Hook up sub (single line in) to vintage amp

[Emile]

Hoping to get some of your expert advice  

Looking at adding a sub (R-115SW) to my 2 channel stereo, but have not been able to figure out "how."  Amp is a Kenwood Basic M2 (220wpc) with A/B speaker terminals which drives CF-3's. (Preamp is a Kenwood Basic C2.)

Only input option on the sub is RCA "SINGLE in" (and a LFE in). Was looking at speaker-to-line converters like this ... Russound ADP-1.2 Speaker-level to Line-level Adapter ...

but all these devices have L/R RCA connectors. Do not think I can combine these via a "Y" connector as I believe (??) that will also screw up my other L/R speakers. No clue ... appreciate your inputs.

Thanks, Emile

 

[WillyBob]

I'll be watching. I'm faced with a similar situation.  I would like to add a sub to my system and all I have to work with is a pair of speaker outs, no sub out...

[Emile]

5 minutes ago, WillyBob said:

I would like to add a sub to my system and all I have to work with is a pair of speaker outs, no sub out...

Yes  should be simple. Actually it is simple if you get a sub with L/R or high level speaker inputs in.  But most newer Klipsch subs only have a single RCA in ... haha; found a 15" for $250 ... hope we get some advise  

[WillyBob]

thanks

I thought I was going nuts. ... I have a junk sub with l/r speaker in and out.  Thought the high end stuff would be similar.  

HaHaHa

If you afford a nice system, you can afford ..... No accounting for vintage amps/receivers.

[Emile]

Just to clarify one of my questions ... if I take let's say speaker B outputs and combine them to mono, will my A speaker outputs be "mono" also???

[Tarheel]

I've assigned your question to Carl.  He should be along shortly.

[WillyBob]

That IS a good question.  I want to say they would have to be isolated from ea other...seems speaker impedance would change drastically otherwise..

 

to be sure, there is a way

I was working on pinsetter machines that were 60 years old... We retrofitted computer scoring and electronic triggering to them.

[WillyBob]

I do have a semi fix for my problem. MWMs, if I care to do some building.

[WMcD]

What you need is a circuit like the one PWK used in his center channel mixing box.  PWK need a mono or Right plus Left signal for the center channel and you need a mono or Right plus Left signal for the woofer.  [Addition by Edit: You can do some creative thinking by visualizing you sub as a center channel speaker with very good bass and not so good treble!]

 

The Dope from Hope has one schematic  where it is shown fed by RCA connectors (line output of the pre-amp) and another schematic where it is shown fed by speaker wires (speaker level output of the power amplifier) .  But the circuits are essentially the same in the use of the three resistors [47k from memory].  The device in photo might be similar too.

 

You are correct that it is a bad idea to connect amplifier speaker or line level outputs together in parallel.  They wind up fighting each other rather than combining i.e. mixing or adding.

 

It is a different situation when the signals combine through the high value fixed resistors.  The signal from the right output does appear at the left output.  However, the outputs have enough authority to not be influenced.  This is actually the effect of a relatively "low output impedance."

[Emile]

OK; did some more searching ... primary us is with an Oppo DV-980H, which does have a "sub out."  Could I just use this??

Thanks, Emile

[garyrc]

3 hours ago, Emile said:

1 hour ago, Emile said:

OK; did some more searching ... primary us is with an Oppo DV-980H, which does have a "sub out."  Could I just use this??

Thanks, Emile

 

 

I believe you can ... but wait for some more technical person to say so.  Since the subwoofer has its own amplifier built in, I would think the OPPO player's "subwoofer out" would be fine.   It has already mixed L & R at the bass end.   At least I hope so.  In this day of home theater (starting about when Thomas Holman came up with .1) there is (AFAIK) no such thing as a R & L channel for subwoofers, because bass is non-directional from about 80 Hz down, where THX recommends crossing to the sub, if your mains go low enough (but they should be set at SMALL).  For people who want 2 subwoofers, there is often a second sub output, but it, too, is mono and contains everything, pre-mixed.

 

But, I don't think you will be able to use the Main Volume Control on your preamp or receiver, unless your OPPO has a "sub volume" somewhere, like on the remote control.  If it doesn't have  a separate volume control, what was OPPO thinking?

 

I agree with WMcD, the "center channel out" on PWK's box should work.  Caution: PWK did the "center channel mix box" twice.  The first one didn't use a separate power amp for the center channel.  Some amps didn't like it.  His second one used 3 channels of amplification, with the mixing to create the center channel done between the preamp and the 3 power amps, with some pots for balancing.  In your case, the third power amp is in the subwoofer itself, so no problem.

 

BTW, McIntosh and others started putting a center channel output on their preamps (for a while).

[Emile]

44 minutes ago, garyrc said:

I believe you can

Thanks Gary ... very helpful  

[CECAA850]

16 hours ago, Tarheel said:

I've assigned your question to Carl.  He should be along shortly.

Answered in his other thread.

[CECAA850]

16 hours ago, WMcD said:

What you need is a circuit like the one PWK used in his center channel mixing box.  PWK need a mono or Right plus Left signal for the center channel and you need a mono or Right plus Left signal for the woofer.  [Addition by Edit: You can do some creative thinking by visualizing you sub as a center channel speaker with very good bass and not so good treble!]

Way too complicated.  A couple Y adapters and he'll be up and running.

[WMcD]

"Way too complicated" ?????   PWK, then, was wrong.  I don't think so.

 

Edit:  I see a possible ambiguity.  I should should have typed: "If it is way too complicated and simply using a Y connector works as well, then this would mean PWK was wrong in the design." 

 

I didn't mean to indicate a time issue: i.e. that PWK was wrong (then) back in that day. 

 

I believe my little rhetorical device is clear though.  Any confusion is regretted.

 

WMcD

[CECAA850]

2 hours ago, WMcD said:

"Way too complicated" ?????   PWK, then, was wrong.  I don't think so.

 

WMcD

My method uses 3 RCA Y's.  No circuit to build.  What could be simpler?  He has low level outputs, which I believe weren't prevalent "back in the day" and simplifies things greatly.

 

 

[CECAA850]

.

[garyrc]

Use this link soon, because these links have a way of disappearing.  If it does, see Dope from Hope Vol 14 No. 4 Revised July 1974, supersedes Vol 11 No.3 July 1971.  PWK started publishing on Wide Stage Stereo (3 channel) in about 1959.  Some others conducted supporting research, maybe John Eargle. 

 

Does your subwoofer have a low pass filter, adjustable or fixed?  If so, I really think this would work, feeding your sub from the "3rd channel out" of the box.  [EDIT: Yes it has a "LOW PASS CROSSOVER AND VARIABLE PHASE CONTROLAllows you to tune the subwoofer to your Klipsch speakers and to your room, establishing the ideal level of bass."]   Your box would not feed a 3rd channel power amp, because you would use the one in the subwoofer itself.  IMO, the line level output version of the box might be better than the speaker output version, if you can use it.  I would be tempted to use resistors of higher wattage, given today's SPL preferences.

 

If the box is located near your control center, you could use the pot to set the center subwoofer volume, without walking over to the sub.  I would really think you would need the pot, because, contrary to the prevailing wisdom, different sub settings can be needed for different recordings.  I'd think being able to set the low bass balance from the listening position would be handy, given room modes and all.

 

http://assets.klipsch.com/files/Dope_740700_v14n4.pdf?_ga=2.41343074.1714091658.1546445054-1500310039.1546445054

 

 

[WMcD]

Some nice comments by Gary.

 

But let me side with PWK and his use of 1/2 watt 27k resistors rather than Gary's thought that a higher power rating is a temptation given today's SPL preferences.  

 

I"ve done some calculations and concluded that it takes a stereo amplifier rated for 3375 watts to reach the 1/2 watt rating.   Please check my calculations.

 

The only part which may be unfamiliar is the analysis that the highest power is delivered into the 27 k resistors in the arms of the Y (on the schematics) is when the stereo amps are operating 180 degrees out of phase.  Maybe some sound sources do that 180 degree thing as when we have only surround in old style Dolby.  In a more familiar sense: It does create a condition like bridging stereo amps. 

 

This results in a voltage of zero at the meeting point where the center channel or mono signal is extracted.  In out of phase condition there is no center channel signal to be had.

 

Anyway. 

 

Assuming you use the speaker output version of the box the calcs show that you need a stereo amp rated for over 3.375  kilowatts (and outputting all of it) to put the 1/2 watt into the 27k resistors.  Further, you'd be putting that 3.375  kW into the speakers.

 

Assuming  you use the line output version, the voltage at the RCA jacks must be 116 volts -- an obvious impossibility.

 

In conclusion, PWK was conservative in his choice of 1/2 watt resistors.

 

Addition by edit:  I hope Gary is not insulted. That is not my intent at all.

 

WMcD

Center Channel Mixer and 27k half watt R.zip

[garyrc]

8 hours ago, WMcD said:

 

In conclusion, PWK was conservative in his choice of 1/2 watt resistors.

 

Addition by edit:  I hope Gary is not insulted. That is not my intent at all.

 

WMcD

Center Channel Mixer and 27k half watt R.zip 11.29 kB · 0 downloads

 

No problem.  I'm glad that 1/2 watt resistors will be O.K.