300B Headphone Amp

[Ray P]

Silence!

Except when there is music playing

Onwards.

[Max N]

What was the source of hum in the end Ray?

[Ray P]

I'm almost embarrased to say!

The problem was the interconnect between the DAC and the headphone amp - I bought a cheap 3.5mm stereo jack to two RCA phonos lead from Wilkos for testing/temporary use and it turns out that in one channel the ground and signal connectors are reversed - not sure how they managed to make it like that! Anyway, using a replacement lead fixes it completely. Annoying that I've wasted so much time on it!

I have to say that the Soekris DAM1121 DAC really sounds very good. I'll start having a listen to the different filter options later and then there are further options to load custom filters - there's a whole thread about them on DIY Audio.

Anyway, onward with the 300B HPA modules that the Soekris will feed into now.

[Ray P]

Now I've sorted out the noise anomaly, I've been having an extended listen to my Soekris dam1121 DAC through my Noir HPA this afternoon/evening - must say I'm impressed with the sound quality. I'm really looking forward to adding the 300B HPA modules into the chassis with the Soekris.

Here's a thing though; Although the Soekris upsamples to 352/384 with its FPGA, I'm finding the best sound is achieved by doing the upsampling using HQPlayer (V4) and I've set the Soekris filter option to 'Minimum' and started to explore the different filters/shapers in HQPlayer, which seem to give you many more options to play with.

I have a nagging reservation about using two lots of filters though?

[Ray P]

I checked the manual for the Soekris dam1121 and it seems that, if you feed it PCM at 352/384KHz the filter options built into the 1121 are not active so it looks as though I'm not using several filter stages. That's probably why I can clearly hear differences when I change the HQPlayer filter settings but struggled to hear any differences between the Soekris filters.

Anyway, I've just been dipping into my music library again - this DAC is seriously good. It will be interesting to compare it to my recently completed DSD decoder.

[Ray P]

A little more progress today, finalised the hook-up wiring for the DAC section and began hooking up the 300B HPA PCBs. Next step is to connect and test the pair of Andrew's DHT filament supplies (top left & right) and build the Maida HV regulator for the B+ (will be installed between the 300B PCBs).



I'm listening to the Soekris dam1121 DAC module as I'm typing this - I know a few here have considered it, if you still are I think you'll be pleased with your purchase...

[simon]

Which bits and bobs do you need to get the Soekris up and running Ray? I think you need more than just the module itself???

I only listen to PCM/ripped CD if that makes a difference.

[Ray P]

I only listen to PCM/ripped CD if that makes a difference.

PCM is perfect, although it can receive DSD all the Soekris does is convert it back to PCM so may as well stick with PCM.

Which bits and bobs do you need to get the Soekris up and running Ray? I think you need more than just the module itself???

It depends on which one you buy (and how deep your pockets are) Simon. Mine is the OEM dam1121 board (0.01% version @ 299Euros) which is just the R2R DAC so I've had to provide power supplies (+/-5V for analogue output stage & +5V for the digital section). If you want to keep it simple/cheap the DIY dam1021 (0.01/0.002% version @ 299Euros or 0.05% version @ 219Euros) has onboard power supplies and just needs a small toroid - I don't think there will be much diference regarding sound quality but remember that the resistor accuracy matters with R2R DACs. There's also a fully featured dam1941 but the cost is quite a bit higher.

http://www.soekris.dk/dam1021.html

In addtion to the dac module you'll need something to give you a PCM data stream to feed it. You could use something as simple as an SPDIF input but IMO you'll do much better with an i2s input. If you wanted i2s there are lots of options depending on your goals, such as RPi/Beaglebone devices, which you can stack with extras such as isolators and reclockers, or there are several good USB input boards. I'm using a JLSounds I2SoverUSB board, which has onboard isolation and reclocking, because it gives me the option of using the 300B HPA project on the home network or using my smartphone as the player. The JLSounds module is excellent and great value at, IIRC, less than 70Euros. You can run the JLSounds module completely off the USB 5V supply but that means having to defeat the isolation and I would recommend giving it at least one good 5V supply to avoid that compromise.

http://jlsounds.com/i2soverusb.html

I'm also using a third party control unit that drives the dam module and the display, purchased from a vendor on DIY Audio, but it's not essential as you can make all the adjustments to the dac, such as the filter selection, via the serial connection (its just less elegant). You can add a simple potentiometer to give you digital volume control (dac operates with 28bits so you don't lose resolution with the FPGA-based volume control).

Does that cover it, if not just ask and I'll try to help.

[simon]

Thanks Ray, very helpful. I can see the benefit of the simplicity of the 1021, and the tweaker's solution of the 1121. Which 5V supplies did you use?

I'm still in the Squeezebox environment so a pi connected via I2S running piCorePlayer would be my way to go.

Do the filters need to be set and tweaked, or can it be used as is? Are the filters more a personal preference?

[Ray P]

You're welcome Simon.

I'm using four TPS7A4700 power supplies, three for the Soekris and another for the 'clean' side of the USB board (the dirty side is powered by the USB bus). I bought the power supply boards from a guy on DIY Audio some time back so thought I might as well make use of them as they perform well and are small with the rectifier and caps on the board (as you can see small was important as there's a lot to squeeze into the chassis). The supply boards are actually two slightly different pairs, one with just a rectifier and cap before the regulator chip (used for the +5V digital supplies) and the other with a rectifier and CLC filter (used for the +/-5V analogue section). I did consider Salas Reflektor-D supplies but they're too big.

The filter options on the Soekris DAC are for subjective taste and you don''t need to do anything to set them up, the DAC will work 'out of the box'. There's a whole thread on DIY Audio discussing custom filters that people have made - you can upload new filters via the serial connection to the DAC and that also allows you to select filters and set DAC parameters (such as the initial volume setting). If you want to be a bit more 'user friendly', here's a link to the control module - I use the Lite version.

https://www.diyaudio.com/forums/vendor- ... ntrol.html

The Soekris DACs have data reclocking after the FPGA but you might want to consider an isolator hat for the RPi to minimise noise getting to the DAC, maybe something like this;

https://www.allo.com/sparky-eu/isolator.html

I don't use RPis but a weakness they used to have was clock quality and data rates (I think everything had to be resampled to 48KHz family rates) but maybe that's fixed now? That's why I use a reclocker to provide the clock to my Beaglebones.

[simon]

Thanks again Ray, very interesting.

Does the isolator just sit between the pi and DAC, connected via the GPIO? Looks like a separate 5V supply can be used for it too, to make 4.

[Ray P]

Does the isolator just sit between the pi and DAC, connected via the GPIO? Looks like a separate 5V supply can be used for it too, to make 4.

Yes, the isolator sits as you describe. Of course, the isolator actually requires two power supplies, one for either side of the isolator chip, otherwise there would be no isolation, but I think there are various options such as powering one side from the RPi and other from the DAC. I've not explored this a great deal because I use Beaglebones, either with Twisted Pear's Hermes/Cronos combo or a DIY isolator/reclocker that the guy behind my DSD decoder developed.

Are you considering buying a dam1021? If so you could start with just the basic RPi/DAC combo and then progressively develop it with isolators/reclockers/power supplies etc. explore the world of filters and, should you wish to be adventurous, there are mods to the dam1021 hardware too. For the RPi I would also investigate the IanCanada modules, which are very well regarded on DIY Audio and available from AudioPhonics;

https://www.audiophonics.fr/en/dac-and- ... 13823.html

[Ray P]

Simon, you might find this blog of interest.

http://www.dimdim.gr/tag/kali/

[Nick]

Rather than trying to fix the Pi's i2s problems, would USB not be a better choice?

[simon]

Dunno, this is a voyage of discovery for me .

I presume you mean using the USB of the pi?