Passive Bi-Amping or Bridge Mode. Worth it?

organ

Just wondering what your thoughts are on passive bi-amping or using a pair of amps in bridge mode?

I have a chance to score on a second NAD C270 at a good price and was thinking about getting it to bi amp or bridge. I'm still not sure about bridging because I understand that the speaker's overall impedance will be cut by half. I know for sure my speakers dip below 8 Ohms.

I'm still not decided if I want to add another amp. I will play my system some more and see if I really feel the need to add more power.

What do you guys think?

tonyb

If it was me, I'd say nay. Most amps in bridged mode don't like impendence swings much below 8 ohms. Seeing that you have Klipsch speakers, I would ditch both Nad's and move up to a tube integrated, or just a tube amp. You will be shocked how well tubes and Klipsch mate up.

Another Idea instead of buying another amp, is to pick up the dared 2000 pre. For about 4 hundies, your sonic pleasure should increase way more than adding another amp in the mix.

BlueFox

I guess the answer is 'it depends'.

I purchased my first Cambridge-Audio 840W a little over 3 years ago. As a stereo amp, it is rated at 200W/ch @ 8 ohm, and 350W/ch @ 4 ohm. Later I was wondering what would be a good upgrade and it occurred to me to get another 840W, and run them in bridged mono mode. Personally, I suspect they were designed as mono amps, and stereo was added to make it easier to sell. In bridged mono mode they are rated at 500W/ch @ 8 ohm, and 800W/ch @ 4 ohm, which is over double the stereo ratings. I can tell you as soon as I added the 2nd amp I could hear an increase in detail with everything being clearer and more precise. In stereo mode, I ran the pre around -25db for a comfortable volume level, and in bridged mono mode I run the pre at -45db for the same output.

The amps operate in class A for some amount, and then switch to class B at higher output levels. They get hotter than Hades so it helps to have AC in the summer. When I bought the first amp it was more of an accident as I was not aware of just how good they were. I just wanted a more powerful amp, but the Halo A21 was to deep to fit on my rack, so I ordered the 840W instead, which was a very lucky move.

Just the other day I was on Audiogon checking the used price, and they are holding their value well, and going for around $1500 used versus $2500 new.

Feel free to Google the Cambridge-Audio 840W amp for reviews that cover this subject. There is plenty of positive press.

organ

Tony,
I already have 3 tube int's and two amps. Also have a tube pre.
This current set up is an unexpected synergy for me. I think it's my cd player. It has a pair of 300B power tubes for gain with output transformers. So it's basically a 300B SET amp.
When I decided to try it out on SS pre and ampr, I was floored. The tone is "tube", but with unlimited power. The bass and slam is incredible. These Klipsch, even though they're rated at 98db sensitivity really appreciate the extra power. With enough tube magic from the source, I'm really enjoying SS amplification.
When I run my tube integrateds, the mids and highs are more open with more air. With SS, I lose some of that but I get extra slam, power, and dynamic swings. I prefer this. There is still enough tube sound that the overall system sounds like it's tube based but the SS dynamics give it away lol.

Blue Fox,
Thanks. Now that's interesting. I really want to try bridge mode but I'm very nervous about impedance dip. I've heard stories about people blowing drivers when they ran their speakers this way. Did you crank up your system when you had that configuration? Do you know the min imp. of the speakers?
Thanks for the heads up on the Cambridge Audio, but I'm trying to keep the current sound/synergy. The used C270 I'm able to get is not expensive at all, that's why I'm thinking about experimenting.

BlueFox

organ wrote: »

I really want to try bridge mode but I'm very nervous about impedance dip. I've heard stories about people blowing drivers when they ran their speakers this way. Did you crank up your system when you had that configuration? Do you know the min imp. of the speakers?

I run it at 100+db (measured with Radio Shack SPL) on Friday and Saturday night while in R&R mode, and in the high 60 to high 70 range at other times while listening to classical. The speakers are PSB Synchrony One towers and are rated at 4 ohm. I do not know what the impedance range is over the frequency response curve.

One point I forgot to mention is that I have MIT Shotgun S1.3 ICs in my system, and I wanted to add the S1.3 speaker cables to have a complete MIT cable system. It turns out the MIT speaker cables did not like the amps in mono mode. After installing the cables and powering up, I was getting pops and other bad sounds from the speakers. Put the amp in stereo mode and everything was fine. Back to mono mode and pop, bang, pow. Fortunately, Joe Abrams took the cables back. Other than that, everything has been fine. The amps have very good protection circuitry built-in that makes them practically indestructible.

tonyb

Organ, Sorry pal, I missed that tube goodness in your sig. Still, those are pretty efficient speakers, how much power do you need ? If you like the nad sound, just move up the ladder in the same brand for more current delivery.

I'm alittle fuzzy on exactly what you want to accomplish by adding another amp. You like the sound, you like the slam, whats missing ? Maybe...just maybe, your at that point where you want more than what your current speaks can deliver. Upgrade time ?? Come on, say it.

CSM41

I have used a passive bi-amp in the past and it sounded awesome. I used a Dared S2000a Preamp, a custom tetrode tube amp, and a Parasound HCA-1500 amplifier mated to a pair of Snell Acoustics Type EII's. I ran the tube amp to the highs and the big Parasound to the lows. I also picked up the lowest octave or two with a subwoofer. The resulting sound was fantastic.

organ

Blue Fox,
Thanks for the info. I will keep that in mind. I think I'm not gonna go for it yet. If the upgrade bug bites again I probably will try it out.
I spent the last few days listening to my system at good spl levels and I'm very impressed with the overall sound and sense of power.
The offer on the NAD amp is very tempting, butI really need to watch my spending. I've been doing very good so far. We'll see how it goes. I'm trying to resist for now lol.

Tony,
You're right. The speaks are already 98db sensitivity. I was curious what bi-amping or bridge is like because I've never tried it before. I'm on a power trip. I just can't get enough of dynamics and slam lol.
But yeah, I already have my next upgrade in mind ha ha. It won't be for a few more years at least. I'm going to save up for the Klipsch RF-7II or La Scala II. Selling my pair of La Scala a few years ago was one HUGE mistake that I still regret to this day.

CSM41,
I going to give that a try but I will have to buy an spl meter first so I can match the level on both amps. Thanks.

CSM41

I was lucky because my Parasound has dual gain controls on the back. I was easily able to dial it in.