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COHERENCE II
Coherence II
1994-2001
new approx 22.000 euro
used 5000-7000 euro
Once revered for its legendary silence and amazing low level detail retrieval, still regarded as one of the best preamp in the world.
Interesting trivia: The Coherence II was about to receive an i-upgrade but somehow this never happened and the circuitry ended up in the Synergy 2i preamp. The only thing letting the latter down is the meager power supply and lack of a BPS.
Coherence II with a Synergy on top
The front panels have exactly the same buttons in exactly the same places. The only physical difference is that the Coherence has two more inputs. Interestingly though, the software is the same with the result that for the Synergy when toggling throught the inputs using the remote control, you pass two empty places between the last available input and the first.
Amplifier section inside
On the rear is the input circuitboard holding the XLR's and relays to switch them, in the middle are 3 modules per side: input transformer, output transformer and attenuation circuitry. Note that the housing is made from a solid block of aluminium.
Power Supply section inside
Housed in this part is the power supply (transformer and capacitors) as well as the Batteries and their charge management electronics. The batteries fit snugly into tightly tolerated holes on the left and right. In fact, when they need replacement they are often swollen slightly and cannot be easily removed withoutr using some tools (and a lot of care!).
Power Supply section - frontpanel - inside
The frontpanel has been taken apart, revealing the nicely hidden charge management electronics inside.
Difference between Coherence II Series I and Series II
The Coherence Series II was released April 1997. The Coherence Series II upgrade involves the redesign of the attenuator amp circuitry. The actual circuit topology is similar; however, all of the circuit components were improved, taking advantage of recently available modern surface mount technology. The output amplifier is a newly developed, dual high-current transimpedance amplifier which handles both phases of the output circuit on one isothermic, copper lead frame power device. This output amplifier and all associated surface mount circuitry allow significant reductions in circuit loop area and path length yielding wider bandwidth, faster setting time, reduced dielectric absorption and greater thermal tracking stability. The overall sonic result is greater clarity during complex music passages and increased resolution of intertransient silence.
Problem Solving
Coherence, Synergy, Concentra, and Concerto IR Remote Control lock-up
The remote controls for the above listed products have an internal capacitor that can cause the microprocessor to lock when the battery has been nearly drained. This problem will continue even after a fresh battery has been installed. This capacitor allows the remote to continue to function even after the battery has become very weak. The solution to this problem is simple: remove the new battery and allow the remote to stand overnight with no battery installed. Once the battery is reinstalled in the morning, the remote should function properly again.
Resetting the Coherence
Press and hold the mode button on the frontpanel of the powersupply for 4 seconds and release. Nothing may happen for a couple of seconds but then a click is heard and the amp comes back online. You will have to re-program the balance offset, phase and gain setting and input/output configuration.
Correct procedure for disconnecting the Coherence Preamplifier from AC power
If you disconnect the Coherence Preamplifier from AC power, you must hold the "mode" button on the power supply for 10 seconds, or until a "click" is heard. If you do not perform this disconnect procedure, one of the two internal batteries will continue to discharge, causing a potential battery failure.
Complete lock-up
It can happen that the Synergy locks up when you operate many buttons at the same time and also adjust the volume. All you need to do is unplug the powercord, wait for 10 seconds and reconnect. If you reconnect too quickly, the Synergy may not work. The same is true if you swap the power cable or change the position in the extensionblock. As a rule of thumb: always wait 10 seconds before reconnecting the power.
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