Gibson GSS-50 speaker question - diyAudio
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Old 23rd January 2010, 12:53 AM   #1
Louie7 is offline Louie7  United States
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Default Gibson GSS-50 speaker question

Hi ~

Finally got a proper tank for the 1966 GSS-50 combo amp.

Now a new issue has arisen... regarding speakers and output ohms.

Ok.. this 2-10" combo amp does not have any spkr jacks on the chassis.

It does have two 1/4" AUX jacks on the back panel.
I read, in an older post here, that these are line-level outputs. For what ? ? I don't know. But I digress..

Actually, the spkr lead is hard-wired directly to the circuit and goes parallel to the two 8 ohm 10" speakers. Two 8 ohm spkrs in parallel should equal a 4 ohm load... correct ?

Thus, we presume that the amp output is 4 ohm.

My understanding is that a 4 ohm amp will use any spkr arrangement above 4 ohms, 4 ohms being the best match, 8 ohms being tolerable, and 16 ohms producing a less than optimum match.

So everything is fine UNTIL I EXAMINE the schematic.... http://www.el34world.com/charts/Sche...son/GSS-50.pdf.... which clearly shows
two spkr jacks coming from the output Xformer - each labeled 8 ohms! - speaker jacks that this amp does not have.
The same schematic shows the two AUX jacks just to the left of the power-supply....(just so there's no confusion).

Soooooooooo...what's going on here ?

Do I have the wrong schematic ? I don't think so...they didn't make this model long enough for it to have go thru any drastic revisions, like the output Xformer and/or adding speaker jacks.

If the output for this amp truly is 8 ohms, then I'll need to rewire the two 8 ohm spkrs in series to create a 16 ohm situation. If the amp does want to see 8 ohms, then I don't want to fry an 8 ohm tranny with a 4 ohm speaker arrangement.


Thanks.... tell me what ya think.
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Old 23rd January 2010, 06:20 PM   #2
Minion is offline Minion  Canada
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If it is a solid state amp and it has 2 8ohms in paralell then the lowest load it will drive is 4 ohms , There is no problem driveing a higher load and in some cases might be desireable as it is easier on the amp .......

i wouldn"t say that it is better to drive 4 ohms with a 4 ohm amp it just is what it is , if your goal is to get as much Power out of your amp than useing a 4 ohm load is better....

A amp that puts out say 100w into 4 ohms will put out 50w into 8 ohms and 25w into 16ohms , the amp will also run cooler at a higher load ....


Cheers

PS: if it is a tube amp and only has a 4 ohm output then you must use a 4 ohm load .....
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Old 23rd January 2010, 07:19 PM   #3
Louie7 is offline Louie7  United States
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....well it is a (nominally) 50w solid state amp (hence, the SS-50)....

So if everything is as it should be, then are we to presume that Gibson wanted an amp theoretically capable of 50 watss to operate at half the available capacity?

That strikes me as bad planning. But, since two 8 ohm spkrs can only operate in 4 ohms parallel, or, 16 ohms series, then I guess 4 ohms is the best of the two choices.

The speakers on the amp are hard-wired to the circuit-board, with no jacks......

The schematic http://www.el34world.com/charts/Sche...son/GSS-50.pdf plainly shows two 8 ohm speakers leading from the output xformer.... at the upper left corner of the page.

Can we presume that these two 8 ohm speakers are laid out in parallel, in the diagram ?

There's a note at the bottom of the schematic that says "...for 50 watts across 4 ohm load resistor..." but there are other words and notations included in this note that I can't quite make out..... I'm assuming that the words "50w across 4 ohms" DOES refer to the output/speaker relationship. If anyone disagrees, then please say so..
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Old 24th January 2010, 01:30 PM   #4
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Quote:
Originally Posted by Louie7 View Post
....well it is a (nominally) 50w solid state amp (hence, the SS-50)....

So if everything is as it should be, then are we to presume that Gibson wanted an amp theoretically capable of 50 watss to operate at half the available capacity?

That strikes me as bad planning. But, since two 8 ohm spkrs can only operate in 4 ohms parallel, or, 16 ohms series, then I guess 4 ohms is the best of the two choices.
Since it's designed for a 4 ohm load, I'd have to agree.

Quote:
Originally Posted by Louie7 View Post
The speakers on the amp are hard-wired to the circuit-board, with no jacks......

The schematic http://www.el34world.com/charts/Sche...son/GSS-50.pdf plainly shows two 8 ohm speakers leading from the output xformer.... at the upper left corner of the page.

Can we presume that these two 8 ohm speakers are laid out in parallel, in the diagram ?
No presumption needed. The schem shows them in parallel. 4 ohm output. What's the problem?

Quote:
Originally Posted by Louie7 View Post
There's a note at the bottom of the schematic that says "...for 50 watts across 4 ohm load resistor..." but there are other words and notations included in this note that I can't quite make out..... I'm assuming that the words "50w across 4 ohms" DOES refer to the output/speaker relationship. If anyone disagrees, then please say so..
It says "20 mV @ 2.5 KC"; that's what you'd set your signal generator at to feed the input. "For 50 watts across a 4 ohm load resistor all controls max"; That's what you'd expect to calculate using a 4 ohm dummy load (resistor; instead of speakers), and "10 mV residual noise all controls max" is what you'd expect to measure across the load resistor with no signal input. The amp wants to see a 4 ohm load.
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Old 24th January 2010, 10:34 PM   #5
Louie7 is offline Louie7  United States
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I really appreciate it.
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