Why is the Max Class AB?
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kelly

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I started a thread over in the Headroom section a little while back but didn't really get a satisfying answer. Of course, I can understand why Headroom might not want to share in detail the design of their amplifiers and why certain decisions were made, but I'm hoping maybe some of you guys might have some insight.

Here's the original thread if anyone is interested:
Max is Class AB?

My basic premise is this:

(Crossfeed and filter issues aside.) I think the Max is a killer amp. It has bass, blackness and speed better than any solidstate amplifier I have heard. What it lacks is high frequency detail (ambient detail, texture). What I wonder is if this was a design goal--not everyone likes the same sound.

When I was auditioning the Max connected to a Sony XA777ES with the Sony R10 headphones at a meet, Edwin (the owner of the R10) said that the Max sounded "distant" compared to the Sugden Headmaster. That's probably the best way to describe that missing high frequency information. It simply sounds like things are further away. Of course, for some people that texture information may be too much--it may be thought to be fatiguing or even surreal. For me, the intimacy is part of the allure of headphones.

Bottom line? I want it all. I want the texture that I hear from Class A amplifiers and I want the other benefits that seem to be reaped from the Max's dual discrete power components. Danny says in essence that they were unable to run the OPA627 in Class A and still use the discrete components they used. Can anyone elaborate on this?

Of course, I know running the OPA627 in Class A isn't the whole solution and a lot of you have really put effort into opening up the treble with the cascode current sources, buffers and different opamp families. I'm still learning this stuff, so I'm just trying to spawn some conversation.

So anyone wanna take a stab at reverse engineering the Max in this thread?
 
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Matt

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...that the amp would posess such characteristics, considering it's "made-for" status for the '600s, which every time I've compared them to other cans, sound distant. Why lay it on double-thick, you know? I guess if it works together, it works together, though.

- Sir Mister Matt
 
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kelly

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Quote:

Originally posted by Matt
...that the amp would posess such characteristics, considering it's "made-for" status for the '600s, which every time I've compared them to other cans, sound distant. Why lay it on double-thick, you know? I guess if it works together, it works together, though.


Matt
Most people would say that only certain ranges sound "distant" on the HD600 and that that's due to an upper midrange dip. But I would agree that this is part of why people label the HD600 as forgiving... but then, most people seem to like the effects of the aftermarket cables so *shrug*.
 
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ppl

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sounds like maby another amp may be more to your fancy. But for those that want it all and want it now i think that is not going to happen unless you learn about Audio design and then make your own That what started me on my Portable Amp quest way back in the 1990's I thought about Headroom but had issues with there way of doing it and the Cosmic thatt i heared at the time sounded Dark with My Beloved sony cans and headrooms reply was sony is junk and get better headphones. Well that was enough to make me build an amp for Low impedance that provided most of what i want and the Prototypes of my latest versions may be just my cup of tea. I think that Folks in your situation are what keeps DIy Audio alive since it surly is not price.
 
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kelly

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ppl
I am doing the very best I can to come up to speed so that I CAN build my own amplifiers but to be honest, this really isn't something I have an aptitude for. If I succeed it all, it will only be through a force of will and with the kind assistance of people like you.

I'm not really expecting Headroom to fix the Max to my liking. What I'm trying to do is learn from their product which things they did that I like or didn't like so that I can better shop for and/or build an amp that better meets my system goals.
 
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Kelly,
I don't think that distant sound you folks are experiencing with the Max is due to the amplifiers Class design. Usually, that sense of upfront/closeness in proximity is due to midrange response rather then high frequency characteristics. Follow the below link for some information on class A, AB designs etc.
http://sound.westhost.com/class-a.htm
 
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morsel

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Since HeadRoom uses replaceable audio modules, perhaps they will eventually offer new modules with Analog Devices opamps for the faster, airier sound you seek. An enterprising person might even beat them to the punch by offering 3rd party modules to improve existing HeadRoom amps.
 
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ppl

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Daa? yup i forgot about the max using the OPA-627 this is is most lickly a large part of the sound but is not the signal also going through other Opamps in the Crossfeed section. This could also be a reason.
 
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kelly

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ppl
When the crossfeed is off, I don't think any signal goes through it. Am I wrong on this? My impressions of the Max (good and bad) are based on crosseed and hf filters set to their off/bypass position.

morsel
So then... would you say the module is the only thing wrong with the Max? In other words, would it truly be better to build a module or would it be better to design the entire amp from ground up learning what Headroom did right and wrong?
 
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aos

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You could "just" replace the module - if you're happy with power supply and jacks. I'm a bit surprised that they don't use edge connectors or some other specialized connectors instead of strip headers.

A moot point anyway, as there is no good reason in fiddling with the Max. When you have Max, you'd need to invest a lot of time and money in DIY and have reasonable amount of experience in order to make something better, and should do that from ground up.
 
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morsel: Good idea... I suggested something along those lines to Todd, and he said they wouldn't mind... Anyone have a module lying around that they could measure/test?
 
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kelly

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Quote:

Originally posted by eric343
morsel: Good idea... I suggested something along those lines to Todd, and he said they wouldn't mind... Anyone have a module lying around that they could measure/test?


Hey whoah if that's true and you guys could actually get Headroom's assistance/info on the project that could really turn out well for everyone. (Me included of course.)
 
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morsel

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Kelly, since the amps are attractive and expensive, it makes sense to just replace the module for people who already have a HeadRoom amp but prefer the Analog Devices sound to the Burr Brown sound. On the other hand, if you are a consummate perfectionist and want everything exactly your way, then DIY is the way to go. Good luck making a case as nice as HeadRoom's.


I think HeadRoom would be in the best position to make Analog Devices based modules. They have the equipment and knowledge to do it more efficently than any of us. It would also be easy for them to market as they already have standard, premium, and reference Burr Brown modules.

If they are truly not interested, it would be helpful if they supplied specs for the existing reference module so we could design the new one based upon that. If I were the one wanting to make this happen, before I spent any time on a 3rd party module I would have a long talk with HeadRoom (Todd and Danny in particular) to see if I could talk them into doing it. Perhaps they might take some ideas from the work done in these forums over the last year. (hint, hint)
 
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wilsonjm

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If the headroom module uses OPA627 then the voltage would most likely be too high for many Analog Devices opamps such as AD8610/20..something to think about if you wanted to replace the opamp
 
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eric343

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Hmmm... Maybe a resistor or two? Or would the current interact with it and muck things up?

Maybe an on-board regulator to drop the voltage?
 
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