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Old 19th December 2007, 08:16 PM   #2031
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Quote:
Originally posted by Bobken


You are very welcome.

Interestingly, if you add the 50k resistors at the output like Fedde's R9 & R10 (and I think Peter's PCB allows for these), this will lower the nominal output impedance from circa 2k7 to not much above 2k5 Ohms, with no other changes.

Regards,


Ok, we can lower the output impedance by putting resistor in parallel at the output, 50k//2k7~2k5 ohms.

I keep this setup in mind just incase I need to match the impedance between stages

I don't have any experience with DAC, but wondering how low we can set the output impedance (using TDA1543) without changing the sonic signature significantly?

Thanks,
Joshua
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Old 19th December 2007, 10:02 PM   #2032
mikelm is offline mikelm  England
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Default o/p impedance

every time you reduce the o/p impedance you reduce the o/p voltage

distortion should be better

mike
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Old 20th December 2007, 01:09 PM   #2033
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Default Re: o/p impedance

Quote:
Originally posted by mikelm
every time you reduce the o/p impedance you reduce the o/p voltage

distortion should be better

mike

That's right.

Joshua
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Old 20th December 2007, 01:59 PM   #2034
Bobken is offline Bobken  United Kingdom
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Hi Joshua,

I'm ducking out of this discussion now, as this is Peter's commercial thread which we are usurping rather, I did only get involved by accident, and I should be attending to other matters.

However, as you are seriously interested in this subject, you owe it to yourself to fully understand what is involved in these matters, as, regrettably, they are rarely quite as simple as at first they may appear. I don't wish to seem patronising here (and I still regularly learn something new about issues which I haven't thought much about before) but with a bit of searching, there is a wealth of information directly related to this subject, both on this Forum, and elsewhere on the 'Net. I am sure that you will find this very useful, and about 2-3 yrs ago, the subject was very fashionable, and occupied entire threads for a while.

IIRC, DDDAC (who is also a member here) has some very illuminating information on his site, and some graphs or charts relating to different loadings for these DACs, the effects on distortion, and the resultant output levels etc., and this might be a good starting-point if you haven't already seen this.

The difficulty in 'generalising' for brevity in a short response (as has just been proved!) is that there are nearly always other matters to consider when making any significant changes to established electronic circuitry. All such circuits are the result of a set of compromises which the designer has chosen, and, in improving (or changing) one parameter, it is quite usual that other parameters will worsen, unfortunately. There are 'no free-lunches' in life, nor in electronics, and it is therefore a good idea to become familiar with all of the related possibilities before contemplating any such modifications, or it is likely that the end-result will not be quite what is desired.

For example, as already mentioned, lowering the output impedance (which can be done to almost zero, by reducing R8 & R9 in Peter's circuit) will also reduce output levels, and will affect the distortion characteristics. Also, ideally the V-ref resistor (Peter's R7) will also most likely need to be changed in value, as this sets the centre-point of the output AC swing in relation to ground, and so on.

Somewhere on this Forum is (or was) an on-line calculator which you plug values into, and it will show the various relationships between rail voltage (which has a great effect on the distortion/sound characteristics), the values of the I/V resistors and V-ref resistor, and predicts the resultant output level etc. You might find this with a search, and it could also be useful to you.

Anyway, good luck with your endeavours.

Regards,
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Old 20th December 2007, 03:56 PM   #2035
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Here's the explanation how I/V resistors are calculated: http://www.diyaudio.com/forums/showt...ht=#post173483
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Old 20th December 2007, 04:01 PM   #2036
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Quote:
Originally posted by Bobken
Hi Joshua,

I'm ducking out of this discussion now, as this is Peter's commercial thread which we are usurping rather, I did only get involved by accident, and I should be attending to other matters.

However, as you are seriously interested in this subject, you owe it to yourself to fully understand what is involved in these matters, as, regrettably, they are rarely quite as simple as at first they may appear. I don't wish to seem patronising here (and I still regularly learn something new about issues which I haven't thought much about before) but with a bit of searching, there is a wealth of information directly related to this subject, both on this Forum, and elsewhere on the 'Net. I am sure that you will find this very useful, and about 2-3 yrs ago, the subject was very fashionable, and occupied entire threads for a while.

IIRC, DDDAC (who is also a member here) has some very illuminating information on his site, and some graphs or charts relating to different loadings for these DACs, the effects on distortion, and the resultant output levels etc., and this might be a good starting-point if you haven't already seen this.

The difficulty in 'generalising' for brevity in a short response (as has just been proved!) is that there are nearly always other matters to consider when making any significant changes to established electronic circuitry. All such circuits are the result of a set of compromises which the designer has chosen, and, in improving (or changing) one parameter, it is quite usual that other parameters will worsen, unfortunately. There are 'no free-lunches' in life, nor in electronics, and it is therefore a good idea to become familiar with all of the related possibilities before contemplating any such modifications, or it is likely that the end-result will not be quite what is desired.

For example, as already mentioned, lowering the output impedance (which can be done to almost zero, by reducing R8 & R9 in Peter's circuit) will also reduce output levels, and will affect the distortion characteristics. Also, ideally the V-ref resistor (Peter's R7) will also most likely need to be changed in value, as this sets the centre-point of the output AC swing in relation to ground, and so on.

Somewhere on this Forum is (or was) an on-line calculator which you plug values into, and it will show the various relationships between rail voltage (which has a great effect on the distortion/sound characteristics), the values of the I/V resistors and V-ref resistor, and predicts the resultant output level etc. You might find this with a search, and it could also be useful to you.

Anyway, good luck with your endeavours.

Regards,

Hi Bob,

Appreciate for the advice.

You're right this subject is a little bit out of the subject, I guess I owe an apologize to Peter for starting the thing.

I just want to understand more about your comment of lowering the output impedance of DAC - if I need a buffer circuit to next stage in situasion where I can not match the impedance.

I'll search more info in some of the places that you suggested.

Thanks,

Joshua
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Old 20th December 2007, 04:07 PM   #2037
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Quote:
Originally posted by Peter Daniel
Here's the explanation how I/V resistors are calculated: http://www.diyaudio.com/forums/showt...ht=#post173483

Thanks Peter!

Very useful information!

Joshua
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Old 20th December 2007, 04:11 PM   #2038
xaudiox is offline xaudiox  Philippines
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TDA1543 Calculator

http://www.diyhifi.org/forums/viewtopic.php?t=104
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Old 20th December 2007, 04:22 PM   #2039
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Quote:
Originally posted by xaudiox
TDA1543 Calculator

http://www.diyhifi.org/forums/viewtopic.php?t=104
Another one, thanks


Joshua
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Old 20th December 2007, 05:32 PM   #2040
mikelm is offline mikelm  England
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I wonder if they give the same results

hehehe
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