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Old 14th November 2009, 06:37 PM   #11
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Quote:
Originally Posted by LikaComet View Post
Thank you Guys for your consideration. . .

On the speaker terminals on the back of the amp there are 2 commons and two positive outputs. What would happen if I connected the 2 8ohm + terminals off of the amp's terminal block to the two speaker terminals of the speaker' xover. I'd then connect the two commons together on the amp's terminal block. I can see how the phasing of the two amp outputs would null each other. Can the polarity be reversed between the two channels coming out of the amp. Couldn't I simply undo the connection between one channel pos output and the speaker and turn it upside down to reverse polarity?
I'm a bit over my head here so i'd check a bit deeper to make sure everything is cool.

Amplifiers like the Dynaco stereo 70 had a switch to convert them to mono. I believe that this allowed you 2 paralel the outputs. the 2 8 ohm taps would be connected and drive one speaker terminal, and the commons connected (in many amps unnecessary (yours likely included) as they are common with ground inside the box) to drive the other terminal. the speaker would ideally be 4 ohms.

The Decware Zen lets you series the outputs, it has the outputs of the OPT secondary floating (one terminal NOT connected to ground). Then you connect one red terminal to a black terminal and drive the speakers off the remaining terminals. Now best to have a 16 ohm load.

dave
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Old 14th November 2009, 06:50 PM   #12
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More info. Attached from Dyna ST70 on running the amp in mono. The switch connected the 2 inputs together.

dave
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File Type: png st70-mono.png (169.7 KB, 30 views)
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Old 14th November 2009, 08:37 PM   #13
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Quote:
On the speaker terminals on the back of the amp there are 2 commons and two positive outputs. What would happen if I connected the 2 8ohm + terminals off of the amp's terminal block to the two speaker terminals of the speaker' xover. I'd then connect the two commons together on the amp's terminal block. I can see how the phasing of the two amp outputs would null each other. Can the polarity be reversed between the two channels coming out of the amp. Couldn't I simply undo the connection between one channel pos output and the speaker and turn it upside down to reverse polarity?
What are those two sets of terminals doing? They're connected in the circuit how?

Without knowing that, this could go very bad :-\

Cheers!
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Old 14th November 2009, 11:03 PM   #14
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MJL. you said:
The resistors are for dropping the output voltage and work as a low rent mixer to combine the channels of the CD player

Does this have to do with impedance? How would I know if its not enough resistance? I like to use these kinds of questions to understand impedance better.

Geekdude and Dave you-all said:
What are those two sets of terminals doing? They're connected in the circuit how?

You are on the money Dave. The commons on the amp's speaker output terminals are wired together and then grounded to the case. And Geekdude. . . The terminals of the positives on the terminals go to the OPTs.

MJL:
The reason for all of this. . .
Recently I bought a EV/University Cobraflex folded horn midrange with a compression driver. I only have one. So, what I've done is I had a small two-way JBL bookshelf (model 2500). I disconnected the tweeter and connected the Cobraflex. Am driving this "thing" with a mono Sony table transistor radio. It sounds pretty good if I don't over drive the "thing". This concoction is what I listen to the news on and keep the cats company when I'm away from the house. The Sony's tone controls work pretty well to attenuate the Cobraflex to match the bass of the JBL. Does that make sense?

I have my Dad's old Marantz 8b and C pre-amp. It also has a setting for combining the two channels. If I can find it I'll look at the schematic of the pre-amp to see how they join the channels.

On the diagram on the attachment. . . Is this series or parallel? Also, If I reversed polarity on one of the channels would this work? If it would work how would I reverse the polarity? What would be accomplished by floating the ground on one of the OPTs (disconnecting the ground)?
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File Type: jpg Admiral amp output.JPG (19.1 KB, 29 views)
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Old 14th November 2009, 11:14 PM   #15
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Given what you have for speaker, i would use one channel to drive the tweeter, and the other to drive the woofer. Balance control gives you level adjustment.

Passive XO is easiest, but as you learn you could do PLLXO.

dave
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Old 14th November 2009, 11:21 PM   #16
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Took the words outta my mouth.
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Old 15th November 2009, 01:43 AM   #17
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Wow. I never thought of using the tweeter on one channel and the woofer on the other. Something of a revelation to me. And the tone controls would still be operational?

Wowwie! I have to try this.

Thanks Guys, I'll let you know what happens.
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Old 15th November 2009, 01:52 AM   #18
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Quote:
Originally Posted by LikaComet View Post
Geekdude. . . The terminals of the positives on the terminals go to the OPTs.
Brainfart... I thought you meant two terminals on the speakers


Quote:
Given what you have for speaker, i would use one channel to drive the tweeter, and the other to drive the woofer. Balance control gives you level adjustment.
aka "How to turn two stereo amps into a true biamp system"

Cheers!
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Old 15th November 2009, 02:07 AM   #19
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I will have to use a capacitor to protect the Cobraflex (mids/highs) from bass signal won't I?
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Old 15th November 2009, 02:14 AM   #20
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Yes. The beauty of using 2 amps for one speaker system is that you can use a smaller cap (read cheaper and more accurate) at line level.
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