[tbrooke]

We were having a discussion on the VMPS forum about bi amping and I am confused about it so I thought I would ask the ampilfier experts here.

Basically the VMPS biamping aproach uses two separate inputs - one for the mid high frequencies and one for the bass with a passive crossover to divide the signal after the amplifier. After some discussion we figured that this results in the amplifier receiving as input a full range signal and the bass amp would have the load of the bigger speakers and lower frequencies and the other amp would have less of a load allowing a less powerful and more refined (?) amp on top. But it seem this would depend on the amp. Some mentioned that certain amps expect a greater load and might not work as well in this situation. Since you folks design amps are we helping things or hurting things by doing this.

A couple folks are using Van Alstine tubes (hybrid) on the top end and solid states on the bottom.

I know this is a vague question but I was just curious

Tom   

 

[Wayner]

Using a Y-cable from the pre-amp to the two amps will halve the impedance value and the drive to each amp will be reduced. If you use 2 different amps in vertical bi-wiring, the gain may be different from each of the amps, puting an imbalanced output to the speakers (to much volume to high or low end), creating either too much bass or too much high end output. If you have 2 identical amps, that would be better.

W

[warnerwh]

Haven't been to the VMPS forum today but I'm one of the people using a hybrid on top and SS on bottom. The AVA 550exr rev.5 I use has a unique quality in that it's unusually clean sounding with excellent timbre, unlike any ss amp I've used. The planar/ribbons are very revealing.

Using a ss amp on top and bottom I don't see much need for if it's a passive setup. If using active crossovers it's well worth it. There's downsides to the active setup too though and personally I'd rather not mess with what a speaker designer does with the circuitry between drivers as you could easily mess things up.

In my opinion if you own any revealing speaker, Vmps or otherwise, I have to recommend one of the Fetvalve amps. Well worth a try at minimum being as I think Frank offers a 30 no questions asked return policy.

[Wayner]

I do want to try bi-amping my Paradigm 40v.3's with my Ultra 70 AVA amp for the top end and the 260EX on the bottom end, but I can't find my Switchcraft y-cables! Yea it might sound out of balance and I really wouldn't know how to correct it if it was, but I do want to try and hey, it might not be that far off!

W

[WEEZ]

Wayner,

Frank can tell you what the gain difference is between the two amps...you could prolly just pad down the one with higher gain with a resistor or two. It would sound sweet.

WEEZ

[Wayner]

I must be losing it WEEZ, the Van Alstine pre-amps have 2 line outs! So now I have a project for tomorrow! I do need to get some more cheap speaker wire, say 16 awg should do it. And I like dual banana jacks. I did order some from that company www.monoprice.com. Maybe I will do that for Friday night. Remind me to buy beer. Could be a long listening session.

 

[WEEZ]

I never run out of beer. 'Cause...well, ya' just never know. Just connect everything before you drink the beer(s). 

[avahifi]

Wayne, the ST-70 has significantly lower gain than the other amplifiers, about 15 dB as I remember.  Your efforts are not going to work unless you have some easy way to make up for the gain difference.  Perhaps feeding the phono out signal from the tape out on the first preamp to a line in on a second preamp connected to the second amplifier so you can match levels.  Kind of a pain in the butt approach.  Padding down the output of the "hotter" solid state amp resistively will destroy its damping factor and you will be using up a lot of power heating resistors (they better be 100W rated or so - the size of footballs) for this to work. Padding down the input ahead of everything to the amp could work possibly.

Probably the best approach would be with an excellent electronic crossover, any help out there for a good choice?  Remember too that this approach puts essentially another solid state preamp into the circuit (all the line and equalization circuits of the equalizer) and Van Alstine's addendum to Murphy's Law is that an audio system performs up to the quality of weakest link in the system.  It is the user's job to identify correctly what is the weakest link and do something about it.  Rarely will the speaker wires or cables be the weakest link.

Regards,

Frank Van Alstine

[Tweaker]

These are expensive but highly regarded and would do the job, I think:
http://www.tweakaudio.com/Ultimate%20Attenuators.html

[WEEZ]

Yeah, something like that was what I was thinking.....

[Wayner]

Yikes, Tweaker, I thought those where my bathroom faucets.  Perhaps I will leave well enough alone and be happy with listening to one or the other amp...and I certainly am. Thanks, Frank for helping me pull my head out of my...well, you know! 

I guess I didn't realize the 15db difference in gain, which I would of discovered if I had done the bi-amping.

It was going to be for fun anyway.

I still got the itch to bi-wire something. Maybe I'll put the 170ex on top and the 260ex on the bottom?

Maybe I should just have a beer and put on some Neil Young and forget about the the idea all together.

Now, what was I thinking about?

[OldCoder]

I use a modified Dahlquist LP-1 with an Ultra 550 for everything from 60 cycles up to drive DQ 10s, and an Omegastar 240EXR to drive a pair of DQ-1W subs, it works very well for me.

Pulling the deep low end off the main speakers allows the Ultra 550 even more control, and level matching to the subs is easy with this crossover.   It was designed to crossover as high as 400 cycles (to allow DQ-10 woofer biamping), although I have never tried that.

Before I got into Dahlquist speakers, it did a wonderful job of mating a sub to a pair of B&W Matrix Ones, again creating greater definition in the satellites.  If my DQ10s weren't so power hungry, I would think an Ultimate 70 with an Omegastar 240 for the bass might create a very sweet sound.

[Tweaker]

Yikes, Tweaker, I thought those where my bathroom faucets.  Perhaps I will leave well enough alone and be happy with listening to one or the other amp...and I certainly am. Thanks, Frank for helping me pull my head out of my...well, you know! 

Actually, that's a pretty good analogy.
You know, sometimes you have to be willing to part with a little of that hard earned cash to to get to that next level, and biamping, especially with quality sounding gear like you have, can reap tremendous rewards.

[Wayner]

I didn't want to start a new topic, but I'll jump on this one. I gave up on the bi-wiring-what-ever idea and started fooling around with different pre-amps/power-amps/speakers.

The AVA T8 with a U70 and vintage Dynaco A25xl's are a marriage made in Heaven. Yes, the T8 and U70 are all tube but....Billy Idol's first album sounds so incredible. If you are a vinyl guy this is the combo!

 

[avahifi]

I meant that the St-70 has a voltage gain of 15, the normal stuff has a voltage gain of 25, not a 15dB difference.

Frank.

[CometCKO]

Another alternative for an active crossover module is the MT-1 module from Linkwitz Labs.  Of course, you will need to populate the board with the right value components for your speaker drivers.  I'm currently using the MT-1 as an active crossover for Magneplanar 1.6 speakers.  The factory crossover is assymetrical (not the same slope for the low pass as the high pass).  The MT-1 let me create an external crossover that exactly matches the factory crossover characteristics.

Avoiding the stock (puny, nasty) internal crossover, and the extra damping power obtained by connecting my amps directly to the drivers has made a huge improvement in these formerly not particularly high-resolution speakers.

highly recommended.  See http://www.linkwitzlab.com/pcb.htm#MT1

Oh, the MT-1 board was something like $40 and the parts were less than $100 including the power supply and case.  So this is a pretty cheap way to get very nice sound.

Hope this helps someone. 

[avahifi]

Just wondering what ICs are used in the Linkwitz crossover boards.

I also wonder about the effect of essentially putting an IC preamp (the crossover board) in series with hybrid or tube equipment.  Since I have always suggested that the system can perform up to the capability of the worst sounding unit in the chain, and with this crossover you would now essentially have an IC preamp in the chain, what the musical effect would be.

Regards,

Frank Van Alstine