I think you should finish your chassis work before you drive yourself crazy. Sometimes these things have a way of resolving themselves. Do you have any hum with the DAC unpowered or with the A20 primaries disconnected from the board.
I received the upsampling version of this DAC today and I am listening to it right now
Definitely a good step up from the internal DAC in the Squeezebox. I have a pair of UTC A-20's on hand to try soon. I want to give it some time so that I can become familiar with the sound and can hear exactly what I am getting with the transformer mods. Anyway, so far it sounds great and I can't wait to hear how it sounds modified!
Definitely a good step up from the internal DAC in the Squeezebox. I have a pair of UTC A-20's on hand to try soon. I want to give it some time so that I can become familiar with the sound and can hear exactly what I am getting with the transformer mods. Anyway, so far it sounds great and I can't wait to hear how it sounds modified!
This thing appear strange to me, transformer of this kind are also used in pro apps to eliminate hum due to ground loop (connecting two successive stage in a chain of equipments keeping the grounds separate), but in your case on the contrary the hum disappear when you connect the ground of the DAC to the ground of the succesive stage (a pre or ampli).
Maybe i missed something because of my scarce knowledge of the entire stuff.
Ciao
Andrea
I don't understand either, but I'll give the earthing of the RCA to main board a try. So this earth return is in addition to the RCA shield to '-' terminals on the A20s then?
Tried a different DAC and no hum so it's definately the DAC/A20s. I just do not undertand why some people haven't got this hum......
My pre-amp is not earthed, and the signalgrounds are all tied together on the circuit board.
The power amp is earthed, and this is the only item where the system ground is connected to the chassis ground, so no hum loops should be possible.
Tried a different DAC and no hum so it's definately the DAC/A20s. I just do not undertand why some people haven't got this hum......
My pre-amp is not earthed, and the signalgrounds are all tied together on the circuit board.
The power amp is earthed, and this is the only item where the system ground is connected to the chassis ground, so no hum loops should be possible.
It cannot be a ground loop originating at the DAC, do you have any hum with the DAC unpowered. Also, try disconnecting the board from the power trafo and energize the trafo. If you then have hum it is the magnetic field from the trafo. Do you have any flouresent lamps or dimmers in the area, thats always a good source of hum.
Hi Bill.
I'll try those suggestions and get back to you. Can add to this that I didn't get any hum at all when using a single op-amp plugged into the board, and was running wire from the op-amp outputs directly to the onboard RCAs.
Incidently even though the 15v-0v-15V are disconnected as not being used, should I still have connected the CT of this winding to the circuit board?
- J
p.s. no dimmers or flouresent lamps in the area.
I'll try those suggestions and get back to you. Can add to this that I didn't get any hum at all when using a single op-amp plugged into the board, and was running wire from the op-amp outputs directly to the onboard RCAs.
Incidently even though the 15v-0v-15V are disconnected as not being used, should I still have connected the CT of this winding to the circuit board?
- J
p.s. no dimmers or flouresent lamps in the area.
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Nope. That would turn the ground plane of the board into a transmitter antenna for any RF trash in the trafo.
OK disconnected the power to the DAC and I only get hum when the volume control is 3/4 of the way around.
With power connected the hum is quite audible from around the 12 0' clock position. Using a piece of cardboard and moving the wires around and/or the A20s does not seem to affect the hum level.
- John
With power connected the hum is quite audible from around the 12 0' clock position. Using a piece of cardboard and moving the wires around and/or the A20s does not seem to affect the hum level.
- John
I have to go soon, but I'm not clear on whether the power trafo is energized or not. Still, I think you should concentrate on getting the chassis buttoned up and earth grounded. I've had problems like this on the bench that mysteriously disappeared once the project was completed.
I tried with and without the DAC plugged in. But I'll also try disconnecting the transformer from the DAC board also.
Agreed about buttoning it all up and then trying again. Once the chassis is earthed properly and I have some proper high quality RCAs installed and the mains cable is neatly routed away etc I'll see where I stand then.
Thanks,
- John
Agreed about buttoning it all up and then trying again. Once the chassis is earthed properly and I have some proper high quality RCAs installed and the mains cable is neatly routed away etc I'll see where I stand then.
Thanks,
- John
Thanks for this suggestion I'll try it later today
I assume the connections from RCA shield to each A20 stay connected, but in addition a wire is run from each RCA shield to the ground plane of the DAC board? I'll use the ground hole for the original RCA outputs which I removed.
Thanks,
- John
Not to beat this to death, but I had a similar question. I'd like to try some high rez recordings from Reference Recordings. They are recorded at 24/176.4 and are typically replayed using a computer/DAC setup. (I have my DAC connected to a Mac Mini via USB.) Currently, I have the DAC's toggles set for 0 and 1 (up to 24-bit) and 1 and 0 (double speed 50 to 100 kHz). If I understand the previous post correctly, I would need to manually change to quad speed (100 to 200 kHz) whenever I want to listen to hiz rez.
I'm curious about this because I can play back a couple of sample tracks without any manual switching. Is the DAC automatically stepping down the music for playback?
Also, I'd be curious to see how the toggle switches should be added if/when someone gets around to it.
Finally, just for laughs, I'll mention that the DAC Reference Recordings recommends for replay lists for $5,000 (US).
Thanks in advance to everyone in this thread for humoring my noob questions.
Steve
I'd bet the DAC is downsampling the file you're playing. Simple to throw a couple of switches though and listen again using quad speed (the correct setting).
Regarding the toggle switches, you'd merely desolder the switches from the DAC board (VERY carefully so you don't damage the DAC with heat, and not to dislodge the tiny SMD resistors on the underside of the board), then run wires from the holes to toggle switches on the front panel. All you're doing is just adding some wire/distance between the switches and the DAC so not changing anything per se. Just make sure you get the switches the right way around so as not to muck up any sampling rate settings etc
EDIT: I seem to remember reading that with this DAC's USB input the max. sample rate was 48khz? Definately need some clarification on this. Generally I don't think you can get 192khz sample rate with bog standard USB (unless you pay for a big bucks converter)... For what it's worth I also bought a Mac mini recently, and am VERY happy using the optical output straight into the DAC. The Mac mini can output up to 24/96 using the optical connection (you have to select 24/96 from the Midi settings screen) and it sounds amazing through this DAC. I truly believe optical isn't as inferior as SPDIF as many would have us believe, at least from my listening tests and a decent optical cable from www.lifatec.com.
Regarding the toggle switches, you'd merely desolder the switches from the DAC board (VERY carefully so you don't damage the DAC with heat, and not to dislodge the tiny SMD resistors on the underside of the board), then run wires from the holes to toggle switches on the front panel. All you're doing is just adding some wire/distance between the switches and the DAC so not changing anything per se. Just make sure you get the switches the right way around so as not to muck up any sampling rate settings etc
EDIT: I seem to remember reading that with this DAC's USB input the max. sample rate was 48khz? Definately need some clarification on this. Generally I don't think you can get 192khz sample rate with bog standard USB (unless you pay for a big bucks converter)... For what it's worth I also bought a Mac mini recently, and am VERY happy using the optical output straight into the DAC. The Mac mini can output up to 24/96 using the optical connection (you have to select 24/96 from the Midi settings screen) and it sounds amazing through this DAC. I truly believe optical isn't as inferior as SPDIF as many would have us believe, at least from my listening tests and a decent optical cable from www.lifatec.com.
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I'd bet the DAC is downsampling the file you're playing. Simple to throw a couple of switches though and listen again using quad speed (the correct setting).
Regarding the toggle switches, you'd merely desolder the switches from the DAC board (VERY carefully so you don't damage the DAC with heat, and not to dislodge the tiny SMD resistors on the underside of the board), then run wires from the holes to toggle switches on the front panel. All you're doing is just adding some wire/distance between the switches and the DAC so not changing anything per se. Just make sure you get the switches the right way around so as not to muck up any sampling rate settings etc
EDIT: I seem to remember reading that with this DAC's USB input the max. sample rate was 48khz? Definately need some clarification on this. Generally I don't think you can get 192khz sample rate with bog standard USB (unless you pay for a big bucks converter)... For what it's worth I also bought a Mac mini recently, and am VERY happy using the optical output straight into the DAC. The Mac mini can output up to 24/96 using the optical connection (you have to select 24/96 from the Midi settings screen) and it sounds amazing through this DAC. I truly believe optical isn't as inferior as SPDIF as many would have us believe, at least from my listening tests and a decent optical cable from www.lifatec.com.
This is strange. I switched from double speed to quad speed and replayed the two high rez samples. Couldn't really hear any difference in sound quality (although these are great recordings). I then tried using iTunes, and my stored music played just fine (even though the DAC was still set for quad speed). Does this mean that the DAC is upsampling the 44.1 quality music in iTunes. (Again, I can't "hear" any difference in the sound from double speed.)
I seem to remember some discussion of owners preferring single speed with de-emphasis for playback.
The high rez samples download to Quicktime. I wonder if that has anything to do with the sound quality.
On the optical connection, I have a first generation Mini, which does not include the built-in toslink connection. I think USB is my best bet for outputting music.
Sorry for the Mac talk. I didn't mean to drag the discussion too far off topic.
You need to find the number of the chip that provides the usb-digital conversion s we can see exactly what is happening here, otherwise you're probably just getting upsampled audio I'd imagine.
As for playback for 99.8% of CDs out there you'd use the setting without de-emphasis.
For those using 16-bit what settings are you using? I have mine set to '0,1' (I2S up to 24-bit data) which I assume is the correct setting for both the optical and SPDIF inputs on this DAC???
As for playback for 99.8% of CDs out there you'd use the setting without de-emphasis.
For those using 16-bit what settings are you using? I have mine set to '0,1' (I2S up to 24-bit data) which I assume is the correct setting for both the optical and SPDIF inputs on this DAC???