An experiment with passive horizontal bi-amping.

[XCop5089]

I have recently been on the hunt for a replacement power amp for my system. I currently use a Conrad Johnson Premier 350SA (solid state) to power my current-hungry TAD CR1 MKII speakers, which are 86db efficient and a nominal 4 Ohm load! The CJ power amp is good for 600 watts into 4 Ohms and has always been happy driving the TAD's.

I have owned the CJ 350 since 2004 and although it still works perfectly, I decided that I would treat myself to a new power amp for my 65th birthday (yesterday)!

Little did I realise how fussy the TAD CR1's would be of a partnering amplifier and an added complication was my Conrad Johnson GAT 2 preamp, which operates in single-ended only, so any balanced power amp with XLR only input, would have to be ruled out on the grounds of complexity in matching and integration. I believe that it can be done with the insertion of a transformer-based gizmo converting the single-ended signal at -10db to a balanced XLR output at +4db, allowing a balanced XLR set of interconnects to connect to the power amp inputs. However, I am convinced that this would be a compromised way of doing things!

Having auditioned a few contenders, I settled on the purchase of a TAD M2500 MKII power amp, which will accept balanced and single-ended connections, with a switch on the rear panel to select the appropriate input. The amp is beautifully built (as are all TAD components) and is hewn from a 90 Kg solid aluminium block, to combat vibration! The finished amp weighs 43 Kg and is constructed as a true dual-mono chassis, with 2 X 1 Kva transformers for the analogue input stage and a Class D output! It delivers 500 watts into a 4 Ohm load and this output doubles as the impedance is halved, indicating a very healthy power supply. The amp runs cool and consumes 250 watts in operation and a measly .5 watt in standby, due to Class D operation!

As a single stereo power amp, it works very well in my system, providing a convincing grip of the TAD speakers and delivering a smooth, highly detailed and dynamic sound with a deep and broad soundstage. The bass is very deep and powerful!

Having the opportunity to borrow a second, identical TAD M2500 MKII power amp, I set about, removing the bi-wire links from the speaker terminals and with another set of stereo RCA phono interconnects from the second set of preamp main output terminals on my GAT 2 preamp and a set of Tellurium Q Ultra Black II speaker cables, I configured my system for passive horizontal bi-amping, with a kilowatt of power available for each channel (I also utilise two REL Gibraltar G2 subs, crossed over at 32 Hz to underpin the sound and enhance imagery and soundstage)!

First track on was "Unfinished Symphony" by Massive Attack and I was relieved to hear that all the faffing around was well worth the effort. The bi-amped mode produced a smooth, totally unforced sound delivery from the speakers, with enhanced separation and headroom. The soundstage was highly detailed and depth/width of image was increased, compared to use in a conventional stereo setup.

I have no doubt, that tweaking further with speaker and interconnect cabling would bring further improvements to the sound.

I have a couple more days to enjoy the bi-amped system, before returning the second loan power amp, but I am glad that I carried out the exercise to see what bi-amplification could do for a decent system.

For those of you with a keen eye who noticed that phase is reversed at the speaker terminals - this is because my CJ GAT 2 preamp inverts phase, which has to be corrected at the speaker terminals!

 

[Blackmorec]

Couple of things to be aware of when experimenting in this area

1. The quality of the bi-wire links can have a major impact on sound quality. Ideally they should be made from the same wire as the speaker cables in order not to introduce an unpredictable variable into the equation.
2. With the bi-wire links taken out of the equation, its a good idea to then compare the SQ of the 2 stereo amps with a single stereo amp or pair of monoblocks with roughly the same value as the 2 stereo amps. For example, lets say the each stereo amp costs $25K, you are essentially comparing 2 x $25K amps in bi-amp mode with a single $50K amp. The differences that show up will be down to a. The relative quality of the respective amps and b. the behavior of the speaker crossover in bi-amp vs stereo mode.

 

[XCop5089]

Couple of things to be aware of when experimenting in this area

1. The quality of the bi-wire links can have a major impact on sound quality. Ideally they should be made from the same wire as the speaker cables in order not to introduce an unpredictable variable into the equation.
2. With the bi-wire links taken out of the equation, its a good idea to then compare the SQ of the 2 stereo amps with a single stereo amp or pair of monoblocks with roughly the same value as the 2 stereo amps. For example, lets say the each stereo amp costs $25K, you are essentially comparing 2 x $25K amps in bi-amp mode with a single $50K amp. The differences that show up will be down to a. The relative quality of the respective amps and b. the behavior of the speaker crossover in bi-amp vs stereo mode.

1. Agreed. My bi-wire links are made of the same wire as my speaker cables.
2. I would have liked a pair of TAD M600 mono blocs, I auditioned and were being sold, mint, ex-demo for £30K (I don't know the dollar equivalent), but they are balanced only, XLR connections and my beloved CJ GAT 2 is single-ended only. They are take up a lot of floorspace and weigh 90 Kgs EACH! I am now 65 and have to think about moving this kit around as I get older!
3. I was able to buy my 2yr old mint condition M2500 MKII for way less than half the price of a new model and it has single-ended as well as balanced XLR connectors, configurable by a selector switch on the rear panel. The second TAD M2500 MKII I am considering purchasing is also ex-dem and half the price of a new model, so representing a total outlay for bi-amplification for the price of a new single M2500 MKII.

 

[Blackmorec]

1. Agreed. My bi-wire links are made of the same wire as my speaker cables.
2. I would have liked a pair of TAD M600 mono blocs, I auditioned and were being sold, mint, ex-demo for £30K (I don't know the dollar equivalent), but they are balanced only, XLR connections and my beloved CJ GAT 2 is single-ended only. They are take up a lot of floorspace and weigh 90 Kgs EACH! I am now 65 and have to think about moving this kit around as I get older!
3. I was able to buy my 2yr old mint condition M2500 MKII for way less than half the price of a new model and it has single-ended as well as balanced XLR connectors, configurable by a selector switch on the rear panel. The second TAD M2500 MKII I am considering purchasing is also ex-dem and half the price of a new model, so representing a total outlay for bi-amplification for the price of a new single M2500 MKII.

Well that combination ticks all the boxes! That’s a lot of amplifier and music for your £££s. Well done!

 

[PGA]

I’m currently using an active biamp with R1s, and it’s the best my speakers have sounded, including a long list of amps such as Spectral DMA360, Pass 600.5, MSB monos, and Constellation Centaur monos. The R1 is more efficient than the CR1, so the comparison may not translate exactly.

The amplifiers I’m using are Benchmark ABH2s in mono. These can be used single ended, although that is not ideal. Turns out Andrew Jones’s twin brother designed these. They are spectacular and each amp is 10% of the cost of one Centaur mono. They are surely worth a try and they have no problem producing 500 watts into a 4 ohm load.

I‘ve had three iterations of the ABH2s. First was a single pair in mono, second was two pairs in a passive horizontal biamp, and now I’m listening to two pairs in an active biamp with a Pass XVR1 as an electronic crossover. Each successive version sounded better than the previous. All sounded better than the Constellation Centaur.

The active biamp is by far the best. Andrew Jones was extremely helpful setting up the XVR1. The low pass in the R1 is completely bipassed and the woofers are now directly connected to an ABH2 in mono. The high pass for the coax remains intact and an ABH2 drives each coax. Dynamics are unlimited and with some judiciously applied DSP running on Roon, bass is flat to about 18 hz.

That said, the passive biamp sounds quite good, and even though in that set up all amps are seeing a full range signal from a voltage perspective, they are not providing current or power outside of the bandpass of the drivers they are supplying power to.

Very important that all 4 amps have the same gain, btw, in the passive biamp.

 

[Avidlistener]

Great report. Thanks. Was it difficult to bypass the crossover in the woofers? Imagine you wired directly to the woofers? How did you route the cables? Through the port?

I’ve imagined running my CR1’s fully active triaamped someday.

 

[PGA]

The Service Manual for the TAD R1s is on the web, and it shows exactly how the speakers are built. The Low Pass Filter (LPF) for the woofers sit right behind the top woofer. It's rather simple to remove the top woofer and splice the wiring bypassing the LPF completely so that the stock terminal connection on the back of the TAD is wired directly to both woofers. It's also very easy to reverse this and return the speakers to stock condition.

The passive crossovers in the TADs do more than just divide the frequency as they also EQ the response curves for each driver. The XVR1 is very flexible in that for each channel you have 4 poles of LPFs and HPFs (High Pass Filters) each with a separate frequency and Q. However, in the XVR1 you cannot combine LPF with HPFs, and therefore one cannot triamp the R1 even with two XVR1s, since EQing would require combining LPFs and HPFs.

One could use a DSP crossover on Roon and a multichannel DAC, however, I was lucky in that with Andrew's help we were able develop a scheme that retains the stock crossover for the coax, while eliminating the LPF for the woofers. There are not many choices for high quality multi channel DACs.

The stock LPF on the R1 woofers is somewhat of a limiting factors in the speaker since it uses one iron core inductor and electrolytic capacitors to achieve a 250hz crossover frequency. The crossover for the coax only has air core inductors and film capacitors. Getting the woofer's LPF out of the circuit and wiring the woofers directly to the amplifiers does make a difference in low end definition, dynamics and distortion. The performance gains from actively implementing the crossover for the coax is not as great as the gains from eliminating the LPF for the woofers.

 

[Stef]

I have recently been on the hunt for a replacement power amp for my system. I currently use a Conrad Johnson Premier 350SA (solid state) to power my current-hungry TAD CR1 MKII speakers, which are 86db efficient and a nominal 4 Ohm load! The CJ power amp is good for 600 watts into 4 Ohms and has always been happy driving the TAD's.

I have owned the CJ 350 since 2004 and although it still works perfectly, I decided that I would treat myself to a new power amp for my 65th birthday (yesterday)!

Little did I realise how fussy the TAD CR1's would be of a partnering amplifier and an added complication was my Conrad Johnson GAT 2 preamp, which operates in single-ended only, so any balanced power amp with XLR only input, would have to be ruled out on the grounds of complexity in matching and integration. I believe that it can be done with the insertion of a transformer-based gizmo converting the single-ended signal at -10db to a balanced XLR output at +4db, allowing a balanced XLR set of interconnects to connect to the power amp inputs. However, I am convinced that this would be a compromised way of doing things!

Having auditioned a few contenders, I settled on the purchase of a TAD M2500 MKII power amp, which will accept balanced and single-ended connections, with a switch on the rear panel to select the appropriate input. The amp is beautifully built (as are all TAD components) and is hewn from a 90 Kg solid aluminium block, to combat vibration! The finished amp weighs 43 Kg and is constructed as a true dual-mono chassis, with 2 X 1 Kva transformers for the analogue input stage and a Class D output! It delivers 500 watts into a 4 Ohm load and this output doubles as the impedance is halved, indicating a very healthy power supply. The amp runs cool and consumes 250 watts in operation and a measly .5 watt in standby, due to Class D operation!

As a single stereo power amp, it works very well in my system, providing a convincing grip of the TAD speakers and delivering a smooth, highly detailed and dynamic sound with a deep and broad soundstage. The bass is very deep and powerful!

Having the opportunity to borrow a second, identical TAD M2500 MKII power amp, I set about, removing the bi-wire links from the speaker terminals and with another set of stereo RCA phono interconnects from the second set of preamp main output terminals on my GAT 2 preamp and a set of Tellurium Q Ultra Black II speaker cables, I configured my system for passive horizontal bi-amping, with a kilowatt of power available for each channel (I also utilise two REL Gibraltar G2 subs, crossed over at 32 Hz to underpin the sound and enhance imagery and soundstage)!

First track on was "Unfinished Symphony" by Massive Attack and I was relieved to hear that all the faffing around was well worth the effort. The bi-amped mode produced a smooth, totally unforced sound delivery from the speakers, with enhanced separation and headroom. The soundstage was highly detailed and depth/width of image was increased, compared to use in a conventional stereo setup.

I have no doubt, that tweaking further with speaker and interconnect cabling would bring further improvements to the sound.

I have a couple more days to enjoy the bi-amped system, before returning the second loan power amp, but I am glad that I carried out the exercise to see what bi-amplification could do for a decent system.

For those of you with a keen eye who noticed that phase is reversed at the speaker terminals - this is because my CJ GAT 2 preamp inverts phase, which has to be corrected at the speaker terminals!

You really have a beautiful system and I would be curious to know your experience with 2 x TAD M2500 MKII power amps
My 2 cents experience with TAD CR1tx
I tried the following 4 power amps set-up all fed by my preamp Esoteric Grandioso C1X:

* Dartzeel 108 = Beautiful sound but really under power and no control
* Esoteric S1 = Interesting with good control but somehow a little boring and flat
* Momentum M300 = More control and more music overall but a bit too warm
* FM30b+FM10b horizontal bi-amping = Beautiful sound with superb mediums and 3D. Enough control for my room

I stick with the FM combo for the time being which gives me the best musical experience. First time for me to experience horizontal bi-amping and I'm very pleased with it.

 

[CKKeung]

You really have a beautiful system and I would be curious to know your experience with 2 x TAD M2500 MKII power amps
My 2 cents experience with TAD CR1tx
I tried the following 4 power amps set-up all fed by my preamp Esoteric Grandioso C1X:

* Dartzeel 108 = Beautiful sound but really under power and no control
* Esoteric S1 = Interesting with good control but somehow a little boring and flat
* Momentum M300 = More control and more music overall but a bit too warm
* FM30b+FM10b horizontal bi-amping = Beautiful sound with superb mediums and 3D. Enough control for my room

I stick with the FM combo for the time being which gives me the best musical experience. First time for me to experience horizontal bi-amping and I'm very pleased with it.

I like FM amps very much!

 

[Stef]

I like FM amps very much!

My 2 FM30b & 10b are old models from FM Acoustics and very suitable for bi-amping configuration. Certainly not the best amps compared to what is produced today but for the time being it gives me the best emotional response!

 

[cal3713]

I have recently been on the hunt for a replacement power amp for my system. I currently use a Conrad Johnson Premier 350SA (solid state) to power my current-hungry TAD CR1 MKII speakers, which are 86db efficient and a nominal 4 Ohm load! The CJ power amp is good for 600 watts into 4 Ohms and has always been happy driving the TAD's.

I have owned the CJ 350 since 2004 and although it still works perfectly, I decided that I would treat myself to a new power amp for my 65th birthday (yesterday)!

Little did I realise how fussy the TAD CR1's would be of a partnering amplifier and an added complication was my Conrad Johnson GAT 2 preamp, which operates in single-ended only, so any balanced power amp with XLR only input, would have to be ruled out on the grounds of complexity in matching and integration. I believe that it can be done with the insertion of a transformer-based gizmo converting the single-ended signal at -10db to a balanced XLR output at +4db, allowing a balanced XLR set of interconnects to connect to the power amp inputs. However, I am convinced that this would be a compromised way of doing things!

Having auditioned a few contenders, I settled on the purchase of a TAD M2500 MKII power amp, which will accept balanced and single-ended connections, with a switch on the rear panel to select the appropriate input. The amp is beautifully built (as are all TAD components) and is hewn from a 90 Kg solid aluminium block, to combat vibration! The finished amp weighs 43 Kg and is constructed as a true dual-mono chassis, with 2 X 1 Kva transformers for the analogue input stage and a Class D output! It delivers 500 watts into a 4 Ohm load and this output doubles as the impedance is halved, indicating a very healthy power supply. The amp runs cool and consumes 250 watts in operation and a measly .5 watt in standby, due to Class D operation!

As a single stereo power amp, it works very well in my system, providing a convincing grip of the TAD speakers and delivering a smooth, highly detailed and dynamic sound with a deep and broad soundstage. The bass is very deep and powerful!

Having the opportunity to borrow a second, identical TAD M2500 MKII power amp, I set about, removing the bi-wire links from the speaker terminals and with another set of stereo RCA phono interconnects from the second set of preamp main output terminals on my GAT 2 preamp and a set of Tellurium Q Ultra Black II speaker cables, I configured my system for passive horizontal bi-amping, with a kilowatt of power available for each channel (I also utilise two REL Gibraltar G2 subs, crossed over at 32 Hz to underpin the sound and enhance imagery and soundstage)!

First track on was "Unfinished Symphony" by Massive Attack and I was relieved to hear that all the faffing around was well worth the effort. The bi-amped mode produced a smooth, totally unforced sound delivery from the speakers, with enhanced separation and headroom. The soundstage was highly detailed and depth/width of image was increased, compared to use in a conventional stereo setup.

I have no doubt, that tweaking further with speaker and interconnect cabling would bring further improvements to the sound.

I have a couple more days to enjoy the bi-amped system, before returning the second loan power amp, but I am glad that I carried out the exercise to see what bi-amplification could do for a decent system.

For those of you with a keen eye who noticed that phase is reversed at the speaker terminals - this is because my CJ GAT 2 preamp inverts phase, which has to be corrected at the speaker terminals!

Did you get a chance to compare the horizontal biamping solution to a traditional monoblock configuration? I've done both on my Coincident PREs and greatly prefer traditional monoblocks. I lost much coherency across the drivers when they were driven by their own amplifiers (all identical).

 

[PGA]

Did you get a chance to compare the horizontal biamping solution to a traditional monoblock configuration? I've done both on my Coincident PREs and greatly prefer traditional monoblocks. I lost much coherency across the drivers when they were driven by their own amplifiers (all identical).

In my case biamp, whether a simple horizontal biamp or an active biamp with a properly implemented active crossover, only made things better vs monoblocks. No loss of coherence.

 

[XCop5089]

Did you get a chance to compare the horizontal biamping solution to a traditional monoblock configuration? I've done both on my Coincident PREs and greatly prefer traditional monoblocks. I lost much coherency across the drivers when they were driven by their own amplifiers (all identical).

Not back to back! I did try a pair of Vitus mono-blocs, kindly loaned by KOG, the UK importer, a couple of years ago! I'm hoping to try a pair of these some time in 2022, which promise to offer the best of both worlds!

 

[cal3713]

Nice. Best of luck. It's just always good to try both ways, since different speaker and amplifier designs may give very different outcomes.

 

[Stef]

Not back to back! I did try a pair of Vitus mono-blocs, kindly loaned by KOG, the UK importer, a couple of years ago! I'm hoping to try a pair of these some time in 2022, which promise to offer the best of both worlds!

What was your experience with 2 x M2500 MKII ?
I'm considering buying it. I'm guessing that TAD amps have good synergy with their speakers....
I have also noticed that you don' t use the same speaker cables for your bi-amping?

 

[XCop5089]

What was your experience with 2 x M2500 MKII ?
I'm considering buying it. I'm guessing that TAD amps have good synergy with their speakers....
I have also noticed that you don' t use the same speaker cables for your bi-amping?

The description of my experience with using two TAD M2500 MKII power amps in horizontal bi-amped mode, is described in my original text in this thread!

You must understand, that it was a BRIEF experiment, conducted over a few days, with additional cables that I had borrowed from a dealer friend.

You are correct. The second set of speakers cables I borrowed were different to my own MIT Magnum MA set.

I bought a single TAD M2500 MKII power amp and yes, it does have very good synergy with my TAD CRI MKII speakers (hardly surprising really!).