Chris's NosDAC

Isaac - tvm for the offer, dont want to push my luck but would you be ok taking pictures of the units internals so i can forward them to Derek for advice - fraid i'm still a film based luddite.
My only concern is that other discussions, now elsewhere, suggest this may not be the only issue? or are they suggesting the scope for tweakery?
Chers
Chris

 

Chris - just asked a question sort of along these lines on the other thread. Its interesting, but I need to learn some basic electronics if I'm to truely keep up with it all!

 

Chris - no probs unless you manage to catch me between digital cameras, as the current one is up for sale.

 

isaac - changing the old D30?, upgraditis is all encompasing.........

 

Hi,

I would think in one of my (now moved) posts there is enough info as what to do.

I do not know how Derek has set up the TDA1543 WRT supply voltages and resistor values, plus I do not know if and how he adjusts the circuit according to the parameters of the individual chip.

I would suggest that the minimum equipment to set up a TDA1543 is a 'cope and good voltmeter. Adjustment "by ear" is possible but should be crosschecked against measurements, as it is easy to use a recording with a lower peak level than 0dbfs and to adjust the circuit for best sound with that, which may lead to a condition where full scale peaks will clip.

My recommended adjustment procedure is as follows:

1) Fit Pots (on wires) as temporary I/V and Reference resistors, I recommend 18-Turn trimmer types.

2) Adjust the I/V resistor as "bogey" value of (Vdd-3V)/2.3mA using a resitor meter.

3) Adjust the Reference resistor to give a quiescent DC output voltage of (Vdd-3V)/2+1.8V

4) Play a testtone of 200Hz -20dbfs (to avoid any problems from clipping) and measure the actual (AC - RMS) output voltage of the DAC. You can calculate the DAC's full scale current as (Vo[rms)*2.82828)/Riv*10 or Vo[pp]/Riv*10

5) Knowing the actual Ifs of the DAC recalculate the I/V resistors and reset your adjustable resistors to that value. Re-adjust the quiescent DC output voltage. If you do not have access to a 'scope and/or distortion analyser you are finished and you can replace all the Pot's with fixed resistors.

6) If you have a 'scope play a 200Hz 0dbfs tone through the DAC and check that no clipping occours. If clipping occours try adjusting first the Reference resistor to see if you can eliminate it that way, if this does not lead to the desired results you need adjust the I/V resistors downwards. This should not be neccesary if you did a good job in the earlier steps but even I make mistakes.

7) If you have access to a Distortion analyser it may be worthwhile adjusting the I/V resistors in small steps and try in each case a range of Reference resistors settings to try to minimise distortion. This does have an audible effect, if subtle.

I hope this clarifies what needs doing.

Please also note that a "misadjusted" DAC may sound subjectively perferable (or not) to one correctly adjusted AS LONG as the signal level remains low.

Ciao T

 

Yeah, it's about time. Basically the EOS 3 is a great camera and the only thing I don't like about it is that it uses film. The D30's digital side is ok but not high enough res, but the camera side is not a patch on the 3. So, going to pick up a 20D in the states for much less than the UK price (and personal imports to £1k are now allowed ). With selling the other two bodies and my birthday coming, the switch won't cost much if any.

Coming back on topic, I could have a look out of hours on the AP, but it's probably best to return to derek from a warranty/support pov.

 

the NOS is currently on its way to HK, thanks for the offer Isaac but i figured it was simpler to get Derek to make the changes.
i'll let you know how things go.

Isaac - another thought - on the distrortion thread discussion bubbled around the running in of electronic components. when the nos is back there may be interest in getting it measured (its only a few hours old) then measuring it again after an agreed run in period to see what actual changes there are - though i guess aural changes will remain subjective?

 

Hi,

The so-called "burn-in" phenomenae tend to be of a nature that seems not ameanable to traditional analysis of audio components. In other words, if a given piece of equipment clips with a given signal "burn-in" will not change this behaviour. However, certain other potentially audbible changes may and do occour.

Ciao T