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Digital Line Level DACs, Digital Crossovers, Equalizers, etc.

Output stage for the Soekris R2R
Output stage for the Soekris R2R
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Old 8th February 2017, 09:38 PM   #111
kumori is offline kumori  Europe
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Hi,
one question: does anything speak against using an analog volume pot after the unbuffered output? I would use a 50k motorized pot, which should work well with the 600-something Ohms output impedance of the dam, followed by a Calvin hybrid buffer.
Normally I would not see a problem here, but most people use the digital attenuation... so I'm just checking...
Thanks
Florian
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Old 8th February 2017, 10:08 PM   #112
TioFrancotirador is offline TioFrancotirador  Poland
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Quote:
Originally Posted by kumori View Post
Hi,
one question: does anything speak against using an analog volume pot after the unbuffered output? I would use a 50k motorized pot, which should work well with the 600-something Ohms output impedance of the dam, followed by a Calvin hybrid buffer.
Normally I would not see a problem here, but most people use the digital attenuation... so I'm just checking...
Thanks
Florian
Why you what to use analog attenuation when you have bit perfect digital available? For me what you want to do does not make sense at all and I do not see any benefit of that. Moreover it will just add lot of distortion and channel imbalance in low volumes levels.
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Old 9th February 2017, 04:37 AM   #113
derekr is offline derekr  Barbados
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Completely agree with Tio, kumori. If you want to use an analog pot use a 10k pot as per the user manual to 'control' the digital volume. You could even use a motorized 10k pot
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Old 9th February 2017, 10:23 AM   #114
markusA is offline markusA  Sweden
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I like tinkering as much as the next guy but I can't help wondering, do one really need a buffer stage for the dam?
I have a couple of Hypex nCore amps with differential input. So, XLR connections but you can drive them just fine with a single ended source. Input impedance is close to 100kohm, I think, much higher than 10k anyway. The dam's output impedance of 600'ish ohms shouldn't pose any problem...
Although I have been wanting to build some buffer stages, I can't really justify it if there is nothing to be gained from it. My speakers are very efficient, no extra amplification of the signal is needed.

So, is there anything for me to gain with a buffer stage or should I just be happy and go with the RAW output from the dam? It'll sure make for a more compact, easier, cheaper and more efficient build. I'm waiting for the 1231 (Pi-dam) to become available.
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Old 10th February 2017, 06:46 PM   #115
kumori is offline kumori  Europe
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Quote:
Originally Posted by TioFrancotirador View Post
Why you what to use analog attenuation when you have bit perfect digital available? For me what you want to do does not make sense at all and I do not see any benefit of that. Moreover it will just add lot of distortion and channel imbalance in low volumes levels.
I know, it would be more convenient, but digital volume controls are normally not bit perfect. Usually bit depth is lost the more you attenuate. Is there somewhere explained how this works in the dam1021? I am happy for any pointers. I only recall someone in the dam-thread measuring THD at different volume settings, and THD rises substantially with increasing attenuation.

My thinking is just: Yes, there is increased distortion and channel imbalance with analog potis, but this is neglible with quality parts. Probably as neglible as the increased distortion that was measured with the dam digital attenuation.
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Old 10th February 2017, 06:55 PM   #116
kumori is offline kumori  Europe
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Quote:
Originally Posted by markusA View Post
I like tinkering as much as the next guy but I can't help wondering, do one really need a buffer stage for the dam?
I have a couple of Hypex nCore amps with differential input. So, XLR connections but you can drive them just fine with a single ended source. Input impedance is close to 100kohm, I think, much higher than 10k anyway. The dam's output impedance of 600'ish ohms shouldn't pose any problem...
Although I have been wanting to build some buffer stages, I can't really justify it if there is nothing to be gained from it. My speakers are very efficient, no extra amplification of the signal is needed.

So, is there anything for me to gain with a buffer stage or should I just be happy and go with the RAW output from the dam? It'll sure make for a more compact, easier, cheaper and more efficient build. I'm waiting for the 1231 (Pi-dam) to become available.
Maybe it depends. If you have long runs of cable from your DAC to your poweramp, maybe you can benefit from a low impedance output. If not, then it should be ok, after all the 100k input impedance is over 100 times larger than the output impedance.
I heard that the ncores benefit from balanced drive, so maybe you consider to add a balancing output transformer after your DAC. In this case a buffer would be totally justified because output transformers very much like low impedance sources.
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Old 10th February 2017, 06:56 PM   #117
TioFrancotirador is offline TioFrancotirador  Poland
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Quote:
Originally Posted by kumori View Post
I know, it would be more convenient, but digital volume controls are normally not bit perfect. Usually bit depth is lost the more you attenuate. Is there somewhere explained how this works in the dam1021? I am happy for any pointers. I only recall someone in the dam-thread measuring THD at different volume settings, and THD rises substantially with increasing attenuation.

My thinking is just: Yes, there is increased distortion and channel imbalance with analog potis, but this is neglible with quality parts. Probably as neglible as the increased distortion that was measured with the dam digital attenuation.
That is true and I agree with that. However as far as I can recall Soren states that with 28bit depth of soekris at -70db level stil first 16bit are played. You can find it somewhere in soekris related thread.
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Old 10th February 2017, 07:00 PM   #118
markusA is offline markusA  Sweden
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They have differential input, so you can just have signal ground as the second input and that'll give you the balanced benefits. My current dac is using trafos on the output but the dam doesn't seem to need it?
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Old 10th February 2017, 07:08 PM   #119
kumori is offline kumori  Europe
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Originally Posted by markusA View Post
They have differential input, so you can just have signal ground as the second input and that'll give you the balanced benefits. My current dac is using trafos on the output but the dam doesn't seem to need it?
you can just use ground as second input, and this should work. While the dam does not need a trafo output, a trafo would balance the output impedances for true balanced operation, and apparently the hypex amps benefit from this. But, if it works for you without buffer and trafo, then it should be also no problem.
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Old 10th February 2017, 07:17 PM   #120
markusA is offline markusA  Sweden
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Since the 1231 hasn't been launched yet, I'm still waiting. At the moment I'm planning the coming build. My old dac uses trafos...
I have schematics for a tube buffer, a DCB1 PCB and hooking a trafo up is a easy thing to do. However, if there is nothing to be gained, why spend the money? I try to focus on building stuff that improves the sound...
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