2007 Micro Amps and Micro DACs
May 21, 2008 at 9:01 PM Post #136 of 163

sbulack

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I've read two seemingly different statements about the Class A Biasing in the 2007 Micro (not Ultra) Amp.

On the webpage describing the 2007 Micro Amp (Electronics) it says:
"The excellent Texas Instruments OPA134 op-amp is used throughout, and all resistors are of truly extraordinary audio quality; Rest assured, all Micro Amp stages are fully biased into true 'Class-A' audio performance!"

In the Manual describing the 2007 Micro (and Ultra Micro) Amps it says:
"The major difference between the Micro Amp and Ultra Micro Amp is that the Ultra Micro Amp uses TI 627s instead of TI 134s, and that all the op-amps are biased into class-A operation with JFET CCDs. The result is improved musical detail resolution, quicker dynamics, more precise tonal presentation, and better soundstage imaging." (And the picture of the PCB's of the two amps encircles the JFET CCDs on the image of the Ultra Micro Amp, with no such circles on the Micro Amp image.)

Also in the Manual describing the features common to Micro and Ultra Micro Amps is says:
"Discrete emitter follower ouput stage, biased into class A operation (the Diamond buffer)"

It would appear from the manual that only the output stage of the Micro Amp is biased into Class A operation, and not the stage in which the TI 134 opamps are used.

Is the statement on the webpage that all stages of the Micro Amp are fully biased into Class A a "copy and paste" error from material intended only for the Ultra Micro Amp page?

My asking this question is not academic. I've placed an order for the Micro Amp and I'd like to know the extent to which its stages are biased into Class A operation.

Thanks very much for any information you can provide to clear this up for me.
 
May 22, 2008 at 12:04 AM Post #137 of 163

JorgeC

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Quote:

Originally Posted by sbulack /img/forum/go_quote.gif
I've read two seemingly different statements about the Class A Biasing in the 2007 Micro (not Ultra) Amp.

On the webpage describing the 2007 Micro Amp (Electronics) it says:
"The excellent Texas Instruments OPA134 op-amp is used throughout, and all resistors are of truly extraordinary audio quality; Rest assured, all Micro Amp stages are fully biased into true 'Class-A' audio performance!"

In the Manual describing the 2007 Micro (and Ultra Micro) Amps it says:
"The major difference between the Micro Amp and Ultra Micro Amp is that the Ultra Micro Amp uses TI 627s instead of TI 134s, and that all the op-amps are biased into class-A operation with JFET CCDs. The result is improved musical detail resolution, quicker dynamics, more precise tonal presentation, and better soundstage imaging." (And the picture of the PCB's of the two amps encircles the JFET CCDs on the image of the Ultra Micro Amp, with no such circles on the Micro Amp image.)

Also in the Manual describing the features common to Micro and Ultra Micro Amps is says:
"Discrete emitter follower ouput stage, biased into class A operation (the Diamond buffer)"

It would appear from the manual that only the output stage of the Micro Amp is biased into Class A operation, and not the stage in which the TI 134 opamps are used.

Is the statement on the webpage that all stages of the Micro Amp are fully biased into Class A a "copy and paste" error from material intended only for the Ultra Micro Amp page?

My asking this question is not academic. I've placed an order for the Micro Amp and I'd like to know the extent to which its stages are biased into Class A operation.



Sorry about the confusion! The HeadRoom Ultra Micro and 'standard' Micro Amp are both technically biased into Class-A, constant-current-sourced operation for their Diamond-Buffer output stages.

However, the Ultra Micro edition has all active-stage Burr-Brown 627 op-amps (summing/gain/crossfeed/output, etc) biased into Class-A operation using JFETT CCDs while the BB 134OPA gain stage of the 'standard' Micro is actually in Class A/B and does not use the JFETT topology... Otherwise, they are basically identical units!

Hope that helps!

Cheers,
Jorge
HR Sales/Product Manager
 
May 22, 2008 at 12:22 AM Post #138 of 163

JorgeC

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Quote:

Originally Posted by The_Duke_Of_Eli /img/forum/go_quote.gif
If you're running your move right out of the G4 mac, then for sure start with the DAC if you can't afford both. Although the MOVE and the MicroAmp are in different size classifications, as the microamp is borderline portable. But it's likely you'll benefit more from a better USB DAC with a good source.


AGREED!.. If digital/computer audio is your main listening source(s), the DAC will likely deliver more sonic improvement benefits right off the bat; the upgraded headphone amp can always come later
smily_headphones1.gif


Cheers,
Jorge
HR Sales/Product Manager
 
May 22, 2008 at 3:43 AM Post #139 of 163

sbulack

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Quote:

Originally Posted by JorgeC /img/forum/go_quote.gif
...The HeadRoom Ultra Micro and 'standard' Micro Amp are both technically biased into Class-A, constant-current-sourced operation for their Diamond-Buffer output stages...
Hope that helps!



It sure does, Jorge. Thanks for confirming the content of the Micro Amp Manual and clearing that up for me. When the Micro Amp and power cable you helped me to order arrive, I'll get to hear that output stage biased into Class A (powered by no less than the DPS). The anticipation is simply delicious!!!
 
Jun 5, 2008 at 1:25 PM Post #140 of 163

warpdriver

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I have an older Micro DAC (9V) and the output seems rather strong compared to any other output device I own. Even with my Micro Amp on low gain, I barely have to turn the volume control on my headphones or speakers to get too loud sound.

Would it be a poor idea to stick an attenuator on the output of the Micro Dac?
 
Jun 5, 2008 at 2:21 PM Post #141 of 163

n_maher

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Quote:

Originally Posted by warpdriver /img/forum/go_quote.gif
Would it be a poor idea to stick an attenuator on the output of the Micro Dac?


Probably not, just make sure that it's a good quality attenuator (not necessarily expensive). Ideally it would be a simple voltage divider made up of appropriately chosen resistors but I haven't really looked into commercial offerings. I'd suggest searching the forums a bit to see what you can find, I'm sure there are threads that discuss options.

Edit: a quick googling yielded a company called Rothwell Audio that would appear at first glance to make exactly the product that I was trying to describe. I have no experience with them or their products so you might want to do more research before buying.
 
Jun 5, 2008 at 3:14 PM Post #142 of 163

orkney

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Quote:

Originally Posted by n_maher /img/forum/go_quote.gif
Probably not, just make sure that it's a good quality attenuator (not necessarily expensive). Ideally it would be a simple voltage divider made up of appropriately chosen resistors but I haven't really looked into commercial offerings. I'd suggest searching the forums a bit to see what you can find, I'm sure there are threads that discuss options.

Edit: a quick googling yielded a company called Rothwell Audio that would appear at first glance to make exactly the product that I was trying to describe. I have no experience with them or their products so you might want to do more research before buying.



The Rothwells work fine, but add a bit of midrange warmth and high-freq rolloff IMO. There are a few pricier alternatives (stepped) and a guy on eBay out of the UK who sells a Rothwell-like version that is a bit more neutral. These are also RCA and are available with 10, 14 or 20 (I think) dB of attenuation. I've owned all three and all work well, but with different tradeoffs in terms of how they colour the sound (the stepped version by far the least) but all do so pretty gently.

best,

o
 
Jun 11, 2008 at 4:55 AM Post #144 of 163

mikeg88

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Quote:

Originally Posted by lextek /img/forum/go_quote.gif
If I use my Macbook as a source (it has optical out). Which would be better the USB or Optical? I'm assuming the optical?


Whoa...sorry to jump in late here, but I just got my micro portable, and I think the USB is much better! I'm coming from 6 months of Bithead use, and I think the USB on the portable micro makes it sound like my Bithead but a shade more sophisticated on top of that. The Optical on the other hand, while more detailed seems more "dry" and "cold" by comparison. Maybe by USB board is really good, but I much perfer it to the optical!

Anyone else found this with thier micro amp?
 
Jun 11, 2008 at 5:05 PM Post #145 of 163

JorgeC

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Quote:

Originally Posted by Fud /img/forum/go_quote.gif
Sorry if the question has been asked, but what are the differences between the 2006 micro DAC and the 2007 version in terms of sound quality and added features?


Thanks for the question, Fud! ...

The discontinued HeadRoom '06 Micro DACs operated from either dual 9-volt batteries when on the go OR from AC-current via a linear 'wall-wart' power supply.

The new 2007 HR Micro DACs are strictly 'plug-in-only' devices operating in true "Class-A" biasing, thus requiring AC-power at all times... The 2007 Micro DACs offer upgraded internals versus the old battery-powered edition, with improved D-A stages & better overall SQ imho. The Ultra Micro DAC features an up-sampling stage for superb sound from just about any digital-output audio source
smily_headphones1.gif


FYI~ Our "mobile-use" Micro DAC is now available as a 'built-in' option within the HeadRoom Portable Micro Amp unit [w/ lithium rechargeable battery power]...

Cheers,
Jorge
HR Sales/Product Manager
 
Jun 11, 2008 at 8:44 PM Post #146 of 163

TheSloth

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Quote:

Originally Posted by mikeg88 /img/forum/go_quote.gif
Whoa...sorry to jump in late here, but I just got my micro portable, and I think the USB is much better! I'm coming from 6 months of Bithead use, and I think the USB on the portable micro makes it sound like my Bithead but a shade more sophisticated on top of that. The Optical on the other hand, while more detailed seems more "dry" and "cold" by comparison. Maybe by USB board is really good, but I much perfer it to the optical!

Anyone else found this with thier micro amp?



In pure scientific terms, in this design, the USB implementation is less accurate. Both USB and Optical will both be bit perfect, however as the USB has to go through a USB to S/PDIF converter, there are more timing errors (aka jitter) introduced along the way. In the Max DAC, which has reclocking to undo some of the damage, there is still a 3 fold increase in jitter going from optical to USB (from the 2xxps range to 6xxps). The DAC's without reclocking will probably show even more difference.

What you prefer to listen to is your call, but the one closer to the 'truth' is optical (unless there is something wrong with your optical output...)
 
Jun 13, 2008 at 12:42 PM Post #147 of 163

warpdriver

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Here's another dumb question.

Is it bad to use the power switch on a power bar to power up the Micro Stack instead of the front panel power switches (keep the power switches on, but use the power bar as a master switch?)
 
Jun 16, 2008 at 9:26 PM Post #148 of 163

velingara

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I thought it was best to turn on the dac-> amp-> (speakers if used) and turn off in reverse order to keep a sound bump from damaging speakers or headphones.
 
Jun 17, 2008 at 8:58 PM Post #149 of 163

JorgeC

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Quote:

Originally Posted by warpdriver /img/forum/go_quote.gif
Here's another dumb question.

Is it bad to use the power switch on a power bar to power up the Micro Stack instead of the front panel power switches (keep the power switches on, but use the power bar as a master switch?)



Hello WarpDriver,
No such thing as a dumb question at HeadRoom!
smily_headphones1.gif


Using the power bar should not pose any major problem as long as the Micro Amp is ALWAYS turned all the way down [.... or preferably off!
biggrin.gif
] during the powering-up/down process.

Cheers,
Jorge
HR Sales/Product Manager
 
Jun 17, 2008 at 9:36 PM Post #150 of 163

PITTM

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Yeah I have accidentally turned off the microdac while my amp is turned up loud and you hear a kind of bump sound that sounds like a couch hitting a wall when youre moving or something. Best to avoid that I imagine.
 

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