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Inside the latest Benchmark DAC1 - Page 9

post #121 of 179
7/20/04 at 3:48pm
What would the high impedance on the unbalanced analog output do to sound quality?
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post #122 of 179
7/20/04 at 3:57pm
Quote:
Originally Posted by dip16dac
There is a RA-1 magic in this.
Indeed. Likely soon to be another FOTM. The parts are off-the-shelf and apparantly to the datasheet.
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post #123 of 179
7/20/04 at 4:02pm
Quote:
Originally Posted by AndreYew
Thanks John. I downloaded the manual shortly after posting my question, and it's a fine manual with much more technical detail than one would expect. Would it be possible to make this an optional setting in future products, perhaps via a jumper? Default setting would be high Z so it acts the same, but people who primarily use unbalanced can open up the DAC1, and reset the jumper?

--Andre

edit: the manual says consumer outputs are around 15k. Most of my consumer audio gear has output Z much less than 100 Ohms, with most hovering from 50 to 75.
Good suggestion. We may even eliminate the need for the jumper.

Here is a quick solution:

Use the DAC1 XLR outputs to drive your unbalanced gear. Wire pin 1 to shield (RCA barrel), pin 2 to hot (RCA pin), and make no connection to pin 3. Do not ground pin 3, it must be left floating.

When wired in this fashion, the XLR outputs will provide a 30-Ohm unbalanced output. If necessary, the output pads can be installed. The pads will raise the output impedance (see manual) but it will still be much lower than that of the RCA outputs.

BTW it is also possible to drive unbalanced gear from the 0-Ohm headphone outputs (with no loss in performance).
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post #124 of 179
7/20/04 at 4:02pm
Quote:
Originally Posted by ITZBITZ
Indeed. Likely soon to be another FOTM. The parts are off-the-shelf and apparantly to the datasheet.
Funny how just about anything I like any more is considered an FOTM. I guess that makes me a trend-setter who would have thunk that?
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post #125 of 179
7/20/04 at 4:04pm
Quote:
Originally Posted by jsiau
Good suggestion. We may even eliminate the need for the jumper.

Here is a quick solution:

Use the DAC1 XLR outputs to drive your unbalanced gear. Wire pin 1 to shield (RCA barrel), pin 2 to hot (RCA pin), and make no connection to pin 3. Do not ground pin 3, it must be left floating.

When wired in this fashion, the XLR outputs will provide a 30-Ohm unbalanced output. If necessary, the output pads can be installed. The pads will raise the output impedance (see manual) but it will still be much lower than that of the RCA outputs.

BTW it is also possible to drive unbalanced gear from the 0-Ohm headphone outputs (with no loss in performance).

Perfect idea! I will definitely try this when we get the DAC1 and 901 together , since Ed already has XLR -> RCA adapters for his SAC amp.
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post #126 of 179
7/20/04 at 4:05pm
Quote:
Originally Posted by ampgalore
What would the high impedance on the unbalanced analog output do to sound quality?
Roll of high frequencies and cause phase shifts in the high frequencies. See the manual for a discussion of cable capacitance, output impedance, high frequency roll-off, phase shifts, and maximum recommended cable lengths.
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post #127 of 179
7/20/04 at 4:19pm
Quote:
Originally Posted by Iron_Dreamer
Funny how just about anything I like any more is considered an FOTM. I guess that makes me a trend-setter who would have thunk that?
You my friend have gone through more gear in the last year than anybody I know (myself included!).

I'm sure it's great, really. It is interesting that the RME has the same DAC as the Benchmark. Putting it into it's own box with a nice power supply surely improves the dynamics a great deal. If you could fit a 3" toroid on the RME, I'm sure it would improve as well!

And the UltiLock circuit really just sounds like a benefit of the AK4114's ability to use it's own internal clock instead of feeding off the SPDIF clock. I like that it mutes the signal if it finds DTS or DD signals, avoiding the crazy garbage that comes out of some lesser receiver chips.
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post #128 of 179
7/20/04 at 4:33pm
Quote:
Originally Posted by dip16dac
The power supply has a three inch torroid, two TL401 rectifiers, a 7818 pos reg, a 7918 neg reg, a 7805 reg, and a LM1085.

Looks like there is plenty to modify in this thing.
Looks can be decieving. The circuit design has an exceptional PSRR (Power Supply Rejection Ratio). Line related Hum and noise measures -135 to -145 dBFS. In addition to the electrolytics, every opamp has a pair of 0.1 uF bypass caps and is fed from a power plane. The printed circuit board is an integral part of the power supply system, and provides additional distributed capacitance, a very low impedance distribution system, and a sophisticated EMI shielding system. The printed circuit board is designed to pass EMI tests without any additional shielding.

BTW we have injected several volts of line related noise onto the power supply rails in order to test the PSRR. Hum was still below -130 dBFS. The DAC1 has also been tested for RF immunity on all inputs (including the AC line). Performance is rock solid in adverse conditions.
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post #129 of 179
7/20/04 at 4:38pm
DTS and DD coming out as "garbage" are not the fault of the receiver chip - they provide information that the signal is not PCM audio, all of them. It is up to the designer of the DAC to act upon those flags and mute the output - not a fault of the receiver chip. Also, regardless of whether they have their own oscillator they still use the SPDIF clock because they have to lock onto it (via PLL). And based on the cutoff frequency of the PLL, jitter will pass through (plus what chip adds itself).
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post #130 of 179
7/20/04 at 5:27pm
Quote:
Originally Posted by ampgalore
Be careful there are 2 models on the DAC1. The older is 24bit/96Khz. The newer one is 24bit/192Khz.

If people are selling used DAC1 at a significant discount, they might be getting rid of the older model.
Could be a bargain, the older models can be upgraded for $50 US + tax and shipping.
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post #131 of 179
7/20/04 at 5:38pm
Quote:
Originally Posted by dip16dac
The RA-1 amp also sounds good even though it costs a lot and has a real cheap opamp in it.

I decided to listen to the DAC1 with my RME Digi96/8 PAD, Sonica, Pioneer 563A, and Toshiba SD-3950. It does sound good on all of them. A couple of things I notice is the clock crystal is 28.322 mHz instead of a common 24.576 mHz. The other thing is the increased power over the normal Buf634 buffer that I am used to. That is because instead of the typical +/- 15 volts, they put the absolute maximum rated voltage on it of +/- 18 volts. It's also wired for full bandwidth mode.
One other very important thing: THe BUF634 is inside a feedback loop. The BUF634 will deliver high distortion if it is operated open loop. And, the BUF634 has an open loop output impedance of about 7.5 Ohms. The feeback loop reduces the output impedance to 0 Ohms over the entire audio band.
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post #132 of 179
7/20/04 at 5:40pm
Quote:
Originally Posted by jsiau
Could be a bargain, the older models can be upgraded for $50 US + tax and shipping.
That's good news. I have the newer DAC1. If Benchmark is offering similar upgrades for future newer version of the DAC1, I'll keep the DAC1 for a very long time.
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post #133 of 179
7/20/04 at 7:03pm
Quote:
Originally Posted by jsiau
Could be a bargain, the older models can be upgraded for $50 US + tax and shipping.
Wow, this is good news indeed.

I like the older polished faceplate rather than the newer satin finish ones.

Me likes the shiny.

-Ed
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post #134 of 179
7/20/04 at 11:09pm
audiophiles are so vain
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post #135 of 179
7/20/04 at 11:18pm
Who me?

-Ed
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