CS1200H

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Richard Bridge
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Joined: Mon Aug 15, 2022 4:21 am

CS1200H

Post by Richard Bridge » Mon Aug 15, 2022 5:15 am

I have just acquired a CS1200H which I THOUGHT I could make do everything I wanted but despite careful reading and re-reading of the user manual I have one actual and one potential issue. If anyone can solve them it would be most helpful.

First issue - Bridge mode operation. The user manual says
"Bridged Mono
Both amplifier channels can be bridged together to make a very powerful single-channel
monaural amplifier. .... To bridge the amplifier, set the rear panel mode select switch
to the bridge position. Apply the signal to Channel A’s input (all Channel B’s input functions are
defeated) and connect the speakers across the hot outputs (the “+” binding posts of Channels A
and B) or between the 1+ and 2+ pins of the Channel A Speakon® connector. The input level
control for channel A will be the master control for input level, the level control for the B channel
is inoperative. The active LED for the B channel will not light, which makes it easy to identify
when the amp is in Bridge mode."

It also says
"Bridge Mode Operation
1. Set AMP MODE switch to BRIDGE.
2. Connect the program signal to the A channel input .
3. Connect the loudspeaker across the two RED binding posts on the amplifier outputs . The A channel is positive
and the B channel is negative or between th 1+ and 2+ pins of the A channel Speakon connector (the 1+ positive
and the 2+ pin is negative)."

It also says "For stereo (dual channel) operation, turn the amplifier off and set the mode select switch to the
stereo position." - so FIRST QUESTION - is there an interlock or something that means that operating the stereo/bridge switch has to be done with power off or it doesn't happen?

SECOND QUESTION - I have made a speaker lead to go from channel A 1+ and 2+ to the usual 1+ 2- at the speaker. No output. No movement of the light bars on the front panel - and of course only the channel A one is illuminated. No fault protection lights on the front panel alight. Has anyone any ideas? My thoughts are (1) maybe the connection from binding post B to Speakon A 2+/2- is not working. (2) maybe the bridge mode switch has a fault and is disabling BOTH Channel A and channel B inputs. The manual is less than clear whether the light bars on the front react to input levels or output levels.

COMPLETE CHANGE OF TACK.
One of the things that was good about this amp on paper was the build-in crossovers. Looking at the block diagram in the manual, after the balancing op-amp the crossover controls are the very first thing in the signal chain, going via the function switch (LF, HF or full range)straight to the high pass (or full range) and lo-pass unbalanced output jack sockets. The Mode switch appears after the protection circuits on channel A but before them on channel B. THIRD QUESTION - so if I set the channel functions on both channels to "low pass", the manual is not clear but I think means that the high frequencies will appear at the HF (or full range) unbalanced output jack socket. Here comes the twist - if I put the power amps into bridge mode, the manual says that "all Channel B's input functions are defeated". So then I'd only get channel A's HF output out via the crossover. That cannot be right can it?

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Enzo
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Posts: 9535
Joined: Fri Sep 12, 2008 10:24 pm
Location: Lansing, Michigan

Re: CS1200H

Post by Enzo » Tue Aug 16, 2022 8:40 pm

Oh you can switch modes with power on, but you risk loud noises into your speakers when you do. Really not hard to flip it off, switch it, and flip it back on.

Your speaker is mono. I assume? And doesn't the usual connection come from 1+ and 1-? As opposed to 1+ and 2-?

I would think nothing changes at the speaker end of the cable. We just need a "bridge wired" plug at the amp end. So 1+ and 2+.

As I understand it, and I could be wrong, the am disables the channel B controls. So I won't think of ays they still work. But if you have the amp, you can flip the switches and find out faster than I can rationalize.

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