Bi-amping with two Marantz 8B's?

[VintTannoy]

I have two Marantz 8B's and I know they can't be run as monoblocks but has anybody tried bi-amping with two Marantz 8B's? Does anybody have any experience bi-amping two stereo tube amps that they can share? The merits or potential pitfalls of bi-amping with two separate tube amps? Thanks.

 

[TriodeLuvr]

One advantage to bi-amping is the ability to use a higher power amplifier for the low frequency grunt work, and a smaller, perhaps sweeter (e.g. SET) for the mids/highs. This not only allocates power more efficiently to each frequency range, it prevents the lows from modulating the higher frequencies. In addition, the tendency of the lows to clip occasionally - due to the higher power demands and dynamic range required - won't create harmonics in the same channel that's powering the mids/highs. The latter might not be a problem in the configuration you're considering, but you will lose the other benefits. The added complexity and potential loss of transparency inherent to the additional low-level crossover circuitry that's necessary for bi-amping must also be considered.

Jack

 

[VintTannoy]

One advantage to bi-amping is the ability to use a higher power amplifier for the low frequency grunt work, and a smaller, perhaps sweeter (e.g. SET) for the mids/highs. This not only allocates power more efficiently to each frequency range, it prevents the lows from modulating the higher frequencies. In addition, the tendency of the lows to clip occasionally - due to the higher power demands and dynamic range required - won't create harmonics in the same channel that's powering the mids/highs. The latter might not be a problem in the configuration you're considering, but you will lose the other benefits. The added complexity and potential loss of transparency inherent to the additional low-level crossover circuitry that's necessary for bi-amping must also be considered.

Jack

Thanks for the insight. So if I use one amp for highs and one amp for lows it could affect transparency? Also, will there be any issues with decibel levels between the two amps if one is feeding the tweeters and the other is feeding the woofer? Also, will splitting the signal from the preamp affect anything in anyway?

 

[Selmerdave]

The "potential loss of transparency" is offset by the loss of speaker crossover in that context...

There are different ways of doing it depending on your speakers and wishes. Generally, I would say that biamping with two of the same amps is good and avoids the possible mismatch that is the issue with using higher power for the lows and less for the tweeters. It's not clear whether you intend to biamp using the crossovers in your speakers (ie if they have four speaker terminals with removable jumpers) or if you intend to use a line-level crossover before the amps and have the amps connected directly to the drivers.

The latter is more complex to implement but there are significant benefits to removing the crossover components between amp and driver, and many would argue they outweigh any downsides of the needed line-level circuitry. Depending on the type of line-level crossover it can definitely get expensive, and yes a cheap active crossover will have a lot of transistors and circuitry. Also this method is only relevant if you have two-way speakers.

The first method is less of a change but does allow the high frequency amp to avoid the load of the woofers. With two of the same amp, the levels should be equal and so all you would really need is to split the signal from your preamp with a pair of y-cables. The benefit to this method is debatable. And again it's only relevant if your speakers already allow for biamped connections.

 

[VintTannoy]

The "potential loss of transparency" is offset by the loss of speaker crossover in that context...

There are different ways of doing it depending on your speakers and wishes. Generally, I would say that biamping with two of the same amps is good and avoids the possible mismatch that is the issue with using higher power for the lows and less for the tweeters. It's not clear whether you intend to biamp using the crossovers in your speakers (ie if they have four speaker terminals with removable jumpers) or if you intend to use a line-level crossover before the amps and have the amps connected directly to the drivers.

The latter is more complex to implement but there are significant benefits to removing the crossover components between amp and driver, and many would argue they outweigh any downsides of the needed line-level circuitry. Depending on the type of line-level crossover it can definitely get expensive, and yes a cheap active crossover will have a lot of transistors and circuitry. Also this method is only relevant if you have two-way speakers.

The first method is less of a change but does allow the high frequency amp to avoid the load of the woofers. With two of the same amp, the levels should be equal and so all you would really need is to split the signal from your preamp with a pair of y-cables. The benefit to this method is debatable. And again it's only relevant if your speakers already allow for biamped connections.

It's for Tannoy GRF 90 and yes, it has 4 terminals with removable jumpers. One amp will feed the high frequencies and the other will feed the low frequencies so I will be using the speaker crossovers. I'm really debating if bi-amping will be beneficial compared to just using a single 8B. And if the amp feeding the tweeters will see a lower load.. I'm assuming it will impact the wear and tear unevenly on both the amps? Will I need to replace the tubes on the woofer amp more often?

 

[Selmerdave]

I would not worry about the amps. They will be biased the same and amplify the same signal, produce the full frequency spectrum and see a similar load. The only difference is that they will have different frequencies filtered out of each output. The question is if there is any benefit to this arrangement, but easy enough to try it and see. The main downside i see is going through two sets of tubes at once rather than one, but it's not like they're not going to last many years and it's not like they're particularly expensive or difficult to replace.

 

[opnly bafld]

Try it and then after being underwhelmed you can go back to a single amp.

 

[mad shadows]

Try vertical bi-amping. Connect one of the amp to both high and low on one side and the other to the other speaker. It might improve the soundstage.

 

[gadget73]

My general concern with bi-amping using the passive crossovers in the speaker is that the amplifier ends up at least partially unloaded. On the amp feeding the highs, any low notes that the amp is fed just get dumped into nothing, which is generally not good for tube amps. If you block it before it ever gets into the amplifier this becomes no concern.


if you put say a 33ohm 10 watt resistor across the output it wouldn't be completely open circuit and that should be enough to prevent any possible damage.

 

[x3workshop]

My general concern with bi-amping using the passive crossovers in the speaker is that the amplifier ends up at least partially unloaded. On the amp feeding the highs, any low notes that the amp is fed just get dumped into nothing, which is generally not good for tube amps. If you block it before it ever gets into the amplifier this becomes no concern.


if you put say a 33ohm 10 watt resistor across the output it wouldn't be completely open circuit and that should be enough to prevent any possible damage.

I don't understand what you're saying here. There's always a load regardless of frequency if the amp is connected to a driver or crossover. Either the crossover is the load, or the driver is.

 

[mcgjohn]

I have two Marantz 8B's and I know they can't be run as monoblocks but has anybody tried bi-amping with two Marantz 8B's? Does anybody have any experience bi-amping two stereo tube amps that they can share? The merits or potential pitfalls of bi-amping with two separate tube amps? Thanks.

have done that many years ago. rather than going horizontal you may want to consider vertical bi-amping where you use one amp for the left channel and one for the right channel. That way each channel will get its dedicated power supply.

 

[gadget73]

I don't understand what you're saying here. There's always a load regardless of frequency if the amp is connected to a driver or crossover. Either the crossover is the load, or the driver is.

When using a crossover after the amp, it shifts the load from driver to driver as the frequency changes. If you remove the woofer from the equation, there is a very high impedance circuit at low frequencies. If you plotted out that impedance curve below the point that the midrange rolls off the impedance would be much higher than it should be. Thats where the resistor comes in, it keeps it from working into a much higher load than it would ever see otherwise.


works similarly going the other direction, lose the mids and tweeter and you end up with a high impedance up there.


passive bi-amping just seems pointless to me. The whole idea is to limit the frequency range the amplifier has to produce. Doing it this way has the amp working full range and throwing away a chunk of what its amplifying into nothingness. Cross it before the amp so its not doing useless work.

 

[62caddy]

I don't understand what you're saying here. There's always a load regardless of frequency if the amp is connected to a driver or crossover. Either the crossover is the load, or the driver is.

This was also my understanding regarding passive bi-amping with tube amplifiers. Since the output covers the full frequency range, the lower portion in effect has nowhere to go when only the upper frequency drivers are being fed. This is the reason why only active crossovers are recommended when bi-amping with tube amplifiers.