pre-amp advice

[Rich4349]

While trying to re-integrate my Buttkicker bass shaker into my home stereo, it seemed at first not to work. I use my el cheapo Best Buy PC as a source into my Crown XTi 4000. I slowly turned up the volume, yet was getting nothing out of it. Digging through the settings, I found one channel attenuated -12dB. Resetting that to 0, I started getting some action out of the transducer, but well short of what a 1,600 watt behemoth ought to be making.

https://www.parts-express.com/ButtKicke ... _gEALw_wcB

I turned up the gain slowly until both PC and amp were maxed out. Bass, but not what I remember it making with a previous PC, that I had been using an external DAC with, that died on me a year or so back.

The highest voltage out of the amp I could measure is 13 volts, with a 20-100 sine wave sweep off Youtube. (I realize Youtube videos can have about any dB level, so that is likely not helping.) My audio out of my PC's jack barely makes the meter's needle vibrate, reading well under 1 volt, likely 0.1 volts or less. I don't know why it's so low. According to my calculations, the 2ohm 1,600 watt Buttkicker should handle up to 55 volts.

So my options are...?

1. Get a decent soundcard which *should* boost the volts over 1v?
2. Get a stand alone pre-amp to do the same?
3. Get another DAC?

I haven't run sound for a band yet, and though that's not a likely situation in the foreseeable future, it's not off the table. Would a rack-mounted mic pre-amp work for both my current situation, as well as having one less piece of gear to buy in the future, should I explore that avenue someday?

edit: I see now that I am confusing line out and mic out levels. Be gentle.

https://www.sweetwater.com/store/detail ... one-preamp

I ask for your recommendations for specific gear / brands.

[Bruce Weldy]

I've run straight out of PCs and iPads to my Crowns for testing and while it's not full power it's certainly enough make some noise. Why are you running from your PC anyway? Can't you use the Sub output on your receiver?

What did you connect the butt shaker to?

[Rich4349]

I use my PC because I don't have a receiver. Between the CD player on my old PC, mp3s, YouTube, and downloaded movies, it's been meeting my needs quite acceptably, other than the reduced output into the bass shaker. It's BEEN in a 4'x4' purpose built platform until now; I've taken it out to see why the output has been nil to minimal to low.

I went ahead and picked up this; we'll see if upping the volts to around 2v cracks the case.

Audioengine 32-bit D1 Portable Desktop Headphone Amp and DAC, Preamp, USB/Optical Inputs, Hi-Res Audio Playback (2nd Gen)

https://a.co/d/hb3w3Nq

[jimbo7]

I'm leaning towards your pc settings as the issue. Are you connected to the green "line out"? Try connecting your phone or ipod to the amp and see what happens.

[Seth]

Hmm. Interesting issue, Rich. Using a mini plug to XLR cord, I'm able to run any of my amps into clipping using my PC or Smart Phone.

Your gain is all the way up?

[Rich4349]

I'll have to check on the green output when I get home from work tomorrow.

Yes, the PC gain, YouTube gain, and amp gains were all maxed out. What I just thought of is downloading the same video, then playing it locally through my GOM player. It's a weird little app: it has two volume settings, like a coarse and fine tuning. It's possible it could squeeze out that extra voltage to the Buttkicker needs.

[Rich4349]

I'm leaning towards your pc settings as the issue. Are you connected to the green "line out"? Try connecting your phone or ipod to the amp and see what happens.

I did have the line connected to the green line out.

I downloaded the same youtube sine sweep from the other day, but when played through GOM player, with both player volumes maxed out, I was able to get 36 volts out of the Crown XTi 4000.

Pulling the signal line off the amp input to see what the PC can output from the GOM player, I got .71 v, MUCH more than through Youtube alone, though still only half of what the Crown is rated up to.

I'll try again once the pre-amp arrives later today.

[Rich4349]

Ok, got the headphone amp / preamp / DAC in and hooked up. Playing the same *downloaded* video through the GOM player, I get ~1.1v out of the PC output, and about 74 (!) volts out of the XTi. At 1600 watts at 2 ohm, it SHOULD be making about 54 volts, so I don't know how it's making 74. The yellow and red clipping indicators only flickered very briefly during audio artifacts in that crappy video. Other than those flickers, the green bars were all lit up nice and pretty.

I am a bit puzzled, as WITHOUT the pre-amp, I was getting about .71v out of the PC, but only ~13v out of the Crown. At 1.54x as much input voltage, I would expect the crown to only make 1.54x as much output, unless volts or something else going on isn't a linear function? Somehow 1.54 x 13v isn't equaling 20, it's equaling 74.

[jimbo7]

Try making a sine wave on Audacity (I can't believe I just now thought of that ) and get rid of those crappy compressed youtube vids. I've made/saved all kinds of tones for testing purposes.

[Seth]

I downloaded the same youtube sine sweep...

Link to the video please.

I've always probed voltage at a single frequency, 60Hz sinewave for sub duty.

[Rich4349]

https://youtu.be/CuQ4dI6kmX4

Or this one

https://youtu.be/EaRYK7gFcIc

[Seth]

Run the tests again with a clean 60Hz sine wave. Both scenarios, with and without the pre amp. Test device output voltage and amplifier output voltage and post the results.

https://onlinetonegenerator.com/

[Rich4349]

Run the tests again with a clean 60Hz sine wave. Both scenarios, with and without the pre amp. Test device output voltage and amplifier output voltage and post the results.

https://onlinetonegenerator.com/

I get
0.1v coming out of the PC line out without the pre-amp
1.0v WITH the pre-amp

27v coming out of the Crown without the pre-amp
54v coming out of the Crown with the pre-amp

At least the Crown is making a much saner and in-spec level of power now.

[Grant Bunter]

A few things:

Check in the audio mixer on your PC that output of the player is maxed out if the master volume is.
Line out (green) varies in values. If it follows convention it should be 1V with an impedance between 100 and 600ohms. But it may be different!
Details should be able to be determined if you can work out the chip set of your PC sound card (even if it's on board).
If only one channel is being used (L or R) from your green line out to drive the but kicker, then output in the but kicker may be down 3dB.

Just remember that amplifiers by their simplest definition are voltage multipliers. Because of that, changes in input will raise output by a ratio, but in a mostly linear fashion..

[Rich4349]

Run the tests again with a clean 60Hz sine wave. Both scenarios, with and without the pre amp. Test device output voltage and amplifier output voltage and post the results.

https://onlinetonegenerator.com/

I get
0.1v coming out of the PC line out without the pre-amp
1.0v WITH the pre-amp

27v coming out of the Crown with the pre-amp
54v coming out of the Crown with the pre-amp

At least the Crown is making a much saner and in-spec level of power now.