amp direct
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kelly

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One of the options Modwright is offering for modifications on the XA777ES is an "amp direct" mode that utilizes his custom tube output stage as an active pre-amp. This eliminates the need for a preamp and a set of interconnects and theoretically preserves the purity of the signal. Modwright's implementation also uses a stepped attenuator.

I've seen this type of output available on some other players--I believe some of the Cary and Wadia models, though I'm uncertain which ones.

Can anyone add any information or opinion on this kind of thing?

What happens when you run the output of something like this to a preamp/headphone amp? Do you simply try to adjust the volume to 2 volts and hope for the best? Do you end up switching the cables manually when you want to listen to speakers versus a dedicated headphone amp?
 
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jopi

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Some phono stages come with an active preamp built in with an attenuator that allows a direct connection to a power amp.
You probably want to use a headphone amp with a loop through into your power amp and leave your headphone amp attenuator into a neutral position.
Heck, perhaps somebody would even built a power headphone amp with no volume knobs, just a power/standby button with a sophisticated LED for power indication.


I guess strict audiophiles tend to avoid two volume knobs in a path.
 
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kelly

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jopi,
Well, if the headphone amp in question has a loopout (tape out, tape loop, whatever) rather than just a lineout, the second hit from the pot. The HeadRoom MOH/Max/Blockhead have this as an option. I'm not sure which other amps do. My RKV does not. In fact, it has not even a lineout. When AudioValve built it, they must have thought, "Why would anyone ever want to listen to anything else?"
 
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jopi

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Good question.

I've meant it originally more as a joke, but come to think of it, why aren't there any power headphone amps out there just like power amps for your speakers (no input selection, no volume control, no nothing)?

Most audiophiles have invested in a neutral preamp already and could just hookup up their headphone power amp to another line out of the preamp.

It seems that Headroom went the other way and designed their high end amps to serve a dual purposs as a regular preamp. It would be interesting to know how successful they are with this strategy. How many are using their Max as a preamp? How neutral does it sound?
 
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kelly

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jopi

I think the reason is that most preamps do not allow you the opportunity to feed to amplifiers at once. Running to a headphone amp and a speaker amp would require manually switching the cables.

Besides that, the headphone amp and preamp functionality are, from my understanding, not entirely different. You'd have to duplicate some of that functionality to seperate the two.
 
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carlo

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kelly,

since the volume control is in the analog domain you don't really need to worry about any signal loss. run the attenuator full blown (unless dan wright adds a gain stage its a passive volume control) which will give you standard output. running direct is great for many things, most notably less components in the signal path and therefore a "truer" signal. however, if you're running a long interconnect or need gain it simply won't work. luckily from what i know of your setup that isn't a problem.

just fyi, volume can be controled in the digital domain, however every -6db is one bit "lost", so it should be avoided at all costs. once again though that isn't a problem in your case. there really isn't a way to avoid switching cables unless the sony has two sets of line outs that can be manipulated by wright's attenuator mod. i suspect dan wright (or jenna crock from jenna labs) can make a little switch box that will be effectively out of the signal path if its absolutely required.

best,
carlo.
 
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kelly

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Here's the quote from Modwright.com:

"*Amp-Direct Mod (Absolute Truth Mods only):
This takes The Absolute Truth Mods unit and adds to it the ability to control the volume of the signal from the player and run directly into your amp(s). The tube stage is configured to allow the signal to fun full range from 0V-12V, with the tube stage acting as a fully active line stage. Volume control is achieved by direct installation of a DACT CT-2 stepped attenuator. This is a manual volume control, with 24 steps. The "Amp-Direct" option gives you the ability to do away with a preamp and an additional set of interconnects, allowing the most pure signal path for your music, directly to the amplifier(s)."

So... it's a "fully active linestage" by that description. I assume this means it's "mucking with the signal" more, but since it's mucking with it in the same flavor that the original 2V signal would be, it seems like this would be a more neutral match than adding any kind of preamp in the path?

Is the way Dan is doing this unique? The other CD players that have a volume control don't have an active linestage then?

I'm trying to follow along--bear some patience with my feeble mind.
 
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carlo

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well, the tube output stage is, in theory, messing with the stock signal. but whatever, from what i've heard from collegues the full blown modwright xa777es (including the tube output stage) is very worthy of reference status. i do not however have any clue about how the direct mod sounds.

if you don't want to "mess" with the signal at all, you'll want to go passive. in other words, get the full mods sans the volume option and add a passive preamp. having an active line stage means you're dealing with buffers, gain, and a hell of a lot more components than a passive stage. benefits (generally) are a fuller sound and a bloomier more expansive soundstage. by using a headphone amp (and its active line stage) in series with wright's direct mod, you are in essence using two preamps when listening to 'phones. obviously a bad idea.

a passive purist will argue that all that stuff is just getting in the way of a signal path, whereas a passive preamp simply controls switching and attenuates volume. no gain, no tubes performing extra gain (the tube output stage wright offers approaches this a bit differently), no power, just as out of the way as possible. note that in this case your sony will just output the 2v and you can only lower that signal, fine for your headphone amp but your power amp will need to have enough gain to handle your speakers. bonus is that may passive linestages offer switching and two outputs.

on a personal note, i love the idea of passive and have been tinkering with it for a few months with a diy design (two attenuators with a load), the creek, adcom gcd750, and a reference preminence 3a... i have yet to approach the decay and soundstage my modded tube line stage offers (both high priorites for me).

what dan is doing is pretty unique, i really don't know anyone who offers a tube gain stage in a cd player mod, you usually have to ask and beg for that type of thing
however, people have been adding passive attenuators to their cd players for some time, and many manufacturers (including wadia if i'm not mistaken) implement volume passively.

hope this helps,
carlo
 
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Quote:

Originally posted by carlo
what dan is doing is pretty unique, i really don't know anyone who offers a tube gain stage in a cd player mod, you usually have to ask and beg for that type of thing
however, people have been adding passive attenuators to their cd players for some time, and many manufacturers (including wadia if i'm not mistaken) implement volume passively.


Wadia's volume implementation is entirely in the digital domain. I don't know that I agree with this but it's what they do. Somebody's buying their stuff though, right?
 
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