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  1. #1

    "Line Level" Mackie to Stereo Receiver

    heyyaaa-

    Well, I've been going out of my Mackie (mono main) and into a keyboard amp. for a few years now using it as my monitoring system...which has an unbelievably bad sound. I tried going from the Mackies "tape outputs" which are phono style "RCA" connectors, and into my Harmon Kardon residential type AVR receiver. Unfortunately...it doesn't take much for the AVR to shut itself off, a protective circuit breaker of sorts no doubt. Even more unfortunately is that the sound i had for a few moments was beautiful in comparison with my keyboard amp.

    So, there must be a way to measure the Amperage (I think that's what I need to know) that is flowing through the various interworkings of my equipment. And...if there is too much in the way of voltage signal coming from the Mackie out, can I put some sort of resister there to taper the signal to an acceptable amount for the Harmon Kardon?

    I know that I really need to go spend $100 on some cheap powered monitors, and that'll happen, but I'd love nothing more than to understand more about "what's under the hood" here. If I've totally butchered all understanding here about signal, feel free to reffer me to any good tutorials you may know of. THANKS ALL!

    J

  2. #2
    Hi

    The first thing you need to establish is what signal level the line out has..typically it's 0db and around 600millivolts. Next determine the correct acceptable signal level that your keyboard amp wants..it will probably be a lot lower but if you have specs you can find out.

    Then what you need is a simple attenuation pad that will drop the signal level to one that the KB amp finds acceptable.

    To make a attenuation pad ..use this link

    http://www.uneeda-audio.com/pads/

    Chris

  3. #3
    Thanks Chris-

    My Mackie's outputs are 120 ohms. The Harmon Kardon powers 50 watts @ 8 ohms. Watts, Ohms, Volts and Amps are still swirling around in my head right now...along with impedance. I've gone through the plumbing analogy a few times, which makes me believe that the Mackie signal has more resistance at 120 ohms, and the Harmon Kardon is actually starving for more signal because it offers less resistance @ 8 ohms. So it isn't powering off because its getting too much from the Mackie, its working too hard to try to pull more from the Mackie. Am I even close? THANK YOU!!!!!!!

    J

  4. #4
    Nope.

    First off, the HK amp's 8-ohm output and the mixer's 120-ohm output are unrelated, they occur at entirely different points in the circuit.

    Second, forget anything you've heard about impedance "matching." The HK amp's actual output impedance is probably .01 ohm or less and its input impedance is probably 10,000 (10K) ohms or more. Connecting a 120-ohm mixer output to a 10K amp input and a .01 ohm amp output to an 8-ohm speaker is normal practice. The mixer probably couldn't drive an actual 120-ohm load and the amp certainly couldn't drive a .01-ohm speaker.

    That doesn't mean load impedances are irrelevant. What speakers are you connecting to the HK amp? Why doesn't it shut down in normal residential use, are you using different speakers then? If you only got "a few moments" out of it, something is seriously wrong with the speaker load. (You're not trying to parallel amp outputs are you?)

    When you talk about a "keyboard amp" - does that mean an amp with a speaker, like a guitar amp? What's wrong with the sound, is it distorted, or is the tonal quality bad? What happens when you run it at a very low sound level?

    If you are serious about this studio business, you are right to want to learn about the nuts and bolts! A person who knows the ropes can get better performance out of cheap equipment than somebody who doesn't can get out of expensive equipiment.

    The best all-around book I know is "Sound Reinforcement Handbook" by Davis & Jones, which may not be in print but can be found on ebay. This is aimed at live-sound people; maybe somebody here who has more studio experience than I can recommend a studio-oriented book.
    Last edited by karl eilers; 28th Dec 2009 at 17:09.

  5. #5
    Thanks Karl-

    First to answer your questions:

    I am using Advent Legacy 2 speakers, here are the specs:

    Frequency response: 42 Hz - 23 kHz, +/- 3 dB.
    Impedance (nominal): 6 ohms (minimum): 4 ohms.
    Power handling (peak): 500 watts. (RMS) 100 watts.
    Sensitivity: 90 dB (2.8V @ 1 meter).
    Crossover frequency: 2000 Hz.
    Resonance: 51 Hz +/- 5 Hz.
    Harmonic distortion: Less than 1% above 50 Hz @ 1 watt; 3% @ 100 Hz;
    Less than 1% above 100 Hz @ 10 watts
    Tweeter dispersion: Less than +/- 1 dB (variance 30 deg. V or H to 13kHz).
    Frequency range (low): 30 Hz -8 dB. (high) 23 kHz -3 dB.
    Tweeter: 1" ferrofluid-filled parabolic soft dome.
    Woofer: 10" high excursion; aluminum coil form.


    The keyboard amp. is a Hartke 200W w/4 ohm speaker out.

    I have used the Harmon Kardon (HK) for years with the same Advent speakers, and although the stereo never put out much volume, it has always worked fine. I simply ran out from the Mackies phono style tape outs into the tape input on the HK. If I keep the level very low, say conversationesque 50-60dB or so, it didn't cut out. But as soon as I tried to get a touch more, it cut out.

    As for not wanting to always use the keyboard amp, there are several reasons. First, yes the sound is not great, and although the amp has a 7 channel EQ, the sound of a recording, say trio Bass/Guit/Drums, just gets muddy through the keyboard amp. When I switch drivers in my apple so that I can play the same track through the USB connected "sound sticks," the sound is much clearer and balanced. The best way I can think to relate the difference is that the Hartke sounds as though it's putting on reverb that's muddying up the sound. Also, being that this is in my own cramped residential studio, that Hartke is not dedicated as a "monitor," therefore everytime I go to playback I need to remember to hit the faders to avoid one of those feedback loops that really scares the snot out of my half/awake 4AM self.

    I will check into "Sound Reinforcement" (I was recommended one overseen by Yamaha I think, maybe they're the same). I'm all about hittin' the books, just would like to get the right ones. Thank you so much.

    Connecting a 120-ohm mixer output to a 10K amp input and a .01 ohm amp output to an 8-ohm speaker is normal practice. The mixer probably couldn't drive an actual 120-ohm load and the amp certainly couldn't drive a .01-ohm speaker.


    With the above in mind...there is no reason I shouldn't be able to plug the HK into the Mackie then?

  6. #6
    Well that was weird, it wouldn't save. Try again, maybe it will save twice.

    "With the above in mind..." Right. The RCA outputs of the mixer and the RCA inputs of the HK are compatible. You are connecting the HK to the Advent speakers then, in a normal stereo hookup?

    Just thought of something - off chance, we may have some oscillation here. Can you get more noise out of the HK when it's used as a receiver? Try turning its treble control all the way down and see if it still cuts out.

    The Davis/Jones book was written for Yamaha, so yes, this is the one.

  7. #7
    Ok- Oscillation occuring in my house current or between the Mackie and the HK? I did as you suggested, and the first thing I discovered was that one of the woofers foam surround was completely gone, and the cap was dented in...so I took that one out of the equation. So at this point, I have one Advent Leg 2 coming out of the left main out of the HK, with a CD player running analog (phono) into the HK. The Mackie is plugged in to the HK as well via the same tape out phono jack as before.

    -10dB on the HK...both work fine. At this point I'm toggling back and forth from the source selction on the HK, increasing the dB 5 at a time, now on 0dB and both are working fine. All that I've changed since yesterday was taking out the broken speaker, and I VERY SLIGHTLY adjusted the output levels in Cubase, the software I was using to play through the Mackie. There was a slight clipping in the Cubase, and I had to reduce one of the track faders as well as the main a touch. Could that have done it? The signal from Cubase was crappy, overdriven, distorted and the HK senses that and sais "no thanks?" I also then blasted a track from itunes. Went up to 0dB....no problem. As a side, I did turn the treble control on the HK all the way down as originally suggested, and noticed that neither the bass or treble, or the balance knobs on the HK were working. I riffled through the preset speaker modes on the HK (surround Logic Theatre...etc) still no Treb/Bass/Balance control. Perhaps they are disabled if not both speakers are hooked up? Although I figure if I only have my left speaker hooked up, and I turn the balance knob all the way to Right, I should hear nothing. I tried adjusting the pan in a Cubase track as well, but still everything seems locked into mono. I just played back from Cubase again, and adjusted every track in the Mixer includeing the main up until it was clipping like crazy, the HK was on o dB....nothing shut off. It was the blown woofer wasn't it?

    THANKS!!!!!!!!!!! J

  8. #8

    Goog Laugh

    Yeah....forget everything. When I was running one speaker at a time, the other speaker cables were danging...and every so often touching. This apparently causes the HK to short out. Well, since I've come this far, would anyone mind telling me why crossing the speaker wires shorts out the system? Is it essentially just like tripping a circuit in my home? It's a safety catch cause the HK recognizes that the resistance is MIA and there is fear of fire....or melting other components of the HK? Thanks
    J

  9. #9
    Well, further on this "stiff voltage source" thing... Yes, it's like tripping the breaker in your home. Very much like that. Here's something of a tech explanation, which you can skip if you find your eyes glazing over.

    Let's forget about impedance and call it resistance for the time being. Impedance is "complicated" resistance, with phase and magnitude anomalies at various frequencies, and it gets simpler to think about if we pretend the speaker is a pure resistive load.

    If you have a stiff voltage source, the lower the load (in this case speaker) resistance is, the more current flows. "Resistance" means "resistance to the flow of current," so less resistance, more current. No mystery.

    With progressively lower load resistances, the point will be reached where you're demanding so much current from the amplifier that it A) burns up, or if it's properly designed it B) shuts down. When wires touch, that's the lowest possible resistance; you only have the resistance of the wires themselves in the circuit. Maybe 1/10th ohm or less. Amp has hernia.

    This is also why it's not okay to connect an arbitrarily low-impedance speaker load, but is okay to connect an arbitrarily high-impedance load or no load at all. Just as, it's okay not to plug anything into an AC outlet.

    And it's why, the lower the speaker load impedance, the more power goes into the speaker, until you reach the point where the amp gives up. Most home stereo amps are okay down to 4 ohms, no lower.

    This pretty much solves the problem, so we can forget about oscillation. However, I'd get those speakers repaired. It's possible the capacitor is shorted, and that would upset the load impedance. If the load impedance is screwy enough, almost any consumer-type amp will go into oscillation. By itself, no matter what input it's hooked up to.

  10. #10
    Well, it's been a few months, and I've only blown up one set of speakers (although this was at my folks house and I doubt they'll notice). I just came across a few monitor type speakers today. A pair of Auratone Sound Cubes and a pair of Stellars. At the moment I am using the AVR 210 as my receiver for both my computer audio (media players as well as Logic/Cubase MIDI etc.) and a separate CDR as well as a record player. I have one Legacy Advent speaker with a 10" and a 1" wired as the center speaker, then the Auratones as the R and L. The Stellars are run from the surround L and R, and the AVR 210 receiver is in Dolby Pro Logic Format which gives a normal signal to the surround speakers. The sound is really nice. The AVR only sends 40 Watts per channel, however, which is fine on most ocassions, but every now and then I'd like to have the headroom to nudge it up a touch. Any recommendatins on amping this signal? There are Phono style inputs in the back that are supposed to be used for pre amps for the individual speaker channels, although I don't know where to find such a thing.

    sleep well-

    j

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