Valab NOS DAC - subjective listening and modifications

[PatOMalley]

Been doing a little research and I've seen cases where using a huge industrial monster toroidal does a better job than the CineMag. The transformer looks to be about $100 with the option of chassis included.

Been in the middle of moving and will settle in over the next few weeks. Maybe by end of March I will get the thing built. It will work as an isolation transformer and can be placed between pre and amp as well. That is actually where I saw the implementation, between pre and amp.

I got the idea after looking at VALABs interconnect using transformers. They, VALAB that is, use a small tranny whereas the implementation I am thinking about would be heavy lifting. [i exaggerate slightly]

Been reading that 600ohm is not good enough and 1000ohm is the target. Iron of that sort costs many $$$. The toroidal would be effective at lower cost.

 

[zzodhi]

While the trans out is purculating -- regarding Super-E. I was just realizing if I do that it will halve the value of the cap, right? So putting in a pair of 10uF will result in 5uF which is too low? Bill was saying 7.5uF is the lowest.

 

[adam2434]

Based on some poking around in catalogs, those Kemet output caps in the 2009 are polar based on their series # T110.

When changing output caps, is there a need to stay polar?

Also, how about swapping in Mills for the IV resistors? I know Mills are supposed to be good for speaker crossovers.

 

[zzodhi]

I like Mills in the i/v of dacs. Bill likes Caddocks. Personal preference.

 

[tubes]

Adam, the Kemet coupling caps are in the Teradak, the Valab still uses the Russian Tantalums as far as I know. It doesn't look like the Kemets in my dac are polar.

 

[zzodhi]

Mine fresh as of last week has the Russian caps.

 

[r8833]

slightly off topic..for you guys that are handy with a soldering iron this is a great match with dac

diyAudio Forums - Finally, an affordable CD Transport: the Shigaclone story - Page 1

Rich

 

[adam2434]

Quote:

Originally Posted by tubes /img/forum/go_quote.gif Adam, the Kemet coupling caps are in the Teradak, the Valab still uses the Russian Tantalums as far as I know. It doesn't look like the Kemets in my dac are polar.

Hmmm, all the pics I've seen of the Teradak (including the eBay ad I just found TeraDak TDA1543 NOS USB DAC with 1ppm clock - eBay (item 150333021346 end time Mar-24-09 07:55:59 PDT)) show the blue output caps. I thought your pic in post 16 was the 2009 Valab showing the silver Kemet caps.

Nonethless, the caps in your pic are the Kemet polar tants (10uf, 20v T110 series). If interested, these caps are on page 7 of the “Tantalum Hermetically Sealed/Axial Catalog F3100_TaHermSeal” catalog if you scroll down here Catalogs, Datasheets and Updates - KEMET Electronics.

After doing some reading, seems like polar caps are usually chosen because they are smaller and easier to obtain in higher values, and not because the caps “need” to be polar for a specific application.

 

[zzodhi]

I was showing a friend the ad for this dac when I read the following in the description.

b. Decoupling capacitors for digital circuit chips: Eight PSC-470uf 16V solid polymer (os-con) Low ESR/Low impedance 105 degree C tolerance


I had been talking to Bill and told him in this application 470uF seemed more correct. I was surprised to see "this week's model" has them.

These guys are making changes so quickly it makes a week old dac obsolete. Grrr.

 

[Bill Allen]

Yesterday I managed to hook up a "regular" 12 volt car to the Valab Dac for the first time.

First I measured the output of the built in A/C transformer and found two 6 Volt legs for a total of 12V dumping into the filter caps. While the transformer clearly states 9V output, that's incorrect the way it's wired. Clearly a 12 Volt battery will work fine if properly tuned.

I started by soldering a pair of 18 gauge wires to the output leg of a rectifier diodes and ground. (In this scenario the 1000uf filter caps are in the circuit). With no better solution on hand, I simply stripped the ends and taped the wire to the battery posts. Surprisingly the power light lit up as did the green lock light. Success.

Sound???? ..... Well......Different!

While it lost some bass dynamics it did pick up slam in the midrange area. For example piano sounds much more dynamically real. There is a sense of openness on the top end but it's hard to describe. There is "clearly" something missing from the total picture. I suspect it's the noise from the AC power supply. Interesting!

Next I will try bypassing the 1000uf filter caps to see how that sounds. More interesting would be hooking up an 8V battery directly to the DAC board. For now I have discovered that the DAC board draws very little power. After 24 hours of use the battery voltage dropped from 12.58V to 12.51V.

Rich- you’re up, I think the 8V battery you pointed out should run much longer than I originally anticipated. Maybe a full 24 hours before requiring a recharge.

The voltage regulator heat sink and DAC chips are also running cooler to the touch. Obviously less current is flowing, probably resulting in the loss of bass dynamics. Maybe we will need that "exact" capacitor after all.

Where the hell is an engineer when you need one!!!

 

[r8833]

hi Bill,

Xenotronix - HPX10 Sealed Lead-Acid Battery Charger

use a DPDT toggle switch and charge when not in use..it will never run out of juice

Rich

 

[Angsila]

Charger and Battery---http://www.audio-magus.com/PowerCenter_Battery_Power_Suppy_p/bps1.htm

 

[zzodhi]

Very cool combo. Unfortunately SLA's have too much internal resistance. I had three in my big dac - one for each power supply of the dac. Beautifully quiet. Typical loss of dynamics. You need a battery with the lowest DCR. Some people have used glass mat or gels with "super capacitors" like the ones for electric cars. Quite expensive though.

 

[Pars]

Interesting thread. I've noticed mention of "rule of 5", which I have never heard before? Can someone explain this?

 

[TeraDak]

There is also another difference. We used LM334 current source with blue trimmer for TDA1543. ^-^

Quote:

Originally Posted by zzodhi /img/forum/go_quote.gif ok, yes it has a red LED. Also has 330 Ohm i/v resistors. There are now some type of silcone/heatsink pads between the dac chips and case. Aside from what I mentioned earlier that's all I see. Oh, it did come with a hundred dollar bill stuffed inside the case. Is that new?