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Author Topic: Unknown (to me) internal switch on power amp. What is it?  (Read 12429 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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Cailen Waddell

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Re: Unknown (to me) internal switch on power amp. What is it?
« Reply #10 on: November 20, 2014, 08:00:21 am »


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.

I learned how the sensitivity switch on amps work when mucking about with some older gear....   I had a small mixer connected to an amp to a loudspeaker.  The mixer was at the bleeding edge of clipping.  The amp was no where near.  The amp was appropriately sized to the speaker.  The maximum output voltage of the mixer was not matched to the input sensitivity of the amp.  As such, I was not able to Achieve full tilt boogie because I was unable to provide sufficient input voltage to the amp.   Flipping the switch, adjusting the gain controls a bit, and I was able to provide sufficient voltage to fully take advantage of the amp and speaker.   This was all for fun and not on an actual production system.... But a good learning experience. 


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Ivan Beaver

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Re: Unknown (to me) internal switch on power amp. What is it?
« Reply #11 on: November 20, 2014, 08:08:59 am »

I learned how the sensitivity switch on amps work when mucking about with some older gear....   I had a small mixer connected to an amp to a loudspeaker.  The mixer was at the bleeding edge of clipping.  The amp was no where near.  The amp was appropriately sized to the speaker.  The maximum output voltage of the mixer was not matched to the input sensitivity of the amp.  As such, I was not able to Achieve full tilt boogie because I was unable to provide sufficient input voltage to the amp.   Flipping the switch, adjusting the gain controls a bit, and I was able to provide sufficient voltage to fully take advantage of the amp and speaker.   This was all for fun and not on an actual production system.... But a good learning experience. 


Sent from my iPhone using Tapatalk
Most mixer have MORE than enough output to drive amplifiers to full output-unless it was some non pro mixer or the meters were off etc.

When you say you "adjusted the gain controls a bit"-exactly what does that mean?  Where were they before you changed the gain of the amp?  Where were they after?

What mixer?  What amp?  All of these things matter when trying to help somebody.
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Cailen Waddell

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Re: Unknown (to me) internal switch on power amp. What is it?
« Reply #12 on: November 20, 2014, 08:20:20 am »


Most mixer have MORE than enough output to drive amplifiers to full output-unless it was some non pro mixer or the meters were off etc.

When you say you "adjusted the gain controls a bit"-exactly what does that mean?  Where were they before you changed the gain of the amp?  Where were they after?

What mixer?  What amp?  All of these things matter when trying to help somebody.

Ivan I don't recall the specific brands.... It was more to illustrate the point on sensitivity.  I had the amp gain maxed in the original scenario, and the mixer (which was also probably from the early 90s or late 80s) couldn't provide sufficient output voltage for the amp.  Flipping the sensitivity switch and then backing the amp gain down a couple clicks, allowed me to bring both the mixer and amp into clip at almost the same time. 

Again this wasn't on a system anyone was going to use, this was a room of old parts and pieces.  It's possible I was doing something else wrong in the above scenario.  I am fully aware that an amp provides a fixed level of amplification of the signal with a maximum output voltage (usually ambiguously specified by some mnftrs, as the amount of time that voltage can be sustained matters) and the gain knobs and sensitivity switches simply attenuate the input voltage before amplification, there by controlling how much input voltage is needed to achieve maximum output voltage. 

Of course, I also may be misunderstanding something here....  It happens, and I find I am always learning something new here.


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John Roberts {JR}

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Re: Unknown (to me) internal switch on power amp. What is it?
« Reply #13 on: November 20, 2014, 10:18:31 am »

Most mixers are capable of overdriving most amps, BUT the mixer master section output meters will light up like a Tijuana taxi cab 10 dB or more before mixer clipping. If the amp requires a lot of drive voltage the mixer operator may be uncomfortable creaming the mixer meters to get there.

 JR
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Michael Bartoli

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Re: Unknown (to me) internal switch on power amp. What is it?
« Reply #14 on: November 20, 2014, 12:31:15 pm »

I had a small mixer connected to an amp to a loudspeaker.  The mixer was at the bleeding edge of clipping.  The amp was no where near.

The maximum output voltage of the mixer was not matched to the input sensitivity of the amp.  As such, I was not able to Achieve full tilt boogie because I was unable to provide sufficient input voltage to the amp.   Flipping the switch, adjusting the gain controls a bit, and I was able to provide sufficient voltage to fully take advantage of the amp and speaker.   This was all for fun and not on an actual production system.... But a good learning experience. 

This is essentially the issue I may be having. Little headroom via the mixer, but not clipping, even on loud kick drum hits on the amp. Like you were saying, this is just for learning, so every little bit of knowledge helps.

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Michael Bartoli

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Re: Unknown (to me) internal switch on power amp. What is it?
« Reply #15 on: November 20, 2014, 10:19:01 pm »

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.

Thank you, Ivan. I have been doing more reading as to what you're saying. Yes, I was very off with my analysis. I was confusing supply voltage with what is actually happening at the output stage. Your guidance is appreciated.

What leads me to believe I'm not getting the wattage I'm hoping for is the fact that I am using this amp strictly for low frequency, which takes more watts to drive and is typically less dynamic (in pre-recorded electronic music) than upper frequency lead synth lines, etc. In my experience, it's a lot of sine waves. I don't think it's hitting as hard as it could be, as my subs are fairly efficient, so the claimed 500 watts I >could< be sending them seems lost somehow.
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Tim McCulloch

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Re: Unknown (to me) internal switch on power amp. What is it?
« Reply #16 on: November 21, 2014, 11:34:49 am »

Thank you, Ivan. I have been doing more reading as to what you're saying. Yes, I was very off with my analysis. I was confusing supply voltage with what is actually happening at the output stage. Your guidance is appreciated.

What leads me to believe I'm not getting the wattage I'm hoping for is the fact that I am using this amp strictly for low frequency, which takes more watts to drive and is typically less dynamic (in pre-recorded electronic music) than upper frequency lead synth lines, etc. In my experience, it's a lot of sine waves. I don't think it's hitting as hard as it could be, as my subs are fairly efficient, so the claimed 500 watts I >could< be sending them seems lost somehow.

I think the chances are good that much of the subwoofer's signal is below its reproduction capability and that the consistent application of such signals are heating the woofer's voice coil, raising it's resistance and creating what is called "power compression."
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bradpospisal

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Re: Unknown (to me) internal switch on power amp. What is it?
« Reply #17 on: July 17, 2019, 05:06:39 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

http://elektrotanya.com/ab_international_900a_1100a_922a_9420a.pdf/download.html
7-17-2019 . i dont know how to post so ill try it this way . contact me at bradpospisal@gmail.com . i have the same question for the ab 1100a and 900a . i plainly see 1 switch at the input on my 1100a,s and 2 switches in my ab 900a,s . i dont need technical details and i already have the service manual . i wouldnt know how to read them if i had to . all i need to know is what position these switches should be in . im getting barley any sound from my 1100a,s or 900a,s . my 600lx.s work great . im trying to use home preamps . everything from adcom to marantz . ive ordered a cleanbox pro to boost the voltage output from my preamps and probably need a pro mixer . but regardless i need to know what position these switches should be in both stereo and mono .i can not see any switch for changing the input voltage but some of you said there there . i need in simple terms where all these internal switches should be . ive bought them from different sellers and all the internal switches i can plainly see are in different positions . thanks for any help .
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Tim McCulloch

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Re: Unknown (to me) internal switch on power amp. What is it?
« Reply #18 on: July 17, 2019, 09:10:29 am »

7-17-2019 . i dont know how to post so ill try it this way . contact me at bradpospisal@gmail.com . i have the same question for the ab 1100a and 900a . i plainly see 1 switch at the input on my 1100a,s and 2 switches in my ab 900a,s . i dont need technical details and i already have the service manual . i wouldnt know how to read them if i had to . all i need to know is what position these switches should be in . im getting barley any sound from my 1100a,s or 900a,s . my 600lx.s work great . im trying to use home preamps . everything from adcom to marantz . ive ordered a cleanbox pro to boost the voltage output from my preamps and probably need a pro mixer . but regardless i need to know what position these switches should be in both stereo and mono .i can not see any switch for changing the input voltage but some of you said there there . i need in simple terms where all these internal switches should be . ive bought them from different sellers and all the internal switches i can plainly see are in different positions . thanks for any help .

Good luck.  Stu hasn't logged into the forums since Sept 2018.

Mono is "bridged mono."  As for input sensitivity switches on AB International amps... it's been too long since we owned any for me to recall but a search shows it to be 1.7v for full rated output without mention of it being changeable.
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"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

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Re: Unknown (to me) internal switch on power amp. What is it?
« Reply #18 on: July 17, 2019, 09:10:29 am »


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