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Author Topic: Setting output without clipping using the LED  (Read 983 times)

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van Sinn

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This is likely for MJMP:
When setting Master level during programming and output using the front potmeter, we of course will be using the LED's.
But.. how are those LED drivers calibrated? Will they start firing up / blink juuust when it's about getting too hot, or what?
Do the start blinking merely as early warning? Do they light up [almost] solid when it's really resulting in distortion, or when it's just about to?

Looking at especially when the tonestack LED starts firing doesn't match my sonic experience, i.e. I seem to notice unwanted distortion right before the LED starts firing, meaning, I'll have to set levels just a touch too hot to actually see the LED firing, and back off a touch.
Would be nice to see the LED firing up just when distortion is about to start taking place..

Regarding the manual potmeter outputs, I don't see much relation to when I can hear distortion and when the LED starts firing - the LED seems to be more of a simple indicator to how hot the output is, like a poor man's VU meter ;)

Further: I haven't re-checked the schematics, but IIRC, those LED drivers do not feature adjustments for calibration, so, what's the procedure, should I want to?
Obviously, some resistors can be changed to facilitate changing when the LED's will fire..
« Last Edit: Time Format by van Sinn »
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MarshallJMP

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Re: Setting output without clipping using the LED
« Reply #1 on: Time Format »

In the mp-1 when the led goes on the signal is still clean ,so it goes on early, same with the output led on the mp-2.But I must say I never checked the other led/levels in the mp-2.
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Harley Hexxe

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Re: Setting output without clipping using the LED
« Reply #2 on: Time Format »

In the MP-1 and the Classic, the LEDs are kind of a level meter for clipping. According to the manuals, the top LED should just flicker slightly, if the top one lights up more than that, you're clipping.

   The MP-2 seems to function differently from these, and I'll admit I haven't really figured that one out, so I just use my ears. If it sounds good, it's fine, don't mess with it.
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van Sinn

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Re: Setting output without clipping using the LED
« Reply #3 on: Time Format »

Yeah, sort of how I sense these circuits does work.
One problem with potentially wanting to technically check out how exactly the MP-2 LED driver does work, is that it's a custom designed circuit, so..

To be honest, it never really bothered me too much either. I just started to get interested in it because of those issues I referred with the headphone clipping shebang - wjich is more a matter of logical thinking and that the hifi preamp in use weren't really designed for such uses ;)
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rnolan

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Re: Setting output without clipping using the LED
« Reply #4 on: Time Format »

There is an explanation of where the LED trigger points are set in the manual(s) I do remember reading it (though I don't recall if was MP1, MP2 or both).
Ok page 11 of MP2 manual: green = 30db below clip, red = 3db below clip (regardless of if that section is switched in or out in the given patch).

MP1 manual 3.4 Using the Clip LEDs, doesn't provide numbers just a description.
« Last Edit: Time Format by rnolan »
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Harley Hexxe

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Re: Setting output without clipping using the LED
« Reply #5 on: Time Format »

So....the MP-2 LEDs are singular in reference to specific sections of the preamp?
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rnolan

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Re: Setting output without clipping using the LED
« Reply #6 on: Time Format »

Yes  :thumb-up: and they monitor that section regardless of in/out status.  So you may see a LED(s) flash in a section(s) you're not using in the current patch (which can cause confusion  :dunno: ).  Personally, I don't take much notice of them apart from "I seem to have signal there/or not" when trouble shooting.  And then it's usually doh  :facepalm: forgot to plug the guitar lead in at both ends or turn the power amp on etc.
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Harley Hexxe

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Re: Setting output without clipping using the LED
« Reply #7 on: Time Format »

Okay, That's the part that was confusing me about those LEDs. Kind of a silly way to do things really if there is no signal present in that particular section.
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van Sinn

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Re: Setting output without clipping using the LED
« Reply #8 on: Time Format »

Okay, That's the part that was confusing me about those LEDs. Kind of a silly way to do things really if there is no signal present in that particular section.

Hehe, yeah, might seem so, but IIRC form the schematics, the LED driver is connected to the various sub-circuits in such a way that it can monitor those, even if the circuit is currently seemingly inactive.

Now, unless I've misunderstood something (absolutely likely), thing is that, even when a cub-circuit, say, chorus, is switched Off, the programming is still applied to it, meaning that it still receives signal - it just isn't 'on the bus' so to speak - so the LED driver can still monitor it. Fun, and a Bit funny-weird ;)
« Last Edit: Time Format by van Sinn »
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Harley Hexxe

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Re: Setting output without clipping using the LED
« Reply #9 on: Time Format »

Then that would mean that even if that section of the preamp is in, i.e. Chorus, Comp, or whatever, then the LED isn't monitoring the level through that section, just the level going into it!
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van Sinn

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Re: Setting output without clipping using the LED
« Reply #10 on: Time Format »

Mmnn.. my memories about the schematics have fainted a Bit, but IIRC, the LED driver actually monitors the level each sub-circuit after the fact.
Or, in other words, if the circuit is being switched Off at its output, with the LED driver being attached before the switch [transistor], then the LED can still indicate how the circuit is performing - the circuit receives signal, but just isn't routed onto the bus.

Disclaimer: I haven't re-checked the schematics, so beware of potential inaccuracy..
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MarshallJMP

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Re: Setting output without clipping using the LED
« Reply #11 on: Time Format »

yes that's correct. But not always on the end before the switch, like the chorus level is checked at the input. Drive is checked at the 1 first 2nd half. Eq's at the end.
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Harley Hexxe

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Re: Setting output without clipping using the LED
« Reply #12 on: Time Format »

That IS weird :crazy:
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rnolan

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Re: Setting output without clipping using the LED
« Reply #13 on: Time Format »

Makes sense to me. It's just routed a bit like a mixer, albeit very dedicated. Like the MP2 loop, it's really just 2 aux sends and returns.  The LEDs are all about helping you get the gain structure right (and you could (depending on how you dial a patch) get it really wrong (well not optimal)). Some things are more sensitive to input overload (eg chorus) so (thanks MJMP for specifics  :thumb-up: ) you put the LED at the input, some you care more whats on the other side of the circuit.  The MP2 seems to be a nice amalgamation of this goes through this but this is a bus to the side and back.

Vans explanation makes sense, (my take) there's a main bus through the MP2 and some things attached to it that can be mixed in or out. One way to think of it.

Anyway, seems there is always signal in the various circuits (sub-systems) and LEDs to monitor them, so lights flash (and look pretty).  This is good to know so you don't get concerned if say the chorus light flashes but you know you have it switched out.
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Studio Rig: MP2/MB1 > Eurorack UB2442FX-Pro > TC M-One XL > Behringer Truths (with Truth Sub) / QUAD ESL 63s
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van Sinn

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Re: Setting output without clipping using the LED
« Reply #14 on: Time Format »

yes that's correct. But not always on the end before the switch, like the chorus level is checked at the input. Drive is checked at the 1 first 2nd half. Eq's at the end.

That IS weird :crazy:

Actually not, it does make sense..
The chorus doesn't add extra gain to the signal; it merely morphs it, so check on the input to make sure not to put more signal into it than to keep it from overloading.
With the EQ, OTOH, you cannot know if it'll clip until you've actually made it gain-up some frequencies too much, so check on the output if it did overload.


And yeah, I should've been a bus driver: Yo driver, can you switch me off on the next patch..
« Last Edit: Time Format by van Sinn »
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