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Author Topic: Unknown (to me) internal switch on power amp. What is it?  (Read 12531 times)

Michael Bartoli

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Unknown (to me) internal switch on power amp. What is it?
« on: November 19, 2014, 04:30:18 pm »

Hi all. I own an AB International 1100a power amp and have used it for many shows.

Most of the time, it pushes a pair of 8 ohm subs (mono signal, 1 per channel) in smaller rooms, where the 525RMS is more than enough to fill out the space. I'm happy with it, but sometimes am left wanting a bit more for slightly larger rooms. I'm aware of the "enough rig for the gig" mentality and will be upgrading my system next season with an additional set of subs and a matching QSC PLX amp to push them. My issue is just finishing up the year with the gear I've got and maximizing it to its full potential.

I've been doing a bit of reading about AB Int. amps and see that many of them in the Precedent series (which is the series mine is) have internally switchable input sensitivity switches. The 1100a isn't listed as having this switch in their online manual (found here: http://www.abamps.com/pdfs/900a-1100a-9220a-9420a-man.pdf ), but I love cleaning out amp internals and poking around, so I opened 'er up anyways. What I found confused me a bit.

Near the inputs, on the inside, there as a 2-way toggle switch.

Position 1 = UP Position 2 = DOWN. That's all it says. Reading that other AB amps have a .775v, 1.0v, and 1.5v switch on the inside means the switch I was hoping to find would have been 3 way.

It appears to be in line with a Ground/Lift switch located on the back of the amp, but I don't understand the redundancy if that's what it affects. Why put a switch on the outside AND the inside?


Is anyone familiar enough with this family of older tech. to teach me what it is I'm looking at? My only theory is that being as this channel is physically on the top side of the amp, it is switched to "UP" to regulate some sort of temperature control for the fan. I can't exactly get to (or see) what the switch is currently set at on the other channel of the amp, as I would have to disassemble a lot of components to get to it, but it sits a couple inches directly below the pictures I've attached here.

I appreciate any help you could lend me.
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g'bye, Dick Rees

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Re: Unknown (to me) internal switch on power amp. What is it?
« Reply #1 on: November 19, 2014, 04:54:52 pm »

Your amp will always and only put out its rated power.  That will not change.  The input sensitivity selector simply lets you match the amp to the source feeding it.  The higher the sensitivity setting, the more voltage required to drive the amp to its rated output.

Others will clarify, no doubt.
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Steve M Smith

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Re: Unknown (to me) internal switch on power amp. What is it?
« Reply #2 on: November 19, 2014, 05:05:29 pm »

The higher the sensitivity setting, the more voltage required to drive the amp to its rated output.

I know what you mean, but that statement could be taken as meaning the opposite of its intent.


Steve.
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Douglas R. Allen

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Re: Unknown (to me) internal switch on power amp. What is it?
« Reply #3 on: November 19, 2014, 05:18:49 pm »

Only guessing but could it change pin 2 and 3 around for Positive input? Its old enough when pin 3 was used as positive input by some amp manufactures. I had a AB International 900a Precedent series and it was a great amp but I don't remember that switch in there. I sent this question to Andy and maybe he will chime in with an answer.
Douglas R. Allen
« Last Edit: November 19, 2014, 05:22:47 pm by Douglas R. Allen »
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John Roberts {JR}

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Re: Unknown (to me) internal switch on power amp. What is it?
« Reply #4 on: November 19, 2014, 07:16:53 pm »

I won't guess... But you can try to trace out the circuitry it is connected to. Not easy if you can only see the top of the PCB but probing with a VOM to see what changes when switched, will help ID what it is connected to and doing.

JR 
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Stu McDoniel

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Re: Unknown (to me) internal switch on power amp. What is it?
« Reply #5 on: November 19, 2014, 10:03:13 pm »

Hi all. I own an AB International 1100a power amp and have used it for many shows.

Most of the time, it pushes a pair of 8 ohm subs (mono signal, 1 per channel) in smaller rooms, where the 525RMS is more than enough to fill out the space. I'm happy with it, but sometimes am left wanting a bit more for slightly larger rooms. I'm aware of the "enough rig for the gig" mentality and will be upgrading my system next season with an additional set of subs and a matching QSC PLX amp to push them. My issue is just finishing up the year with the gear I've got and maximizing it to its full potential.

I've been doing a bit of reading about AB Int. amps and see that many of them in the Precedent series (which is the series mine is) have internally switchable input sensitivity switches. The 1100a isn't listed as having this switch in their online manual (found here: http://www.abamps.com/pdfs/900a-1100a-9220a-9420a-man.pdf ), but I love cleaning out amp internals and poking around, so I opened 'er up anyways. What I found confused me a bit.

Near the inputs, on the inside, there as a 2-way toggle switch.

Position 1 = UP Position 2 = DOWN. That's all it says. Reading that other AB amps have a .775v, 1.0v, and 1.5v switch on the inside means the switch I was hoping to find would have been 3 way.

It appears to be in line with a Ground/Lift switch located on the back of the amp, but I don't understand the redundancy if that's what it affects. Why put a switch on the outside AND the inside?


Is anyone familiar enough with this family of older tech. to teach me what it is I'm looking at? My only theory is that being as this channel is physically on the top side of the amp, it is switched to "UP" to regulate some sort of temperature control for the fan. I can't exactly get to (or see) what the switch is currently set at on the other channel of the amp, as I would have to disassemble a lot of components to get to it, but it sits a couple inches directly below the pictures I've attached here.

I appreciate any help you could lend me.
I found the service manual and and it appears to be MONO/DUAL switch. Bridge or Stereo.
Go to this link and click download pdf.
Page 58 and zoom in is schematic and block diagragm is page 59

http://elektrotanya.com/ab_international_900a_1100a_922a_9420a.pdf/download.html
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Tim Perry

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Re: Unknown (to me) internal switch on power amp. What is it?
« Reply #6 on: November 19, 2014, 10:16:59 pm »

Micheal. I believe the internal switches are the "Soft clip" circuit. 

When being serviced, one would turn the clippers off when running a sine wave into a dummy load to check operation.

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Michael Bartoli

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Re: Unknown (to me) internal switch on power amp. What is it?
« Reply #7 on: November 20, 2014, 12:09:43 am »

I found the service manual and and it appears to be MONO/DUAL switch. Bridge or Stereo.
Go to this link and click download pdf.
Page 58 and zoom in is schematic and block diagragm is page 59


Stu, you saved the day! This service manual is leagues more informative than the owners manual (which I always found was lacking in the first place)! On page 27 of this manual, it answers my question.


Gotta love modular designs!

And then I scroll down one more page and BAM!
It's as if they wrote a page specifically for me. So due to you answering my original post, you've helped me find what I originally set out to do beforehand. Many thanks!
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Michael Bartoli

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Re: Unknown (to me) internal switch on power amp. What is it?
« Reply #8 on: November 20, 2014, 12:29:03 am »

Your amp will always and only put out its rated power.  That will not change.  The input sensitivity selector simply lets you match the amp to the source feeding it.  The higher the sensitivity setting, the more voltage required to drive the amp to its rated output.

Others will clarify, no doubt.

Correct, and I am aware of this, but still learning it's true meaning in the field. A mixer fed to a system controller (2-in/6-out) fed to an amp doesn't change voltage depending on the volume, does it? Voltage should be constant? I guess curiosity just got the better of me after reading some manuals online. Sometimes I feel like I'm not getting 500 watts a side out of the old girl while having perfectly fine levels on the top end of things. Probably means I need to add to the more amps and cabs to the equation, eh?
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Ivan Beaver

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Re: Unknown (to me) internal switch on power amp. What is it?
« Reply #9 on: November 20, 2014, 07:30:52 am »

Correct, and I am aware of this, but still learning it's true meaning in the field. A mixer fed to a system controller (2-in/6-out) fed to an amp doesn't change voltage depending on the volume, does it? Voltage should be constant? I guess curiosity just got the better of me after reading some manuals online. Sometimes I feel like I'm not getting 500 watts a side out of the old girl while having perfectly fine levels on the top end of things. Probably means I need to add to the more amps and cabs to the equation, eh?
NO.

As you turn the level up the voltage of the signal everywhere after it goes up.

What "voltage" were you referring to that "stays constant"?  The only thing that stays constant is the power supply voltages in the units.

What makes you feel you aren't getting the power you think you are?

Music is VERY dynamic and in many/most cases the voltages you read across the speaker are less than 1/10th of the peak voltages going to the speaker.

So with 500 watt peaks, you "average level" could easily be in the 25 watt or less range.
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Ivan Beaver
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Re: Unknown (to me) internal switch on power amp. What is it?
« Reply #9 on: November 20, 2014, 07:30:52 am »


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