Friday, 28 October 2016

Hughes & Kettner Red Box Classic DI

Original info:
The Hughes & Kettner Red Box Classic converts Line, Out and Speaker Out signals into balanced, frequen- cy-compensated signals, enabling a direct feed to a mixer. The Red Box Classic features two voicing options, a 4x12" cabinet and a 2x12" combo.
You can find the original manual PDF here (must read!)
Original schematic is available here.
You can use an adapter or the 48V Phantom power via Balanced Output jack.



...and without Ground Lift switch

45 comments:

  1. This comment has been removed by the author.

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  2. This is super, a DI box without an audio transformer. Thanks Alex!

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  3. So what's the downside of not having transformer?

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  4. Can this be used for bass as is?

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  5. Yes! A good DI box is what we've been missing, this is a very useful build. I'll be building mostly for recording with the speaker emulation, but I don't have an actual DI with me to verify it all, so I hope someone verifies this. Thanks Alex!

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  6. I have a TL084 in my box of cack, would this work ok?

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  8. Stupid question: Is it really okay for amplified signal to be on the little traces of the tagboard and all these 1/4 Watt resistors? I mean it's like... a 100 Watt amp...?

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    1. Not a stupid question at all, I was wondering that as well and I'm waiting for someone to tell us if he had success and how he used it. That said, I don't have an answer for you :)

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    2. Not a stupid question, but it is NOT a 100 Watt amplifier. In fact it is not any kind of amplifier at all.

      What it is, is a DI (Direct Injection) box - a simple recording/PA interface. You simply plug your guitar into the input jack and plug the output straight into a mixing desk. This way you can record straight to a recording device WITHOUT the need for amplifier/speakers/microphone.

      You can also plug straight into a PA system with one of these, either without the need for an amp, or in parallel with an amp - most sound engineers will do this with your band's bassist.

      There is a clever little tone shaping circuit included in this DI box that mimics the sound of a guitar signal run through a 2x12 or a 4x12 speaker cab - basically, it caps off the extreme high and low end of the signal.

      It's a very good DI box, especially for recording - I have been using one for years.

      I hope this helps.

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    3. I think I'm misunderstanding this too Beaker. I thought Geoff meant he was planning on plugging a 100W amp into this, and was concerned that it would damage the amp.

      Am I understanding this correctly that I can plug the speaker output of my amp directly into this pedal without damaging the output transformer? My amps don't have an output for direct in, but the info on this unit seems to indicate we can hook this unit right up to the speaker output?

      If I can plug it into the speaker output then I may have to give it a go. That sounds useful. Otherwise I'd probably just rather mic up the amp in an iso-box because I'm not really a fan of plugging my guitar right into the DI box

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    4. OK nevermind I just read the manual and now I see you need to connect the speaker(s) or load resistor to the "to speaker cabinet" jack.

      My question now.. When you have speakers hooked up to this jack, does the sound come through the speakers as well as the DI output?

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    5. This device taps off some of the signal to process as it passes through on the way to the speakers. Sound will come through to your speakers. If you choose to send that signal to a load box or power soak, that is fine. If you attach this device to the speaker out of your tube amp without letting the signal continue to a load or speakers, get ready for smoke and an expensive repair.

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    6. This device taps off some of the signal to process as it passes through on the way to the speakers. Sound will come through to your speakers. If you choose to send that signal to a load box or power soak, that is fine. If you attach this device to the speaker out of your tube amp without letting the signal continue to a load or speakers, get ready for smoke and an expensive repair.

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  9. Quick question about the "12v+" power input: Does this circuit REQUIRE 12v or can it run on other voltages? The reason I ask is that the manual mentions: "48v phantom power", a "9v e-block battery", and both "9-15v AC" and "9-24v DC". On top of that, I read an online review that said something about using an adaptor capable of "6-18v".

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  10. XLR 1 and 2 should be swapped. XLR1 should be ground.

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  11. Does anyone have a layout for a charge pump that converts +9v into +12v?

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    1. Muad'zin how bout a Zener or one of these?

      http://www.ebay.com/ulk/itm/381823859663

      Can't believe this seller is in the same city as me! Never seen a good electronics store around here, must be a fellow DIY geek

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  12. Btw just to clarify I meant tack that on to the output of one of the 18v charge pumps that are available here

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  13. Like this one and will probably build one for shts and grins. Anybody seen the schem or layout for the new H+K number 5?

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  14. Someone asked above but didn't get a reply..

    Does this work as is on a Bass? Keen to build it for that purpose to use in a live situation

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    1. Hi Rex, Our Bass player used one of these for years for his Bass.
      Ran his Fender P-Bass straight into a Sans-amp, then into the red box, then from it into the PA.
      Worked fantastic. Fantastic tone.
      I occasionally played fiddle - same story. Piezo pickup from the fiddle to a sans-amp then into the red box then into the PA.
      Similar story with my guitar amp (Tiny 5watt Champ clone). Put it in between the power output and speaker (instead of using the line in, which we did for the Bass & Fiddle).
      Worked equally well.
      Used phantom power since the mixer had it, so we never had to worry about batteries.
      These boxes are worth their weight in gold. Sure saved on wear & tear on our backs not having to lug big amps in & out of whatever venue we performed at.
      A real Godsend for any working musician, especially if you rely on analog gear.

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    2. Awesome thanks for the reply! This will now be going on my too build list, the ever growing list!

      I wonder if it can also be used to "re-amp" a recorded signal. I guess sort of the opposite way it works right now, like I would want to record a clean signal and then feed that signal from an interface into the Red Box and then into an amp?

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    3. Hi Rex! Actually you can (sort of) do that with a red box. Couple things though:

      1st, there were a couple of times that for one reason or another both our Bass player, or I didn't have a sans-amp or other preamp available, so we simply plugged straight into the red box and from it into the PA.
      Had to adjust the EQ a bit on the PA but this actually provided acceptable (emergency!) results for the piezo pickup in my fiddle (would also presumably work with an electrified acoustic guitar, although I haven't tried that) and the Bass. It wasn't ideal but it did work and gave acceptable sound/tone when we didn't have an alternative.
      However this setup doesn't work well for an electric guitar. Definitely need an amp/preamp or active pickups if for one reason or another you need to use just the red box alone to run an electric guitar signal into a PA or other recording device.
      Strangely it was not a huge problem for a Bass guitar with passive pickups although there significant hum. It worked with just the red box inserted into the PA. Must have something to do with the Bass's frequencies.

      2cd: The red box really isn't designed for an instrument level input. It's designed for line level or speaker level signals. Even though it did work with a Bass (in a pinch!) It was horrible using it by itself with an electric guitar with passive pickups. Piezo pickups (like in my fiddle, or an amplified acoustic guitar), can give a strong enough signal level to drive the input on the red box but you have to be able to EQ that signal after it leaves the red box(like with a mixer or other type of preamp) to get a decent sound (tone).

      So; Although you could use it to re-amp a sufficiently strong enough recorded signal, I doubt you would be happy with the results. We did use it in a similar way in a live situation when we didn't have an alternative and made it work with creative use of our mixer but I certainly would have used any other system had I one available at the time.

      Emergency - hook it up and save the gig, for sure!
      Re-amp - You really need a preamp or dedicated re-amping device.

      I hope my experience helps you Rex. Good Luck!
      Will

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  15. thanks for sharing this with us.. nice informative post

    MCX Silver Tips for today

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  16. I assume that since there is an earth lift switch, the jack sockets should be insulated, certainly looks like they are on the original? The xlr socket looks like it is earthed to the box so I guess the earth lift wouldn't do anything if the other sockets aren't insulated.
    Also looking at the manual it seems that 9v is OK but doesn't give the headroom of 12v or 48v, as you would expect.
    By the way excellent work with this it is just what I was looking for but didn't know existed, at least not with the speaker input option.

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    1. Dave, I don't believe that the Red Box classic or even the Mk II had a ground lift switch. The manual (see above under the "Original Info" section for a link to it) or either of the schematics I've seen (RB Classic by Bernard d'Ur, link provided above, or RB MkII by Gottfried Divos) show such a switch or discuss it.
      In fact, in the manual it states in the Troubleshooting section:
      "The Balanced Out signal hums: .... The amp and the mixer/recorder’s earth circuits have formed a ground loop. Activate your amp‘s or the mixer/recorder’s ground lift switch, or use a transformer to galvanically separate the line circuit."
      No mention of a ground lift on the Red Box itself.

      Will

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    2. According to the veto layout, sw1 is ground lift?

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    3. Having just looked online, the red box pro has a ground lift switch but also has a switch to select between Lin or speaker input which this layout doesn't have?

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    4. But having looked further, the Pro version has a transformer in the output - not knowledgeable to know if that is essential to having ground lift or not?

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    5. Well spotted! The schematic by Bernard d'Ur has it but I think it shouldn't be there. Just remove the switch, 470R resistor, 100n cap and connect XLR 1 to ground.
      I've changed the layout.

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    6. Ever wished that you had researched a bit more before posting... I have now found a review of the "classic" that states "On the bottom of the unit there is a ground lift switch which is not labeled." it also says it is not mentioned in the manual. I therefore think that the original layout might well be correct - although I'm not sure whether it is really a ground lift or actually a ground filter since the XLR is still connected to ground but through a resistor and cap in parallel. I'm thinking that it may be done this way to allow phantom power to still work?

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  18. Has anybody built this yet and used it to record into a computer just wondering how it sounds.

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  19. I am in the process of building this.

    just to confirm, is the switch in the layout the combo/4x12 voicing switch?

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    1. It is. There's only one switch in this box,

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    2. Alex, see my revised comment above, there is apparently an internal ground lift that is accessible through a hole in the bottom of the box - not mentioned in the manual but I think this means your previous layout was right

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