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Old 13th April 2011, 02:36 PM   #1
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Default Qustions about centre speaker connection

Hi all,


I have a vintage tube amp that has provision to connect a centre speaker. The ground terminals for the left and right channel speakers have a jumper connecting them. The instructions are to remove this and connect a third (centre channel) speaker there if it is so desired. The questions that I have in this regard are:-


1) Is the centre speaker a mono channel?
2) Is the power output equal to the sum of both channels?
3) Can only the centre speaker be connected, without the L/R channels and the amp run safely?
4) Is this possible with all tube amps?


Regards,


analogadikt
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Old 13th April 2011, 04:14 PM   #2
DF96 is offline DF96  England
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It might help if you tell us the name of the amp.

My best guesses are:
1. no not mono, perhaps L-R difference signal?
2. I doubt it
3. no, probably not
4. no, I have never heard of this connection before

I can't think why the amp designer thought someone might want to do this, as it would play havoc with stereo imaging.
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Old 13th April 2011, 04:34 PM   #3
kevinkr is offline kevinkr  United States
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Just to add to DF96s comments based on the description of how this connection is done would probably degrade the performance of the left and right speakers as this center speaker probably appears in series with both of them. This is a connection I would not use.

HH Scott and a number of other US hifi manufacturers provided options for a center speaker in some models, but this was usually a mono sum of left and right just after the volume control and required an external amplifier.

As for the reason some manufacturers did this, in the early days of stereo a lot of speakers had relatively poor MID and HF dispersion and widely spaced speakers could result in a " hole in the middle" between the speakers. Installation of a center channel was thought to mitigate this. Knowledge of speaker placement and room design was pretty much non-existent at the time, but the limited experimenting I did with the idea some 20yrs ago indicated it would usually have substantially degraded performance. I found the best compromise was the run the speaker at considerably lower levels than I would have expected, but ultimately best of all was with it turned off. (Note this is different than true three channel stereo such as recorded on some reissues of RCA LSC recordings on SACD which are 3 channel stereo, and active steering of two channel stereo with true mono into a center channel with left and right reproduced by their respective transducers can work pretty well with identical speakers, but IMHO is entirely unnecessary with stereo speakers that image properly.)
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Last edited by kevinkr; 13th April 2011 at 04:38 PM.
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Old 14th April 2011, 07:41 AM   #4
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Quote:
Originally Posted by DF96 View Post
It might help if you tell us the name of the amp.

.
The amp is a Dynaco SCA35.

The stereo imaging with two speakers is perfect and I have no intentionof trying a third speaker for that. I have been looking at the possiblity of having a dedicated mono vinyl playing system, I do not have a mono amo right now but have several stereo amps, and was wondering if I can use one of them.Hence these questions.

Regards,
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Old 18th April 2011, 12:34 AM   #5
rman is offline rman  Canada
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Good old Dynaco!

I have an old Dynaco SS amp that has connections for rear speakers. They make a L-r and a R-l output with some stereo blended in. Depending on the recording this can sound really good.
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Old 18th April 2011, 12:49 AM   #6
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by rman View Post
Good old Dynaco!

I have an old Dynaco SS amp that has connections for rear speakers. They make a L-r and a R-l output with some stereo blended in. Depending on the recording this can sound really good.
The old quad adapter thing.. Think it was pretty much variable L-R though IIRC. I had one of those outboard Dynaco boxes and also built one of BB Babani's ersatz transistor quad decoder circuits in the mid 1970s. Clever but not very convincing..
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