[Ruahrc]

Looking back through Headroom's product lineup, I realized that the Ultra Micro + Ultra Micro DAC and a maxed out Desktop are very close in price. Looking at the Headroom premade packages, indeed you can score a Maxed out Desktop amp plus DAC and DPS and headphones for about $75 more than you can get their maxed out Ultra Micro package. The only difference between the two is that there are a few cables and converters in the Ultra Micro package.

Is there a sound difference between the two amps/DACs, or are they more or less the same- only in a different form factor? Considering that the maxed out versions of each amp are both featuring "Max" components and "Max" DAC design, the only real significant difference might lie in the fact that the Desktop system has a DPS whereas the Ultra Micros are relying on wall-wartish supplies. The larger format might be a good thing as far as usability goes (giving you RCA connections, 1/4" heapdhone jack, dual headphone outputs, etc- as well as the fact that the thing probably runs cooler given its larger size.

So is there a real difference between the amps as far as sound goes? Is it due at least in part to the better power supply of the Desktop system? Is the power supply that large because it has 6 power outputs (seems like an awful lot), or because it needs to be that big anyways (to provide the proper voltage transformation, rectification, and filtering)?

Ruahrc

P.S. Is it possible to upgrade a Desktop amp you bought with upgraded electronics modules or to add a DAC, or do these items need to be decided on at the time of initial purchase? For example, say I buy a Desktop amp with no DAC to save some money because I don't need the digital right now- can I send it back later and get it upgraded with a digital module, or is that not possible?

 

[JorgeC]

The HeadRoom Ultra Micros are certainly the very close sonic equivalents of our "fully-loaded" (max module & max DAC) HeadRoom Desktop Amp. However, the larger chassis size of the Desktop Amp series allows for much broader input/output flexibility, including full-size headphone connections as well as stereo RCA input / output arrays.

That said, the 'maxed-out' HeadRoom Desktop Amp -- along with our superb DPS cleanly powering it to its full performance potential -- might perhaps have a tiny overall sound quality edge versus the Ultras [imho] although the audible differences are nuanced and VERY subtle... The overall choice might boil down to your actual component size & space requirements and/or desired audio interconnectivity options!

Cheers,
Jorge
HR Sales/Product Manager

 

[JorgeC]

Quote:

Originally Posted by Ruahrc /img/forum/go_quote.gif P.S. Is it possible to upgrade a Desktop amp you bought with upgraded electronics modules or to add a DAC, or do these items need to be decided on at the time of initial purchase? For example, say I buy a Desktop amp with no DAC to save some money because I don't need the digital right now- can I send it back later and get it upgraded with a digital module, or is that not possible?

Hello Rhahrc,

We can gladly retro-fit most HeadRoom Desktop Amps with upgrades of your choosing after purchase. Typically, the cost of the work is the actual cost of the 'new' part (as shown on our website), plus $100usd HeadRoom in-house labor charge for the installation.

Cheers,
Jorge
HR Sales/Product Manager

 

[MD1032]

I compared the Ultra Micro to a Maxed-out Desktop at the NJ meet and IMO, the Ultra Micro is at least a minimum of 90% of the Desktop. Extremely good amp for the money indeed.

 

[kboe]

Would you then compare the micro stack of Amp and DAC to the rough equivalent of the base line Desktop minus the Desktop Power supply?

 

[JorgeC]

Quote:

Originally Posted by kboe /img/forum/go_quote.gif Would you then compare the micro stack of Amp and DAC to the rough equivalent of the base line Desktop minus the Desktop Power supply?

Indeed, Kboe... The HeadRoom Desktop Amp with the 'Home'-level internal componentry is the approximate rough equivalent of our standard HR Micro Amp / HR Micro DAC units; all utilize Burr-Brown 134OPAs [or dual-package 2134OPAs in the Desktop] in forced Class-A biasing for their active stages.

Cheers,
Jorge
HR Sales/Product Manager

 

[JosephJFK]

Sorry about responding to a posting so late, but I was surprised by this answer. I just ordered a standard (non-ultra) Desktop w/ DAC to replace my 2005 micro stack, and I was told by Mike that there was a significant difference between the current micro stack and the current desktop.

Apparently the desktop is class A biased while the micro is class a/b. Also, I was told that the amp circuitry differs a fair amount.

So which one is right?

 

[mrarroyo]

Joseph as I recall your 2005 micro is quite different from today's version of the micro amp.

 

[JosephJFK]

Thanks for the response. Here's my issue though. I called headroom about an upgrade to my 2005 micro stack. I was told that getting the current Desktop (not the "ultra") would be a significantly more noticeable upgrade than getting the current Micro stack (again, not "ultra").

Is this correct? It would seem to contradict the above assertion that they're the same. I have no idea what the difference between class "a/b" and "a" bias is, but I got the impression that it matters.

 

[noparanoia]

Quote:

Originally Posted by JosephJFK /img/forum/go_quote.gif I have no idea what the difference between class "a/b" and "a" bias is, but I got the impression that it matters.

Same here! Anyone able to clarify that for us?

Thanks

 

[nattonrice]

Electronic amplifier - Wikipedia, the free encyclopedia

You can read those to help.

 

[Born2bwire]

Quote:

Originally Posted by noparanoia /img/forum/go_quote.gif Same here! Anyone able to clarify that for us? Thanks

In a transistor, there are three modes of operation: cutoff, triode and saturation. The inputs on the source, gate and drain (or the BJT equivalents) all impact which mode you are in. The problem with an amplifier is that we want the transistors to always be saturated, because a small signal on the input gets amplified roughly linearly on the output when the transistor is saturated. However, this is very inefficient because we need to provide bias currents to keep the transistors in saturation when the signal drops too low on the inputs.

If we set bias currents to keep all of the transistors in saturation, then we are operating in Class A and are always amplifying all input signals.

Class B is when the transistor falls out of saturation unless the input signal crosses a certain threshold. This makes it much more power efficient since we are not amplifying or running bias currents when the amplifier is not being sent a signal. Unfortunately, this means we can only amplify half of the signal (since we need to cross a threshold to turn on, so we need one amplifier for the positive cycle and another for the negative cycle). However, the small threshold between when we have a signal and the transistor saturates causes non-linearity. This is called crossover distortion (I looked it up on Wikipedia, I never heard the shop term). Basically, a very small signal near zero will not be amplified because it is not strong enough to turn on either amplifier. Having the two amplifiers here is called a push-pull configuration.

The compromise is a class AB. Instead of having one amplifier only take care one-half of the cycle, we will bias them so that the positive cycle amplifier will turn on near the end of the negative cycle and vice versa. So there is a bit of overlap in the turn-on, but we still sacrifice linearity.

So the main difference for us is that class A is generally more linear but more power inefficient while class AB sacrifices linearity for power efficiency. How much linearity is sacrificed would depend on the amp's design and components I'm sure.

EDIT: Oh sure... just link Wikipedia. Damn kids and your internets and music...

 

[noparanoia]

Thanks for the advice guys. Truth is I have already checked the Wikipedia on this, the thing I couldnt find any mention of in the article is what "Class A biased" means

 

[nattonrice]

Quote:

Originally Posted by Born2bwire /img/forum/go_quote.gif EDIT: Oh sure... just link Wikipedia. Damn kids and your internets and music...

Hehe I try my best

 

[Born2bwire]

Quote:

Originally Posted by noparanoia /img/forum/go_quote.gif Thanks for the advice guys. Truth is I have already checked the Wikipedia on this, the thing I couldnt find any mention of in the article is what "Class A biased" means

We control a transistor generally by two sets of voltages (or currents, depending on how you look at it). For a MOSFET, I can't remember BJT's anymore, we have to setup a voltage between the gate and source pins. This voltage is generally our input voltage and it regulates the current flowing between the drain and source pins. However, to get a current between the drain and source, we also need to have a voltage across it to incite the currents.

So the drain to source voltage creates the bias for currents between those pins, but the gate to source voltage regulates how much current can flow. Both of these voltages need to be above certain values for the transistor to be saturated. Class A biased means that we have set up a constant current flowing between the drain and source, meaning that it is always ready to react to the gate to source voltage.