Valab NOS DAC - subjective listening and modifications - Page 134

Good Day Mates ,

Can i request contributors in this thread to point to the valab 2009 v 2.5 schematic. Your help will be much appreciated.

Thanks
 

Hi, mine is valab 3.0.

I successful modify the signal output, from 10uf. down to 2.2 uf. cap. russian k75-10 modified, and from 47k to 2k7ohm/200Henry plate choke (signal to ground). And enjoy so much this way.

Now what happens is my unit is faulty, and don't know how to test the TDA1543 ic. to discard they are broken or not.

-also welcome some guidance to find the place damaged, voltage values seems correct, and soldering points, everything is clean and good looking. I use only USB input.

Thanks in advanced.

1. Can you elaborate on the "plate choke" mod?
2. Can you test optical / coaxial input?
3. Try to remove the TDA1543 from their sockets and then put them back.
4. Remove all 7 TDA1543 so you have only one chip. Try different chips in different sockets.

1-"plate choke"

   I reach to lower the output impedance and place a 50k pot to substitute the SMD 47k at the circuit. A trick is soldered wires on tested component and terminated with alligator clips. Then raise the value turning the pot while listen music.

I test the value chosen, and seems to be 3,6k.

Looking to spare parts I need a good quality fixed resistor and knowing from past experience a "choke" to compare.

Lucky, I have 3k3 Vishay TX2352, and 200H ANODE GRID FILAMENT CHOKE
 with a resistance 2k7. To compare I put on alligators place: vishay little better than pot as expected and -no need to say- never return back to original mudded 47k. Then, the best part, choke outperforms by a large margin the vishay, which is in turn a great compliment. 

 

2-USB is my only source. Maybe tomorrow Sunday I can pick a big television with optical, but don't know sure.

 

3-remove and put back. Done yesterday to test for differences or continuity between pins. No luck.

4-Just finish right now to play one chip and also no luck.

1. Where is this 47k you are talking about?

2/3. I guess you'll have to order some TDA1543's to check.

47k are output resistors (signal to ground) two small SMD after the 10uf. the last components before signal leaves the board.

 I found this values completely wrong.

Concerning the capacitor substitution.

I proceed as resistor explained before, with two more wires soldered on capacitor holes and alligators, I test the whole range of Elna silmic-II.

Start from 10uf, which betters the stock Russian, then 4,7uf. fount it more coherent, then 3,3uf. further coherency and balance, finally 2,2uf. best of all, highs opened without loss on bass depth. Easy. Now I have on the unit this litlle Elna Silmic-II and Vishay to ground for easiness in faultfinding, but when finish the whole upgrades of this good thread, back to bulky PIO k75-10 and choke.

Modification of K75-10 capacitor is a must to juice at full potential:

 

 

Ah! concerning the repair, thanks so much LosNir for help , I agree for damage on TDA1543 IC's.

By chance, do is someone able to test on a healty IC, the diode value (from ground to other seven pins)?

Has anyone tried other resistors except 47K?
 

You mean to check continuity? I can do that.
What you did to the K75? it looks interesting. I have the FT-3 and the K42-11 combined.

To check an IC health must proceed as any transistor, position diode/continuity on meter, there it beeps when shorted the leads, and "1" when no signal.

Then tie the black wire to ground (pin 4) on TDA1543 and read the remaining pins. 

Mines eight IC read very close to the following values:

1..BCK..1830

2..WS...1828

3..DATA.1831

4..GND

5..VD....1820

6..AOL..1

7..VREF.1985

8..AOR..1

 

The K75-10 has praised somewhere as the best Russian PIO capacitor,  I compare only to K42Y-2, and agree that is a good performer, but it excels when removing the iron magnetic case as seen on pictures. 

Sadly it's not an easy task to cut the thick iron case.

Hello everybody, I finally fix the problem, I got faulty transistor, nothing related to modifications on the DAC output.

So I can confirm now, I run only one IC TDA1543 and left the other seven remaining shokets unused. 

As I/V resistor substituted 340R for 2k7 Riken and then got a major surprise when substitute this for a choke rated 200H/7mA/2K75R.

The increase on dynamics and gain are astounding! HIGHLY RECOMMENDED.

On pin 7, ar Vref. resistor I place Riken 1k5. Transistor and trimmer deleted.

As capacitor output 2,2uF.

And finally, as resistor output to ground, substitute 47k for an smaller 3k6 Ohm. and preferably a choke around 250/300H so close you can to referred 3k6.

I ordered right now one customised. Meanwhile running on this position a little lower, the same iron as placed on I/V resistor 200H/7mA/2K75R and plays very, very well.

Hi, I finally find the problem, at reading with multimeter, suddenly is no more reading on V+ pins TDA1543. It was the floatng lead that carries 6.7v. to Dac board. Bad connexion due to extensive handling at modifications.

74ac74

I have a Teradak v2.6. The DAC always pops loud before a start of a song.

It is quite loud so I worry about my speakers.

Please help me how to resolve it.

 

Many thanks everyone!

Edited by rattosecond - 3/1/13 at 5:37am