Tom Cram

[tubedude]

Hey,
What are the differences between the 376 and the 586, aside from the obvious digital outputs on the 376 and the dual preamp design of the 586. Mainly, I'm wondering how the preamps themselves compare, and what the true differences are.
Thanks,
Paul

 

[tubedude]

123

Also, I didn't see any specs onthe converters on the 376. What are the quality of these converters? Standard grade, better than standard, Lucid quality?
Thanks again,
Paul

 

[Tom Cram]

Bigger question,

e-mail me offline and I'll give you our head analog engineers e-mail address and direct line. He can give you all the specs and lowdown. You're asking a bigger question than I have time to answer. Or you can give me a couple days to scrape up the info, and then I'll post it.

Tom Cram
dbx Senior Technical Support
(801) 568-7530
tcram@dbxpro.com

 

[Tom Cram]

Is this enough?

Here is what I have so far;


500 series
Chinese 12au7's selected and matched here at the factory.
"W" taper pots
Tube power supply is 235v.
AKM 5392 converter chips
converter is optional and will do up tp 24/48
Tubes biased differently than 300 series (makes it easier to overdrive).


300 series
Chinese 12au7's
"B" taper linear pots
Tube power supply is 200v.
AKM 5383 converter chips
Converter is included and will do 24/96
Has tweaked version of the 500 series pre circuit (same but different?)

p.s. this probably belongs in The Rack forum.

Tom Cram
dbx Senior Technical Support
(801) 568-7530
tcram@dbxpro.com

 

[tubedude]

Hmmm...

If you want me to email them myself, I will, if you want to look up more info or ask around, thats cool too...
WHat I'm wondering mostly is... how the 300 series stands up, sonically, to the 500 series. Maybe its a better preamp!
Whats the difference between "w" and "b" taper pots and the converter chips? If anyone knows where I can hunt down some info on those coverter chips, let me know.
And lastly, what does a "tweaked" version have/not have that an untweaked version doesnt?
Thanks for your help~
Paul

 

[tubedude]

If anyone is interested in this preamp..

Heres the link for specs on the converters from the manufacturer..
http://www.asahi-kasei.co.jp/akm/usa/index.htm
It appears that the 5392 is a better converter, and boasts a 116db spec, similar to the the Lucid. The 5383 sits at 110db specs. Both have bnc clock capability, which is good.
Looks like the 586 with digital outs might be my ticket. If these converters can stand up close to the lucid, I should be able to save a few dollars and buy a Lucid clock instead of the 2 channel converters.
I still want some idea of what your engineers think are the deciding factors in between the two, though.
For those of you that would like to hear the 586 at work, look on prorec.com, there is a review and a song that was recorded using it. Sounds really good.
Hmmm, $1200 preamp with digital, or some cheapo RNMP's and a Lucid 24/96? Oh geez, there goes my brain thumping again... I'll never decide on anything without having something change my damn mind...
Paul

 

[Tom Cram]

Oh, I gotcha,

I didn't realize you were asking for a sonic comparison, and impressions. The following is my opinion only;

The 300 series sounds a little "darker" in character to me than the 500 series. This "darker" character lends itself well to the brighter mics that are so prevalent now, very complimentary. I like the A taper on the 300 series better than the W taper on the 500. The A taper feels more natural. The de-esser on the 376 is VERY cool. It is based on the dbx 902 de-esser and is worth the price of admission alone. The flexibility and options of the 500 series smokes the 300.

The thing to remember is that the 500 series came first. So, when the 300 series was proposed the engineers saw it as a chance to improve on the 500 series circuitry. These improvements changed the sonic character between the two lines. They are based on the same designs but they sound different from each other. Not better or worse...Different.

I use them both...a lot. I have other pre's, and I also can't wait for the FMR RNMP. I feel that pre-amps and compressors are like an artists paint pallette. You can't paint a picture without different color paint. If you only have black paint, you can't paint a sunrise.

Tom Cram
dbx Senior Technical Support
(801) 568-7530
tcram@dbxpro.com

 

[tubedude]

Hmmm... darker, you say? Wish I could hear these things. If you were stuck with only one of them, which would it be? By darker, do you mean warmer? I like warm, but I don't want to lose my brightness either. I feel like professional sounding vocals need that certain brightness.
Is the 300 series a true tube design like the 500's, or is it a reflected plate design like most other cheaper tube preamps?
And while we're on it, what is your favorite pre in your aresnal?
Have you ever posted an MP3? (hint hint)
Paul

 

[Tom Cram]

uh, um...

Darker implies (to me) a rolling off of highs in the 12-16kHz range. Warm implies (to me) enhanced third order harmonics due to tube compression/saturation. The 500 and 300 series are hybrid mic preamps. This means that the front end and back end are solid state while the middle is tube. If the tube is removed from the 500 and 300 series, signal cannot pass through them as the tube is in SERIES with the signal path. this allows you to get both tube and solid state tones. If you have the drive set low you are not hitting the tube very hard, this means less tube saturation. If you turn up the drive knob you start to hit the tube a lot harder, this generates more tube saturation and compression. A lot of cheaper designs (not ours) have the tube in parallel or not even in the circuit at all.

I would choose the 500 over the 300 because it has more features and more flexibility.

I have two favorite clean pre-amps; the dbx786 and the Langevin dual mono. I have heard good things about Vintech, but I haven't had a chance to hear them yet.


I have MP3's posted on my studio page www.friction.pair.com (I haven't had the chance to update this page in a while so some of the info is outdated).

 

[tubedude]

123

Thanks for your help!
One other question you might be able to answer... what exactly is considered a "class A" preamp? Or these class A preamps?
Thanks,
Paul

 

[Tom Cram]

A or B or A/B,

This description is greatly simplified, but here goes;

Class A runs on mostly all positive voltage typically 0 to 30v for solid state. The transistors/tubes are always "on" it's not as efficient but some say sound better because it has no crossover distortion. Class A is hard on tubes and transistors.

Class A/B runs -15 to +15 for solid state, still 30v., but it crosses from pos/neg and back in operation. This design is efficient/less hard on tubes and transistors, but you can get crossover distortion. Thus the preference for class A designs.

Most of the newer Class A/B designs have VERY low crossover distortion and sound great. So listen to the unit instead of dismissing something because it's not class A.

Tom Cram
dbx Senior Technical Support
(801) 568-7530
tcram@dbxpro.com

 

[Harvey Gerst]

Does this help?

Here's a drawing that might help explain "Class A" operation.

You basically have the whole signal running thru one device. Most preamp tubes have a characteristic "S Curve" transfer function (black line in the drawing). Transistors tend to be less rounded at the bottom and the top.

The designer tries to stay inside the straight line portion of the curve, producing a higher voltage image (the big red sine wave labelled "Output") of the signal going into the device (small red sine wave labelled "Input"). The mid voltage line of the device is the "zero" of the sine wave. As you can see, this means the device is always working.

In class "A/B", they run the top half of the sine wave to one device, and the bottom half thru another device, so that each is only working 1/2 as hard. But getting the wave put back together is really hard if they don't line up at "zero" exactly. It creates a nasty sound called "crossover distortion".

 

[Tom Cram]

Whew,

Thanks Harvey,

I was hoping somebody would jump in and flesh out what I was talking about.

 

[Harvey Gerst]

Re: Whew,

Thanks Harvey,
I was hoping somebody would jump in and flesh out what I was talking about.

No Problem, Tom - I actually had fun drawing it.

 

[Dolemite]

Cool graph, Harvey....now I just wish I understood it better!

Hey Tom, any comment on this new DBX product:

http://www.musiciansfriend.com/ex/shop/rec/?pid=183538

Looks like DBX wanted to cash in on the ART Tube MP Market.

 

[Harvey Gerst]

Maybe this'll help more

Cool graph, Harvey....now I just wish I understood it better!

It's really not that hard, but I didn't put in all the stuff except for a few of the basics. Here's a more detailed explanation, but still without a lot of the techie stuff. Let's say we're looking at a small tube amplifier output stage. Look at the drawing again:

The tube's "transfer characteristic" is shown as the black "S curve" in the drawing, with the input signal coming in (in red) from the bottom of the drawing:

As long as the input signal stays in the straight line portion of the transfer curve (inside the blue lines), the bigger output signal (also shown in red on the right side of the drawing) will be an exact, but louder, copy. If the input signal gets too big (wide), the output signal will start to flatten out on the top and the bottom. As long as the input can all fit in the flat portion of the tube transfer curve, no problems. Perfect fidelity, but you're limited to how much one output tube can put out (which ain't much if you're trying to crank your home stereo to concert levels).

Enter the class A/B amp

So, how do you get an even bigger signal out? You can use two tubes and divide the work load. Use one tube for just the positive (plus) side of the signal, and a second tube to handle just the bottom half (minus) side of the wave. Crank em both up and then combine them later. That's A/B class, but splitting and combining the two halves of the signal can be real tricky. If ya fuck up, the place where it "crosses over" from one tube to the other (at the zero line) may not be exactly perfect, and you'll hear a nasty distortion called (you guessed it) "crossover distortion". It's caused by the two halves of the signal not lining up perfectly.

Is that better....

....or do I hafta draw ya a picture?

 

[Dolemite]

OMG, I think I get it.

Thanks for the explanation, Harvey! That made it much clearer for me. So is the "S-curve" of the tube transfer function versus the less-roundedness of the transistor transfer function what causes the apparent difference in sound? Also, do the same ratings (Class A and A/B) apply to discrete IC opamp based designs that you might find in a cheap mixer or low-end dedicated pre? It seems to me it must be easier to make a Class A solid state pre as opposed to a Class A tube pre, or am I way off on that?

 

[Harvey Gerst]

Yup, you got it. Some solid state stuff has other problems which can complicate things. A lot of solid state equipment aren't very wide band, unless you use a lot of negative feedback to lower the gain, and increase the bandwidth. But that causes another kind of distortion, TIM (Transient Intermodulation Distortion).

All this stuff is basically "tricks and trade-offs", comprimises to bring in stuff at a decent price that doesn't sound like shit. EVERYBODY knows how to make killer equipment - it ain't rocket science. How to make stuff that sounds good for cheap is the hard part. And the bottom line is always the same: What are we willing to give up to achieve "X" performance? The design engineer is forever walking a tightrope, trying to find a good balance point.

 

[tubedude]

qwe

Hmmm... the dbx "Mini Pre Tube Mic Preamp"
Well, Tom... whats the deal on this thing? Hows it sound? Deal the specs man we WANT SPECS!!!!!

And uh, Harvey... you know WAY too much dude... kinda scary... you should be building this stuff yourself and selling it to US for cheap!

 

[Dolemite]

So Tom, what's the story on this new dbx pre? I just wanted to make sure you saw that this thread was still alive and kickin', it has your name on it after all, hehe....