Adcom 555 power amps. Bi-amping

[jelly head]

Can anybody tell me how to bi-amp these, I have the Adcom pre-amp as well. Diagrams would be very helpful, Thanks all.

 

[redcoates7]

So you have a second GFA-555?

What sort of speakers are you using, and more importantly, do they have bi-amp/bi-wire connections? Let's assume they do, as that is a requirement for bi-amplifying a speaker

1. Turn everything off.

2. Remove the "straps" between the upper and lower speaker binding posts. These are usually gold-colored bars that connect the two red posts and black posts respectively
FAILURE TO DO THIS WILL DAMAGE YOUR AMPLIFIER

3. Connect Amplifier #1 to the top set of binding posts of each loudspeaker. Adcom #1 will now only be used to power the tweeters

4. Connect Amplifier #2 to the bottom set of binding posts of each loudspeaker. Adcom #2 will now only be used to power the woofers

5. Connect Amplifier #1 and #2 to the two sets of preamplifier outputs on your preamp.

6. Turn everything back on and enjoy

 

[winters860]

What redcoates described is "horizontal bi-amping", where you use one stereo amp for the high frequencies and one for the lows.

Another option is "vertical bi-amping", using one stereo amp to power the highs and lows of one speaker and another for the other speaker. That's what I'm doing.

 

[RickB]

Bi-amping will do very little in absolute terms without some kind of outboard crossover, but if the amps are the same, I would do the vertical mode, one amp per speaker, vs the other way as the bass load will be reduced on the amplifiers...i.e., it takes more energy to run the bass section of your speakers than the high frequencies, so one amp will loaf while one will chug along...therefore, spread the load of the bass over the two amplifiers rather than just one....

Now, horizontal biamping can be a boon when you use amplifiers of different power capabilities or characteristics...i.e, in Adcom terms, a GFA-555 on bass and a GFA-535 or 545 on mid/treble....but, you must use an outboard crossover and adjust levels accordingly...or, another example, a big solid state amp on bass, a small, but refined, tube amp on the mid/high...

 

[RickB]

With the 555's, the most common usage is to "mono-block" them, in other words, strap each amp into mono and use them to each power one speaker...

My 555-II has a switch on the back for "mono" and shows how to connect up the speaker cables for single channel use....

 

[redcoates7]

Bi-amping will do very little in absolute terms without some kind of outboard crossover, QUOTE]

You're still using the internal passive crossover when bi-amplifying as I describe it...the HP section remains engaged for the tweeters, and the LP section remains engaged for the woofers. Adding an external crossover to this will create issues, as you would then be cascading crossovers, which introuces all sorts of strange phase a frequency response anomalies.

The benefits of this arrangment vary depending on your system, but the method I describe has always made a big difference in my systems, especially when used with 3-way systems where the "upper" amplifier is driving the midrange and tweeter and the woofer now gets its own dedicated amplifier.

 

[redcoates7]

If you do decide to bridge your amplifiers, be careful about the impedance of the connected speaker. A good rule of thumb is that an amplifier that is 4-ohm stable when run in stereo is only 8 ohm stable when bridged.

Some complex full-range loudspeakers can easily drop below 4 ohms, so bridging a typical stereo amplifier could result in clipping, blown rail fuses, or possibly even damage, as it would now "see" a 2-ohm load

 

[jelly head]

Can anybody tell me how to bi-amp these, I have the Adcom pre-amp as well. Diagrams would be very helpful, Thanks all.

How do I wire from pre amp to power amps?

 

[rtate]

I have a 555 MK1 and have read several articles that say that the 555's do not like to run in bridged mode , even though they have a switch for it

 

[RickB]

RickB: Bi-amping will do very little in absolute terms without some kind of outboard crossover,

You're still using the internal passive crossover when bi-amplifying as I describe it...the HP section remains engaged for the tweeters, and the LP section remains engaged for the woofers. Adding an external crossover to this will create issues, as you would then be cascading crossovers, which introuces all sorts of strange phase a frequency response anomalies.

The benefits of this arrangment vary depending on your system, but the method I describe has always made a big difference in my systems, especially when used with 3-way systems where the "upper" amplifier is driving the midrange and tweeter and the woofer now gets its own dedicated amplifier.

And that's why I said what I did about vertical bi-amping, you get an amp that stresses the power supply reserves a lot less than horizontal biamping does....which is where the biggest difference comes from, that and the interaction between the mid/high and woofer's back emf are eliminated....unless, of course, as I said before, you have different amps for different uses...still, if the treble amp is prevented from taking on the low frequency duties then the whole amplifier can work more efficiently and cleaner...it takes work, and obviously jelly head is a noob when it comes to this stuff and has a long learning curve ahead of him to go through to get to proper biamping....

On the other hand, if you have speakers that do not have separate connections for bass/treble..like the Quad 2805's at work, then all you can do is to run dual monos....we have a set of Spectron Musician III Sigs strapped into mono on those...there's no way to hook up the speakers any other way to the dual amplifiers....

But first we need to know a bit more about jelly head's system....

What speakers are you using?

Do they have connections on the back for more than one set of speaker cables?

Let us know that and then we can begin to help a little more...

 

[jelly head]

Hi, thanks very much for helping. The set up is two GFA 555 power amps, GFP 555 pre amp, speakers are KLH 317's with just one set of terminals on each. Ps your not kiddin about being new to this bi amping lark, I'm totally baffled.

 

[RickB]

OK, you can't biamp.
No way to do it.
You can run them as mono amps.

There should be nomenclature on the back of the amplifiers that tell you where to plug in the RCA cable plug for mono operation, which two binding posts to hook your speaker cables up to, and a mono/stereo switch...


Got it so far?

 

[jelly head]

Hi, Rick B and everybody who helped, thanks very much. Nobody over here in the UK know much about them, thanks again.