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  1. #1
    Join Date
    Oct 2009
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    Default OT: Hi-Z Input versus DI

    Good day,

    Not too sure about the title for this post, but over the years I have not had too much success obtaining a suitable audio interface with a Hi-Z input for use with a guitar using humbucking pickups.

    Interestingly, in a call to the folks at RME some time ago, they intimated to me that they do not recommend using the Hi-Z input on a number of their interfaces - but rather they suggested using a DI appropriate for your device, which in my case would be an active DI.

    As a previous owner of a number of ADA8000's - with the subsequent upgrade to the ADA8200's, as these devices did not provide Hi-Z, I used an active DI - A Radial PRO48, to obtain the optimal input level.

    And as I have now down-sized my current configuration, I am using a Behringer UJMC404HD - as these interfaces use the same preamps as do the ADA's.

    However, the Hi-Z inputs have too much gain - even with the PAD enabled, and am, as a result, noticing a small amount of distortion. With the PAD disabled, I am unable to obtain a satisfactory input level without the clipping of the input signal.

    So, should I therefore, use an active DI with the input set for 48v?

    Thoughts...suggestions? Thanks in advance...

  2. #2

    Default Re: OT: Hi-Z Input versus DI

    Dell, without having any experience with this converter, I wonder why the signal into your UMC404HD is so hot that it overdrives the converter preamp. Are you running a preamp between your guitar and the UMC404HD? If so, can you turn it's output gain down to a level that is acceptable to the UMC404HD's preamp?

    Also - there are reports out on the web of issues with the drivers causing distortion on some computers, but not others, in case it's not a preamp being pushed too far.
    Last edited by John Ludlow; 07-27-2019 at 07:18 AM.

  3. #3
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    Default Re: OT: Hi-Z Input versus DI

    John,

    Q1: Are you running a preamp between your guitar and the UMC404HD?
    R1: No...and I would have been aware of this. Also, if I were using something prior to the interface, I would have performed the necessary testing without that device prior to the use of that device.

    Q2: If so, can you turn it's output gain down to a level that is acceptable to the UMC404HD's preamp?
    R2: See R1 above.

    I have tested both of these interfaces on two different systems with the same end result. I have contacted Behringer - but being so BIG, I am really doubtful of any immediate response.

    The guitar that I am using is an Epiphone ES-339 and which has pickups made by Glen McDougall - now sadly deceased. Also, the switch and the output jack have been replaced with Switchcraft components and the pots are by-passed. So, from pickups-to-switch-to-output-jack. This particular configuration I have been using on all of my electric guitars for over 30 years now.
    Last edited by mr_es335; 07-27-2019 at 09:51 AM.

  4. #4

    Default Re: OT: Hi-Z Input versus DI

    Sorry if it seemed like I was not giving you the technical credit you deserve. Didn't mean to.

    Well... that's really weird then. That seems to imply that your pickup's signal is so strong that it's overwhelming the preamp - which seems unlikely. Those are supposed to be Midas pres, which are very highly regarded. I suppose that there's nothing left in the signal chain to point fingers at besides the preamps instrument circuit though. Have you tried using your DI? I would suppose that it would result in the same issue if the input signal from the pickups was that hot. So, if that works then that must be it (unless you're using a long hi-z cable that is passing by something with an electromagnetic field). That's all I can think to try though.

  5. #5
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    Default Re: OT: Hi-Z Input versus DI

    John,

    Yes, I tested this interface using a Radial PRO48. Even then, I have to enable the PAD on the DI to prevent the signal from clipping.

    The GAIN knob on the interface defaults to 7:00 - and I have the GAIN knob set to approximately 7:02!!

    I am going to be very, very interested to see what Behringer has to say - if the indeed they do get back to me.

    As an aside, I would be very interested to know if using a DI is preferable to using Hi-Z in the first place? This particular "point" is what I had gleaned from a past conversation with RME.

    Anyone care to comment?

  6. #6
    Join Date
    Jul 2006
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    SF Bay Area
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    Default Re: OT: Hi-Z Input versus DI

    Quote Originally Posted by mr_es335 View Post
    John,

    Yes, I tested this interface using a Radial PRO48. Even then, I have to enable the PAD on the DI to prevent the signal from clipping.

    The GAIN knob on the interface defaults to 7:00 - and I have the GAIN knob set to approximately 7:02!!

    I am going to be very, very interested to see what Behringer has to say - if the indeed they do get back to me.

    As an aside, I would be very interested to know if using a DI is preferable to using Hi-Z in the first place? This particular "point" is what I had gleaned from a past conversation with RME.

    Anyone care to comment?
    There is nothing magical about using a DI. DI's are really only intended as a way of converting a high-impedance non-balanced signal into a low-impedance balanced signal that can be plugged into a microphone input.

    A properly designed hi-z input built-in to a preamp should adequately serve the same purpose.

    The key point there being adequately designed.

    In the case of the Behringer preamp I wouldn't expect there to be a lot of effort put into the hi-z input circuit (Midas inspired design or not).

    The entire Behringer U-PHORIA UMC404HD is only $150. (4 mic pres, A/D, D/A, headphone amp and MIDI) Even if we divide the cost as $100/$50 input to output, even generously thats still only $25/ch.

    The Radial Pro48 is $100 for a single ch hi-z preamp with a low-z balanced output.

    The radial costs 2/3 the price of the entire UMC404HD and is dedicated to the single task of converting a hi-z input to a balanced low-z output (no mixing, A/D, D/A, headphone Amp, MIDI). Its just the front-end preamp circuit all by itself. So, yes I would expect it to do a much better job of both impedance matching your guitar as well as supplying a clean balanced low-impedance signal for what ever signal chain you plug it into.
    ---------------------------------------
    Philip G.

  7. #7
    Join Date
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    Default Re: OT: Hi-Z Input versus DI

    cgrafx,

    So, yes I would expect it to do a much better job of both impedance matching your guitar as well as supplying a clean balanced low-impedance signal for what ever signal chain you plug it into.
    ...As always Philip, you responses are always "to the point", and indeed, always very helpful. Molte grazie!

    PS: I often never consider the "price per feature" aspect and such is certainly most worthy of note.

  8. #8

    Default Re: OT: Hi-Z Input versus DI

    Quote Originally Posted by mr_es335 View Post
    So, should I therefore, use an active DI with the input set for 48v?
    Yes, if it does what you need it to.

    Sounds like your special humbuckers output extra hot. You'll need to account for that with correct gain staging. You could also put an attenuator in front of your Behringer interface, if you wanted. Though I've never seen a 1/4-inch to 1/4-inch (unbalanced) box.

    You could probably make your own with a few resistors.
    Last edited by Dave Labrecque; 08-01-2019 at 01:30 PM.
    Dave "it aint the heat, it's the humidity" Labrecque
    Becket, Massachusetts

  9. #9

    Default Re: OT: Hi-Z Input versus DI

    Video of Glen McDougal discussing details of his Fury guitar - including the pickups:

    https://youtu.be/An733uEMxyU

    Sounds like they really were unique.

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