Can you help

the weakest link we love so much

Can you help

Postby 6B4G » Sun Apr 03, 2011 2:15 am

Am I able to use both 4 and 8 ohm outputs from my amp to drive two sets of speakers?
Sorry for the stupid question, but I've been asked many times from friends and I just don't know.
User avatar
6B4G
KT88
 
Posts: 287
Joined: Sun Jul 06, 2008 1:02 pm
Location: Greece

Postby Geek » Sun Apr 03, 2011 6:02 am

Hi,

No, sorry. You need to use one or the other on one channel. Or a combination to make the correct impedance tap (use two 16 ohm speakers in parallel, tied to the 8 ohm tap for example).

Cheers!
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
User avatar
Geek
KT88
 
Posts: 3585
Joined: Sun Oct 21, 2007 3:01 am
Location: Chilliwack, British Columbia

Postby TomMcNally » Sun Apr 03, 2011 8:54 am

Here's a link to a nice calculator to help figure it out ...

http://www.bcae1.com/spkrmlti.htm
User avatar
TomMcNally
Darling du Jour
 
Posts: 2729
Joined: Sat Nov 19, 2005 2:19 pm
Location: Northfield, NJ

Postby 6B4G » Thu Apr 07, 2011 8:53 am

Call me silly but, my amp has two sets of 8 ohm and two sets of 4 ohm.
So you are telling me that I cant have my 8 ohm speakers in, and also plug in a set of 4 ohm speekers.
User avatar
6B4G
KT88
 
Posts: 287
Joined: Sun Jul 06, 2008 1:02 pm
Location: Greece

Postby TomMcNally » Thu Apr 07, 2011 3:04 pm

Is it a solid state amp? Does it have an A/B selector switch?
But normally, no, you can't use 4 and 8 ohms at the same
time, you'll overload the amp.
User avatar
TomMcNally
Darling du Jour
 
Posts: 2729
Joined: Sat Nov 19, 2005 2:19 pm
Location: Northfield, NJ

Postby 6B4G » Thu Apr 07, 2011 10:28 pm

Sorry for that, I supose that the amp is a key factor here. (lol)
It's a AMC CVT2100 tube power amp with no selector.
The OPT is a easy wire with a common ,4 ohm and a 8 ohm conection.
User avatar
6B4G
KT88
 
Posts: 287
Joined: Sun Jul 06, 2008 1:02 pm
Location: Greece

Postby Geek » Thu Apr 07, 2011 11:04 pm

OK then, you can choose to add an 8 ohm speaker, or a 4 ohm speaker, but not a 4 *and* 8 ohm speaker, or you'll overload it as Tom said.

Why this happens is the speaker impedance is reflected to the tubes. Too heavy of a load causes the tube to draw too much current and *poof!*

Cheers!
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
User avatar
Geek
KT88
 
Posts: 3585
Joined: Sun Oct 21, 2007 3:01 am
Location: Chilliwack, British Columbia

Postby 6B4G » Fri Apr 08, 2011 6:13 am

Thanks for that.
The "poof" (lol)
User avatar
6B4G
KT88
 
Posts: 287
Joined: Sun Jul 06, 2008 1:02 pm
Location: Greece

Multi speakers

Postby msmpe » Mon Jun 20, 2011 10:58 pm

There's a couple ways to do it. Run the speakers in series, that will add up to 12 ohms, which is not what your amp wants to "see" so you'll be down on volume. I've never liked the results.

You could hook em up in parallel, but in parallel the impedance the amps sees is 4x8/4+8=2.7 poof! But you could then run a 5 ohm resistance in series 2.7+5=7.7, close enough. The resistance should be non-inductive, PatrsEx has some non-inductive speaker resistors, make sure the wattage of the resistors is as high as your amp or almost as much. Maybe it sounds OK, maybe not! I do like 2 pairs of speakers, but it depends on the tube amp.

One last possibility. This one comes from a little book written in 1963 titled HiFi Projects for the Hobbyist by Leonard Feldman. In chapter 6 he describes a way to hook up two speakers of differnt impedances. He hooks the postive of the 4 ohm speaker to the positive of the 4 ohm tap on the OPT and the respective same for the 8 ohm speaker, with the speaker negatives connected in common to the negative/common on the OPT. Feldman also shows how to connect a 3-way switch to selct A, B, or A+B. Quoting from the text, "it is true that the prescence of a speaker across the other tap of the output transformer alters the total impedance of the transfomer slightly, the effect is more negligible than would be the case if the two speakers were simply wired in parallel."

Does anyone know how to calculate what the impedance is that the amp sees hooked up this way?
8>) Mike

If there's no sound in a vacuum, where'd the music come from?
msmpe
KT88
 
Posts: 305
Joined: Wed Mar 26, 2008 12:31 pm
Location: central california coast

2 pair of speakers

Postby msmpe » Thu Jun 23, 2011 11:09 pm

Hi 6B4G,

I thought of another possibility to consider. I've tried this with a SS amp years ago, but SS amps are typically very tolerant of mismatched speaker loading. Get an 8 ohm L-pad and hook the 4 ohm speaker to it. Check the hook up diagram first- can't find mine. Then with the L=pad and 8 ohm speaker in parallel connect it all to the 4 ohm tap on the rransformer: 8x8/8+8=4.

When I did this I did not like the result as much as just using the one set of speakers. Also, I have tested a few L-pads for tracking equally between a pair, and they do not match well, so you have to rely strictly on your ear for balance.

Here's one more suggestion - use the extra pair of speakers as "rears" or "ambiance" as originally suggested by the infamous Mr. Hafler. Go to tubeaudio.com/page 24.html for a hook up diagram. Also go to Mapletreeaudio.com (Mapletree Branches Issue #4) for a similar hook up. I've done this and liked the result.

My last suggestion - if you even care at this point - is the best! Build a little tube amp for that extra pair! Guaranteed to sound good!!

Cheers
8>) Mike

If there's no sound in a vacuum, where'd the music come from?
msmpe
KT88
 
Posts: 305
Joined: Wed Mar 26, 2008 12:31 pm
Location: central california coast


Return to loudspeakers

Who is online

Users browsing this forum: No registered users and 8 guests