[rhodes54]

@dannie01: Great work! It is a bit how my Valab will look within' a few weeks.
What does the little print with the regulator and cap, left from the transformer do?
I also notice a few extra caps in the digital circuit: The yellow and black one. Are they meant as bypass caps? I'm curious

 

[dannie01]

Thanks for the compliment rhodes54. The little print on the left hand side with a regulator and a 100uf cap is a power supply circuit (I draw the lines out from one of the filtering cap)for the LED of the latch switch. The yellow one is a Auricap 4.7uf to replace the original SMD cap and the black one is a 75ohms Vishay resistor replaced the SMD in the digital path.

 

[rhodes54]

@Pat & Bill:
I received my Dexa 7808 replacement last week but I didn't put in in my Valab DAC yet.
The main reason for it is that i've got an unanswered (and important) question:
A normal 7808 requires at least a 3V difference between the in- and output voltage. The 7808 needs this voltage difference to be able to deliver enough current on the output.
With a normal 7808 this would be a problem in this design as the transformer delivers a 9V voltage (10,5 Volt in Holland as we have approx. 235V here) and that's too low to feed a 7808.

In the specs of the NewClassD/Dexa 7808 replacement I can't find what the minimum required voltage is. I already dropped them a mail but didn't receive an answer from them so far.

Any ideas on this? I can of course try to exchange my recently purchased 9-0V,9-0V tranny for a 12-0V,12-0V but it would safe me the hassle if the NewClassD accepts a 9V input voltage.

By the way: I measured the current of the The TDA1541 chips in my Valab and all together they use 384mA at 7,62V so that won't be a problem for the NewClassD/Dexa as it can deliver 600mA @ 8V.

 

[adam2434]

Quote:

Originally Posted by shogo33 /img/forum/go_quote.gif Btw, just out of curiousity, does your Valab power supply hum or emit a low buzzing noise that can be heard about a foot away? Mine seems to be doing this. I've narrowed it down (by just powering the dac directly to a power socket at the wall) and swapped the power cables to different ones and the noise is still there. I've even plugged it around several power sockets around the house to see if it made a difference, but it didnt. I've sent Kevin an email about this, but he hasnt replied back. I hope the power supply unit isnt faulty, but its hard not to suspect it as the hum/buzzing noise seems to be coming from it.

You're talking about a mechanical hum from the DAC itself, right?

If so, others have reported this too. Mine has this. I found that weight on top of the chassis damps the vibration. I use two 2.5 lb barbell weights sitting on and separated by some foam shelf liner.

I found that if I used my hand to put some pressure on the top of the case, I could damp the vibration, so this led to adding the weight.

When I had the case open to do some mods, I also put 4 small balls of Blu Tack on the transformer to decouple it from the case.

 

[shogo33]

Ditto Adam,

I did some googling and have narrowed it down to mechanical hum from the transformer on the dac. I'll damp it down with a 2kg block of wood or something heavy to decouple it from vibrations. Thanks for the tip, as i was thinking that the mechanical hum was due to some problem with the transformer. Btw, i'm really loving the sound of this dac, I would love to get it modded, but alas i have no electronic/soldering skills.

Kevin responded this morning and said that the transformer will hum to a certain extent but shouldnt affect the sound much.

 

[PatOMalley]

rhodes54,
The Dexa's "Dropout Voltage" is: 2.00V
So it is a 2v difference and should work.

Looks like I am stuck using the Dexa for the board only[7805].
But that's what I was thinking to do anyway to feed the DIR9001 with better power to cut down on jitter.
The only things is that some EPI speakers showed up here today that need recapping. And my tonearm needs replacing. I am dragging my feet on the transformer thing.


dannie01,
That looks like a professional shrink wrap job. Nice chassis.

 

[dannie01]

Thanks Pat. It really sound wonderful especially after the DIR9001 mod, overall more spacious in soundstage and impactful bass.

 

[awkwardbydesign]

Output cap question. Using a Prometheus TVC instead of a pre -amp, do I need output caps at all?

 

[PatOMalley]

I think if you have a cap at input large enough on the Prometheus then you are effectivly blocking incoming DC. Can't get away with that coupling a transformer, or so TERADAK tells me.

So match the cap value or exceed it at input on the Promethius.

 

[awkwardbydesign]

Thanks again Pat, I'll stick with the Valab's output caps.
I am so glad there are people with brains worth picking, and are prepared to let me pick them!

 

[guitarplayer]

OK, first off, I am not interested in modding these Teradak/Valab DAC's for anyone else, so please don't ask. I also don't have the time to answer "what parts where" questions, so please don't ask those either, reference this thread and one should be able to glean all the knowledge one wishes from it.

In the interest of full disclosure--I don't sell most of the below parts and have no vested interest in the Teradak, in fact, I declined the opportunity to distribute them here in the US. I do not think they are the "greatest thing since sliced bread" either. I do, however, think they are a good value. The BEST value under $500, probably not, but quite good.

This is an interesting thread, so I thought I'd throw a few different part choices in the mix to add to the collective knowledge.

I have reworked two of these DAC's now, a late 2008 Valab model and a 2009 Teradak model and have found these parts/mods to really work well.

Cryo the thing!
OSCON 1000u reservoir caps (3)
OSCON 47u bypass caps (18)
22u Black Gate output caps (2) 2008 model
10u Mundorf film output caps (2) 2009 model
.001u Sonic Cap bypass (4)
.01u Vishay MKP 1837 bypass (6)
350ohm Riedon output I/V resistors (2)
Furutech IEC inlet
WBT NexGen RCA's (or your choice of good RCA's) (3)
.5mm silver/gold Mundorf wiring (or your choice of good wire)
1.0mm Neotech SPC power wiring
Arctic Silver thermal compound
ERS fabric
Damping sheet
...and some other stuff, I'll update as I remember.

So, that's my $.02, its worth what you paid for it!

Peace,

Lee

 

[PatOMalley]

guitarplayer,

Since you are a cryo guy do you know of any places in the metro Phila area where a cool cat can get their stuff cryo'd?

I did a yahoo search and a lot of the stuff is sperm banks and such. I might look like a real geek walking into a place like that with the DAC under my arm.

 

[guitarplayer]

Quote:

Originally Posted by PatOMalley /img/forum/go_quote.gif guitarplayer, Since you are a cryo guy do you know of any places in the metro Phila area where a cool cat can get their stuff cryo'd? I did a yahoo search and a lot of the stuff is sperm banks and such. I might look like a real geek walking into a place like that with the DAC under my arm.

Umm, that is going into an area that is too close to my own business interests, so I will decline to comment publicly, sorry. I don't want to use the general forums on HF to promote my business or financial interests.

Lee

 

[PatOMalley]

guitarplayer,

PM time.

 

[krisno]

I did the obbligato 4.7uf output cap. Really sound amazing now... but I orderd some of those .22u ampohm paper in wax as a bypass. Still regretting the paper in oil, but well, wth how big difference can it be?

Bill.. that pacecar, does it really make the valab even better? How does your jupiter .22uf bypass work? I guess my bypass will be about the same as both are paper in wax. any comments?.... what did your .22uf bypass do to the sound of the DAC?

It really can be sharp and edgy at times, is this gone with a .22uf PIW bypass?

K