How about a DHT output DIY DAC?

Mags · « **on:** 12 Jan 2015, 04:40 pm »

Just finished it up. 26 output tube, Buffalo IIIse DAC board, Sonore asynchronous USB board. Lundahl LL1676 amorphous cobalt core xformers between the DAC and tube. Bent Audio silver slagleformers on the outputs.

Sound is amazing...

Mags · « **Reply #1 on:** 12 Jan 2015, 04:42 pm »

Pic with the lid on...

jtwrace · « **Reply #2 on:** 12 Jan 2015, 04:43 pm »

Very cool.

How about some more pics?

Mags · « **Reply #3 on:** 12 Jan 2015, 05:25 pm »

More Pics? Sure!

Here's the power supply box. From right are the filament supplies for each channel, the high voltage plate supply for the 26, and the DAC power supply. The DAC supply has another LC section in the preamp box, along with two Salas Reflektor-D power supplies for the DAC board and the Sonore asynchronous USB board.

Here's a pic of the DAC section:

Here are the input and selector switches. The top switch toggles from S/PDIF to USB, the bottom one turns the DAC OSF on and off. Will play PCM or DSD through USB.

JoshK · « **Reply #4 on:** 12 Jan 2015, 06:25 pm »

What four tubes are in the front, a pair look like OD voltage reference tubes?

Mags · « **Reply #5 on:** 12 Jan 2015, 07:06 pm »

All four are VR tubes. Each channel has a 0D3 and a 0A3 in series to produce a regulated 225V. The VR tubes are fed with a CCS for each channel.

JoshK · « **Reply #6 on:** 12 Jan 2015, 07:14 pm »

Very cool project! I am still working on my Bent preamp with K&K Raleigh Audio active line stage.

Do you find the 26's to be microphonic? What about start up?

jtwrace · « **Reply #7 on:** 12 Jan 2015, 07:28 pm »

mags

That's looks great! I'm sure it sounds just as well too.

Mags · « **Reply #8 on:** 12 Jan 2015, 08:00 pm »

Quote from: JoshK on 12 Jan 2015, 07:14 pm

Very cool project! I am still working on my Bent preamp with K&K Raleigh Audio active line stage.

Do you find the 26's to be microphonic? What about start up?

If you look closely at the pics, you'll see the rather elaborate mounting of the 26s. There are teflon sockets mounted to a massive plate consisting of two 4mm thick pieces of aluminum sandwiching a sheet of Soundcoat damping material; that plate is then mounted to wooden posts using gaskets cut from Deflex damping material. The mass, damping and dissimilar materials are all intended to eliminate microphonics. I have no issues with microphonics in this system.

What about start up? There are two power switches on the PS, one for filaments and one for B+; I usually start the filaments, wait 15 -30 seconds or so, then start the B+. The filament switch also turns on the preamp control circuits and energizes the DAC power switch located on the back of the preamp box. When the DAC power switch is off, the preamp functions as it normally did before. When the DAC power switch is on it energizes the DAC power supply and also throws a 9V relay that disconnects the preamp inputs from the 26 and connects the DAC to the 26. Pretty seamless.

JoshK · « **Reply #9 on:** 12 Jan 2015, 11:00 pm »

Killer

randytsuch · « **Reply #10 on:** 12 Jan 2015, 11:32 pm »

Adding in my admiration for your project.

Also wondering why the slagleformers, for volume control?

The ES9018 DAC has volume control, and I think TPA supports this feature.

Randy

Mags · « **Reply #11 on:** 12 Jan 2015, 11:52 pm »

Quote from: randytsuch on 12 Jan 2015, 11:32 pm

Adding in my admiration for your project.

Also wondering why the slagleformers, for volume control?

The ES9018 DAC has volume control, and I think TPA supports this feature.

Randy

The Slagleformers perform three functions - they are volume controls, they are left/right balance controls, and they are the output "transformers" for the 26 tube. As outputs they are run in a lossy parafeed configuration as they do not block DC, being autoformers. Also, keep in mind that this is a full-function preamp, with 6 RCA inputs, so it needs a way to attenuate ALL sources, not just the DAC.

ElliottStudio · « **Reply #12 on:** 13 Jan 2015, 12:23 am »

Very nice.

randytsuch · « **Reply #13 on:** 13 Jan 2015, 01:24 am »

Quote from: Mags on 12 Jan 2015, 11:52 pm

The Slagleformers perform three functions - they are volume controls, they are left/right balance controls, and they are the output "transformers" for the 26 tube. As outputs they are run in a lossy parafeed configuration as they do not block DC, being autoformers. Also, keep in mind that this is a full-function preamp, with 6 RCA inputs, so it needs a way to attenuate ALL sources, not just the DAC.

I didn't realize it was a preamp too, I missed the RCA jacks in one of the pics.
So can you independently control the Slagleformers for left/right balance? I had a TVC for a while, but I used one switch so it couldn't do balance.

Mags · « **Reply #14 on:** 13 Jan 2015, 12:51 pm »

Quote from: randytsuch on 13 Jan 2015, 01:24 am

I didn't realize it was a preamp too, I missed the RCA jacks in one of the pics.
So can you independently control the Slagleformers for left/right balance? I had a TVC for a while, but I used one switch so it couldn't do balance.

It started out as a preamp, to which I added the DAC. Yes, you can independently control the channels Notice the two level displays on the front panel. It is done via the remote, so you can get just the right balance while seated in the listening position; it really helps to correct for an asymmetric room.

lokie · « **Reply #15 on:** 13 Jan 2015, 01:57 pm »

Very impressive.

Curious about a few of your decisions.

Why Buffalo board?
Why Sonore usb board? Did you consider http://luckit.biz/

What is the origin of your inspiration for this project?

Thanks for sharing a really top notch DIY project.

Mags · « **Reply #16 on:** 13 Jan 2015, 02:36 pm »

Quote from: lokie on 13 Jan 2015, 01:57 pm

Very impressive.

Curious about a few of your decisions.

Why Buffalo board?
Why Sonore usb board? Did you consider http://luckit.biz/

What is the origin of your inspiration for this project?

Thanks for sharing a really top notch DIY project.

I had a gathering of audiophiles at my house in November, and someone had brought a DAC made with the Buffalo IIIse and I liked what I heard compared to the DAC in my CD/HD player (which is based on the highly regarded Burr-Brown PCM1704 chip). That inspired me to add the Buff IIIse to my preamp and have it double as a tube output DAC. It also happened to be the right size to fit in the available space.

I chose the Sonore board because it has the capability of running synchronous clocking with the Buffalo IIIse, which I may use in the future if I get the itch to tweak. It can also take over the oversampling and filtering from the Buffalo and they claim it has better performance in that regard, with more sophisticated filters - I'll have to see if that's the case in my application. Finally, it was designed with the Buffalo DAC in mind, so it should integrate seamlessly.

randytsuch · « **Reply #17 on:** 13 Jan 2015, 03:34 pm »

Quote from: Mags on 13 Jan 2015, 12:51 pm

It started out as a preamp, to which I added the DAC. Yes, you can independently control the channels Notice the two level displays on the front panel. It is done via the remote, so you can get just the right balance while seated in the listening position; it really helps to correct for an asymmetric room.

From the pics, its a little hard to tell what the displays are for, and what the buttons are for.

So do you also have a microcontroller in there to handle balance, volume, the display and remote control? Does it handle the source selection with relays?

I'm more and more impressed by this project.

Randy

Mags · « **Reply #18 on:** 13 Jan 2015, 03:45 pm »

Quote from: randytsuch on 13 Jan 2015, 03:34 pm

From the pics, its a little hard to tell what the displays are for, and what the buttons are for.

So do you also have a microcontroller in there to handle balance, volume, the display and remote control? Does it handle the source selection with relays?

I'm more and more impressed by this project.

Randy

The remote control (picture in the second post above) allows one to increase/decrease volume, adjust left/right balance, select any of the 6 RCA inputs, and turn the display on and off via a microcontroller in the preamp. Source selection is via relays. In fact, the volume control itself operates via high-quality Pickering relays installed on each autoformer module, with 61 1dB steps per channel. The entire autoformer/display/input selector package used to be available from Bent Audio as a passive preamp for DIY, but as of January 1, 2015 I think he has ceased selling to the DIY market and is concentrating on his OEMs. Basically, I took the Bent Audio passive preamp modules and built an active preamp out of it, now I've added a DAC as well.

JoshK · « **Reply #19 on:** 13 Jan 2015, 10:45 pm »

Quote from: Mags on 13 Jan 2015, 03:45 pm

The remote control (picture in the second post above) allows one to increase/decrease volume, adjust left/right balance, select any of the 6 RCA inputs, and turn the display on and off via a microcontroller in the preamp. Source selection is via relays. In fact, the volume control itself operates via high-quality Pickering relays installed on each autoformer module, with 61 1dB steps per channel. The entire autoformer/display/input selector package used to be available from Bent Audio as a passive preamp for DIY, but as of January 1, 2015 I think he has ceased selling to the DIY market and is concentrating on his OEMs. Basically, I took the Bent Audio passive preamp modules and built an active preamp out of it, now I've added a DAC as well.

Good thing I grabbed my kit from him a few months back as well then! I had always wanted to build the Bent with an active stage ever since I first heard a Bent. I really only want active because I am running longish cables ~15' or so.