[Samgotit]

Excellent!!!!!!!!!! Caps look great.

Thanks for getting to bottom of this little mystery.

LM7808? What will voltage do for sound quality? That is the question.

Take Care,
Sam

 

[shlomomofo]

Quote:

Originally Posted by Samgotit LM7808? What will voltage do for sound quality? That is the question.

+2V or not +2V... that is the question.

 

[tilt]

now who's going to take the plunge and do the mods to replace C5, 6, 7, 8, 12, 13, 14, 15

 

[shlomomofo]

my query to diyshop...

Quote:

i bought a dac-ah from you a while ago. i've been doing some slight mods, and i noticed that the voltage supplied to the dacs from the regulators is only 6v (measured between pins 4 and 5 on any 1543 chip). isn't it supposed to be 8v? why is it lower and how do i fix it? dac-ah sounds awesome anyway...

... and their respone.

Quote:

Hello, The new DAC-AH is 6V Regards Johnny

after deciphering the nuances of their response, it seems to me that the switch to 6v was fully intentional.

 

[tilt]

C5, 6, 7, 8, 12, 13, 14, 15, 28, 37 are all on the way, i'll post impressions.

 

[Samgotit]

Quote:

Originally Posted by tilt C5, 6, 7, 8, 12, 13, 14, 15, 28, 37 are all on the way, i'll post impressions.

Me too. Ordered last night. I'm going to try Frankensteining the DACs with an 8V regulator (LM7808) as well.

Sam

 

[tilt]

change the reg before you change anything else!! i wanna hear what the 2v does

 

[tilt]

if 274 is optimum for 8v, what IV vaule should we use for 6v?

 

[Samgotit]

Quote:

Originally Posted by tilt if 274 is optimum for 8v, what IV vaule should we use for 6v?

6V-1.2V-1.8V=3V (The other values are from Voc on the data sheet)

We have 8 DACs connected in series with each resistor for L and R channels, so for each resistor:
3V/(2.3e-3*8) = 163 ohms

Here some backgroud provided earlier:
The link in the quote is where the equation is provided.

Quote:

I/V Resistors These exert a large influence on the final sound. The correct resistance depends on the TDA1543 supply voltage. Thorsten Loesch explains how to calculate it in this diyAudio.com post. I use +6v, I/V 1k2, 1k3 Iref. http://www.diyaudio.com/forums/showt...ht=#post173483 With a +8V supply, the dac functions well with 3k0 I/V and 1k5 Iref. Welwyn RC55 sound rather dark, grainy and harsh. Not recommended. For a less brutal version of this more aggressive sound try SMD resistors from Multicomp, 0.125W 1% 1206. Audio Note tantalum resistors have a lush, chunky sound without much air. Vishay bulk foils sound luminous and very detailed, to the point of sounding a little fuzzy and soft. Cheap carbon resistors from Farnell.com seem to impose the least sound, leaving you to tweak the dac elsewhere, and the tiny 0.125W version fits into awkward places. Try them if you like but can't afford Vishay bulk

Sam

 

[shlomomofo]

Quote:

Originally Posted by Samgotit 3V/(2.3e-3*8) = 163 ohms

here's a question to show my utter lack of understanding of electrical systems...

why is it (2.3e-3*8) instead of just (2.3*8)?

and another question about the following....
Quote:

To get the output to the new midpoint of 1.8V+(5.6V/2) = 4.6V. We will have to have 4.6V/2k4 = 1.92mA flowing in our 2k4 resistor, plus our 1.15mA DAC digital silence current, so 3.07mA. In our reference resistor 3.07mA/2 = 1.535mA need to flow, so 2.2V/1.535mA=1.43k, NPV 1k5.

is this to get the values for the resistors that come before the dacs?

thanks

 

[Samgotit]

Quote:

Originally Posted by shlomomofo here's a question to show my utter lack of understanding of electrical systems... why is it (2.3e-3*8) instead of just (2.3*8)? and another question about the following.... is this to get the values for the resistors that come before the dacs? thanks

The e-3 (1x10^-3) is the conversion factor for mA to A (1mA = .001A).

Our Vref is controled by that lonesome 1k trimpot at VR1. You can measure Vref b/w pins 4 and 7 on the DAC. Trim pot may need to change to get optimum Vref. I need to read more on this.

Sam

 

[Samgotit]

I forgot to add:

Minimum Vref is 2.10V at only 5v supply voltage. I'm getting a scant 2.05V with a 6v supply. The trim pot is maxed. A fixed resistor may be a better option here. I just have to figure out how to calculate it based on that post.

Anyone care to comment? Please?

Sam

 

[shlomomofo]

i'll take a stab at the ref resistor for an 8V supply...

Quote:

Now Vref is fixed at nominal 2.2V... Our output Voltage swing can now be 1.8V to 8.6V - 1.2V = 7.4V or 5.6V peak-peak (2V RMS). Our full scale current is still only 2.3mA, so our I/V resistors become 5.6V/2.3mA=2.43k NPV = 2k4. To get the output to the new midpoint of 1.8V+(5.6V/2) = 4.6V. We will have to have 4.6V/2k4 = 1.92mA flowing in our 2k4 resistor, plus our 1.15mA DAC digital silence current, so 3.07mA. In our reference resistor 3.07mA/2 = 1.535mA need to flow, so 2.2V/1.535mA=1.43k, NPV 1k5.

8V-1.2V-1.8V = 5V peak-peak
5V/(2.3e-3*8) = 272 ohms I/V
1.8V + (5V/2) = 4.3V midpoint
4.3V/272 ohms = 0.0158A = 15.8mA
15.8mA "plus our 1.15mA DAC digital silence current" = 16.95mA
16.95mA/2 = 8.48mA = 0.00848A
2.2V/0.00848A = 259 ohms

well, i tried!

 

[shlomomofo]

and with a 6V supply, for the sake of completeness....

6V-1.2V-1.8V = 3V peak-peak
3V/(2.3e-3*8) = 163 ohms I/V
1.8V + (3V/2) = 3.3V midpoint
3.3V/163 ohms = 0.0202A = 20.2mA
20.2mA "plus our 1.15mA DAC digital silence current" = 21.35mA
21.35mA/2 = 10.68mA = 0.01068A
2.2V/0.01068A = 206 ohms

not sure if any of this is correct, as sam seems to be getting only ~2V at Vref with ~1000 ohms of resistance... (right sam?)

 

[tilt]

wouldn't it be better to leave the dac at v6, and just change the IV's to 160ohm.

The TDA1543s get pretty hot at 6v, i'd hate too see them at 8. Also, does heat shorten the life of the chips. Would ram sinks help?

either way, LM7808's are on the way