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Old 6th September 2005, 06:37 AM   #1
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Angry DDDAC questions

I recently bought the DDDAC kit from Deode in Germany. I assemled the kit but I have a few questions to those out there that have constructed the same kit:


1) It was easy to adjust the supply to pin 5 of the dac tower to 8.5 volts but it is difficult to adjust pin 6 and 8 to 3.85 volts average. The problem is that i turn the screw of the potentiometer and the readings change very quickly from 1.5-2volts to over 4-5volts even with the slightest turn of the
screw. I finally managed to adjust pin 8 to 3.95-4volts and pin 6 to 3.80-3.85volts. After a while when I recheck these measurements they have altered.Is this normal or am I doing something wrong. I get the readings from the pins of the dac or from the output connecting pads. Did you have any problems adjusting the 3.85 volts?


2) About the grounds on the schematic: The input coaxial and toslink grounds are connected to the chassis? The output ground of the pcb connects to both left and right rca chassis connectors? By doing this the output ground is also connected to the previous nput grounds from the coax and digital input. Is this correct? Should all grounds on all the schematics connect together?

3) I also have a battery problem. I have bought a new 12volts 7amps/h lead acid battery and a suitable charger. When I connect the charger to the battery it only supplies 11.99 volts max. This is ti low to charge the battery. How can I check if the battery or the charger are ok?

Thats all,
Thanks for your help beforehand,
George
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Old 6th September 2005, 07:13 AM   #2
garbage is offline garbage  Singapore
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1) no idea about this, but looks like you need a multi-turn trim pot in there. my experience with bourns multi-turn trim pots are that they do not drift that much.

2) the schematic should be correct. all the signal grounds should be eventually connected for the dddac.

3) the 11.99vdc that you measured could be the charging voltage with load, if you connected the battery to it. try measuring without battery connected. you should get a higher voltage. when you leave the battery and charger alone for a while and remeasure, you should see an increase of voltage due to the battery being charged. fyi, a fully charged 12v/7Ah sla is about 13.6 odd vdc.
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Old 6th September 2005, 07:34 AM   #3
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The pot I am using is a multiturn pot.
The battery charger when not connected to the battery gives a voltage around 10,60 volts.

Thanks for your answer.
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Old 6th September 2005, 07:38 AM   #4
garbage is offline garbage  Singapore
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Quote:
Originally posted by gchrist

The battery charger when not connected to the battery gives a voltage around 10,60 volts.
i guess the only way is to actually try charging the battery to see if it reaches a voltage that is higher than what's measured off the battery itself.

the l200cv charger that i built required me to preset the output voltage of the charger to the final charged voltage of the battery, hence my comments above. your charger circuit most probably would differ.

i'll leave the pot problem to other dddac builders, but you might need to replace the pot in the long run.

cheers.
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Old 6th September 2005, 07:41 AM   #5
dddac is offline dddac  Germany
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Default Re: DDDAC questions

Quote:
Originally posted by gchrist
I recently bought the DDDAC kit from Deode in Germany. I assemled the kit but I have a few questions to those out there that have constructed the same kit:


1) It was easy to adjust the supply to pin 5 of the dac tower to 8.5 volts but it is difficult to adjust pin 6 and 8 to 3.85 volts average. The problem is that i turn the screw of the potentiometer and the readings change very quickly from 1.5-2volts to over 4-5volts even with the slightest turn of the
screw. I finally managed to adjust pin 8 to 3.95-4volts and pin 6 to 3.80-3.85volts. After a while when I recheck these measurements they have altered.Is this normal or am I doing something wrong. I get the readings from the pins of the dac or from the output connecting pads. Did you have any problems adjusting the 3.85 volts?


2) About the grounds on the schematic: The input coaxial and toslink grounds are connected to the chassis? The output ground of the pcb connects to both left and right rca chassis connectors? By doing this the output ground is also connected to the previous nput grounds from the coax and digital input. Is this correct? Should all grounds on all the schematics connect together?

3) I also have a battery problem. I have bought a new 12volts 7amps/h lead acid battery and a suitable charger. When I connect the charger to the battery it only supplies 11.99 volts max. This is ti low to charge the battery. How can I check if the battery or the charger are ok?

Thats all,
Thanks for your help beforehand,
George
Hi George,

I also read your email, but let me answer here as it might for interest to others aswell (by the way, poor ICON you have choosen for this topic...)

1) You are doing nothing wrong I guess, as you have the correct reading now. What you could do is check the value of the trimmer. I had unfortunatley a few occasions where my supplier mixed a few 20k trimmers in the delivery of 2k trimmers. As always you find out after shipping This obviously would make the trimming process less easy, but for the functionality of the DAC it is does not matter as long as you arrive at a voltage between 3.7 and 4 volt. At least it would expalin why it was so jumpy...
Do not forget, that there is a pretty large thermal effect on the final value and you need to readjust after half an hour after switching on the dac. You will see at cold start a different reading, but that is normal.
2) All grounds should be tight together and I would suggest to make only one conection to the chassis from the ground from the output

3) The battery should read at least 13.8 Volt when a charger is attached ..... have you tried another charger ?

good luck and let us know if you succeeded


doede
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Old 6th September 2005, 08:06 AM   #6
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Deode,

You are correct! The icon was not very good but you know how you feel when you think you have finished a project and something does not work.
I think I checked the pots sent and both are 20k but I will check again.
Concerning the battery I must say that the most probable fault will be the charger. Maybe it does not work.

Thanks
George
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Old 7th September 2005, 06:55 AM   #7
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I solved the problem with the battery. The wire from one of the crocodile clips was not soldered correctly and was loose. I soldered the wire to the clip and the charger chargers the battery ok giving it more that 13.6 to 14 volts.

Now concerning the trim pot I checked and it is 20K. I also checked all power supply connections and all points on the pcb for correct voltage. I had no problems and all points measured ok. I also checked the dac tower. All legs of each vertical series are connected ok. I checked for shortcircuits between the legs but everything was fine.
I will check again today with a fully charged battery and I will post my results. By the way what is the value of vref when the pin 6 and 8 are correctly biased?

And a final question. I have installed a 12volt brushless fan near the dac tower. When the dac is on the dac tower is very cool but I am wondering if this fan will affect the audio cables going to the output rca. I have not auditioned the dac yet waiting for a new toslink input receiver that I destroyed by mistake applying wrong voltage supply. So in the meantime I can change the wiring of the output audio cables if the fan inteferes. What do you think?

Thanks
George
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Old 7th September 2005, 07:57 AM   #8
dddac is offline dddac  Germany
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Quote:
Originally posted by gchrist

1. I solved the problem with the battery.

2. By the way what is the value of vref when the pin 6 and 8 are correctly biased?

3.And a final question. I have installed a 12volt brushless fan near the dac tower. When the dac is on the dac tower is very cool but I am wondering if this fan will affect the audio cables going to the output rca. I have not auditioned the dac yet waiting for a new toslink input receiver that I destroyed by mistake applying wrong voltage supply. So in the meantime I can change the wiring of the output audio cables if the fan inteferes. What do you think?

Thanks
George

1. good ...

2. It is always aproximately 2 Volts, regardless what the bias is. That is why it is a Vref .... (see datasheet if you like to see how the 1543 works internally ...

3. I don't think it will interfere... but why not try when all works to switch the fan off shortly and just listen if you hear any difference, that is what matters ...

doede
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Old 7th September 2005, 09:18 AM   #9
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Deode,

You are correct the vref is about 2 volts.

Regards
George
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Old 8th September 2005, 06:05 AM   #10
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Having solved the problem with the battery I connected a cdrom's spdif digital output to the coax input of the DAC and finally heard music through a small computer active speaker. The only final problem I am facing is the one of static noise. With nothing playing on the cdrom or without having connected the input coaxial cable I can hear spurious noise from the speaker. When music playes it overlaps this noise but when there is a blank in the music I hear the noise.
So I beleive it has something to do with the earthing scheme.
I have connected all power grounds together at on point.
The input and output rca ground touch the chassis also so they are all grounded together.
From the output L and R grounds on the pcb I have connected the L and R grounds of the rcas.
The input digital rca ground is connected on the digital ground on the appropriate pcb tab.

Also note that I have used cat5e cable for all connections power and signal. Should I use a different cable?

Is this correct?
How have you made the grounding?

Regards
George
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