[kck]

I have found that the sound quality improved (to my ears) when using a quality tube preamp between the source and the mighty little JVC. But with or without the pre, I am feeling a bit of  lack of slam/attack. Bass quantity is ok, just seems a little woolly and, well, some attack would be welcome. I don't think it is my room 'cause when I owned an Aragon 8008 (yes, yes, I know) it had plenty of cojones with the same room, same equipment.

I have been reading more and more about impedance matching and wonder if this might be the culprit; certainly an easy place to start. So here are my numbers... any with  skill in deciphering these please chime in.

CDP: output voltage: >= 2V, 47 kilo-ohms, into...
Tube preamp: input imp: 100 kilo-ohms, output imp: 180 ohms into...
JVC F10: input imp: 330mV, 47 kilo-ohms, passive biamping into...
full-sized speakers: 4 ohm nominal (am told it is fairly stable), 90 db eff, 28 hz bass-rated (realistically I think 35).
Also using REL Strata II subwoofer wired using Neutrik connector to bass (surround) output of JVC.
Room is fairly large and has a mix of surfaces, carpet and soft furniture along with some wood, glass and stone (fireplace). One thing is, it has virtualy no back wall but a large opening behind the listening position, leading to another room.

Any problems you see here? Theoretically, and not counting the tube effect, should the sound be better or worse going direct to the F10 and removing the preamp? Or do I just not have enough power there, given the speakers (not about to change) and the room (ditto) , and should consider a more gutsy amp?

[TheChairGuy]

You might be looking to hard for reasons why it ain't got 'oomph'...it's not a big, powerful amp...but it's a fine one for small and medium rooms. It specs at 100 watts...I'd say it's an honest 40 watter.

It's probably gassing out trying to drive (even stable) 4 ohm speakers in a big room.

It's $229.00...it can't do it all, but for many, it's better than you'd ever have a right to expect  for that amount  

[JohnnyLightOn]

It's really frustrating, because the top end on this cheap little F10 is so open and detailed and sweet.  But the bottom end - at least on my 4 ohm 90db B&Ws - just isn't there.  It's a very lopsided presentation in my system.  

But to get this top end in a more powerful amp, I suspect we'd be spending five times as much.

Have you tried bi-amping using the surround channels on the F10?  If so, how much has that improved the bass attack and slam?

[TheChairGuy]

The bottom end on my 4 ohm Maggies on the JVC is different than the bottom on the Audio Source Amp 3 (SS, 150 watt AB amp).  

It's the only other amp I've had on the Maggies, so it's hardly rates as slam dunk comparo, but the bass is a different quality when you listen hard at it vs. SS.  Not necessarily better, or worse, just different.  It sounds a like it is a little tauter, but less volume, overall.  

The Amp 3 is a pretty fair comparo as it retails for $599 and less at retail - so it's not the superbuck league, but it does the job.

Anyway, that's how and what I hear with it  

[timbley]

It's really frustrating, because the top end on this cheap little F10 is so open and detailed and sweet.  But the bottom end - at least on my 4 ohm 90db B&Ws - just isn't there.  It's a very lopsided presentation in my system.  

But to get this top end in a more powerful amp, I suspect we'd be spending five times as much.

Have you tried bi-amping using the surround channels on the F10?  If so, how much has that improved the bass attack and slam?

I've tried biamping with the surround channels with my RF-7s. The passive route doesn't yeild much gain. But if you go with an active crossover, it's a substantial improvement in bass power.

[JohnnyLightOn]

timbley, I assume that the crossover in my speakers is passive, not active.  
I removed a set of jumpers from inside each speaker, and ran the surround outs to the LF inputs on my speakers, and the main L+R outs to the HF inputs.  Is this the passive route?

The result was that there was a substantial increase in lower-midrange richness and also more bass.    But there was a strange side-effect: I felt a distinct disconnection between the upper frequencies and the lower frequencies.  It bothered me enough that I switched it back.  Could it be possible there's a very slight but uncorrectible timing difference between the two amp outputs?

[timbley]

timbley, I assume that the crossover in my speakers is passive, not active.  
I removed a set of jumpers from inside each speaker, and ran the surround outs to the LF inputs on my speakers, and the main L+R outs to the HF inputs.  Is this the passive route?

The result was that there was a substantial increase in lower-midrange richness and also more bass.    But there was a strange side-effect: I felt a distinct disconnection between the upper frequencies and the lower frequencies.  It bothered me en ...

Yes, they're passive in your speakers, and yes, what you've done is passive bi-amping. How did you get sound to the surround channels? Were you using the analog inputs? It's important that the signal not be delayed or processed differently for surround channels. If you have the receiver in DVD multi mode and use the 5.1 analog inputs, the signal to each channel will not be altered or delayed in any way.That's great to hear you got some increased midrange richness and bass. I wouldn't have expected it.
I used to run my Klipsch RF-7s as you described, but it didn't give me the same improvement you're getting. Of course, on the RF7, the midwoofers are doing most of the work. So giving the horn tweeter it's own amp was doing little to help the amp that was running the woofers.

[JohnnyLightOn]

Thanks for the response.  I'm kind of surprised myself, wondering just how much power the tweeters were using.  I figured the woofers took up most of it.  

But there was still too big a deficiency in the sound for me to enjoy it.  It was the lack of cohesiveness to the sound between the upper and lower ranges, as I described.  

Admittedly, I accomplished the bi-amping by using a pair of $3 RCA Y-adaptors to split the output from my DAC, so that may have had something to do with it.  I might try it again when I buy or make a better cable.  Furthermore, I was using HD14 speaker cable for the lows which I didn't give a proper chance to break in.  The improvements weren't huge, but they were large enough for me to want to make this work.  In addition to the filling-in of the lower midrange and the bass, the sound presentation was more relaxed.

[timbley]

I don't think the cheap y-cable or the speaker cables are causing the discontinuity in sound. When the speaker manufacturer designs the passive crossover, they are intending that you will be using the dual binding posts for bi-wiring, not bi-amping. With bi-wiring, the upper and lower portions of the passive crossover network and drivers still interact with each other. When you bi-amp, the crossover components are completely isolated, changing the characteristics from what was initially designed and tested for. I noticed something seemed a little odd with my Klipsch too when I did that, although it wasn't too bad. I ended up going back to one amp and preferring it.
Removing or bypassing the speaker's passive circuit and using an active crossover is definitely the way to go if you want to bi-amp and get a real substantial benifit.

[JohnnyLightOn]

This makes sense.  Thanks, timbley.  

[Horizons]

I've tried biamping with the surround channels with my RF-7s. The passive route doesn't yeild much gain. But if you go with an active crossover, it's a substantial improvement in bass power.

Ditto:

I am using the F10 to biamp my Maggie 1.6QRs. Removing that high level passive crossover did wonders for the bottom end.

FWIW, I am also running a tube stage between my DAC and F10. Here is my signal chain:

Sony 222ES transport
Non-OS, filterless DAC with passive output stage (.7V) (Monica DAC)
Tube stage (12AX7s)
Line level passive 2 way xover (low level clone of Maggie 1.6QR xovers)
JVC F10 (bass into front, highs into surround)
Front speaker outputs driving bass panels
Surround speaker outputs driving tweeters

In this setup, the JVC digital amps are hooked directly to the Maggie panels.

I am planning on adding my powered sub but right now I don't miss it much.

[timbley]

Your passive line level crossover implementation sounds very interesting. I tried a very simple implementation once with some NHT super zero speakers. Cory Greenberg was writing for Stereophile, and he had a series of articles about high end sound on the cheap. He recommended using the Super Zero's with a subwoofer, but not using the subwoofer's crossover. He gave instructions on how to attenuate the bass frequencies to the Zero's using a simple first order line level crossover. It worked perfectly as far as I could tell, and was very clean. I may have to give that idea a try again and see how it compares to using the active digital crossover.  The Klipsch horn tweeter needs some pretty significant EQ, but I suppose it could be accomplished in a passive line level circuit.

[timbley]

Ditto:

I am using the F10 to biamp my Maggie 1.6QRs. Removing that high level passive crossover did wonders for the bottom end.

Have you noticed improvements in the midrange and treble? Imaging?

Thanks.