HIFIDIY.net PCM1798 USB DAC with Tube Buffer

bongoman

Member
2007-11-06 6:47 pm
Has anyone come across or bought one of these yet?

hifidiy.net USB Tube DAC

Specs are as follows:

DAC: PCM1798
USB Receiver: PCM2707
OP-AMPS:
NE5532
OPA604
3PPM master clock
with an option of adding a tube buffer to the output stage.

They do a lower spec version of the kit, which has lower spec discrete components and a more jittery clock. That version is listed on the US site at $90
here.

I think it all came to around £70 and I had to order it through their US agent (which meant the price went up a bit). It should hopefully be turning up soon and I was wondering if anyone else had done one, if I get stuck?

Annoyingly the kit does not feature any sort of S/PDIF in, there are only S/PDIF outputs. I plan to surgically implant a CS8416 to feed into the I2S bus from the existing USB receiver. Also if I can get it to work, an upsampling CS8421 ASRC (I can't seem to get this part to do anything with my TDA1543 as a prototype yet though).
 

bongoman

Member
2007-11-06 6:47 pm
I was told that they are unable to accept Paypal in China, so that is why they set up a US agent. I'm assuming that the price difference is simply because they can and because you are ordering through a reseller, but in any case it's still very cheap for what you are getting. If you are lucky to have a friend in China who you can order through, you would be much better off!

I previously ordered the mini-TDA1543 kit from them and it's a lovely little DAC. After adding a further 3 TDA1543 chips on top of the existing one and tweaking the I/V it performs admirably.
 

bongoman

Member
2007-11-06 6:47 pm
I'm glad to report that I assembled the DAC last night and it started up fine first time!

Unfortunately the kit doesn't come with any English instructions and it's not really possible to make any sense of the Chinese ones that came with it. Basically I had to rely on looking at photos dotted around the web on Chinese forums and the partial schematics to do the assembly. Generally speaking it wasn't that hard though and managed it in a night.

The kit itself consists of the main PCB, with the USB receiver and DAC ICs taped to it. All of the other components just come in a bag which meant a couple of bent pins on the opamps, but nothing drastic. The PCBs are very good quality and thick, with gold plated double thickness copper tracks.

The instructions consist of a page of Chinese and a partial schematic. A daughter board is provided for the optional tube buffer stage, but you need to get a dual triode valve which they will supply for about $5. I would also recommend buying their matching R-Core transformer (~$20), especially if you intend using the tube buffer as it needs a 60V supply and that transformer does all the voltages.

My first impressions of the sound are that it is very very good. This DAC sounds very detailed, clear and warm with my Tripath TA2024 amplifier. I hate to say it, but it generally sounds a lot better than my 4 x TDA1543 DAC. At times it can sound more predictable, but there is a much much better noise floor and it doesn't suffer from the annoying quantization cockups that the TDA1543 produces at low amplitudes. It's also a massive improvement on the sound that comes out of a standard Squeezebox 3, although that's not surprising really. I certainly don't feel a need to upgrade the DAC chip to a PCM1794 at the moment, the PCM1798 sounds great!

The next task is to give this little beauty a S/PDIF input, as currently it's USB input only with S/DIF outputs. I plan to piggyback a CS8416 to inject I2S and possibly make use of the existing low PPM onboard clock.

If anyone needs a hand with building this DAC, I'd be glad to help where I can.
 
Any more news about this HIFIDIY USB Tube DAC kit?

Still on the sidelines but would really like to try it out if there is some more info or review on it.

From what I can tell all one needs to add is a tin case, tube and a power supply to get the thing running. Is this correct?

Any pics or links of it built other than manufacturers website?

I would like to try a battery power suppy with it.

Cheers

.[IMGHTTPDEAD]http://us.hifidiy.net/editor/UploadFile/2007-11/25/2007112517157448.jpg[/IMGHTTPDEAD]

PS. As I've read in a couple of previous post's; it's becoming very hard to find out which one sounds better than the other as there is a slew of new usb dac's becoming available on the market but no real evaluation performed between them. All I hear a lot is "it sounds very good" comments but compared to what?

How would a would a Scott Nixon DAC, DAC707 Super Pro, Fubar, HeadRoom Micro DAC or Bel Canto compare? I am aware some of them cost more. Thanks
 

bongoman

Member
2007-11-06 6:47 pm
I'm Glad to report that my DAC is still running well, although I still do need to put it in a case.

From what I can tell all one needs to add is a tin case, tube and a power supply to get the thing running. Is this correct?

You are correct, basically you get all of the electronic components and PCBs, excluding the valve. I would seriously recommend buying the R-Core transformer that they can supply, as it's inexpensive and does all of the required voltages. I wouldn't have thought that running from a battery would be a good option with this DAC as it requires an inverting 15v input and 60v for the tube heater, just buy the transformer it sounds great!

The only downsides that I had with this DAC was the lack of S/PDIF input. I have since rectified this by adding a CS8414 S/PDIF daughterboard that MUXs the I2S output into the DAC input (4 wires connected to the left wire on the row of the resistors to the left of the USB chip).

As far as comparisons go, as noted before, I have only really a TDA1543 based NOS-DAC and a Squeezebox 3 to compare to. It sounds much much better when compared to the analog out on the Squeezebox, but despite having a lower noise floor it can sometimes sound more clinical than the NOS-DAC. This isn't a bad thing though, the NOS-DAC really just has a different sound and it's probably a matter of taste which you like most.

All said I'm very happy with it and I would recommend anyone with a spare night and a soldering iron to have a go at building one. The hardest part was soldering the 3 SMD components and then looking at pictures on the web to work out where the discrete components go. It wasn't that bad.

I have also bought the HA-2 daughterboard for this kit. As far as I can work out it's basically a little opamp based headphone amplifier stage that neatly plugs into a socket on the DAC. I've yet to build it, but I will report back when I do. Again the quality of the PCB/components look to be superb.

I will post some pictures of my build asap.
 

bongoman

Member
2007-11-06 6:47 pm
If I understand correctly, the switch at the back is used to choose if the Tube is in the circuit or not? Have you tried it out?

I haven't actually tried the switch, but I think it switches between S/PDIF outputs (optical/coax). It definately has nothing to do with the tube buffer, the advised way to disable the tube is to bridge 4 points on the tube connector with solder.
 
bongoman said:


I haven't actually tried the switch, but I think it switches between S/PDIF outputs (optical/coax). It definately has nothing to do with the tube buffer, the advised way to disable the tube is to bridge 4 points on the tube connector with solder.


Alright, thanks.
I've seen another Chinese DAC use this "optional tube method" and thought it was the same. :smash:
 
bongoman said:


I'm Glad to report that my DAC is still running well, although I still do need to put it in a case.

You are correct, basically you get all of the electronic components and PCBs, excluding the valve.
The only downsides that I had with this DAC was the lack of S/PDIF input.

As far as comparisons go, as noted before, I have only really a TDA1543 based NOS-DAC and a Squeezebox 3 to compare to. It sounds much much better when compared to the analog out on the Squeezebox, but despite having a lower noise floor it can sometimes sound more clinical than the NOS-DAC. This isn't a bad thing though, the NOS-DAC really just has a different sound and it's probably a matter of taste which you like most.

All said I'm very happy with it and I would recommend anyone with a spare night and a soldering iron to have a go at building one.

I will post some pictures of my build asap.

Thanks Bongo for the reply,

Pictures would be great, there's none really posted on the web and would be interested to get a sense of physical scale and to see the transformer you spoke about.

Hopefuly I don't sound too ignorant but what would the S/PDIF output be used for? I agree it's dissappointing that it does not have a S/PDIF input but my specifuc use for this is the USB input.

In regards to comparison, are you using the tube stage?

I'm now thinking of either building this DAC or pulling out a Enlightened Audio Designs (EAD) DSP-7000 DAC that I just remembered sitting in the garage collecting dust and using it with a usb-S/PDIF convertor box like the HagUsb.

Cheers
 

kvk

Member
2008-01-25 4:37 pm
bongoman said:
I'm Glad to report that my DAC is still running well, although I still do need to put it in a case.

...
I have since rectified this by adding a CS8414 S/PDIF daughterboard that MUXs the I2S output into the DAC input (4 wires connected to the left wire on the row of the resistors to the left of the USB chip).

[\quote]

Can I ask what the board is and web link if posssible?
 

bongoman

Member
2007-11-06 6:47 pm
Hopefuly I don't sound too ignorant but what would the S/PDIF output be used for? I agree it's dissappointing that it does not have a S/PDIF input but my specifuc use for this is the USB input.

I honestly have no idea why you would want the S/PDIF output under normal circumstances, but conceivably you could use this DAC as a massively overcomplicated USB->S/PDIF converter to feed into another DAC. I shall not be using it.

In regards to comparison, are you using the tube stage?

Yes, I haven't tried using it without the tube stage as yet. As far as I can tell the tube is just used as a buffer to colour the sound and adds no gain.

I'm now thinking of either building this DAC or pulling out a Enlightened Audio Designs (EAD) DSP-7000 DAC that I just remembered sitting in the garage collecting dust and using it with a usb-S/PDIF convertor box like the HagUsb.

If possible I would avoid converting USB into S/PDIF, from a jitter perspective it's not a good idea. S/PDIF receivers always introduce jitter to some extent, USB -> I2S -> DAC is the best way to go.

Can I ask what the board is and web link if posssible?

It's not a very pretty solution but I took a HIFIDIY.net Mini TDA1543 DAC board that I bought a while ago and stripped out all of DAC side of things. I then just took the 3 I2S output wires and the MCK from the CS8414 S/PDIF receiver and fed it directly into the PCM1798.

As suspected, you can't just mux I2S signals from different sources, it seems that you need some kind of switch between them. If I don't feed the S/PDIF receiver with a S/PDIF source and try feeding the USB receiver with a USB signal I get some horrendous noises coming out of the DAC. Conversely if I leave the USB unconnected and feed the S/PDIF receiver, despite sounding ok, I think that the noise floor is higher than it should be. I have ordered a 74VHC157 (Quad 2-input multiplexer) which will hopefully allow me to switch between the I2S sources, essentially acting as a 4 pole digital relay.

I have also built the HA-2 headphone daughterboard for this DAC. It's basically just a stereo single OPA604 gain stage with a power supply and decent quality components. From my initial tests it sounded horribly noisy, but I think this is just because of the I2S muxing problem. I'll sort out the I2S DAC inputs and give it another chance.
 

bongoman

Member
2007-11-06 6:47 pm
Once I get all of this DAC completed I plan to plan to reuse the chassis from an old Watchguard Firebox II firewall that I have laying around doing nothing.

watchguard.jpg


The neat thing about this box is that it has a ready made display panel on the front that normally displays network stuff. This panel normally connects to the parallel port on the watchguard motherboard but after removing the unwanted ICs and adding a couple of LM3916N bar display drivers should make a decent VU meter.

I'm also going to add in a 41hz.com AMP-10B Tripath amplifier to make an integrated DAC/AMP.

Unfortunately this chassis has a Watchguard logo screen printed across the front that I can't seem to remove which means I will have to give the case a respray and lose the nice red powder coat.
 
mr_macgee said:


I'm now thinking of either building this DAC or pulling out a Enlightened Audio Designs (EAD) DSP-7000 DAC that I just remembered sitting in the garage collecting dust

Cheers

Sorry to disturb this post but I'm interested in buying an EAD 7000 (MKIII version ?) and could not contact you as your mail is not activated.

Could you please contact me if dust onyour ead is not already removed ?