QSC MX 1500 NOT 1500a

[Byron Walker]

I have a couple of QSC MX 1500 amps. These seem to be different than the MX
1500a (most likely older). What I'm trying to find out is this. In bridge
mono mode the 1500s I have say on the back they will run at 4 ohms. The
1500a says minimum 8 ohms. Does anybody know what the volume knob settings
on the 1500 should be when set to run bridge mono? I have been unable to
locate a manual for these amps. The MX 1500a looks enough different that I
don't want to assume they are set up the same way.
Thanks

[Phil Allison]

"Byron Walker" <byro...@charter.net> wrote in message
news:ujcdqq1...@corp.supernews.com...

The manuals I have show both amps as rated at 1500 watts into 4 ohms in
bridge mode. However, there are warnings in both manuals that such operation
may cause problems with overheating and current limiting - this is under the
heading of 2 ohm load operation, which is the same as 4 ohms in bridge mode.

The 1500a is quite different to the 1500. The "a" has only half the
number of output transistors!!

Regards, Phil

[Ralph Staub]

We have some MX4000's that also claim 4 ohm stereo (8 bridged) on the
back panel, but 2 (4) ohms in the manual. My understanding is that
because the amp was capable of drawing more than 15 amps from the mains
at lower impedance loads, they were unable to acquire a UL listing with
a standard 15A edison plug without the 4 (8) ohm disclaimer on the back.
QSC wanted to sell an amp everyone could plug in. We have a dozen
MX1500/MX1500a's that we've run to 2 ohms on a regular basis over the
last 12 years. Not a single failure to date.

As far as the bridge settings, Let me dig up the manual at the office
today and I can answer you tonite... I don't recall ever bridging one.
Ours have been built into the same four channel biamped monitor amp
racks since 1990.

Ralph

[ChuxGarage]

Both the MX-1500 and the MX-1500a are fine amps, and you would bridge them in
the same way.

As someone has pointed out, there are less output devices in the 1500a. The
older 1500 is a true dual mono amp. There are two power transformers and two
separate power supplies. The only thing in common between the two channels is
the AC cord. With the newer 1500a the power supply is shared like most other
conventional power amps.

Both amps are quite reliable. I used to own well over 100 of them and my
service problems were few and far betwen. As far as I know they are still in
reliable service. I just sold the whole company, amps and all.

[Ralph Staub]

ChuxGarage wrote:
>
> Both the MX-1500 and the MX-1500a are fine amps, and you would bridge them in
> the same way.

I must correct this, as the manuals for the two amps disagree with your
statement.

MX1500: Standard input to ch.1, inverted input to ch.2, both input gains
matched.

MX1500a: Standard input to ch.1, Switch to "Bridged", ch.2 gain is set
to full (0), and ch.1 gain is used to attenuate.

I do agree with the fine amps part though. ;-)

Ralph

[ChuxGarage]

Ralph, you are right. There is no switch on the 1500.

How soon one forgets....

[Ralph Staub]

ChuxGarage wrote:
>
> How soon one forgets....

Heck, I've got a dozen in service right now and I still had to go to the
manual. ;-)

Ralph

[Byron Walker]

I'd like to thank everyone for their help with this question. I looked
everywhere trying to find a manual for the 1500s. Your input has helped me
figure out how I want to reconfigure the system.
Byron Walker
"Ralph Staub" <mra...@ccconline.net> wrote in message
news:3D38A97B...@ccconline.net...

[hain...@gmail.com]

Could you explain this for new guys? I have two 8 ohlm bass bins I want to hook to this amp bridged. Can you break down how I do it from start to finish and I'm 100% new so please be detailed..

Thanks.

[David L. Martel]

The manual is here.
http://qsccinema.com/files/7013/9567/8978/QSC_MX_1500_2000_InstallersManual.pdf

Dave M.

[giroux...@gmail.com]

tech sheet is here http://audio.manualsonline.com/manuals/mfg/qsc_audio/mx_1500.html?p=2
2x750W @ 2 Ohm channel / 1500W bridge @ 4ohm

[Peter Larsen]

On 06-11-2015 20:52, giroux...@gmail.com wrote:
> On Wednesday, July 17, 2002 at 11:34:52 PM UTC-4, Byron Walker wrote:
>> I have a couple of QSC MX 1500 amps. These seem to be different than the MX
>> 1500a (most likely older). What I'm trying to find out is this. In bridge
>> mono mode the 1500s I have say on the back they will run at 4 ohms. The
>> 1500a says minimum 8 ohms. Does anybody know what the volume knob settings
>> on the 1500 should be when set to run bridge mono? I have been unable to
>> locate a manual for these amps. The MX 1500a looks enough different that I
>> don't want to assume they are set up the same way.

>> Thanks

Usually a bridged amp uses the left channel input and it should have the
left channel flat out and the right channel input turned down if there
are input level controls. Output "hot" is left channel "hot" and output
"return" is right channel "hot". That is how it "usually is".

What you want to know is minimum allowed load in stereo mode, double
that for bridge mode.

QSC is still around ... http://www.qsc.com/

Kind regards

Peter Larsen

[Phil Allison]

Peter Larsen wrote:
>
>
> Usually a bridged amp uses the left channel input and it should have the
> left channel flat out and the right channel input turned down if there
> are input level controls. Output "hot" is left channel "hot" and output
> "return" is right channel "hot". That is how it "usually is".
>
>
>

** Then there are the exceptions where both input level controls have to be turned up full.

The trap being that if one is turned down, the amp still works but the quiet channel overheats something fearful as it acts as a virtual ground for the speaker.

Lotsa current with no voltage swing, very similar to having that channel's output shorted.



.... Phil

[Peter Larsen]

Thank you!

> .... Phil

Kind regards

Peter Larsen

[pasou...@hotmail.com]

Christ ! You're correct for once but it only applies to shitty amplifiers. In decent designs, the Ch1 gain control / attenuator is all that matters. Ch2 can be anywhere. RTFM !

Graham

[Phil Allison]

pasou...@hotmail.com wrote:

> Phil Allison wrote:
>
>
> >
> > ** Then there are the exceptions where both input level controls have to be turned up full.
> >
> > The trap being that if one is turned down, the amp still works but the quiet channel overheats something fearful as it acts as a virtual ground for the speaker.
> >
> > Lotsa current with no voltage swing, very similar to having that channel's output shorted.
> >
>
>

> Christ ! You're correct for once but it only applies to shitty amplifiers.

** Shame those "shitty amplifiers" are made by QSC or are clones of same.

Not that you would have one tiny a clue abut that.


> In decent designs,

** Yawwnnnnnnnnnnnnnnnnnnnn.............


> Graham


** Tell us, did you escape or were you let out ?

I either case, better keep up the meds.



... love, Phil

[acort...@gmail.com]

It should always be in full.

[allthebe...@gmail.com]

On Wednesday, July 17, 2002 at 11:34:52 PM UTC-4, Byron Walker wrote:

https://www.qsc.com/resource-files/productresources/amp/discontinued/mx/mx_1500/q_amp_mx_mx1500_specs.pdf

[Tropical Innovation]

*** I tested the amp on bridged and used the left channel. my volt meter set to AC 150V for testing. shows 60V, I wondered because this is the same voltage of the channel when in stereo mode so I turned up the right volume and there was signal even though the left channel alone was connected at the back. to voltage started raising to over 120 Volts. the manual also says that the amp can output voltages up to 120V when bridged. So both channels should be turned right up in bridge mode.