Ashamed to ask

Is this amp OK?
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Bones
Posts: 361
Joined: Wed Dec 24, 2008 4:22 pm

Ashamed to ask

#1 Post by Bones »

...but how do i monitor the voltage from my amplifier?

SeisTres
Posts: 2688
Joined: Fri Apr 24, 2009 3:53 am
Location: Dallas, tx

Re: Ashamed to ask

#2 Post by SeisTres »

Just like daisy chaining cabs, just parallel the voltmeter. Basically, just attach the voltmeter to the banana plugs on the back of the amp.

EDIT: and just in case, yes, you can measure without the speaker being hooked up.
Built:6 t39, t18, 4 Jack10, 2 autotuba, 2 SLA,2 wedge, 2 TT, 2 Tritrix, curved sla, 2 otop212, 2 SLA pros, Ported 8" sub, 2 ported 210, dual ported 8" sub

petegt
Posts: 155
Joined: Sun Nov 01, 2009 4:35 pm
Location: Norfolk, United Kingdom

Re: Ashamed to ask

#3 Post by petegt »

SeisTres wrote:
EDIT: and just in case, yes, you can measure without the speaker being hooked up.
I wouldn't recommend running the amp up without a load/speaker. Im sure it can be done safely on most amps, Iv just had an amp blow up because of it.

One time I blew one side of my lem 2.420 when i was measuring the voltage@50hz to set my limiters. Something started oscillating inside the amp and it blew 3 ouput transistors.
2 TAT 16" loaded with JBL GTO 804 + V plate
Tannoy Precision 8D monitors, Tannoy System 800 monitors
Minidsp 2x4, Berry DCX2496, Lem 420 amplifier

To do:
17" Autotuba with JBL GTO 1002D 10"

Bruce Weldy
Posts: 8543
Joined: Fri Nov 27, 2009 11:37 am
Location: New Braunfels, TX

Re: Ashamed to ask

#4 Post by Bruce Weldy »

hmmm.....never heard of that happening on a solid-state amplifier. Was that a tube amp that blew up on you?

6 - T39 3012LF
4 - OT12 2512
1 - T24
1 - SLA Pro
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

SeisTres
Posts: 2688
Joined: Fri Apr 24, 2009 3:53 am
Location: Dallas, tx

Re: Ashamed to ask

#5 Post by SeisTres »

petegt wrote:
One time I blew one side of my lem 2.420 when i was measuring the voltage@50hz to set my limiters. Something started oscillating inside the amp and it blew 3 ouput transistors.
Is that a tube amp? googled it and really couldn't find anything save a few things about a transformer and then univox came up.
Built:6 t39, t18, 4 Jack10, 2 autotuba, 2 SLA,2 wedge, 2 TT, 2 Tritrix, curved sla, 2 otop212, 2 SLA pros, Ported 8" sub, 2 ported 210, dual ported 8" sub

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Rune Bivrin
Posts: 521
Joined: Tue Aug 19, 2008 5:42 pm
Location: Stockholm, Sweden

Re: Ashamed to ask

#6 Post by Rune Bivrin »

I think the biggest risk is that you either accidentally cross the probes when measuring (which will short the output) or have the meter set to measuring amps. An amp that blows because there's nothing plugged in deserves to blow. It certainly isn't something I'd like to use in a mobile setup...

But this inspired me to build a banana to speakon adapter. Bananas go in the meter, and then just plug the Speakon into the output of the amp or the daisy socket on a speaker.
In build order:
O12 with no tweeter.
3 x WedgeHorns.
2 x Jack 10 without tweeters.
2 x DR250.
2 x 16" T39
1 x Tuba 24
2 x SLA Pro (sort of...)

petegt
Posts: 155
Joined: Sun Nov 01, 2009 4:35 pm
Location: Norfolk, United Kingdom

Re: Ashamed to ask

#7 Post by petegt »

SeisTres wrote:
petegt wrote:
One time I blew one side of my lem 2.420 when i was measuring the voltage@50hz to set my limiters. Something started oscillating inside the amp and it blew 3 ouput transistors.
Is that a tube amp? googled it and really couldn't find anything save a few things about a transformer and then univox came up.
No solid state. So hard to find info on this amp. 8 ohms RMS 2X240W 4 ohms 2X420W RMS with 2 toroidal transformers http://www.wikizic.org/LEM-2-420/gallery-1.htm.I'd never heard of it happening before. I did use banana plugs into the binding posts so no danger of shorting. Maybe just bad luck.
2 TAT 16" loaded with JBL GTO 804 + V plate
Tannoy Precision 8D monitors, Tannoy System 800 monitors
Minidsp 2x4, Berry DCX2496, Lem 420 amplifier

To do:
17" Autotuba with JBL GTO 1002D 10"

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Bill Fitzmaurice
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Joined: Tue May 02, 2006 5:59 pm

Re: Ashamed to ask

#8 Post by Bill Fitzmaurice »

petegt wrote:Maybe just bad luck.
Probably. With no load there's nothing to cause any oscillation. The other possibility is the meter. Meters typically have very high impedance, so they're essentially not a load, but you never know.

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