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    Helix as the FX for a GM40- 4 Cable method

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    spikey

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    Join date : 2016-10-14

    Helix as the FX for a GM40- 4 Cable method

    Post by spikey on Fri Jan 20, 2017 11:35 pm



    Drawing out loud here-

    Using Helix as the FX rack for the H&K GM40. Not sure if the GM40 FX loop is Line or Inst level, so adjust accordingly.
    In this diagram the front end of the GM40 gets the Helix wah, a dirt pedal. After the GM40's preamp it gets a Helix volume pedal, delay and verb.
    All switchable on or off by the Helix controller.

    Use the Cabs in Helix or use the Redbox in the GM40, or both (or none and use the cab).


    You can also set up Helix (in the control area) to send midi CC messages to the GM40, to switch the GM40's midi changeable functions cheers
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    guitarsoul

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    Join date : 2017-04-24

    Re: Helix as the FX for a GM40- 4 Cable method

    Post by guitarsoul on Wed Apr 26, 2017 7:29 am

    Hi!!!
    This is very interesting ...
    I'm going to buy both now in June and I want to use it that way ..
    I just do not know how to configure Helix to control the amp presets through Midi.
    Can you help with that part?
    hug
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    bordonbert

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    Age : 97
    Location : Southern England

    Re: Helix as the FX for a GM40- 4 Cable method

    Post by bordonbert on Thu Apr 27, 2017 6:18 am

    Purely as a reference, from the owner manual Tech Specs:

    Fx Send Nominal Level, (Clean without Boost all pots centred) = -10dbV (316mV RMS)

    Fx Return Nominal Level, (Clean without Boost all pots centred) = 0dbV (1V RMS)
    Fx Return Nominal Level, (Clean without Boost all pots centred except Master set max) = -10dbV (316mV RMS)
    Fx Return Max Input = +14dbV (5.02V RMS)

    dBs confuse a lot of people and it isn't surprising! For those who don't work with them every day, they are NOT a measure of anything in themselves, they are a comparison of two quantities. i.e. they are telling you how many times bigger one thing is than another. e.g. A gallon of milk is 8 pints, so a gallon is +9dB (8x) above a pint. Or a more relevant example, an amplifier's frequency bandwidth -3dB points are the points where the power has dropped -3dB (1/2) in comparison to its mid range level for equal inputs.

    The H&K levels are specified as "dBV". The "V" is the standard suffix to tell us the voltages we are considering are compared to 1V as a reference. So they are "[so many times] as big or small as 1V".

    The outputs mentioned will of course be affected by the input level. The specified input sensitivity of the amp is -23dBV (71mV). This would be the input level which gives those specified Fx Loop levels. The max input signal without boost is specified as 0dBV (1V). In my experience most guitars are capable of putting out signals a fair bit above that 71mV level.
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    Syn666

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    Re: Helix as the FX for a GM40- 4 Cable method

    Post by Syn666 on Mon May 29, 2017 9:20 am

    Sorry to barge in, but the flexibility and effects quality of the newer Helix LT have been under my radar, since the price is around € 500 cheaper then the full Helix here in Europe.

    So my question is as follows: I have already quite a few sounds (with and without FX) progreamme don the GM40; if I use the Helix to swiitch channels, does it use the programmed sounds on the GM40 just by using PC messages via MIDI, or would I have to program each and every MIDI setting in the GM40 on the Helix LT itself?

    Of course I'd switch off effects on the GM40, since I'm interested in using the Helix as a pedalboard substitute.
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    Syn666

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    Re: Helix as the FX for a GM40- 4 Cable method

    Post by Syn666 on Mon May 29, 2017 9:49 am

    Also, is the GM40's loop line or instrument level. Not to ignore Bordonbert's input, but for the technically ignorant, an easier answer would come handy...
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    bordonbert

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    Re: Helix as the FX for a GM40- 4 Cable method

    Post by bordonbert on Mon May 29, 2017 12:51 pm

    It's line level Syn666, but only in the sense that it is "a line" coming out and returning, but that doesn't really tell you anything.  I could just say "Line level" and leave it at that but it would give you absolutely nothing real to work with in a practical sense.

    What is their definition of line level?  It isn't necessarily the same as everyone else's definition.  There is no standard definition other than to say we use 1V as a reference and quote our own choice for line level with respect to that.  That's what decibels are there for but that is too deep for most non-tech people to want to grasp naturally.  The idea is simply that an instrument level signal is taken in at the front end where it goes through a few amplifying and processing stages.  It then goes through the Fx Loop section at a higher level than at the input so it is less sensitive to noise which will get added.  We would always want to get signal levels up higher where we can for that reason.  My guess would be that the power amp wants to see about the level I quoted from the manual for full output so it is set to that to match.  And as you can now guess, there is also no standard as to the input level for a power amp.

    Likewise, instrument level is not defined anywhere, it just means the signal of that particular instrument.  As a guide, guitar output can be anything from a few 10s of millivolts to about 1V.

    And we haven't even considered the impedances the signal comes from and goes into which will change all levels drastically.  Now that IS getting more technical than most people understand.




    The best we can say is that if you put in 71mV from your guitar, (H&K's specified nominal input sensitivity), you would get 316mV out if you select the Clean channel with Boost off and keep everything else centred, and the amp would expect to see the same 316mV back at the return.  Call those line level if you wish, they are within the ballpark to be considered standard as levels at preamp outputs and loops.  These levels are all very rough as you have oodles more gain on tap and controls to take levels down where necessary.  For example the Return would accept signals up to just over 5V before anything inside overloaded and you couldn't turn it down internally to prevent it.
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    Syn666

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    Re: Helix as the FX for a GM40- 4 Cable method

    Post by Syn666 on Mon May 29, 2017 1:22 pm

    Thanks, Bordonbert!

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