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Two Channel "High Current" receiver

 

New member
Username: Johnharper

Pasadena, CA

Post Number: 9
Registered: Apr-05
I have been told that my speakers require a "high current" receiver and I do not understand this terminology nor what is considered "high current" versus a "low current" receiver. I am planning to hook up 4 Bose 901, Series II 8 ohm speakers to a two channel system and come up with 100 watts per channel. BTW, does this mean I will be getting 50 watts per speaker and will this prove adequate?
 

Silver Member
Username: Paul_ohstbucks

Post Number: 793
Registered: Jan-05
No, that's 100watts per channel. Each speaker represents it's own channel.
 

New member
Username: Johnharper

Pasadena, CA

Post Number: 10
Registered: Apr-05
Thanks for the response, Paul. That helps. Do you know what 'they' mean when they speak of high current versus low current receivers?
 

Silver Member
Username: Frank_abela

Berkshire UK

Post Number: 497
Registered: Sep-04
John

I doubt anyone would talk about low current receivers or amps. Usually, what people mean is that an amp can swing a lot of current in a short amount of time. In other words when the signal demands a sudden burst of power, such as when an orchestra gives you a 'crescendo' or when a bomb goes off in your movie, the amplifier has to deliver that signal in a sudden burst of current.

Why current? Here's a slightly incorrect but useful depiction of what happens. At any one frequency, the resistance of a speaker is a constant value. In order to maintain a certain voltage across the speaker's terminals (that's the signal), the amp has to push a certain amount of current through the resistance (V=IR). The lower the resistance (R), the higher the current required (I) to maintain the volts across the speaker terminals.

Now, if you connect two sets of speakers to an amp instead of one, you change the resistance they show to the amp. If you connect them in series, you double the resistance. If you connect them in parallel, you halve the resistance. If you halve the resistance you need to double the current. It's usual that people connect speakers in parallel (i.e. negative terminals of both speakers to the negative terminal on the amplifier, and positive terminals of both speakers to the positive terminal of the amplifier). This makes it work very hard. I've never tried connecting speakers up in series.

Some amplifiers have outputs for two sets of speakers. These amplifiers are designed to be able to handle the extra requirements, but even so may not be able to swing that much current. What they do is to make sure that thigns should be OK electrically so the amp isn't overloaded.

So why don't I talk about power? Power is Voltage times Current (i.e. P=VA). Since both voltage and current are changing constantly with any signal (because resistance changes with frequency too), power becomes very difficult to gauge things by. For example, if your amp is said to deliver 200 watts, you need to know what the resistance of the load was when it was tested. Very often you'll see quoted power into a certain resistance and sometimes you'll see it quoted as two sets of power - e.g. 50 watts (8 ohm) and 75 watts (4 ohm). These are usually RMS values meaning there is some hgeadroom in the amp to deliver more power under more difficult conditions. An amp that can deliver 50 watts into 8 ohms and 75 watts into 4 ohms has pretty good current capability. The best amps double into 4 and double again into 2 ohms, but they are few and far between. More usually, amps will do half again into 4 and some amount more (not much) into 2.

So if you attach 2 sets of speakers to an amp designed to take just one set, you're making life pretty hard for the amp...not recommended.

Regards - and I hope this proves some use (and hasn't completely bamboozled you),

Frank.
 

Silver Member
Username: Petergalbraith

Rimouski, Quebec Canada

Post Number: 467
Registered: Feb-04
John,

A 2-channel system with 4 speakers? As Frank suggested: Don't do it. If you must do it, get a receiver with pre-outs so you can connect an external power amplifier to one of the pairs of speakers.
 

Bronze Member
Username: Johnharper

Pasadena, CA

Post Number: 11
Registered: Apr-05
Wow, shoulda signed up with eCoustics' folks as my high school physics teachers! Frank, I believe I understood the majority of what you relayed to me. Peter says don't do it it and you are almost as direct. However, I have been doing it for about 8 years now. My Scott 325R stereo receiver has connections for four individual speakers that I have hooked up in parallel, each speaker to its own separate negative and positive terminals. The Scott doesn't seem to get hot although I run it for 3 or 4 hours at a time.(This whole thing started with the Quadrophonic jazz back in the 80's when I had a Kenwood quadrophonic receiver). With my current arrangement, I am really only able to set the Scott volume control at 3.5 to 4.0 on a 1 to 10 scale without incurring the wrath of my neighbors. I do not know the Scott specs and had no luck with Google (unless I want to buy a manual). Maybe I should keep what I have but this has been too much fun and educational for me to quit now. I don't think the room layout I have is conducive for a 5.1 or 'bigger' system but maybe I should do that anyway, using my existing speakers for 4 of the 5 (or 6 or 7 speakers) as an interim upgrade? Thoughts from all are most appreciated.
 

Silver Member
Username: Petergalbraith

Rimouski, Quebec Canada

Post Number: 471
Registered: Feb-04
It sounds like your old stereo receiver didn't have a problem with low impedence. It's rarer these days. Or it'll work but sound thin.

You can buy an HT receiver and run it with 4 speakers (main and surrounds) without a center speaker. That's often called phantom mode. Or, if it has pre-outs, you can use the TV speakers as the center channel.
 

Bronze Member
Username: Johnharper

Pasadena, CA

Post Number: 12
Registered: Apr-05
OK, some of this stuff is starting to make more sense to this newbie. If I do this the way Peter G. has outlined, what will be the difference between this and what I have been doing heretofor and advised not to do-run my existing two channel stereo setup through 4 identical speakers? My Scott and most other two channel receivers have A and B Channels with two speakers per channel which gets me to four, I think. Please correct me if I am wrong. By the way, try and not confuse me with TV speakers as I am using this solely for music delivered by CD and FM radio! I have a problem with high impedence.
 

Silver Member
Username: Petergalbraith

Rimouski, Quebec Canada

Post Number: 476
Registered: Feb-04
(If you are only listening to stereo sources, why do you want to feed 4 speakers? Surely it doesn't sound any better, does it?)

Most receivers with A and B switch recommend you select A or B rather than A and B at the same time.

If you used a multi-channel HT receiver for stereo sources, you could select some simulated effects modes to add surround sound to the back speakers (Dolby ProLogic, DTS neo, Logic7, various hall or room effects). Or you could use "5-channel stereo" which ressembles what you have now except that each speaker will be driven by a dedicated amplifier section.
 

Silver Member
Username: Edster922

Abubala, Ababala The Occupation

Post Number: 365
Registered: Mar-05
Actually when I was a poor starving college kid I had this German-designed Korean-built stack stereo called Eroica (probably appealed to me becaused it resembled "e rotica") that let me hook up 4 speakers at the same time, so I had speakers facing each other on opposite walls of my living room.

It was actually quite pleasant, since the couch was in the middle of the room. An enveloping/immersion effect of sorts, such that I didn't need to crank up the volume very high.
 

Silver Member
Username: Frank_abela

Berkshire UK

Post Number: 498
Registered: Sep-04
John

Sorry - I thought I might have overdone it!

As I said in my last post, some amps are designed to take two sets of outputs - it sounds to me like your Scott is designed to do that. That's why it doesn't suffer the way you've got it setup. the Bose speakers aren't particularly difficult loads for an amp to drive and Stereophile suggest that you get plenty of sound from a 35watt amp so I don't see your Scott having any problems - as you yourself have found.

There's no *need* for a modern surround sound amplifier unless you want the surround capability, and in many ways your Scott may be more rewarding than a modern amp anyway, just because it's what you like and what you're used to.

Regards,
Frank.
 

Bronze Member
Username: Johnharper

Pasadena, CA

Post Number: 13
Registered: Apr-05
Maybe I don't have a need, more like a burning desire! My setup is much like Edster's was in college and thus I have my own "surround sound". To answer Peter, I and two friends did a sound test and all 3 of us felt the 4 speaker arrangement sounded better than using only two. So I think I would stick with what I have for now and think about perhaps a "phantom" setup for the future. Frank, I got to Stereophile but could not locate where you got your quote re 35 watt amp. Just curious!?
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