Biamplified RF7's with Push-Pull Tube Amps

[Deang]

Well, my DJH version of the Super Amp showed up on my doorstep today. Since I still had my other Super Amp (because it had not sold yet), I decided to horizontal biamp just to see what the outcome would be.

I couldn't vertical biamp because the amps are in fact quite different. One is Class A with 15 watts, the other is Class A/AB with 35 watts. Besides the power difference, there are some other differences as well, including the substitution for EL84's in the DJH version for the 6GC7's used in the base version.

Since I had to horizontal biamp for the experiment, I e-mailed Bob Gassel earlier in the week asking if he could find out what the impedance of the individual driver sections are for the RF7's.

The response came back that the top is 6 ohms and the bottom is 3.1 ohms. I was a little concerned with the latter number until I remembered the SVS does everything 51Hz and below, and so I figure the impedance doesn't drop that low.

What seemed like destiny in the making, was finding out last night from the seller that Dennis Hadd had actually used this amp with his Magnepans -- and had therefore soldered it up to the 4 ohm taps. Kewl.

So, I took that extended lunch break today just to tear everything down and build it back it up. Kind of had to rearrange that rack you see. I powered everything up and went outside to enjoy an indonesian clove cigarette while things warmed up.

As usual, I started with something a little laid back and familiar. I would save Godsmack for later. I put on Rush Moving Pictures and forwarded to one of my old favorites, 'Witchhunt'. If you are familiar with the song then you know why I picked it. Intense transients on the drums, slamming bass, and Geddy Lee doing 'his thing'. Kelly likes to talk about 'bloom', and I'm sure what he means by this is the opening up of the soundstage, the instruments separating out some, and the whole thing being pushed out towards the listening postion. What I experienced in the first 30 seconds of this cut was more like a mushroom cloud.

I pick up the remote, turn it down a little, and try to go with it. There is certainly more HF energy than before, and the bass is all enveloping. The bass catches me completely by surprise. It was really 'all enveloping' before, or, at least -- I thought it was. The only way I can describe it is to say it now has 'grip'. The SVS certainly isn't doing anything differently than it usually is, the settings are the same as always. This bass is coming from the RF7's, and is nothing short of unbelievable.

The midrange is more forward, way forward. It's not out of balance with the rest of the sound -- just more forward -- and clean. Very, very clean. I look at my horns trying to figure out where all this is coming from. It's almost 'Heritage' in nature, and I try to decide what I think about it. I end up moving my chair back another 2 feet, not because I'm trying to hide from it, but more like the RF7's are telling me to back off so they can breathe a little.

I turn the system down and walk out of the room.

Silence as a reference point.

Cup of Coffee.

Cigarette.

Back upstairs.

Alice Cooper. Now at a more reasonable volume level. It's very wide open, and clean, with dynamics out the wazoo. The RF7's are just cruising along, and it sounds really, really good. The thing that strikes me however, is that it is also sound VERY different, much like if I had just moved a different set of speakers into the room.

The sonic signature has actually changed. The balance it seems, has shifted to the midrange. I know some of you will simply not believe this, but it sounds less like cones and more like horns. At the same time however, it also seems as if the cones are now free to roam and do their thing. The bass coming from the RF7's now seems to be 'hinged' to the SVS.

What I find odd about the experience is that I know much of that midrange output is emanating from the cones, and not the horns -- yet it sounds more horn-like in it's signature.

My ears begin to adjust to the change, and so I begin to ease up the volume. It's tremendous sounding, and I am trying very hard to find fault. With the increase in midrange output, I'm paying very close attention to the midbass -- to make sure it's still there. It is. It's layered perfectly beneath the intensity of the midrange. Previously, the midrange was back a little more, and the midbass was more forward in comparison. The roles have now been reversed, and I decide this is what is accounting for the dramatic change. By the end of the CD, I decide that the upper bass and lower midrange are separated by a hairs width, and I can't really tell anymore where one leaves off and the other begins.

I finish my long lunch with the last 20 minutes of 'Matrix'. At the conclusion of this assault, I decide that this configuration will be very hard to part with.

If I had to characterize the sound overall, I would say it sounds like solid state without the 'film', or 'grain'. The clarity is crystalline, and the soundstage sits in your lap. It's glorious and bombastic, and I love it. I would say it only sounds like tubes in the area of projection and soundstage. This setup appears to be perfectly suited to the type of music I listen too, and it's absolutely killer with movies.

I think I might go on a search for another DJH version of the AE-25 and give vertical biamping a whirl -- mostly because of impedance issues. It would also be nice to get some of what the DJH version does, and put it to the tweeter.

I may do something transitional in the meantime however. I may buy either Ed's DJH AE-3 or a Cary SLP-94L I'm looking at right now, change the leads on the DJH Super Amp from the 4 ohm taps to the 8 ohm, and go back to one amp until I find another DJH Super Amp so I can vertical biamp. I could buy the amp once I unload the SF Line 1, and the base Super Amp. My only fear here is that I would lose the sharpness of the transients -- which I really like.

At any rate, it sounds darn good right now, though probably not a sound that Kelly, or any other die hard tubie would go ape over -- but a sound that would definitely rock Ears back on his heels, and I'm thinking the likes of Tom Brennan might tip his hat as well.

So, in conclusion -- I would say horizontal biamping with push-pull amps works very well with the RF7's.

[timbley]

Your description of the sound you got by bi-amping your RF-7s is similar to the effect I've gotten a few times with my solid state amps, and the new Panasonic digital amps. I was overwhelmed by the improvement in dynamics, clarity, and presence I heard when I bi-amped recently using the Panasonic SA-XR25. This was done using the surround outputs to run the tweeters, and feeding the stereo analog signal off my Denon 2200 DVD/CD/SACD player into the main and surround channel inputs on the amp.

Encouraged by this, I bought 2 SA-XR50s hoping to acheive a cheap bi-amp Nirvana.

So far, this setup hasn't quite taken me to Nirvana. There's a thinness to the sound. Vocals sound slightly hushed and lost behind the instruments. I hope it's just because the amps need some serious break in time. They are brand new after all.

Listening to Qeen's DVD Volume 1 has shown some promise with the 2 SA-XR50s. I have always been disappointed with the sound of this DTS surround music video set. It always seemed muddy and lacking any kind of punch. With the 2 50s, the sound coming form the RF-7s was much, much better than I'd heard before. Even the surrounds and center (which are cheap RCA Linaeum tweetered units bought from RadioShack) sounded better than before, but they were clearly lagging behind the RF-7s. It's now easy to notice how flat the sound goes when an instrument or voices moved to those speakers.

If these SA-XR50s show some improvement, I'm seriously considering buying the RC-7 and RS-7s and bi-amping the whole thing!

I've heard a bit of the sound the RF-7s can make passively bi-amped, and I think it's really what makes the speakers shine, as long as all the equipment is appropriate for the job.

[Deang]

That was an expensive experiment. I would have loved to have kept that setup for longer than I did, but there was no way I could afford to keep both amps at the time. Talk about moving some air.

[maxg]

Interesting experiment you got going there Dean ole boy. Cant help wondering how the performance would compare to a similar single amp with more power - say 50 wpc (the sum of the 2 you used).

From the description of your observations it sounds to me like the main benefit you achieved was additional control of the woofer. That is exactly the effect I achieved going from a 45 wpc PP amp to a 70 wpc ultra-linear with much larger power supply.

The additional benefits of sound stage enlargement, better imaging and image definition also look familiar.

As a sidenote I have also looked at bi-amping, but only for the day when I eventually weaken and get a pair of B&W 802's (they really do need the power).

The problem I will face is that my current "dual-mono" amp (shared power supply - all else separate) is 70 wpc with el34's (prefered tube over KT88/6550 W.H.Y.) and that just aint enough for 802's.

One thought I have toyed with is merely to get a 2nd identical amp. My pre-amp has 2 sets of ouputs. I could, therefore, run the system with one amp per-side feeding both left channels into one amp and both right channels in the other.

If I have understood bi-amping I am describing vertical bi-amping. It would give me 140 wpc per channel which, even for 802's should be enough. I suppose if it isnt I would have to go for all KT88's and have 200 wpc - but with 16 of the buggers to buy that would hurt!!

Of course Tsakiridis already makes a 150 wpc (EL34) or a 200 wpc amp (KT88). What I cant get me head around is which solution would be better - costs are much of a muchness.

[Deang]

Max -- check the date on that first post!

[maxg]

Well that fooled the hell out of me!!

Questions still stand though.

[dbflash]

I'm with Max,

I thought you sold the KHorns and went back to RF7's (not that there is anything wrong with that).

I was all ready to cut you a deal on my AES AE3 preamp.

Danny

[NOSValves]

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On 9/9/2004 3:01:43 PM dbflash wrote:

I'm with Max,

I thought you sold the KHorns and went back to RF7's (not that there is anything wrong with that).

I was all ready to cut you a deal on my AES AE3 preamp.

Danny

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Nothing wrong at all we would just have to tar and feather the fool

Craig

[Deang]

I just read that whole post over again, and remembered it was the setup that started tipping me towards the desire for more power. Believe it or not, though I prefer the sound of the Klipschorns and QUADs -- the setup doesn't walk all over the one described above. Modded RF-7s with a killer sub and powered by clean tube gear is an awesome sound.

Max, I can't really answer the question. It's never apples to apples with this stuff. I did eventually move to the Quicksilver M-60s, but quit running the sub because I thought it sounded more cohesive without it. I definitely had better integration with the sub using the four Superamps.

I think when go to 104db/w speakers, one good amp is plenty good enough, and if one is going to biamp -- they need to go the very expensive route of tube based external crossovers to take it to the next level.

[timbley]

I read an extensive article by one of the amplifier producers about the effects of passive bi-amping. They found it to be far more effective than simply doubling up the power of a single amp or doubling up the power supplies, or of running a separate amp bridged for each channel. I'll look for that article again, since I can't remember why they concluded there was such an improvement with the passive bi-amping.

[rigma]

dbflash

you have PM

rigma