Dynaco Center Channel

Stumbled across this the other day ...



This method of deriving the center (third) channel of a stereo system is an exclusive Dynaco development which provides the proper in-phase (A+B) signal without loss of stereo separation and without the need for an additional amplifier. It is useful where the left and right speakers must be widely separated, and it also enables the use of the third channel speaker as a monophonic system in another location.

Doesn't look like the circuit will work in an ST-120 as designed using my 8ohm speakers, due to the lack of 16 ohm taps for output.

UPDATE > > See Post #13 ... apparently the ST-120 DOES have 16 ohm taps, and Bob gives a step by step on how to make it happen.

Credit where credit's due ... here's the PDF I pulled it from ...

http://www.the-planet.org/dynaco/Misc/Center%20Channel%20System.pdf

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Buy 4 ohm speakers. Sorry I had to say that.

sKiZo would probably build 4-ohm speakers... and with custom cabinets, of course.

Quite happy with my McIntosh XR16's, thankewverymuch ...

Center channel doesn't really work for me here. I have a small listening space, and adding a center channel tends to muddy things up a bit when it comes to the sound stage in a confined area. I speak from experience there as I've experimented some with center channels using an L+R output from a Carver H9-AV holographic generator.



That requires a separate amp, and though I really thought I liked it when I first hooked it up, turning it off proved me wrong. I liked the additional punch in the center stage vocals, but found I was missing too much instrumental positioning from the sides. Given a choice, I'll stick with two channel here ... unless ...

I DO run a center channel off my Oppo SACD using the same amp, but for that, it works. Difference being, it's a dedicated channel scored for the program material - that maintains the unique mix for the side channels also.

Now, on a larger room, I can see where it could really make a difference done right.

Mostly just wondering if anyone here has had any experience with the three channel setup, or whether Dynaco ever really pushed it as an option ...

Does this play back a mono signal of both channels? If so, could it be used for a passive subwoofer in the center?

If you look at the Carver I pictured, it has two additional outputs, L+R and L-R. L+R is recommended for the center channel as it acts as a high pass filter, and the L-R output does the opposite for a sub. That's the usual recommendation.

Can't say for certain on this setup ... I'd think the same would hold true with the dynaco center channel hookup, with the only change being to drive the center with the bridged leads from the POSITIVE side of the speakers outputs ...

One thing I noticed is the Dynaco hookup assUmes three identical speakers, so I imagine they're all full band, including the center. Depending on your sub, it should automatically be setup as a low pass and ignore the high band information.

PS ... I don't do subs myself ... my big boxes are more than capable of creating all the bass I need and/or want ... I'm sure somebody out there has figured out all the do's and don'ts ...

My primary system includes a set of Boston Acoustics A200s in the front and A150s in the back wired through a Dynaco Quadaptor and powered by a VTA converted ST-70; plenty enough base for me. But my secondary system consists of a set of Klipsch Hereseys powered by a Fisher 800B. Its a little lacking on the bottom end and I was wondering if the diagramed setup could work for a center channel subwoofer to extend the base a little more.

Looks like you have a few options to add a powered sub. My preference would be in the following order:

If the Fisher has a pre out/amp in (is that what the jumpers are?), just replace the jumpers with "Y" cables and hook the sub's line level inputs up to those. Adjust the crossover and line level at the sub.

If your tape monitor is a true loop, you could also try hooking a sub directly to that using the line level inputs ... once again, the sub gets the full signal and you adjust the line level and crossover point at the sub. Not gonna work if the tape loop kills any other signal from the preamp section when engaged.

Looks like the Fisher only has the one set of speaker outputs? If line level isn't gonna do it for you, I'd suggest getting a sub with speaker level inputs - most do have those as well as line level. You'd have to gang connections to both your front speakers AND the speaker level input on the sub. Best you use good terminal ends on the wires as it'll get a bit crowded on the screws and you don't want to have any whiskers shorting things. Probably be easier to just make the sub connections at the speaker terminals themselves. Once the connections are made, the crossover on the sub should isolate the left and right channel signals so you won't have to worry about crosstalk, impedance matching, or feedback, and it will also do a low pass so all that's fed to the subwoofer itself is the bottom end. Only problem I see with that is if you have distortion on the bottom of your A200s ...

Some subs also have dual coil windings for even better channel isolation, but those tend towards wOw on pricing ...

As always, do some of your own research first and make sure you're getting what you need.

Thanks much. I'll have to give this a better read in the morning. The Fisher does have a preamp in/out with jumpers. I'd like to give this a try with the Heresys. Thanks again.

Be sure to post back with your results ...

I've been tapping my quad receivers for decades using the best available line level outputs. The old QR series Sansui's had the pre out/amp in which was the logical choice for me to feed an external amp. The QRX series got rid of that, but added so much more. For those I had to go to a tape loop, which works fine. Here's the current setup on my McIntosh MC2205 ...



Difference being I went the extra bucks for hard "Y" connectors instead of the cables. Pricey, but pretty.

Next up, I'm currently building an ST-120 and plan to feed that the same way. Custom case, so I added two sets of inputs at the back ...



Those will be bridged internally, so I won't need the "Y" cables. Like your pre out/amp in jumpers, only inside, An innie instead of an outie?  One set of cables from the receiver tape loop, and one set out to complete the loop. If I ever decide to just feed the amp direct from a real pre, just use either set of inputs and cap the other.

Sorry to confuse the issue ... for your setup, using the pre out/amp in connections, you'll need two "Y" cables and one dual RCA cable to feed the sub's line level inputs. And put those jumpers in a safe place ... they get lost easy and are mostly irreplaceable if you ever want to go back to the stock setup.

My amp has a single channel RCA output for a center channel speaker. Can this be used with a Y-connector for a sub?

I'd try hooking it up direct to a sub first to make sure you're getting the full range out of the jack. The sub won't have anything to work with if the amp's center channel output is set up as a high pass ...

You'll also want to do the math and make sure the ohms rating running two separate (three really, as most sub speaker level inputs are fed to a dual coil) are within the tolerance for the amp. Bigger concern would be whether your amp has the power reserve to drive the sub also, as they tend to suck a lot of watts.

I'd think the better and safer option would be to use the center out as intended driving just a center speaker, and do the "Y" thing on the pre-amp or receiver's line level outputs to the sub's line level inputs. The Dynaco schematic I posted is to eliminate the need for another amp - and that's not an issue with a powered sub anyway.

Worth mentioning ... I doubt if Dynaco had big box super low bass speakers in mind when suggesting three identical speakers for the mod. Bass is non-directional, so having full range down that low in the center wouldn't accomplish anything except maybe overdriving the amp. Long as whatever speaker you use can get you down to around 120hz, you should be golden. What you MAY encounter using a smaller speaker is having that too loud - simple enough to add a load balancing volume pot for that output if it's an issue ... I'd want that anyway as the channel balance is critical between center, left, and right for a good soundstage.

I use a Bose AV speaker here - real nice sound to it, super inert cab so it's not bouncing around in the cabinet, and additional shielding to keep any stray RF out of the speaker due to proximity with all the electronics around it.

Thanx for the heads up on that ... I added a note to the first post ...

So, use the 16 ohm tap and that gives 8 ohms x3 using the diagrammed circuit?

Brilliant! Seeing as the 'new' AV receiver was DOA, and I wanted to use the center speaker in the TV room, wired up the center as shown (two Klipsch Heresy I's and Klipsch center

Wow -- sounds nice! The basement was sounding 'thin' with just the two H1s (suspended ceiling, carpet, large room which just absorbs sounds). This really added some punch.

Until the exchange AV receiver comes in, this will work fine. Amazing what you can do with an old ST70

You may find that you prefer what you get with the current setup. If nothing else, keep it handy for variety ...

Still happy with tapping a center from the Carver H9AV here. I've noticed I've backed both those and the rear channels down a bit over time and actually get better definition of those channels by doing that - go figure.

Will this set up help bring older recordings back more towards the center?

I notice on older music, say recorded in the 60's, that many songs have the drums firmly in the left or right channel. Voices will appear from the center and guitars, bass and harps will also take a side. Modern recordings have the proper staging. This occurs from any of my sources for instance Tom Petty's Buried Treasure on Sirius Internet, Fleetwood Mac Blues Jam in Chicago 1969/2014, or MoFi Dire Straits Brothers In Arms 1984/2014.

The system is Cornscalla Type D's set at 9' center to center with a half inch of toe, MLP is about 14' back in the center. Power is a VTA-70 to a Mini DSP Dirac 88BM, 1200 MK2 w/Ortofon 2M Black. A Sonos Connect controls the Internet and FLAC files and is coax connected to a Cambridge Audio Dac Magic Plus D/A Converter then to the 88DM from its analog out. The TT is connected direct to the 88BM through a PH-16, and is routed through it via the mixer tab on its own configuration tab. In the mixer I can send both inputs to both outputs, but I think this results in a mono signal and the staging is not as good.

Overall the sound staging is fantastic, but its weird to people who have not heard such separation and staging before. So I am wondering if its worth the reconfiguration to try it out. I would test with a Klipsch Hersey and if its better build a 3rd Corscalla.

TIA
Lon

ltusler wrote:Will this set up help bring older recordings back more towards the center

There are quite a few benefits to adding a center channel speaker to even a small room setup. It should help bring the image more toward the center and fill in any holes in the image. I would suggest you try like you said with the Hersey and decide if you like the way it sounds before building a third custom speaker. Here is some good information about the subject.

Here is a "Dope from Hope" article that has some very good information straight from the source that is worth a read.

(Older Article, still has good info)
http://assets.klipsch.com/files/Dope_710706_v11n3.pdf

(Newer Article)
http://assets.klipsch.com/files/Dope_740700_v14n4.pdf

There are some good posts about the subject on the Klipsch forum, in this one the guy is using two klipschorns and a la scala as the center channel, a popular setup with larger rooms.
https://community.klipsch.com/index.php?/topic/19799-arttos-klipschorn-room/&

Thanks, I will read them!

http://2.bp.blogspot.com/-slQaf-9iMlg/ToYI10YekdI/AAAAAAAAA5A/-fnKxadGgDM/s1600/surround+1.gif

Above is a link to the Hafler Circuit, which is, effectively, a poor man's surround sound, and quite an interesting phenomenon when executed well. It helps to have speakers of similar characteristics - though they need not be identical. With the addition of a couple of L-pads, pretty much any speakers will do - as long as the 'rear' speakers are not far less efficient than the front speakers.

Noting the date on the "center speaker" link (1969), this harks back to the day when a goodly number of manufacturers offered "center-channel out" features, some self-amplified as per the diagram (add/remove a jumper on the back of the amp (Fisher and Scott), and some un-amplified (AR and a few others). AR was entirely unabashed at their explanation of the feature - to accommodate exaggerated stereo effects and over-engineered recordings. And keep in mind that adding a center channel will often muddle some features of very well engineered recordings - and for those 'narrow-end' adherents of speaker placement, it will almost entirely wipe all but the most basic stereo effects, making a single -but very wide - sound stage. That Triangle played in Beethoven's 9th all the way up on the right of the percussion section has no place in the 'middle' speaker as one example.

Now, some of us, for our sins, also keep one of these (not mine):

https://www.youtube.com/watch?v=9G0EDV07HwU

For the record, something like this has no real place in a audiophile system - yet it is an entire hoot to have around. Want the Bat Cave? Gotcha! Want a bathroom shower? Got that too! This does need a rear-channel amp, however.

Above all, Enjoy!

so then one could do this added 4 lugs and 4 pole 2 way switch mod
and simply switch to and fro(moving common wires of coarse.
(wish i had something better than paint :/ )

I modded my ST70, capping off the 4 ohm output and replacing it with the 16 ohm.
Then I added a Crites modded Hersey as the center speaker and wired it as in post 1.
The left and right speakers are Cornscala Style D.

The overall sound centered up a bit more, but the Hersey could not keep up with the Type D's and the high end got a little too harsh for my taste. I think the phantom center set up needs identical speakers.

So the next step was to install another pair of speaker runs and biamp the speakers with 4 channels and the passive xovers.  The VTA ST-70 for the horns and a Carver TFM6CB on the woofers.  The Crites CS500 xover's have the ability to feed the HF and LF separately.  I used a 400hz tone through each channel and adjusted the output level to match measuring with a sound meter a meter away from each speaker.  The channel volumes were adjusted in the MinDSP DDRC88A. I also set the crossover points in the DSP to 500 so the amps were only receiving their respective Hz.

This sounded the best yet, the sound stage was nice and wide and all instruments well separated.

At this point I figured I may as well go all in, so I bypassed the passive xovers and wired the amps direct to the drivers. I left the xovers the same in the DSP and used Dirac room correction to set up the delays for the drivers and apply the room correction.

Now it sounds really dialed in. Well at least I think it is. I haven't made the effort to learn REW so I can actually measure it and adjust more from there. That is next. I am also considering adding another Cornscala D and amp for a center and 2 more channels of power.

OTH, I am going to retire in another year or so and want to get a pair of Klipsch Jubilee's, so I may just leave well enough alone and continue to learn the tools, so that setup goes smoothly.

The original Hafler Circuit is quite sensitive to differences in speaker efficiency. And, should the impedance curves be substantially different between them, that will also affect sound color.

Generally, if speakers from the same family are used, there are no issues.

From your description, you took the process to an entirely higher level. Enjoy!

I did the setup as described but I'm now trying to figure out if/how I can add an L-pad attenuator to regulate the center volume.
Is that possible? If so, how?