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Preamping an RH450

Discussion in 'Amps and Cabs [BG]' started by StrangerDanger, Jan 10, 2012.


  1. StrangerDanger

    StrangerDanger Supporting Member

    Jan 3, 2010
    I noticed there is a preamp I/O and switch on my RH450. Anybody tried this? What were your results like?

    Thanks!

    Ive got the GAS for an Alembic preamp. The tone quest continues . . .:bassist:
     
  2. GrowlerBox

    GrowlerBox

    Feb 10, 2010
    Nude Zealand
    The preamp I/O is basically what everyone else calls an effects loop, so by all means plug another preamp into it. The switch is the pre/post EQ switch for the DI; I don't have the circuit block diagram in front of me, but I don't imagine it affects the preamp I/O circuit.
     
  3. silky smoove

    silky smoove Supporting Member

    May 19, 2004
    Seattle, WA
    Pure speculation here, but I would guess that the APM in that head would fight with a lot of external preamps, especially widely voiced ones. Similar to how early versions of the Bergantino IP's DSP was really picky about preamps.

    Again, just speculation on my part.
     
  4. StrangerDanger

    StrangerDanger Supporting Member

    Jan 3, 2010
    Wow I guess thats what happens when you get an amp without the instructions! OK well now I know I have an effects loop and I can use it for a preamp. Thanks GBox.
     
  5. I use an Alembic F-2B into my RH750 when I use my series 1 Alembic bass. There are no problems whatsoever

    Slawie
     
  6. StrangerDanger

    StrangerDanger Supporting Member

    Jan 3, 2010
    Allsum, thanks for the info.
     
  7. GrowlerBox

    GrowlerBox

    Feb 10, 2010
    Nude Zealand
    Yes - I assumed, but without the manual in front of me, didn't want to state outright, that the APM is after the loop (now confirmed). It's going to be a bit hit and miss with external pres -- to me it sounds terrible (choked and nasal) with my Fishman Plat Pro into the return (with DB, at least), and a lot better with that pre into the instrument jack. On the other hand, it's not half bad with my Tone Hammer pedal, although not even as good as the RH's own pre for DB (which is serviceable but not ideal).

    Whatever external pre you wind up with, don't expect to be able to use the same settings you would with any other amp, and be prepared to twiddle, even to what you otherwise consider to be extremes.

    (Oh, and just for the record, the DI post switch taps the signal from the preamp out but does not interrupt it. Pretty standard, I would think).
     
  8. One question, Does anybody know if the High Pass filter around 60 or 70 Hz is built AFTER the pre outs?

    I know this sounds strange, but when I bought the RH750 I measured it and I think (not sure, hence my question) that I got the strong voicing from the pre IN to the speaker out. This means the pre OUT should have the un-filtered signal (but after EQ). I agree what I think I saw was unexpected, but it could make sense if one wants to get ultra-deep lows from the PA. This could be practical for me.

    If none answers I will take my RH750 back home to measure more freq. response... some day.

    Thanks!
     
  9. GrowlerBox

    GrowlerBox

    Feb 10, 2010
    Nude Zealand
    Hey P-tep -- this might be covered in part in the other thread. The voicing you're hearing is the APM, which is after the pre-in, as discussed. I don't know whether there is a true HPF built in to that circuit or not. TCE have told me that they have a HPF set at 15 Hz (presumably in the preamp), but they provided no further details; I suspect that's the -10 or -24 dB point or something, and there's a shallow slope running from something like 70 Hz, but that's a barely educated guess. As I say, whether that's in the preamp or the APM is hard for me to tell. I look forward to your results, if you care to publish them here.

    If nothing else, this amp gives us a lot to talk about, right?!
     

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