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ADCOM GFS-6 Speaker Selector question

wirewood

wirewood

Wirewood
Hi,
I just got the Adcom and the manual says to hook up your amp but does not say witch impedance to use? I'm sure it makes a difference weather I hook up the "input" to my Mac-275 to the 4,8,16 ohm taps. Thanks for any help! I don't want to hurt my amp and I do like it loud! If it makes any dif I have several large Bozak speaker pairs I'll be using. Thanks!!

Brian
 
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Don't take this for gospel as I don't use tubes on my switcher, but I believe the switcher is designed to show a flat 8 ohm load when the protection switch is used no matter how many speakers you use at a time.

However, when the protection switch is used it also tends to take the life out of the music. I'm not sure if it is because it doesn't allow the amp to respond to the changes in speaker impedance during play or what, but it is very noticeable. Since this is the case, I usually only use it with single speaker pairs and use it as a switcher exclusively. This makes it a breeze to A/B speakers or switch pairs out depending on where in the room I am.
 
I agree with the "sucks the life out of the sound" post above, but the only correction I'd make is that it generally shows a 4 ohm + load to the amp...a 4 ohm resistor plus whatever the load is from all the speakers that are on at that time.

The manual for this unit is on line, by the way.

je
 
I thought it showed a safe load to the amp no matter what the speakers on the other end are? I could be wrong though. Unless it is just designed to show a steady load which depends on your setup.

Is the 4 ohm resistor what kicks in when you hit the protection switch?
 
VinylHanger said:
I thought it showed a safe load to the amp no matter what the speakers on the other end are? I could be wrong though. Unless it is just designed to show a steady load which depends on your setup.

Is the 4 ohm resistor what kicks in when you hit the protection switch?
Click to expand...

Yep, but the best Adcom can do is guess as to what you're going to switch into play...4 ohms plus 8 is 'safe', plus 4 is safe, plus 2.x is still pretty safe...this would be for solid state, maybe not so 'safe' for finicky tube amps.

I'll have to take a look at my Adcom & Niles when I'm home, pretty sure they're 4 ohm resistors in there. I know we used to use big 2 ohm resistors & Crown power amps for whole-house applications back in the day.

je
 
Speaker switcher

Hi guys,
I posted about my 6 way adcom? speaker selecter and my mac 275 and I got a few replies but no one said which impedance I should hook up to the "input" of the switcher! there was some talk of theory but I just need to know , should I go 4 ohms or 16 ohms to the only input on the device. Thanks!

B
 
wirewood said:
Hi guys,
I posted about my 6 way adcom? speaker selecter and my mac 275 and I got a few replies but no one said which impedance I should hook up to the "input" of the switcher! there was some talk of theory but I just need to know , should I go 4 ohms or 16 ohms to the only input on the device. Thanks!

B
Click to expand...

Thanks for the reminder, I'll go get mine now & test it with some different loads, and tell you what readings I get with & without the protection in line.

je (actually, my overall advice was not to use it, 'cause it ruins the sound)
 
Here's what I just measured on my Adcom GFS-6, tried with two different types of speakers (Celestion ~6 ohm & Canton ~8 ohm)

Celestion direct - 5.6 ohms
Celestion via GFS - 5.8 ohms
Celestion via GFS w/protection - 8.2 ohms

Canton direct - 7.8 ohms
Canton via GFS - 8 ohms
Canton via GFS w/protection - 10.5 ohms

Both spkrs via GFS- 3.6 ohms
Both spkrs via GFS w/protection - 6.2 ohms

...opened the unit up, and found two big 2.5 ohm resistors.

My suggestion is to get a meter, and hook up all of the speakers you want to use, and test to see what range you fall into. Keep an eye on heat from the selector box, too- if you like it loud, you'll be pushing that amp to overcome the resistors, and things could get hot. The GFS is rated for 200 Watts, I'm not familiar with your model amplifier at all.

I'll check my Niles next, just for kicks.

je
 
Niles SVC-4L also has 2.5 ohm resistors, but much smaller. This unit is rated for 100W, and has autoformers. A couple pics attached regarding use of the Niles with tube amps...

je
 

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I guess the easiest way to describe it would be to put the meter on the resistance setting (usually an ohm symbol) and pretend the probes are replacing the output of your amplifier. You won't get an accurate reading with the amp attached, so disconnect that & replace with the meter.

You can test directly at the speaker's terminals, or work backwards: after the speaker cable leading to the selector, or at the input side of the selector (protection on or off), or after the speaker cable leading to the amp. Each place will potentially show you a little difference in resistance as more things are added in line. For example, with two sets of speakers running with the protection on, each side's signal runs through: six terminal sets, three switches, three sets of speaker cable and one resistor (compared to a normal setup of two terminal sets and one cable). If your selector also has volume controls or A/B amp switches, they add in line as well- these are all ways that the signal gets degraded.

In the OP's situation, I'm suggesting that all speakers get connected to the selector as desired, but use the meter to see what the amp's load would be, with and without the protection added in. For all I know, his Bozaks might be 16 ohm each, and if there's only two per side he might be good without the protection.

Then, you should also check to see if the comb filtering from multiple tweeters playing the same signal bothers you enough to go back to only two speakers at a time...:yes:

je
 
I've posted much more info in the original thread...we'd need to know the impedance readings you get once all of your speakers are hooked up to recommend which amplifier tap to use, any way. Your particular selector adds an additional 2.5 ohms when the protection resistors are selected.

je
 
wirewood said:
Hi,
I just got the Adcom and the manual says to hook up your amp but does not say witch impedance to use? I'm sure it makes a difference weather I hook up the "input" to my Mac-275 to the 4,8,16 ohm taps. Thanks for any help! I don't want to hurt my amp and I do like it loud! If it makes any dif I have several large Bozak speaker pairs I'll be using. Thanks!!

Brian
Click to expand...

I just use a multi meater set to read ohms to find that out
 
Fred Sanford said:
Here's what I just measured on my Adcom GFS-6, tried with two different types of speakers (Celestion ~6 ohm & Canton ~8 ohm)

Celestion direct - 5.6 ohms
Celestion via GFS - 5.8 ohms
Celestion via GFS w/protection - 8.2 ohms

Canton direct - 7.8 ohms
Canton via GFS - 8 ohms
Canton via GFS w/protection - 10.5 ohms

Both spkrs via GFS- 3.6 ohms
Both spkrs via GFS w/protection - 6.2 ohms

...opened the unit up, and found two big 2.5 ohm resistors.

My suggestion is to get a meter, and hook up all of the speakers you want to use, and test to see what range you fall into. Keep an eye on heat from the selector box, too- if you like it loud, you'll be pushing that amp to overcome the resistors, and things could get hot. The GFS is rated for 200 Watts, I'm not familiar with your model amplifier at all.

I'll check my Niles next, just for kicks.

je
Click to expand...


Great info, thanks!
Do you think it is safe to assume this would be the same for the GFS 3? :scratch2:
 
Any speaker selector device should absolutely be 0.0000 ohms when tested without any input and without any speakers connected. You connect your amp to the selector input the same as you would connect your amp to your speakers, instead the signal goes through the selector then to your speakers. In other words use the same impedance from your amplifier as you would normally use. Most amps do not have selectable impedance matching; McIntosh and a few other high end ams do...
I would keep the circuit protection to off. My reasoning is, I did not have circuit protection before, why now..?? The protection circuit adds
a coloration that I do not like.
IMHO any speaker selection box should be a passive only and act like a straight wire with switches...that is all; no resistive, inductive capacitive components need exist inside a speaker selection device.
I would be happy to respond to any questions..
 
pdwoods said:
Any speaker selector device should absolutely be 0.0000 ohms when tested without any input and without any speakers connected. You connect your amp to the selector input the same as you would connect your amp to your speakers, instead the signal goes through the selector then to your speakers. In other words use the same impedance from your amplifier as you would normally use. Most amps do not have selectable impedance matching; McIntosh and a few other high end ams do...
I would keep the circuit protection to off. My reasoning is, I did not have circuit protection before, why now..?? The protection circuit adds
a coloration that I do not like.
IMHO any speaker selection box should be a passive only and act like a straight wire with switches...that is all; no resistive, inductive capacitive components need exist inside a speaker selection device.
I would be happy to respond to any questions..
Click to expand...
I would add also that the ADCOM GFS-4 is essentially a "straight wire" with switches as with the GFS-6 with circuit protection OFF...OFF
 
I just got the adcom speakers selector, can I use it in reverse to share the same speakers with many amps ?
I have not get it yet
 
I don’t see why you couldn’t use it in reverse. One could use a pair back to back to switch between up six amps to play up six pairs of speakers. I may buy another one so I could do this.

Larry
 
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