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Connecting headphones directly to DAC's tube output?

post #1 of 7
7/20/11 at 1:04pm
Thread Starter 
First of all, two things:

1. I don't quite know where to post this, but this forum seems like the best bet. If it is incorrectly placed, please move it.
2. I don't know much about amplifiers, electronics, signals, impedance matching etc. so forgive me if I seem to be missing some obvious things.

With that out of the way, I currently own both a Sennheiser HD650 and a Maverick TubeMagic D1 DAC. I would like to use my headphones with the D1's tube output, but I don't have any good amplifier. The only amplifier I have is some '90s cheap marantz amp that sounds absolutely horrible, no matter what I use it with.

However, I've found that if I simply connect my headphones to the D1's tube pre-out, they are driven at an acceptable volume level, at about 60% or so volume. (I usually have the volume on 100% aka “direct mode” if connecting the D1 to an amp) I've only tested this briefly but it seems to work fine, so I'm considering soldering a dual-male RCA to female-TRS connector so I can do it permanently.

I have one worry though: Is there anything that can go wrong or damage my components by doing this? I mean, obviously sound is at an acceptable level, and it works - but that doesn't tell anything about how long.

I checked Maverick's web-site and they've listed the D1's tube output impedance as “5 kOhm”, though my headphones have an input impedance of “300 Ohms” only. What does this mean and can it damage my DAC (by, for example, forcing it to draw more current than it's design to handle)?

If so, is there any alternative I could use? I've always been using the D1's integrated headphone amp for my headphones (I also use speakers), but I've really wanted to do some critical listening of the tube as well so I can decide whether I prefer the tube or the solid state, but I don't have a high quality amplifier and I don't want to waste lots of money on something if I end up not using it.
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post #2 of 7
7/24/11 at 3:08pm
Thread Starter 
I believe a slight bump is in order. I would really like a solid answer to this: Will it damage my components or not?
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post #3 of 7
7/29/11 at 3:29am

this question has been answered a few times in the D1 thread.

You should NOT use the Senns directly out of the D1 as the outputs are considered "Hot", you will damage your headphone

 

From the thread:

 

Do not attempt to connect headphones directly to the "Tube Pre Out" connections on the back of the unit. Several users report the output being electrically hot and would require hardware such as a dedicated amplifier before connecting headphones.

Quote:
Originally Posted by hodgjy View Post
Most hi-end gear sends a line-level output of 2.0v, and is the norm in Europe. In the U.S.A, a lot of mid and low end gear send a line-level output of ~0.5v. 2.0v is still within specs of most gear.
When I measured the output of the D1, using a combo if the "direct button" and then maxing out the volume pot, I got these measurements:
Tube pre-out in direct mode maxes out at 2.2v. Using the volume pot, 3:00 maxes out at 2.2v as well.
Non-tube out is slightly cooler. It still maxes out above 2.0v, but doesn't hit the 2.2v as often as the tube pre-out.

 

http://www.head-fi.org/forum/thread/470639/maverick-audio-tubemagic-d1-dac-amp-condensed-faq-and-info-thread#

 

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post #4 of 7
8/11/11 at 8:27pm
Thread Starter 
So in other words, I'm fine as long as I don't turn the volume to the maximum or use direct mode?

I would have the volume knob at a very low level.
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post #5 of 7
8/11/11 at 8:47pm

2.2v (RMS or P-P, dont care) is nothing for most 300(ish)ohm headphones. I rocked with my HD800 with 8vp-p. Beyers are rated for at least 5v (been there done that). They shook it off after blasting like 124db. Your problems will come from other things. As long as it does not come with compromises to SQ, moar voltage swing potential is moar better. 

 

The 5Kohm output impedance will do you in. It sounds like the DAC takes the approach of driving the output direcly off of the plate of the tube with a coupling cap. The output impedance will cause the output voltage to sag a LOT, which means the 2.2v or whatever is meaningless. You will be lucky (unlucky, keep reading) to get 0.2v into 300ohms. More importantly is how poorly triodes behave when driving loads less then ~10*Rp, in other words, anything less than 50Kohms. I predict the suck. Mucho distortion. Depending on your luck the amp may be unable to supply the current necessary to drive the headphones and then things reallllly get bad. If it does actually run without clipping audibly, Id bet that the coupling caps are too small to get the bass into the headphones.

 

So, no, dont try it. 

 

Do the headphone outputs run off of the tube outputs? use them. 

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post #6 of 7
8/11/11 at 8:51pm
Thread Starter 
Thanks for the reply, and taking the time to explain why this would not be feasible.

Unfortunately, no, the headphone amplifier does not run off either of the back outputs - it uses a dedicated solid state amp. I'll keep using it, just wanted to see if there was a way for me to easily test what the tube sounds like using my headphones (instead of my speakers).

I have an amp but it unfortunately distorts even the solid state output quite noticeably, so that's a no-go.
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post #7 of 7
8/12/11 at 1:06pm

The D1 HP amp doesn't sound all that great. It's passable but once you hear a dedicated amp through the SS out of the D1 you will wonder why you listened to it any other way. I have the SS out of my D1 going to my Lyr (integrated tube HP amp). The tube out of my D1 goes to my preamp and then to my speakers. Both speakers and HP sound pretty darn good for a relatively low budget set up. I did the standard opamp and tube upgrade on the D1 and this was also a noticeable improvement over stock.

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