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Ultimate Twin TDA1541a Non-oversampling DAC with tube buffer & reclock set.......

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#562
Safety Question

On v2 dac, is the DAC board and Tube board designed with bleeder resistors, so that if one were to turn off the dac and unplug it, the boards could be handled without fear of electric shock (caps, etc.)? If so, how long after the dac is turned off and unplugged is it safe to touch the caps and other parts? Minutes? Hours? Thanks javascript:smilie(':smash:')
smash
 
#566
Wow, given this is my first pcb-level project, it's been really challenging muddling through how to assemble this Dac without a basic instruction manual. I would greatly appreciate some assistance on these basic Qs:

1. What amp rating for ac fuse? If I use a separate power switch (spst toggle), what amp rating for the switch? Can I use the spare toggle switch that came with the dac.

2. How did you guys connect your digital input coax to the SK5 input on Dac board? Did you solder coax's main conductor to pin 3 (U+) and solder the 2nd conductor (that wraps around the main conductor to pin 2 (U-)? Or did you use some type of female 2-prong connector? If so, did you crimp the entire coax cable (conductors, shield, insulation) to the connector?

3. SK5's pin 4 is blank (schematic shows R49 33R resistor. ???

4. From reading this thread, seems like I need to connect J2 and J3 on the tube buffer if not using battery bias. J2 and J3 have a + and - pin. Do I run twisted pair from J2 to J3, or should I use single conductor hookup wire from J2 + to J3 +, and another conductor bridging the minus pins?

5. Basic safety Qs. Are their resistors built into the design of both dac and tube board that DRAIN boards so one can safely handle them after unplugging ac?

Any feedback is greatly appreciated!
 
#567
Mike,
I cannot answer all your questions, but here is what I know.

1- I am using a 4A fuse for the whole DAC. So 6.3A is overkill and I guess you could go lower. About creating a standby mode if have not done this yet so I cannot help you there

2- Signal line to U+ (pin 2) and shield to U- (pin 3). I do not use a connector, because every connector you use means signal loss so my advise is no connectors unless it is absolutly necessary.

3- pin 4 is not connected to anything so a resistor is also not necessary.

4- you put a jumper in J2 and J3. So do not connect J2 to J3, because you will then short the left and right input

5- Do not know.

I do not think the folowing mod's are posted yet and it it is up to you if you want to do it or not.
On advise of some expierenced tube amp builders you should add a 1k resistor between pin 3 and 7 of 6x4 tube socket.
This resistor will connect the heater zero to ground and will increase the life span of your rectifier tubes.
For the same reason you should remove R35, for the other tubes.
(R36 will then do the same thing as the 1k resistor)

C29, C30, C49 and C50 must be off the highest quality you can find or you could even remove them (but that's a question of taste). I am running without right now.

Hope this helps
 
#568
JeroenVl, I am so grateful for your prompt and helpful reply. With your and Quantran's input, I am almost there. Can I bother you for a few final questions on Grounding this Dac? I apologize for the long post, but I thought I should error on the side of specificity. Thanks, in advance, for any further feedback:

1. Planning to use an all-wooden chassis. But I will spray paint on conductive nickel paint for some shielding. The transformers will be isolated from chassis with microsorb. In addition to tying each insulated black ground lead from each transformer to the Single AC Ground Point, do I also have to mechanically ground the transformer casing (i.e. at transformer mounting bolt) to this AC Ground Point? Or is this redundant?

2. On the dac board, there are two copper clad through holes marked Ground. One in the center of the board, and one near the left corner of power supply area. What is the difference between these two? Is one the AC ground of the psu section, and the other the signal ground?

3. On the dac board, it looks like there are little copper etched leads that come very close to each of the four through-hole mounts (that could touch mounting bolt). Is this to ensure the board is mechanically grounded to the chassis? If I’m using a wood chassis, do I need to do anything other than mount the board to the wood, like run a copper wire from one of the pcb mounting bolts to chassis ground?

4. On the tube board, I just notice one copper clad through hole for Ground. If I decide to ground the tube board, would I run a wire from this ground point, and a wire from the Dac board ground pin to star ground at the AC ground point noted in #1 above?
 
#569
Sorry Mike,

I have not, at least not directly, grounded my boards.

Because I am affraid of ground loops. My reason for this is, the DAC an tube board grounds will be connected through the left and right in and output cables (Sk2,3 on Dac and J8,10 on tube)
So when I use the center ground points on the boards there is a change ground loops could appair.

Maybe someone else could help you here better.
 
#572
And? Sorry to appear a bit demanding but I ordered this Dac in June '05. It didn't arrive until December. I couldn't get schematics until February when one of the other builders was kind enough to send them. The chassis was drilled wrong and appears small. There's no hookup instructions. I asked several questions through this board and many through email to you. Very few if any were answered. If it weren't for a few helpful folks that have offered guidance on this board I'd be at ground zero. I have a long holiday weekend starting today, and my goal is to get this component to play music. I would appreciate if you could reply to the Qs I've posted on this board. Thank you.

Regards, Mike
 
#573
Also, I have received conflicting feedback from experienced builders on the transformer leads:

There are five primary leads for each transformer: 2 red, 2 brown, 1 black. The black is ground. What to do, A or B:

A. Use ONLY 1 red and 1 brown (after checking for continuity) as positive and neutral. Insulate and cap the OTHER red and brown because they are NOT used; or

B. Connect two red together for positive; connect two brown together for neutral

Which one? A or B? The reason I ask is because I received different feedback from very experienced builders. Just want to be extra careful here. Thanks, Mike
 
#575
hi riotubes,

Very sorry to hear this problems. I change several power transformers already. can U tell e which type of the power transformers that U collect now. Secondly, pls every power transformers take one photos & send to thomas_siu@hotmail.com
I will tell U how to connect for them. s it Ok. then every questions I will setp by step to help U to solve. Regarding the detail. Every users I also send the circuit only. U can check the parts value & fit into the PCB & connect will be OK.

regardin the chassis, finally I know the holes was reserved for several no of chassis already. Some was right. Because I had three period to call the factory to produce the chassis. This is factory's mistake. I stop production already.

As I said, I did not like any users cannot fix problems. I will only produce all funish product now. At least I can one funish items exchange to one funish item to them. if they finall still cannot solve problems. same as U, mike If at last U still cannot sound, I will exchange one to U.


thx

thomas
 
#580
hi mike,

for the Allthree.pdf file

There are five primary leads for each transformer: 2 red, 2 brown, 1 black. The black is ground. What to do, A or B:
Click to expand...


the s/n 8408 one,

brown & red = 0~110
brown & red =0~110.

this is multi tapping for 110 & 220V area to use, pls understand.


if u use in use only use one winding will be OK.

not need parallel. pls try this first & the sec is it 230~0~230 AC output??

8405 & 8407 will be same, pls try.

one by one we solve the questions. Don't worry for this.
Diy will be interesting.

thx

thomas
 
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