A NOS 192/24 DAC with the PCM1794 (and WaveIO USB input) - Page 52 - diyAudio
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Old 8th August 2013, 05:08 PM   #511
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Quote:
Originally Posted by dddac View Post
Hi Ken,

what makes you think a higher voltage would lower life span? It is only the analog section which runs at the higher voltage. On other Projects I have had very positive experience running Chips at higher voltage without any Problems. The proof will be in the eating though
Hi, Doede,

Supply voltage is a basic semiconductor breakdown acceleration factor. While part of this breakdown acceleration is power dissipation related, a greater part is typically due to an increase in semiconductor junction leakage current carriers as Vcc is increased, leading to failure of the junction.

Chips are routinely operated at elevated voltages and temperatures to rapidly 'age' them to determine their expected long reliability, or MTBF. Maybe, think of it this way, if the chip is nominally designed to operate at up to 6.5 volts Vcc for some number of years, and immediately failed at 11 volts Vcc in your tests, then there is some implied curve between those two voltages which plots the expected lifespan of the chip versus Vcc.

Therefore, an 8 volts Vcc can be expected to shorten chip lifespan more than if it were operated at 5 or 6.5 volts Vcc. Perhaps, by a relatively significant amount, since the datasheet specifies a maximum Vcc of 6.5 volts.
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Last edited by Ken Newton; 8th August 2013 at 05:12 PM.
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Old 8th August 2013, 06:26 PM   #512
Almeg69 is offline Almeg69  United Kingdom
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Even if it will reduce it`s life span, I would prefer the better sound quality :-)
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Old 14th August 2013, 12:04 AM   #513
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Hi Doede,
what is the current draw of the SPDIF module ?
Thanks Johann
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Old 14th August 2013, 05:29 AM   #514
dddac is offline dddac  Germany
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Originally Posted by Lauscher View Post
Hi Doede,
what is the current draw of the SPDIF module ?
Thanks Johann
I believe it is something like 50mA...
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Old 14th August 2013, 05:33 AM   #515
dddac is offline dddac  Germany
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Quote:
Originally Posted by Ken Newton View Post
Hi, Doede,

Supply voltage is a basic semiconductor breakdown acceleration factor. While part of this breakdown acceleration is power dissipation related, a greater part is typically due to an increase in semiconductor junction leakage current carriers as Vcc is increased, leading to failure of the junction.

Chips are routinely operated at elevated voltages and temperatures to rapidly 'age' them to determine their expected long reliability, or MTBF. Maybe, think of it this way, if the chip is nominally designed to operate at up to 6.5 volts Vcc for some number of years, and immediately failed at 11 volts Vcc in your tests, then there is some implied curve between those two voltages which plots the expected lifespan of the chip versus Vcc.

Therefore, an 8 volts Vcc can be expected to shorten chip lifespan more than if it were operated at 5 or 6.5 volts Vcc. Perhaps, by a relatively significant amount, since the datasheet specifies a maximum Vcc of 6.5 volts.
I am afraid this could become a very long discussion... So let’s not start a long thread in a thread about it. All true you state, but also undefined in terms of time. Let’s consider this: If VA is 5 Volt and the output is zero volts (as per datasheet) the voltage over the current source is 5 volt right? Now I have 8 Volt and an output of 2,7V DC, so over the current source is 5,3V. May be after all it will last long enough. I guess TI designed their chips for continuous operation for 20 years or so? Most Audio hobbyist, use only a fraction of this time actually playing music. I guess we are good….
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Old 14th August 2013, 01:43 PM   #516
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Originally Posted by dddac View Post
I am afraid this could become a very long discussion... So letís not start a long thread in a thread about it. All true you state, but also undefined in terms of time. Letís consider this: If VA is 5 Volt and the output is zero volts (as per datasheet) the voltage over the current source is 5 volt right? Now I have 8 Volt and an output of 2,7V DC, so over the current source is 5,3V. May be after all it will last long enough. I guess TI designed their chips for continuous operation for 20 years or so? Most Audio hobbyist, use only a fraction of this time actually playing music. I guess we are goodÖ.
Hi, Doede,

Perhaps, I should clearly state that I have no desire to pour cold water on your DAC project. In fact, I find your suggestion to simply raise the PCM1794A's analog supply voltage in order to obtain greater signal voltage complience amplitude (while maintaining low distortion) when utilizing a passive resistor I/V, to be clever. It's the kind of solution which only seems obvious after it's been proposed. I've been working with the PCM1794A in a passive resistor I/V implementation for some time myself, so I was very intrigued by this elegantly simple solution to the problem of obtaining greater signal amplitude without resorting to an active analog output stage.

However, my background in the semiconductor industry tells me that increasing the Vcc will almost certainly shorten chip lifespan. By what amount it will be shortened seems the only question to me. While I agree that the bias voltage appearing across the PCM1794A's output current sources due to increasing the Vcc will be greatly mitigated by the increased bias voltage appearing across the now larger value I/V resistors, you can bet that there are other semiconductor junctions inside the the chip's analog section which remain referenced to ground, and thus will experience the full effect of any increase in Vcc.

None the less, I'm very glad to hear that you've apparently not experienced any such premature chip mortality, and I may experiment with this otherwise interesting technique on my own PCM1794A passive I/V DAC board.
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Old 16th August 2013, 09:42 AM   #517
IanS1 is offline IanS1  United Kingdom
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Originally Posted by Bas Horneman View Post
Just letting my Cinemags burn in before I give them a serious listen.
Hi Bas, any further thoughts on the performance of the Cinemags?
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Old 16th August 2013, 10:26 AM   #518
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Hallo Ian,

Not yet. Kinda busy at work. Lazy at home. Just one short listening session so far.
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Old 16th August 2013, 11:28 AM   #519
IanS1 is offline IanS1  United Kingdom
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Hallo Ian,

Not yet. Kinda busy at work. Lazy at home. Just one short listening session so far.
Must be catching, I've been pretty lazy at home most of the summer too.

Considering the price, I'll probably just order a pair of Cinemags and try them for myself.
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Old 16th August 2013, 11:47 AM   #520
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Considering the price, I'll probably just order a pair of Cinemags and try them for myself.
Perhaps try to set up a GB. We got them for a very decent price in 2005 with the DIYAUDIO GB.
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