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Sebatron ,
If you wouldn't mind to take a minute for explanations, a couple of questions about the preamps:
1. What frequencies get boosted or cut when the "Air", "Bright", "Deep", and "Low Cut" features are activated? Confirm: the first three of those are boost while "Low Cut" is a cut? How much is the boost/cut? Please describe the character of the boost/cut (shelf, peak, Q, etc).
2. The pad is the only way to control input gain-true? What if the input signal is weak and needs some gain?
3. What kind of tubes are in there? What kind of transformers?
Inquiring minds want to know. Thanks, David

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Sebatron Thu, 09/18/2003 - 13:51

1/The E.Q functions on the vmp series preamps are intended for subtle enhancement or correction before committing sounds to tape/DAW.They are wide-Q and either open up the top or bottom register.
DEEP:
This is , yes , a boost type E.Q.Starts very low , from 15 hz.
+1db @ 20 hz
+8db@ 40hz ….. peak
+5db @ 55 hz
+1 db @ 320 hz
I actually think the peak is the bottom ‘E’ in frequency .

AIR: The ‘air’ and ‘ bright ‘ settings have a different curve/Q , depending on the pad level switch setting.
With 0 db pad selected:
+1 db @ 6.2 khz
+ 4 db @ 14.5 khz……… peak
+1 db @ 30 khz
flat again at 38 khz

With –15 db pad selected:
+1 db @ 4.2 khz
+5 db @ 9.4 khz
+9 db @ 26.4 khz ………peak
+5 db @ 62 khz
flat again at 88 khz

With –30 db pad selected:
+1 db @ 4.2 khz
+ 5 db @ 12.6 khz
+ 6 db @ 20.6 khz………peak
+ 5 db @ 33 khz
flat again at 58 khz.

BRIGHT:
With 0 db pad selected:
+1 db @ 3.3 khz
+ 4 db @ 5.8 khz
+ 5 db @ 11.8 khz ………peak
+1 db @ 30 khz
flat again at 38 khz

With –15 db pad selected:
+1 db @ 2.4khz
+ 5 db @ 5.4 khz
+9 db @ 20 khz ………peak
+5 db @ 60 khz
flat again at 88 khz

With –30 db pad selected:
+1 db @ 4.2 khz
+ 5 db @ 6.2 khz
+ 8 db @ 16.8 khz………peak
+5 db @ 38 khz
flat again at 58 khz.

These are just basic plots but you can see how sweet those frequencies are… particularly those peaks , they are way above that horrible top-mid area.

2/ The new vmp design features an upgraded gain structure/circuit giving up to 60 – 70 db of gain.
If more gain is required , you can easily link two channels together for a massive magnification.

3/ We use J.J tubes ( 12at7 ) , and locally sourced hand wound audio transformers.
Occasionally I have used OEP audio transformers with identical results. :w:

Sebatron Mon, 09/22/2003 - 17:35

…good idea SC…
I’ve been meaning to plot those graphs for a while ,
I didn’t realize they peaked so high ‘till I did that recent sweep.
Most of what I do is dictated by ear.

Yes , the variable pad level makes the circuit quite flexible from being transparent to coloured and the EQ circuit interacts with the negative feedback loop to provide many options….
Let’s see…. 3 * 3 * 3 => 27 colours in all.

:w:

anonymous Mon, 09/22/2003 - 23:07

Hey Sebatron,
I got a hold of Chris's vmp today. I tracked some electric guitar, and compared it to the Universal Audio 2-610. I am impressed. The vmp held up well against the 2-610. I found the vmp to be a little more defined in the high end. I do prefer the eq of the 2-610, in both sound and functionality, but I understand that the eq function on the vmp is designed to perform corrections to pre-DAW signals. Not a knock on the vmp, however, all the eq buttons sound right. All in all, serious kudos- the UA is my favorite preamp and I was NOT disappointed by the vmp. Tomorrow I hope to track some bass. David

KurtFoster Mon, 09/22/2003 - 23:54

David,
One thing I have found that the vmp really shines on is acoustic guitar. I used a U87 aimed at the point where the neck joins the body of my Martin D28 and the sound is absolutly huge! I also really like the front panel 1/4" inputs, using them for drum machines and synths. The vmp really warms up these digital 16 bit babies! Give both these techniques a shot while you have Chris' unit there.