[cobaltmute]

And that is why I make sure my calculations are public, because I know I don't always get it right.

 

[keyid]

Quote:

Originally Posted by Billyk /img/forum/go_quote.gif I want to check mine.

checked dc offset by connecting OG (output ground) to OR or OL with a meter and turning off the amp or unplugging the usb.

 

[Billyk]

Quote:

Originally Posted by keyid /img/forum/go_quote.gif checked dc offset by connecting OG (output ground) to OR or OL with a meter and turning off the amp or unplugging the usb.

Thanks, I knew that... Once you told me!

 

[keyid]

symptoms of a old timer

pls let me know if this is the case of your carrie

 

[joneeboi]

Quote:

Originally Posted by cobaltmute /img/forum/go_quote.gif Big Warning I just realized that the USB jack on the Bantam is grounded as well as the case will be from the Carrie. This mod may not work at all as the case might/will tie the two together anyways.

There's also the issue of connecting signal ground because it is still connected to USB ground. But like, stwspoon mentioned, all the currents are accounted for anyway.

I'll get a chance to make some measurements soon, so I'll report my results back when I get that chance. I've been super busy with school and extra curriculars, but I'm keeping up with the thread and all the issues you guys bring up. I really want to scope the rails. I'll try and formalize my test method and results for the thread when I get that chance.

DK, did you check if C8 was the one shorting to the case? If it isn't that one, it could be L3.

 

[cobaltmute]

I did a test last nite with my second Carrie board. Using a USB pigtail I bought to make a cable DAC, I powered the Carrie directly off the USB (without the DAC being in line). The Carrie powered up fine, with no shutdown of the USB port.

My Carrie + Grub when first plugged in to the computer (a Thinkpad X61), has Windows 7 shut down the port. If I disable/enable the port in Windows, the pair will run fine. Plugging the same combo into a Dell laptop works fine. It should be noted that on my Thinkpad, power is always delivered to the port and only the data interaction with the DAC is shutdown. After re-enabling the port, if I look through device manager, the PCM2707 is reporting its power requirements as 20mA.

This leads me to believe the issue is not the actual power draw of the combo, but the way that the GrubDAC is reporting its power needs to the PC. stwspoon deserves credit for bringing this up in the GrubDAC thread. Depending upon the hardware/driver, some machines may decide to "shut" the port down.

The workaround at this point is to lift PSEL (pin 16) on the PCM2707 and air-wire it to power (3.3V). Pins 2/3 (Vccp and HOST) are likely a good choice as they are both tied to Vdd and gives you two pins to work with for easier soldering. This has the GrubDAC report to the host that it is bus powered and will be using 500mA.

With PCM2706/07s in short supply, I'm stuck waiting on testing this. My current Grub board has been mutilated a bit with some bad soldering so I don't dare take it apart from the Carrie to work on it.

EDIT: I should add that I'm going to try another workaround as well. I'm going to place a thermistor between the Grub and the Carrie and see if using it as a Inrush current limiter will work.

EDIT: Revised info here http://www.head-fi.org/forums/f6/car...ml#post6075302

 

[nightanole]

Does the input/output/volume control need to be isolated from chassis? Im using an all metal case and panel mount jacks.

 

[joneeboi]

Only the output ground needs to be isolated. Input ground, volume pot, USB ground can all be safely connected to the case. Then again, I'm not sure what exactly is going on with your gamma-2+Carrie build, so you have to the ultimate judge of that.

 

[joneeboi]

Quote:

Originally Posted by cobaltmute /img/forum/go_quote.gif My Carrie + Grub when first plugged in to the computer (a Thinkpad X61), has Windows 7 shut down the port.

My Toshiba on Vista and 7 don't work with the Bantam. It was great on XP, but it isn't working for me with the new ones. It works for others on 7, but my computer seems really temperamental. I've gone through every "solution" on Google, so if anyone can offer me another idea, I'm game.

 

[Billyk]

Quote:

Originally Posted by keyid /img/forum/go_quote.gif symptoms of a old timer pls let me know if this is the case of your carrie

Very interesting... FWIW
Carrie offset when I turned off using the power switch on the pot was about -25 on average. Unplugging USB seemed to result in just a tad less.
Mini^3 with the inputs shorted or not averaged about -110

 

[cobaltmute]

Quote:

Originally Posted by joneeboi /img/forum/go_quote.gif My Toshiba on Vista and 7 don't work with the Bantam. It was great on XP, but it isn't working for me with the new ones. It works for others on 7, but my computer seems really temperamental. I've gone through every "solution" on Google, so if anyone can offer me another idea, I'm game.

So it doesn't recognize it or it shuts down the port? What do you see in Device Manager under USB controllers when your plug in?

 

[nightanole]

Im just gonna throw this out there. The gamma 1 has beads on both the 5v+ and the ground of the usb port to isolate them from chassis. This would be REAL easy to impliment in the carrie. Im goning to be tapping power/ground after the beads on my gamma 2 so i should be good. If all goes well i shouldnt need to implement a 5v external power supply. So far i havent heard anyone complaining about noise from using just usb.

 

[cobaltmute]

On the Carrie, biggest source of noise will be from the DCP, not the USB power. And post the DCP there is the low-pass filter created be C1F, L1F, C2F.

The ferrites in the Gamma1 do the same thing (and the always need to be followed by a cap to make it work).

 

[daBigR--]

Hi, I received the mouser parts late last week and assembled both Carrie boards during the weekend. So far I've only connected one of them to a DMS1, and I was getting a loud hum that I later found was caused by an interconnect I left pugged to the mp3 player output with the other end unconnected, duh! So getting rid of the cable got rid of the noise, but I still have a high frequency hiss, barely noticeable at normal listening levels but stil present, I'll do some testing while setting up the 2nd amp to try and solve that noise issue. Regardless of that, the amp sounds really good, I've been doing my listening on HD-595s mostly to classical music and some jazz. The most noticeable thing is the imaging, IMO better than the PIMETA and I think even better than my Ear+ HD, every intrument is placed on a very defined place in space. It also has a lot of detail and a very likeable bass, quite to my taste, very controlled and good transient response too. As for the USB problems, not an issue for me since I'm powering directly from the mp3 player's regulated power source, not from it's USB out ports, but I'll try and measure inrush current at switch on/off to compare with your figures. I don't know if any part of my post will be of any help during this prototype stage as I'm not a very experienced DIYer, please let me know how I can help further.

 

[joneeboi]

Quote:

Originally Posted by cobaltmute /img/forum/go_quote.gif So it doesn't recognize it or it shuts down the port? What do you see in Device Manager under USB controllers when your plug in?

Sorry for the lack of clarity. It turns on, plays music, shows up in Device Manager and everything, but every once in a while (I can't seem to pinpoint when), the sound just turns to static for a few minutes and then goes back to normal. I think it might have something to do with ReadyBoost, but I still have to test that. It seems when I get really active on the computer, it goes to static. Using the computer solely for music reduces(/eliminates?) the frequency of these occurrences. Everything seems to work fine but the PCM.

Thanks for sharing your measurements, BillyK. That's really interesting stuff.

nightanole, are you suggesting having two filters in series? If it's already on the gamma, then why do you need one for Carrie? This filter also exists on the Bantam.