Bridge 2 Adcoms to Adcom pre to MLogansArius - AVS Forum
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post #1 of 8 Old 01-18-2013, 02:57 PM - Thread Starter
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Hi All, I'm getting ready to hook up my 2 Adcom gfa-555 power amps @ 200w per chan x 2 driven.. Here we go!! Questions is :: Adcom says to hook up in bridged mode of course , out from power amps to preamp. Or vice versa actually.. So. they say to come out of the right side only on each amp so I just want to be sure that when it comes to left channel I hook up from right side of amp#2 but go to the left at pre. You follow? amp 1, right to right to right, amp #2, left from pre to right on amp and right out again to the left! Don't want to blow anything as in this case we are talking 800w per side. THX MUCH IF U CAN MAKE SENSE OF THIS AND CONFIRM with one who is concerned.. Thx, Again, Bob
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post #2 of 8 Old 01-18-2013, 05:20 PM
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Originally Posted by bob800adcmlogn View Post

Hi All, I'm getting ready to hook up my 2 Adcom gfa-555 power amps @ 200w per chan x 2 driven.. Here we go!! Questions is :: Adcom says to hook up in bridged mode of course , out from power amps to preamp. Or vice versa actually.. So. they say to come out of the right side only on each amp so I just want to be sure that when it comes to left channel I hook up from right side of amp#2 but go to the left at pre. You follow? amp 1, right to right to right, amp #2, left from pre to right on amp and right out again to the left! Don't want to blow anything as in this case we are talking 800w per side. THX MUCH IF U CAN MAKE SENSE OF THIS AND CONFIRM with one who is concerned.. Thx, Again, Bob

Your description is a little confusing...LOL
I've owned four Adcom products...nice equipment. I'm still using the GFA 7700 five channel x 150 watts.
You have two very nice amps!

Switch to bridge position,single input cable is used plugged into the right channel input only, connecting a single speaker in bridged operation...positive terminal of the speaker connects to the right channel positive (red) output post on the GFA555. The negative terminal of the speaker to connect to the left channel positive (red) output post. I would make sure that the amps are VERY well ventilated. They will surely heat up a room.

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post #3 of 8 Old 01-18-2013, 08:11 PM - Thread Starter
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Thanks for your reply my friend! I understand that part but what about the other channel? If I keep typing I will get get more confused!!! HA! Ha! I know I know... But really, two channels, a right and a left. Could and would you be so kind as to go thru all the way??!! Greatly appreciated Honestly! By the way, I have four of these amps, all without a scratch and just about the same age and use which is about maybe 50 hrs?!!! Nothing at all.. I know this is not a sales outlet but I am thinking about selling one or maybe two of them. Let me know if you have any interest. I'm not looking to hit a home run either.. THX for your help! Bobby
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post #4 of 8 Old 01-18-2013, 10:14 PM
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Right preamp output --> right input of the right-channel amp
Left preamp output --> right input of the left-channel amp

Both amps in bridge mode.

Make sure the amps can drive the impedance of your ML speakers when the amps are in bridged mode (I did not look up your model; electrostatic speakers generally exhibit low impedance at high frequency).

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post #5 of 8 Old 01-19-2013, 07:01 PM
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Originally Posted by DonH50 View Post

Right preamp output --> right input of the right-channel amp
Left preamp output --> right input of the left-channel amp

Both amps in bridge mode.

Make sure the amps can drive the impedance of your ML speakers when the amps are in bridged mode (I did not look up your model; electrostatic speakers generally exhibit low impedance at high frequency).

Those amps can drive just about any load....down to about 2 ohms!

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post #6 of 8 Old 01-20-2013, 12:00 PM
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In bridged mode? Maybe, but the owner's manual does not say. The ML Aerius specs say 4-ohm nominal dropping to 1.7 ohms at 20 kHz, not unusual for an ESL. Most amps will not drive such a load in bridged mode as it effectively halves the impedance the amp sees. That is a pretty hefty load for any amp. I liked Adcom amps but not sure I would drive those speakers in bridged mode.

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post #7 of 8 Old 01-20-2013, 02:09 PM
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Originally Posted by DonH50 View Post

In bridged mode? Maybe, but the owner's manual does not say. The ML Aerius specs say 4-ohm nominal dropping to 1.7 ohms at 20 kHz, not unusual for an ESL. Most amps will not drive such a load in bridged mode as it effectively halves the impedance the amp sees. That is a pretty hefty load for any amp. I liked Adcom amps but not sure I would drive those speakers in bridged mode.

The speaker is 4 ohm. The Adcom manual states 325 watts per channel @ 4 ohm, both channels driven. Bridged mode power of 600 watts into 8 ohm load.

Your right, the manual does not clarify being able to go to 2 ohms. It only states "the ability to drive very low impedance loads", which I assumed meant less than 4 ohm...perhaps to 2 ohms...not sure now what to recommend...

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post #8 of 8 Old 01-20-2013, 04:41 PM
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Check out the specs on the ML website, Stereophile measurements, or other reviews. Nominal ratings are just that -- most speakers exhibit significant variations from their nominal impedance over their operational frequency range. The ML Aerius speakers are nominal 4 ohms but dip to below 2 ohms at high frequency. This is characteristic of electrostatic panels due to their design. The good news is there are no other low-Z dips I saw in the impedance plots, although they are capacitive over much of their range (of course).

I would also assume the Adcom can handle loads below 4 ohms in normal mode, but not in bridged. A 4-ohm load looks like a 2-ohm load to a bridged amp, and that 2-ohm HF dip the MLs have thus looks like 1 ohm to a bridged amp, and capacitive which can cause stability issues. I have heard the Adcom on low-impedance speakers (Apogees) in the primordial past. It did not fail, but ran very hot and after a little while (do not recall, less than an hour) of moderately loud playing shut down (thermal protection). That was NOT in bridged mode, but was a very low (~1.5 ohm) load.

I do not know if the Adcom would be OK in bridged mode with those ML speakers or not. If it was an 8-ohm speaker I'd say go for it; if 4 ohm I'd be nervous but if the impedance was fairly flat, or at least no large dips, I'd probably try. We obviously have our own opinions but with the MLs I just don't know. I imagine the OP will try and let us know; I suggest he monitors the amps closely at first.

In any event I have had my say and do not feel this debate adds anything significant. It will be interesting to see how the amps work on the MLs (or not).

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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