polarity of vintage JBL power amps

[pyonc]

Hi friends,According to JBL Technical Notes, titled Polarity Conventions of JBL Professional Transducers and Systems,
it says as follows:
"The majority of JBL transducers at that time exhibited inward motion ofthe cone when a positive-going signal was applied to the red input terminal, and this convention was, in many cases, carried over int loudspeaker systems as well...Beginning in the early 1990s, JBL began an orderly transition to the positive-to-red standard in accordance with practices recommended by the AES...

Now, this is my question: what about the polarity of the input jacks of JBL's vintage power amps such as SE400S and SE408S, both produced in the 1960s? They're still much sought after among JBL fans. Does the negative polarity also apply to those vintage amps, too? In other words, is the Red input jack of amp actually (-), and Black (+) just like JBL transducers?
I'm curious as I use them in bi-amped mode for my 4343 at the moment. 4343 transducers and cone drivers are all negative in polarity. Thanks for your comment and feedback in advance.

[hjames]

As long as you use them consistently, all black jacks as NEG and all red jacks as POS, you should be fine.
presuming that they are all amps of the same era, of the same series and have not been dinked with internally.

You can start with the basics and work your testing up to confirm they are consistent.

For instance, you can take a unmounted speaker and hook the amps up, one at a time, and test (at low volumes)
with a simple signal (short the input, battery test, etc) and make sure the speaker moved the same way with
all of your amps - all should work exactly the same on your single driver test.
For instance, they should all move out (or in) when you connect the battery with a specific polarity.




Hi friends,According to JBL Technical Notes, titled Polarity Conventions of JBL Professional Transducers and Systems,
it says as follows:
"The majority of JBL transducers at that time exhibited inward motion ofthe cone when a positive-going signal was applied to the red input terminal, and this convention was, in many cases, carried over int loudspeaker systems as well...Beginning in the early 1990s, JBL began an orderly transition to the positive-to-red standard in accordance with practices recommended by the AES...

Now, this is my question: what about the polarity of the input jacks of JBL's vintage power amps such as SE400S and SE408S, both produced in the 1960s? They're still much sought after among JBL fans. Does the negative polarity also apply to those vintage amps, too? In other words, is the Red input jack of amp actually (-), and Black (+) just like JBL transducers?
I'm curious as I use them in bi-amped mode for my 4343 at the moment. 4343 transducers and cone drivers are all negative in polarity. Thanks for your comment and feedback in advance.

[pyonc]

As long as you use them consistently, all black jacks as NEG and all red jacks as POS, you should be fine.
presuming that they are all amps of the same era, of the same series and have not been dinked with internally.

You can start with the basics and work your testing up to confirm they are consistent.

For instance, you can take a unmounted speaker and hook the amps up, one at a time, and test (at low volumes)
with a simple signal (short the input, battery test, etc) and make sure the speaker moved the same way with
all of your amps - all should work exactly the same on your single driver test.
For instance, they should all move out (or in) when you connect the battery with a specific polarity.

Thanks for your kind comment. In my case, LF for Crown DC 300 II from the 1990s, MF/HF for JBL SE408S from the 1960s.
I've no problem with Crown in terms of input jack polarity, while I'm not so sure about SE408s, though. At the moment, I've got SE408S leads hooked up just like Crown, namely Red for Red, Blk for Blk.

[hjames]

Thanks for your kind comment. In my case, LF for Crown DC 300 II from the 1990s, MF/HF for JBL SE408S from the 1960s.
I've no problem with Crown in terms of input jack polarity, while I'm not so sure about SE408s, though. At the moment, I've got SE408S leads hooked up just like Crown, namely Red for Red, Blk for Blk.

So like I said, if you have different amps, you test them as I explained to be sure they respond the same to the same signal -
the idea is to make sure either NONE of them invert your signal, or that ALL of them invert your signal.

For instance, if you find out the Crown amp inverts compared to the JBL amp,
you would just reverse speaker Out polarity (red to black, etc) on the crown to make sure all your signals stay the same polarity.

I don't know that it does invert, I'm just explaining what to do if your experiential testing shows something unexpected like that.

[pyonc]

So like I said, if you have different amps, you test them as I explained to be sure they respond the same to the same signal -
the idea is to make sure either NONE of them invert your signal, or that ALL of them invert your signal.

For instance, if you find out the Crown amp inverts compared to the JBL amp,
you would just reverse speaker Out polarity (red to black, etc) on the crown to make sure all your signals stay the same polarity.

I don't know that it does invert, I'm just explaining what to do if your experiential testing shows something unexpected like that.

Got it! Thanks again.