ShinyMetal

TedS · Joined: 13 Jun 2007 Posts: 41 Location: Culpeper, VA

Hi Evan and everybody else,

I've finally gotten my EzDual and EzDAC boards to the testing stage. I'm using a 15V 1A transformer (DigiKey P/N TE62053-ND) to feed the EzDual board. At first I wasn't getting the correct output, but with the assistance of an electrical engineer at work was able to trace the problem to the polarized caps C7 and C8, which I had installed backwards. So now everything appears to be working. My question is, what is the output voltage supposed to be? I'm measuring +/-13.9V at the V+ and V- outputs, respectively.

When I connect the EzDual to the EzDAC, I measure +3.34V, +5.06V, and +10.74V, and -10.8V at the ouputs of the different regulators. The 3.3 and 5.0 appear normal, but aren't the other two supposed to be +/-12.0V? My friend looked up some info on the regulators, and it looks like they may be operating near their minimum voltage drop with only 13.9 V at the input.

What do you think? Are these normal values? Should I be concerned?

Thanks,
Ted

leo · Joined: 12 Jun 2007 Posts: 124 Location: UK

Hi Ted,

I don't have the Ezdual but just had a look at the schematic, what value resistors are you using for R3,R4,R5 and R6 on the Ezdual?
Did you replace the capacitors that was fitted in reverse? I'd imagine they are now damaged.

For the Ezdac using 240R for R7,R8 and 2k1 for R6,R9 it should give just over +/-12v
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Leo

leo · Joined: 12 Jun 2007 Posts: 124 Location: UK

BTW did you use tantalum caps for C7 and C8? if so tants do not usually survive reverse voltage, be careful with them as they tend to go pop or suffer from internal shorts Wink

Just had a look at the fancy BOM for the Ezdual, shouldn't R4 and R6 be a higher value than 1k1? if R3 and R5 is 240R using 1k1 gives about 7v
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Leo

TedS · Joined: 13 Jun 2007 Posts: 41 Location: Culpeper, VA

Hi leo,

I used the Fancy BOM for the EzDual, including C7 and C8 and R3, R4, R5, and R6. R3 and R5 are 200R, and R4 and R6 are 2000R. What should that give for the output of the regulators?

For the EzDAC, I also followed the Fancy BOM. R6,9 are 1.5k, R7,8 are 200R.

After discovering C7 and C8 were backwards, I just reversed and re-soldered them in. They appear to be working, since the + and - sides of the board are giving the same output (+/- 13.9V). If they are working now is there still a chance they could be damaged?

Thanks,
Ted

leo · Joined: 12 Jun 2007 Posts: 124 Location: UK

Hi Ted,

If R3, R5 is 200R and R4,R6 is 2000R that sould give you 13.75v so your 13.9v is not far off.

If your using 200 and 1500R on the Ezdac that would give you +/-10.63v so your voltages are correct with the resistor values you are using:)

I run the op-amps on my Ezdac at +/-14v but I use a different op-amp, If you are using AD8610 op-amps +/-10.63v is fine for these so I would not worry about it
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Leo

TedS · Joined: 13 Jun 2007 Posts: 41 Location: Culpeper, VA

Thanks leo,

That's reassuring. I didn't realize that the resistors determined the regulator output. How is the output calculated from the resistor values?

I was simply assuming that the regs on the EzDAC board would be set for +/-12V, since that was the nominal value on Evan's circuit diagram. I wonder why he chose resistors to give +/-10.63V? Is the BOM correct?

Ted

ezkcdude · Posted: Sun Jun 24, 2007 12:44 am Post subject:

Hey, guys! I missed a lot of action today ;).

Because not a lot of people have built the ezdual, I haven't really kept up with it. Ted, there is a very simple equation given in the data sheet for those regulators that determines the voltage.

Vout=1.25*(1+R2/R1)

For the ezdual, this equates to:

V+=1.25*(1+R4/R3)

V-=1.25*(1+R6/R5)

So, 1.25*(1+10)=13.75

For the ezdac, V+=1.25*(1+R6/R7); V-=1.25*(1+R9/R8). Right now, the Fancy BOM would give V=+/-10.625. So, you are getting correct values, but it is true that the standard BOM would give +/- 12, because it lists 2000R resistors, not 1500. I can't remember now if there was a good reason for that. It could be that there were no "fancy" resistors at 2000K, but I doubt it. So, I will look into it, and change the BOM, if necessary. I think it's a good idea.

Having said that, you should have no problem running the ezdac at +/-10.6V. Some op amps run better at lower voltages, some at higher. The nice thing about having adjustable regulators (or programmable), is that by changing the resistor values, you can accomodate a very wide range of components, without actually changing the design or layout of the PCB. In other words, for me, the BOM was sort of an after thought, because I didn't realize who and how many people would actually be building these things (and following instructions, at that!). Now that I kind of know the typical ezdac/ezdual builder, I can make adjustments. You're actually helping me in this process, by validating and testing the design in the real world. So, to sum up, it appears to me you have everything done correctly (reversed caps aside), and you can proceed to charge up the DAC.
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He's not hi-fi, he's my stereo.

TedS · Joined: 13 Jun 2007 Posts: 41 Location: Culpeper, VA

Hi Evan,

Thanks for the explanation. I'm just glad I didn't screw anything up! The DAC has passed the smoke test (I didn't let any out), and has correct voltage measurements. My last test on Monday will then be to hook up the digital input(s) and try to get music out!

I was curious if you had dropped the voltage setting so that the output wasn't as close to the input from PSU, making sure that the regulator actually had to do some regulating and wasn't just at "full open". I know from my fluid dynamics background that if you really want a regulator to be in control you want a minimum pressure drop across it; otherwise it just goes full open and is more like an orifice than a regulator. In that case if the supply pressure goes up or down, the outlet pressure will go up and down with it, until the minimum delta P is restored. I don't know if voltage regulators operate in an analogous way or not, but was curious.

Ted

ezkcdude · Posted: Sun Jun 24, 2007 3:24 pm Post subject:

Ted, I just realized why I had chosen 1.5K resistors for the Fancy BOM. It's because, I also use 1.5K feedback resistors in the output stage. I guess my reasoning was that, since these are rather pricey resistors, if I could consolidate the values, some money could be saved by buying more of the same value. And since the voltage difference between 10.6 and 12 is not significant (AFAIK) in effecting sound, I thought that made sense at the time.
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He's not hi-fi, he's my stereo.

rtalcott · Joined: 15 Aug 2007 Posts: 2 Location: Albuquerque NM US

Do you have any ezdual boards?
thanx
rt
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whale oil beef hooked

ezkcdude · Posted: Sat Nov 17, 2007 7:47 pm Post subject: Re: ezdual boards