in a pair of dedicated DHT filament supplies.
The filament supply is an LT1085 based regulator and is set to 2.8VDC delivering 500mA to a dummy load.
The B+ supply is a Maida regulated supply delivering 125VDC delivering 50mA to a dummy load. 125V is a little higher than specified on the 3A5 schematic but is 10V under the max plate voltage so should be OK. I could change some components on the reguulator board to lower the voltage but i would prefer to avoid messing with it.
I've started putting the 3A5 circuit together on some vero type PCB and have ordered the 1800pF caps I need.
The 3A5 is a DHT so if the breadboard shows promise I'll look to swap in a pair of dedicated DHT filament supplies.