Hi there,
I have an Audio Alchemy DDE V1.0 attached to my computer via S/PDIF. Well, S/PDIF is the only way to connect it, it is an DAC from the nineties IIRC. I used a passive preamplifier box with only a potentiometer in it to connect to my active monitors FOSTEX NF-01A. I sold my passive potentiometer box and connected the DAC directly to my monitors - in order to go the clean direct way.
The output level of these DAC boxes is pretty high (my multimeter measures 1.5V when outputting a 50HZ sine at max) so I was used to listen in the evening at pretty low audio mixer settings (low around 10%). This means, from the 16BITs depth the DAC can deliver there are only a couple left because this is done on the digital side, right?
I investigated the original circuit.
The V- pin is powered with -7.6V to GND, the V+ pin with 7.8V. So full V+ V- span is around 15V.
The left pin of each channel is connected to the output of the DAC chip, the right one goes to the hot pin of the RCA output. I calculated the gain to 3.
I thought, lower this to 1, no problem. I would have the tripled bitdepth listening with the same volume. I removed the 10k resistor and replaced the 20k one by 0R. Gain 1. The original OP was an AD746 which is not unity gain stable, I put an OPA2107 in.
My multimeter measures at 100% sine output 0.5V as expected.
The bass is gone. The punch in the lower frequency are is away. When I concentrate to remember my old DAC I think this sounds like a telephone receiver in the low area. How can this be? Both setup should have the same sound or not?
Kind Regards, Konsti
I have an Audio Alchemy DDE V1.0 attached to my computer via S/PDIF. Well, S/PDIF is the only way to connect it, it is an DAC from the nineties IIRC. I used a passive preamplifier box with only a potentiometer in it to connect to my active monitors FOSTEX NF-01A. I sold my passive potentiometer box and connected the DAC directly to my monitors - in order to go the clean direct way.
The output level of these DAC boxes is pretty high (my multimeter measures 1.5V when outputting a 50HZ sine at max) so I was used to listen in the evening at pretty low audio mixer settings (low around 10%). This means, from the 16BITs depth the DAC can deliver there are only a couple left because this is done on the digital side, right?
I investigated the original circuit.
The V- pin is powered with -7.6V to GND, the V+ pin with 7.8V. So full V+ V- span is around 15V.
The left pin of each channel is connected to the output of the DAC chip, the right one goes to the hot pin of the RCA output. I calculated the gain to 3.
I thought, lower this to 1, no problem. I would have the tripled bitdepth listening with the same volume. I removed the 10k resistor and replaced the 20k one by 0R. Gain 1. The original OP was an AD746 which is not unity gain stable, I put an OPA2107 in.
My multimeter measures at 100% sine output 0.5V as expected.
The bass is gone. The punch in the lower frequency are is away. When I concentrate to remember my old DAC I think this sounds like a telephone receiver in the low area. How can this be? Both setup should have the same sound or not?
Kind Regards, Konsti
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Top image has no feedback path. Connect the minus input of the opamp to the output to make a buffer.
New image
I am very sorry, the image is an old and wrong version, where the connection is missing from the feedback resistor to output in one channel. The other channel has a capacitor like the other channel too, of course. I attach the right one here until I find out how to exchange the original one 😱
I am very sorry, the image is an old and wrong version, where the connection is missing from the feedback resistor to output in one channel. The other channel has a capacitor like the other channel too, of course. I attach the right one here until I find out how to exchange the original one 😱
Possibly there is some low-pass-filter capacitor (i.e. parallel with the 20k resistor) that will lose its effect when you reduce the gain to 1?
Nah, you would gain around 1.5 extra bits. But let's save this for another time.
Nah, you would gain around 1.5 extra bits. But let's save this for another time.
Hi, this afternoon I figured out my Naim Unitiqute from my main rig could do the same job like my modified DAC for an A/B test. I set it up it puts out the same volume level and switched the RCA connectors from A to B (S/PDIF routed through the AA DDE V1.0 output to the Naim). I wanted to check this out before soldering the original setup into my DAC for a test.
My Brain/Ear system bitched at me. The modified DAC has same low frequency response and punch as my Naim. Naming it "telephone receiver" like was totally wrong. I yesterday listened more carefully and/or to the lowered gain setup by trend more at lower volume to my modification and I was wrong. Anything is OK, the new OP setup is like the old one but has lower gain - that's it. One only observes the rather old AA DDE V1.0 DAC technology against the more modern Naim 🙂
@wwenze: And you are right abought the 1.5BITs...
My Brain/Ear system bitched at me. The modified DAC has same low frequency response and punch as my Naim. Naming it "telephone receiver" like was totally wrong. I yesterday listened more carefully and/or to the lowered gain setup by trend more at lower volume to my modification and I was wrong. Anything is OK, the new OP setup is like the old one but has lower gain - that's it. One only observes the rather old AA DDE V1.0 DAC technology against the more modern Naim 🙂
@wwenze: And you are right abought the 1.5BITs...
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