pupDAC Step-by-Step Build Thread
Jul 20, 2016 at 8:38 AM Post #346 of 359
Yikes, rereading my post makes me wonder what I was doing when I typed that mess out.  Anyway, I don't know why I didn't actually check voltages, I'll do so tonight and report back.  Thanks!
 
Aug 8, 2016 at 11:48 AM Post #347 of 359
I'm not understanding how you worded your post. What is the difference between "5v" and "5v tp?" Aren't they both the same test point? Forget about "shorted," what is the actual voltage to ground that you measure at those points?

If the "-5V" test point does not measure -5V referenced to ground, then something is wrong with U7, the voltage-inverting charge pump.

 
I finally got a chance to take a look and a few of the voltages were completely messed up.  I replaced the various parts to get the voltages reading as expected and everything is working as it should.  I appreciate your help, I had been away from working on this stuff awhile and I completely spaced checking the voltages.  Thanks for the assist!
 
Aug 8, 2016 at 11:18 PM Post #348 of 359
 
I'm not understanding how you worded your post. What is the difference between "5v" and "5v tp?" Aren't they both the same test point? Forget about "shorted," what is the actual voltage to ground that you measure at those points?

If the "-5V" test point does not measure -5V referenced to ground, then something is wrong with U7, the voltage-inverting charge pump.

 
I finally got a chance to take a look and a few of the voltages were completely messed up.  I replaced the various parts to get the voltages reading as expected and everything is working as it should.  I appreciate your help, I had been away from working on this stuff awhile and I completely spaced checking the voltages.  Thanks for the assist!

 
Glad it all turned out OK.
smily_headphones1.gif

 
Feb 9, 2021 at 4:56 PM Post #350 of 359
Hello Everyone,

I just finished soldering my Pupdac! It sounds great! There's only one problem... The volume cannot be adjusted. I read earlier in this thread that someone had the same issue, but it wasn't clear to me how they fixed it.

The problem:
  • Windows volume control does not have any effect on volume output to my HD599s
  • Volume is very loud.
Some diagnostic info:
  • The board is detected as: "3- USB AUDIO DAC"
  • Windows volume bar can be adjusted but has no effect.
  • Volume can be reduced through applications such as Spotify and YouTube.
  • Music sounds great with reduced volume from applications with internal volume control.
  • No noise can be heard when nothing is playing.
  • Test Pad voltages
    • Test Pad 3.3V-1 = 3.294V
    • Test Pad 3.3V-2 = 3.287V
    • Test Pad 5V = 4.940V
    • Test Pad -5V = -4.923V
    • Test Pad 4V5 = 4.746V
    • Test Pad 2V5 = 2.496V
    • Test Pad -2V5 = -2.499V

After some reading of the PCM2706C datasheet, it seems as though it is operating in its default control interface. In which, the spdif output to the PCM1794A is not volume controlled? Is my reading of that correct?
" The master volume control is not supported. A request to the master volume is stalled and ignored. " (Section 9.5.1.2 - Ti PCM2706C datasheet).

Where should I look next for fixing this issue?

Thanks in advance for the help :)
 
Last edited:
Feb 13, 2021 at 3:56 PM Post #351 of 359
Hello Everyone,

I just finished soldering my Pupdac! It sounds great! There's only one problem... The volume cannot be adjusted. I read earlier in this thread that someone had the same issue, but it wasn't clear to me how they fixed it.

The problem:
  • Windows volume control does not have any effect on volume output to my HD599s
  • Volume is very loud.
Some diagnostic info:
  • The board is detected as: "3- USB AUDIO DAC"
  • Windows volume bar can be adjusted but has no effect.
  • Volume can be reduced through applications such as Spotify and YouTube.
  • Music sounds great with reduced volume from applications with internal volume control.
  • No noise can be heard when nothing is playing.
  • Test Pad voltages
    • Test Pad 3.3V-1 = 3.294V
    • Test Pad 3.3V-2 = 3.287V
    • Test Pad 5V = 4.940V
    • Test Pad -5V = -4.923V
    • Test Pad 4V5 = 4.746V
    • Test Pad 2V5 = 2.496V
    • Test Pad -2V5 = -2.499V

After some reading of the PCM2706C datasheet, it seems as though it is operating in its default control interface. In which, the spdif output to the PCM1794A is not volume controlled? Is my reading of that correct?
" The master volume control is not supported. A request to the master volume is stalled and ignored. " (Section 9.5.1.2 - Ti PCM2706C datasheet).

Where should I look next for fixing this issue?

Thanks in advance for the help :)
Just to be clear, this was resolved off-line.

We thought a few years ago that the PCM2706/7C was a solution, but a software control is necessary that is not included in the PupDAC design.

The PupDAC is just like most sources in the high-fidelity headphone world (or speakers, too). It isn't intended to be connected directly to a headphone, nor do we recommend that as a regular practice. Connecting to a headphone amplifier makes the need for a software volume control moot.

Also, any software volume control is going to lower the music stream resolution. There are some technical calculations that can be done with the ENOB headroom of the DAC vs. the digital stream that argue against this as a real worry, but again, better to use a headphone amplifier with am analog volume control and remove all doubt of damaging the music resolution.
 
Jul 7, 2021 at 6:53 AM Post #352 of 359
Curious if anyone has any thoughts on this as i keep blowing the arse out of the voltage regulators. PupDAC has worked perfectly for years, until recently when i got a second hand Schiit Vali headphone amp, the original model with two sub miniature 6088 tubes. The unit is powered with a 15v AC adapter.

Problem is if the PupDAC is connected to the Vali, and i then connect the USB to the computer there is a chance it will blow the voltage regulators in the PupDAC. First time it happened it took out the two (3.3v) regulators U2+U4, and the 4.5v regulator U5. I have just done it again by accidentally unplugging the USB and plugging it in again, this time U2 went bye bye.

I am assuming its to do with the Vali not being ground referenced and letting its ground plane float, as i dont have a problem if i connect the PupDAC USB first, then connect power the Vali.

I am wondering if any clamping diodes across the input of the PupDAC would help cure this issue, or any other ideas anyone has? ....i know the obvious answer is to not use the Vali and go back to my old amplifier, but i kind of like it, and pairs well with my headphones.

P.S. As a backup i am using a Skeleton DAC and not having the same issue, seems to be a little more resilient.
 
Last edited:
Aug 16, 2023 at 10:14 PM Post #353 of 359
I wish someone would make a kit like this, but include four burr-brown DAC chips and make it fully balanced... I'd buy it in a heartbeat
 
Aug 21, 2023 at 8:42 AM Post #354 of 359
Curious if anyone has any thoughts on this as i keep blowing the arse out of the voltage regulators. PupDAC has worked perfectly for years, until recently when i got a second hand Schiit Vali headphone amp, the original model with two sub miniature 6088 tubes. The unit is powered with a 15v AC adapter.

Problem is if the PupDAC is connected to the Vali, and i then connect the USB to the computer there is a chance it will blow the voltage regulators in the PupDAC. First time it happened it took out the two (3.3v) regulators U2+U4, and the 4.5v regulator U5. I have just done it again by accidentally unplugging the USB and plugging it in again, this time U2 went bye bye.

I am assuming its to do with the Vali not being ground referenced and letting its ground plane float, as i dont have a problem if i connect the PupDAC USB first, then connect power the Vali.

I am wondering if any clamping diodes across the input of the PupDAC would help cure this issue, or any other ideas anyone has? ....i know the obvious answer is to not use the Vali and go back to my old amplifier, but i kind of like it, and pairs well with my headphones.

P.S. As a backup i am using a Skeleton DAC and not having the same issue, seems to be a little more resilient.
This is way out of date, but it's the first I've seen it and even heard of it. It is true that the PupDAC is skirting the amperage limits of USB power. That may be why you're experiencing this issue. Most likely, the 6088 tubes in the Vali have a huge instantaneous current draw from their heaters and it's blowing out the regulators before the overamperage protection kicks in on the USB power supply. An SMD current fuse in the USB power circuit would probably fix this.

We did not address this, because the recommendation is to use the DoodleBug USB power supply with the PupDAC, instead. This relieves any power demands on the USB power supply and uses a very highly-linear-regulated power supply for the DAC inside the DoodleBug. It also contains an SMD, automatically resettable fuse in the power circuit. Again, our recommendation is to always use the PupDAC with the DoodleBug. Operation is superior in all respects (both sound and operation) when you do that.
 
Aug 21, 2023 at 8:44 AM Post #355 of 359
I wish someone would make a kit like this, but include four burr-brown DAC chips and make it fully balanced... I'd buy it in a heartbeat
Thank you for the compliment, but am curious about your suggestion for four Burr-Brown DAC chips. The single Burr-Brown DAC already used in the PupDAC is outputting a fully balanced signal. We use the opamp on the output to combine those balanced outputs into single-ended. This is actually similar to an ESP Audio DSHA circuit, in that the balanced-to-single-ended at the output is still vastly superior in sound quality than single-ended throughout.
 
Aug 21, 2023 at 4:03 PM Post #356 of 359
okay, how about two then? could you do one for L and one for R, and create fully balanced XLR outputs? Using one per channel in mono should increase the SNR, correct?

how about stacking them in parallel, does a burr-brown DAC chip support that?

how about switches to toggle oversampling on and off (if that burr brown chip supports it) and/or 4x / 8x oversampling (depending on support from the chip, of course)

I'm just a crazy audiophile and am willing to pay for well-designed things that let me experience new sounds
 
Oct 17, 2023 at 1:35 PM Post #357 of 359
Hey all, I built my pupdac about a decade ago or whenever it first came out, with Tom's help. I recently moved and post move, the pupdac has lost its left channel. I obnoxiously emailed Tom for advice and realized it was probably less annoying for him to ask here.

The solder points for the outputs looked like they were loose, so I reflowed them. Everything looks good on the output, I see no other loose solder points, and yet still no left channel. It's worked reliably for about a decade, so I'm thinking whatever the issue is results from a physical jostling or dropping during the move.

All test points measure about 0.25v above the spec voltage (I think the doodle bug is set to 6v).

Where would you look first?
I'm considering just re-flowing everything through hole in case something is slightly loose. Any other ideas?

Thanks!
 
Oct 17, 2023 at 3:47 PM Post #358 of 359
Hey all, I built my pupdac about a decade ago or whenever it first came out, with Tom's help. I recently moved and post move, the pupdac has lost its left channel. I obnoxiously emailed Tom for advice and realized it was probably less annoying for him to ask here.

The solder points for the outputs looked like they were loose, so I reflowed them. Everything looks good on the output, I see no other loose solder points, and yet still no left channel. It's worked reliably for about a decade, so I'm thinking whatever the issue is results from a physical jostling or dropping during the move.

All test points measure about 0.25v above the spec voltage (I think the doodle bug is set to 6v).

Where would you look first?
I'm considering just re-flowing everything through hole in case something is slightly loose. Any other ideas?

Thanks!
Upon reflowing all the connectors, cleaning and drying, the left channel is louder and clearer, but still sounds clipped and distorted. This leads me to think that everything is working, but there's a weird/broken solder joint near the output. I will reflow all through holes and see if that helps.
 
Oct 17, 2023 at 6:31 PM Post #359 of 359
I tried reflowing all of the through-hole components and many of the SMD stuff, too to no avail. Do op-amps ever die in one channel, and not both? I'm wondering if I need a new opamp. Could it be the stabilizing caps on the power for that side of the opamp (C26/11)?

Any other ideas?
 
Last edited:

Users who are viewing this thread

Back
Top