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[A Man]

Reprinted from dave's digs :

I've been using the Avalon U5F DI's on our bass and acoustic guitars with stunning success. There is a passive filter bank ( 6 selectable tone banks ) and class A pre's, line and mic outs, headphone jack (great for tracking line rezz).
I've found it particularly useful when driving long subsnake/snake lines, stepping up the pre by just 3db. Amazing clarity. Most of the time I'll bypass the console EQ and just use a sweepable HPF to clean up the bottom.
I've had several people ask what I was doing to the bass to make it sound so good and I tell them "nothing, it's the Avalon".

I wouldn't expect to see these in a provider's stock, but for a BE, they are well worth a look/listen....

http://www.avalondesign.com/instrudi.html

[Phil Ouellette]

So what happens when that DC coupled baby gets plugged into a channel with phantom power on?  To me a DI is basically a problem solver, not a malfunction waiting to happen.

Phil

[John Roberts {JR}]

Phil Ouellette wrote on Fri, 23 April 2004 19:56

So what happens when that DC coupled baby gets plugged into a channel with phantom power on?  To me a DI is basically a problem solver, not a malfunction waiting to happen. Phil

If it's properly designed... nothing. Phantom power will look like a current source to any low impedance output (actually 48V voltage source with a 6.8K resistor in series.

Depending upon the polarity of the Class A output stage, phantom power being active will either add to or subtract from the nominal Class A current. While possible, I would be surprised if this was not anticipated as a possible operating mode.

A better question might be why pay more money (box doesn't look cheap) for an obsolete technology   (Class A).

JR

[A Man]

JR

A better question might be why pay more money (box doesn't look cheap) for an obsolete technology   (Class A).

They called the Shure Vocalmaster obsolete technology at one time too.

You are right, absolutely nothing happens w/ phantom.

I went through a number of DI's before we went with the U5.

98% I couldn't tell the difference between them. When we tried the U5 on the acoustic guitars, I could tell a definate difference. (for the better)

Like I said, I found it very useful when driving looooong subsnake / snake lines by stepping up the pre and the tone banks are very helpful to 'pick ' different curves for different guitars (and their respective tones).

Not to sound like a ass, but why the "obsolete" comment when the unit itself has proven to be very 'workable'. Would you say that the Lexicon PCM60 is obsolete too?

[Shaun Wexler (MacFOH)]

Have you tried the ADL 300G?  I've had both and it seemed to breathe better and sound more open and natural than the Avalon, which was warm/fat but gave me the feeling like the transient response was getting rounded off, and the highs were more constricted although a bit denser going thru the unit (could it be the type of tubes?).  I kept the ADL (and bought another one).  Absolutely the best DI for keys & synth units, and so far has been pretty awesome on most bass guitars... I use a pair of Symetrix 501's for bass comp/lim.  The ADL S/C/L 1500 rules for bass.  I don't know why I haven't been an Avalon fan (tried the 737, hated it).  I hope to learn why some day...  

[John Roberts {JR}]

Triple-J wrote on Fri, 23 April 2004 23:19

JR A better question might be why pay more money (box doesn't look cheap) for an obsolete technology   (Class A). They called the Shure Vocalmaster obsolete technology at one time too. You are right, absolutely nothing happens w/ phantom. I went through a number of DI's before we went with the U5. 98% I couldn't tell the difference between them. When we tried the U5 on the acoustic guitars, I could tell a definate difference. (for the better) Like I said, I found it very useful when driving looooong subsnake / snake lines by stepping up the pre and the tone banks are very helpful to 'pick ' different curves for different guitars (and their respective tones). Not to sound like a ass, but why the "obsolete" comment when the unit itself has proven to be very 'workable'. Would you say that the Lexicon PCM60 is obsolete too?

While my comment was intended tongue in cheek, thus the smiley face, I did try to be specific that I was talking about the Class A topology.

Class A has acquired an undeserved, IMO association with higher fidelity. Class A is the cheapest, most primitive circuit topology. Before opamps became so inexpensive, everything was Class A.

Probably at some point in the evolution of circuit design, a good Class A execution was better than Class B (with crossover distortion) or early class AB with inadequate transition speed, but these days it's become a marketing affectation. Depending on how the Class A is biased it will have more low order harmonic distortion which may be perceived as good sounding.

I don't have any first hand experience with this box and if they've paid as much attention to detail inside as they have to the outside it will work fine. I don't agree with any characterization that Class A is any cleaner ("pure") than well executed modern circuitry. If you're using a box because it introduces euphonious distortion lets call a spade a spade and label it an effect.

Just my $.02

JR  

[Phil Ouellette]

JR wrote on Sat, 24 April 2004 09:27

Class A has acquired an undeserved, IMO association with higher fidelity. Class A is the cheapest, most primitive circuit topology. Before opamps became so inexpensive, everything was Class A. Probably at some point in the evolution of circuit design, a good Class A execution was better than Class B (with crossover distortion) or early class AB with inadequate transition speed, but these days it's become a marketing affectation. Depending on how the Class A is biased it will have more low order harmonic distortion which may be perceived as good sounding. JR

Hi JR,

There is nothing obsolete about Class A, it totally eliminates crossover distortion and is used where ever possible.  The only time you use other classes of operation (A/B, B, etc) is in power amps where the quiescent power consumption of Class A operation limits how much power you can get out of the amp.  Op-amps used for audio operate in Class A.  However bragging about Class A operation in this case is bogus because virtually all small signal gear operates in class A.  This is a case of marketing using an audiophile term inappropriately (class A power amps are special and very expensive) to try and make the ordinary and standard way of doing things sound special.

The reason I mentioned phantom power is due to the DC coupled outputs.  DI's normally either use a transformer or DC blocking capacitors in the outputs to protect themselves from phantom power (amplifiers break down when you put higher voltages than the supply voltages on their inputs or outputs).  Unless Avalon is using supply voltages greater than 48V (which I seriously doubt) they are risking dead boxes in order to be able to claim DC performance (which nobody in their right mind needs for audio).

Phil

[John Roberts {JR}]

 
[/quote]

Hi JR,

There is nothing obsolete about Class A, it totally eliminates crossover distortion and is used where ever possible.  The only time you use other classes of operation (A/B, B, etc) is in power amps where the quiescent power consumption of Class A operation limits how much power you can get out of the amp.  Op-amps used for audio operate in Class A.  However bragging about Class A operation in this case is bogus because virtually all small signal gear operates in class A.  This is a case of marketing using an audiophile term inappropriately (class A power amps are special and very expensive) to try and make the ordinary and standard way of doing things sound special.
[/quote]

Huh.... If you look at the internal topology of opamps they look very much like tiny Class AB power amps. Otherwise the typical console would require multiple cooling fans to deal with the heat load. For a little esoterica, I do recall some audiophiles experimenting with hanging a resistor to the negative rail from the outputs of conventional opamps to force them into Class A operation. This never caught on as even 20 years ago you could get adequately fast opamps at moderate cost.

Class A topology was common before large scale integration, but these days it costs more even for a machine to pick and place most parts than they cost. Perhaps my casual characterization of such circuitry as obsolete is incorrect as there are blocks of Class A within all linear integrated circuits. While I don't recall ever seeing a Class A opamp I do recall seeing a mic preamp chip many years ago that was designed for low voltage battery operation and may have been Class A or open collector output.

We're on the same page regarding Class A being a marketing conceit. I am unconvinced that Krell and the like are much more than a conversation piece but that just may be a personal problem   .

[/quote]
The reason I mentioned phantom power is due to the DC coupled outputs.  DI's normally either use a transformer or DC blocking capacitors in the outputs to protect themselves from phantom power (amplifiers break down when you put higher voltages than the supply voltages on their inputs or outputs).  Unless Avalon is using supply voltages greater than 48V (which I seriously doubt) they are risking dead boxes in order to be able to claim DC performance (which nobody in their right mind needs for audio).

Phil[/quote]

As I previously stated, it is no big deal to tolerate phantom power as long as you anticipate it. For that matter, I can't imagine designing a DI and not (I did when I did). Depending upon the polarity of the Class A output stage used, connecting to an active phantom powered input will either increase or decrease the Class A operating current all of 7 milli-amps. In a clever design using PNP or P-channel outputs the current density and linearity would actually be increased by phantom power.

re: DC response, agreed again. Any imagined benefit from DC response will be forfeit upon interfacing with any mic preamp which in my experience are 99.99% capacitor coupled, or any microphone which AFAIK 100% don't pass DC. Of course offering DC response means never having to say you're sorry about where you set the LF pole, and will "sound" good on paper to the folks who like to brag on their equipment's spec sheets.

JR

[Andy Peters]

JR wrote on Sat, 24 April 2004 14:42

Huh.... If you look at the internal topology of opamps they look very much like tiny Class AB power amps.

An extreme example (one that shows my relative youth!) is the LM324.  I remember the first time I put a sine wave through one and looked at the output on a 'scope.  Yikes! "This thing's broken!"

Quote:

For a little esoterica, I do recall some audiophiles experimenting with hanging a resistor to the negative rail from the outputs of conventional opamps to force them into Class A operation.

I came across a variation on that one (I think it was on a web page for some guy's tweaky DAC) which used a transistor in the pull-down circuit.

Quote:

We're on the same page regarding Class A being a marketing conceit. I am unconvinced that Krell and the like are much more than a conversation piece but that just may be a personal problem   .

Rent a copy of the old sci-fi chestnut "Forbidden Planet."  You'll recognize it as the source material for much of "Star Trek," right down to the away team that features the captain (Leslie Neilsen!), the first officer and the ship's doctor.  They come across this planet that has a huge power generating station (row upon row of big meters), and it was all built by the Krell.

Back to the Avalon DI.  I'm sure it sounds good.  It's got some interesting tone control built in, and it's designed to talk to guitar and bass pickups.  So, in the interest of callin' 'em as I sees 'em, it's a preamp optimized for unbalanced high-Z sources.  Besides, it's easy to say, "I don't have to use the channel-strip tone controls" when you've got all of the tone controls built into the DI!

--a

[John Roberts {JR}]

Andy Peters wrote on Mon, 26 April 2004 01:14

JR wrote on Sat, 24 April 2004 14:42   Huh.... If you look at the internal topology of opamps they look very much like tiny Class AB power amps. An extreme example (one that shows my relative youth!) is the LM324.  I remember the first time I put a sine wave through one and looked at the output on a 'scope.  Yikes! "This thing's broken!" Quote: For a little esoterica, I do recall some audiophiles experimenting with hanging a resistor to the negative rail from the outputs of conventional opamps to force them into Class A operation. I came across a variation on that one (I think it was on a web page for some guy's tweaky DAC) which used a transistor in the pull-down circuit. Quote: We're on the same page regarding Class A being a marketing conceit. I am unconvinced that Krell and the like are much more than a conversation piece but that just may be a personal problem   . Rent a copy of the old sci-fi chestnut "Forbidden Planet."  You'll recognize it as the source material for much of "Star Trek," right down to the away team that features the captain (Leslie Neilsen!), the first officer and the ship's doctor.  They come across this planet that has a huge power generating station (row upon row of big meters), and it was all built by the Krell. Back to the Avalon DI.  I'm sure it sounds good.  It's got some interesting tone control built in, and it's designed to talk to guitar and bass pickups.  So, in the interest of callin' 'em as I sees 'em, it's a preamp optimized for unbalanced high-Z sources.  Besides, it's easy to say, "I don't have to use the channel-strip tone controls" when you've got all of the tone controls built into the DI! --a

Always glad when I can make the "over the hill" feel young again .

Yes, and Forbidden Planet is also the better way to remember a young Anne Francis.

FWIW, early opamps were valued for high DC loop gain and accuracy in computing circuits... lots of tricks and trades had to be made to get "decent" audio performance. I for one don't miss those good old days. Some modern, ultra-low current opamps are quirky too, reminds me why we bread board circuits.  

The Avalon probably does sound good. Attention to detail, not because of Class A "purity".

JR