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Neil 25th September 2001 11:32 AM

Im a novice to electronics, but I purchased some full-range, bi-amplifeid "plate" amplifiers that I want to hook up to my speaker project. They came out of some powered Alesis loudspeakers.

Basically, I have this question: On the back of the AC plug recepticle, there is a metal prong with a "ground" symbol below it. Where do I attach this ground to? The metal of the amp itself, or..?

I cannot recieve support from the mfg. with this question.
Other than that, the only other connection of question is that the leads from the amp to go to the speaker drivers are not labeled as +/-...does it matter, as long as I kep the scheme consistant?

Also, I tried running the amps (made music) for three minutes without connecting this ground wire. I turned them off because I smelled a faint electronics burning smell from the power supply. Wasnt sure if this was just a normal break-in smell or overheating, but nothing appeared to blow. Any damage likely as a result of not grounding the AC plug recepticle itself?

I appreciate any help,

Nelson Pass 25th September 2001 06:10 PM

Probably had nothing to do with the grounding, and
there's a good chance that it's just the "new amp smell".

I would recommend attaching the AC earth ground pin to
the heat sink through a power thermistor, such as
the Digikey # KC006L-ND. You can of course make the
connection directly, but the thermistor gives some
ground loop reduction while offering protection from
AC primary leakage.

Neil 26th September 2001 07:33 AM

Grounding required, or optional then?
Hey Thanks Nelson!

Well I wasn't expecting to get help from someone like you. Is it required* electrically that I make some type of ground connection from the AC, or will it just improve things sonically?

(I know I should start studying up on this stuff on my own.)

BTW, here are the specs on my amp: Does this change the Digikey part# you would recommend to me?

Low Frequency Driver: 6.5" non-woven carbon fiber with Santoprene surround and dual magnet shielded configuration

High Frequency Driver: 1" silk dome with medium viscosity ferrofluid coolant and dual magnet shielded configuration

Crossover: 1500Hz, 8th-order, 48dB/octave filters

Input Impedance: 20k_ balanced, 10k_ unbalanced

LF Filter: 2nd order, "optimal Q" high pass, +1dB boost@50Hz

LF Amplifier: 75 watts, 8_ load

LF Amp Distortion:less than 0.03% thd @ 30w
lf amp slew rate:<>19V/µsec

LF Amp S/N Ratio: >110dB, ref. 60W @ 8_, A-wtg., 1kHz

HF Amplifier: 25 watts, 4_ load

HF Amp Distortion:less than 0.06% thd @ rated power

lf amp slew rate less than 9V/µsec

HF Amp S/N Ratio: >112dB @ rated output

Frequency Range: 38 Hz - 23.5 kHz (-10dB point)

Connectors: Combination XLR-1/4" jack with input level control

Dimensions: (WxHxD) 8.5"x15"x9.75" (381mm x 216mm x 248mm)

Weight: 19.5 lbs. (8.9kg) each.

Neil 26th September 2001 07:51 AM

Heres what someone recommended in order to determine the polarity of unmarked speaker taps on an amplifier. Does it sound like a good approach, or is it even necessary to do this at all?

Seeing these aren't marked and 1 is + from the amp the other will be at chassis ground. Why not just take a DMM or better yet a speaker and test them back to chassis ground. One should show ac present and the other nothing? in other words hook 1 wire from the amp to the + teminal on the driver, then from the drivers - terminal run a wire to chassis ground. then swap one wire from the amp at a time. This should tell you very quickly which is which.

Super 26th September 2001 12:09 PM

For every driver I've handled, the + has been on the right, and the - on the left. Not sure if this holds true in your case though, but its more than likely.

Also, this connection DOES matter. If not connected properly, your output will suffer dramatically, particularly in the bass region. There are few exceptions to this, although the connections are reversed sometimes in subwoofers, for push/pull alignments.

GRollins 26th September 2001 04:37 PM

Are you trying to determine the polarity of the connections for a driver or for an amp?
If it's a driver, hook a battery (something like a 6 or 9 volt will do) to the terminals. One polarity will cause the cone to jump backwards, the other forwards. When the driver jumps forwards, the + terminal of the battery is connected to the + terminal of the driver.
If it's an amp that you're trying to determine the polarity of, don't even turn it on. For most amplifier topologies the - terminal will be connected to ground. Simply use a meter to check continuity from the output terminals to a known ground. (You may have to pull the cover to get to a clean ground, as paint doesn't conduct well, and you won't want to scratch off the paint to get to bare metal. Ditto for anodized aluminum.)


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