ADA Depot - A Forum To Support Users of ADA Amplification Gear
ADA Preamps => MP-2 => Topic started by: rickeb1 on September 18, 2014, 10:29:04 AM
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Can someone explain the MP-2 gain controls, i.e. how the Drive, OD and Master interact? I have an MP-1 (3TM), and I understand how OD1 and OD2 relate to each other and to the Master setting. Is the MP-2 Drive and OD kind of like the MP-1 OD1 and OD2, or do they work entirely differently?
Thanks!
~ Rick
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They work way different.There are also 2 vactrols but in different places.One controls the volume just before the first tube and one that controls the amplification of also the first tube.
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Hey MJMP, whats a vactrol (is it like a VCA ?) Can you give us a description of how the MP2 circuits work ? (bit like the MP1 description you posted)?
Cheers R
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a vactrol is an opto coupler,light dependend resistor controlled by a led.So it not like a VCA but it can be used in a VCA circuit like the OD1 control in the MP-1 is a sort of VCA.
http://www.excelitas.com/downloads/dts_vtl5c42b.pdf
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So what's the advantage, ie why use one over the other, though I get (I think) they should be very accurate. Ok so more accurate, and low noise so perfect for a high headroom tube circuit ? My rudimentary understanding so far ?
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These things are used alot in tube amps, even the triaxis is full of these.They can handle higher voltages then vca's.
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So the OD boost the signal before the tube, like a pedal would do?
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Yes sort of.It build different but the result is the same.
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Is there somewhere where we can get the info on how the different voicings works, and what is the role of V1 and V2 ?
I found some info in the manual, but not much.
Page 4 :
Gignal flow : Drive>OverDrive>Voicing.
Then, on page 36:
- Tube Voicing : Selects basic character of tube sound by configuring the four tube stages and biasing them for the proper gain and interstage EQ. There are ten Voicings available: [list of voicing]
- Drive : Determines the amount of gain in the tube preamp.
- OD : Determines how extreme distortion generated in the preamp is.
I understand there is 3 main voicing categories (clean, vintage, hi gain), but they're not just EQ variations. i.e Warm Hi Gain sounds smoother than dynamic hi gain at high gain settings (drive 100, od 80), but when I turn down the gain (drive 40 od 10), I can get a more clean sound on the dynamic hi gain channel than on the warm hi gain channel.
I guess it has to do with the 4 tube stages?[/list]
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Both tubes are always used,doesn't matter if it's clean or distorted sounds.What happends is resistors are switched in and out to get more or less gain and some caps are switched in and out to get different sounds.Some in a feedback loop and some over the kathode resistors.
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If you understand how tube circuits work you could study the schematic and work out what does what and the affect it has on the signal as it flows through the 4 triodes (gain stages, 2 per tube as 12AX7 is a twin triode tube). So as MJMP says, some resistors control the gain and some capacitors change the eq (sound). Each voice has its own configuration (combination of resistors/caps etc) and, as you say, in 3 basic groups (clean, warm, high gain).
Drive>Overdrive>Voicing (page 2 of my manual) may be a little misleading, the voicing kind of wraps around the drive(s) altering the character (available gain, eq) in the 2 tube circuits. The drives control how much of the available gain is applied.
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The tube preamp in the MP-2 is control-wise build very differently than that in the MP-1
The MP-1 pre is quite a simple design, where each tube simply has it's own gain control.
The MP-2 preamp is a different design, which has a lot of control/setup voltages (these are handled by the vactrols MJMP mentioned).
So, instead of handling a relatively simple 'each tube it's own control' scenario, ADA chose to implement ten differently sounding voicings, each of which will setup the two tubes using the control voltages I referred, and you, the user, will use a single gain control to affect all of this in a rather smart way, methinks.
The Master Level control is simply a.. well.. master level control, positioned after the whole tube assembly.
In other words, the gain control and master control have no 1-to-1 interrelation; however, when you turn up the gain, the signal level will of course rise, so master needs to trimmed. But there's no interaction, like master inflicting pain on the gain.