Practical Devices XM5 - Page 14

Ha Ha so funny as I accidentally made a few extra mouse clicks just about 15 mins ago and somehow managed to order a pair of WhiteCat AD8065's for the XM5.

I'm pretty happy with the synergy right now but I cannot resist the urge of playing with different combinations. Love the fact this portable amp has so many built in features plus you can swap out buffers and op amps at will.

Great great product.

OK, so the XM5 crossfeed being active is designed to keep the volume constant. Re the delay, I believe this to be a basic part of all designs in addition to the actual cross-feeding:

HeadRoom amplifiers cure the problem by allowing you to cross-feed a little of the left and right channels across to each other through a short time delay using the crossfeed switch.- HeadRoom

The CORDA headphone amplifiers can electronically simulate this process and, with appropriate attenuation and delay, add some of the right audio signal to the left channel and vice -versa. -Meier Audio


...and I think the 8065 is calling me. I just need to actually order them.

I was googling for linkwitz crossfeed since one article referenced it and explained active vs passive.
But i finally read tangent's link and maybe it now makes sense that greatdane hears a bass boost in the xfeed:

Modified Linkwitz Crossfeed PCB

HeadWize - Project: An Acoustic Simulator for Headphone Amplifiers by Chu Moy

HeadWize - Project: An Enhanced-Bass Natural Crossfeed Filter by Jan Meier

seems quite common? wonder why i still don't notice it.

Interestingly, not sure where the link is that explained active vs passive, i tink it's a matter of components used, but memory is not strong enough to repeat what i said, in case i am not remembering correctly. Either way, i know it works on the XM5
(You will notice a lot graphs showing delays on these curcuits too)

sorry to go off topic from opamp rolling but this is my first battery powered headphone amp and/or DAC and I'm still running on my first battery charge but it seems the DAC performance has diminished with the battery power. It's not warning me the power is low but it seemed the DAC quality was noticeably lower once power dropped below 8V. Not bad at all but I hear a little bit of distortion during more complex and full sounding passages, especially if there is a lot of low frequency sound. Is that just typical with these battery powered devices, a weakness of the XM-5, or maybe a problem unique to mine?

I haven't noticed that - I will have to try testing it out soon and see what happens as voltage drops. Do you only notice when listen through the DAC, or also listening to the amp with an analog input like from an iPod?

I've only been using it on my old Dell computer at work through the USB input, but I can use an LOD on my ipod tonight and on my home Mac Powerbook and see if I can replicate or isolate the source. Great idea, thanks =)

I wonder if you are getting issues with noisy power via your USB as a possibility.

Did you check the note about this in the troubleshooting section of the XM5 manual? any of that helping?

Listen to the DAC with 13Ohm phones to get an idea, luckily it's pitch black with 32Ohm phones, but with 13Ohm phones (yeah outside their spec'ed range) it's a party!

Here is a thread on headfi that explains the active vs. passive crossfeed on XM5, which set me straight on the subject. Only XM5 has an actual active crossfeed. If you read the thread, James (aka MaxAmplitude the Practical Devices guy) posted, explaining the difference.

I think that active crossfeeds are overlooked (read: cheaped-out on!) with most portables.

Thanks Keppel, I knew that I read that explanation from James somewhere here.

Crossfeed done right!

Please post your impressions compared to the stock chips.

Will do when it arrives, probably at least a week to get here

Thanks for the suggestions on troubleshooting my 'dirty' sound issue. I tried a number of different configurations and came to the conclusion the distortion I was hearing had nothing to do with the voltage level of the XM-5 batteries. I believe with the master volume on my Dell computer set at one notch down from the top (around 80%) it was introducing distortion. The sound is much cleaner at one notch lower (around 65%) with the volume turned up higher on the XM-5. I also heard distortion from my iPod LOD, but it sounded different and I am pretty sure its the not so great DAC in the iPod revealing itself in all of its splendor on my K702's.

The DAC in the XM-5 still sounds like it gets a bit overwhelmed with certain complex or bass heavy passages but it's much better after making adjustments at the source. I'd say 90% of the problem was resolved. My music seems to sound a bit better playing from Foobar over iTunes too. I think I'll hear a marked improvement in these little SQ nuances as it burns in. I only have around 40 hours on it now.

For a few days I thought I might want to send it back and pick up a Pico or Predator but I'm thinking that was just user error blaming the XM-5. It's amazing considering the quality you get at this price.

The xm5 looks like quite the little champ. I've got one on the way, but I was wondering if it can drive 600ohm beyers. I've got a pair of 250 880s that I love and Im already thinking about upgrading to the 600 ohm version through beyer de. So does anyone have any experience driving 600 ohm phones through the xm5? I got the version with the BUF634, I hoping that will cut it.