Bi-Amping

Merlot

I have a pair of RTi8s and a PSW505. I will be building two - two channel tube amps (four channels in total). Rather than building the amps and paralleling the outputs, I was told it is best to bi-amp the speakers. Paralleling the amp outputs can degrade the sound quality due to nonlinearity in the output transformers (apparently).

Each amp will share an output from the preamp, i.e., one amp will get a left feed across both inputs and the other a right feed across both inputs. One amp channel will feed the low frequency input on the RTi8 and the other will feed the high frequency input. The PSW505 is fed directly from the LFE on the preamp. The other amp will be similarly connected to the other channel. The amp will be wired for 8 ohms. I am told I need to connect an 8 ohm non-inductive resistor across the high frequency input of each speaker. This needs to be done to match the output transformer of the respective amps.

Has anyone heard of this before? Will it work? Is there any downside to this?

Thanks for your help!

TG Meat

I have tried with my Rti 10, but I am not sure I was able to hear a major difference. Some say yes, some say no.

Merlot

Did you have to use the resistor across the high frequency inputs on the speaker?

Thanks....

nikolas812

I don't have the answer you are looking for. But there is a member here that vertically bi amps a pair of his speakers. He might be able to answer your question. His member ID is SolidSqual if you want to send him a message.


Other than that. Your idea sounds cool. I'll be interested to hear you thoughts on it after you get it all wired up. Information on the related equiptment would be nice also.


And Welcome to the Club!



Nick

Merlot

Thanks.... I'll do that. One of the main reasons for doing this is I really want to build the amps....

SolidSqual

First, I've been drinking . . . legal job interviews. So bear with the grammar and nonsense. I'll do my best to answer your question.

You want to vertically biamp your speakers. What you are suggesting is called horizontal biamping. People will argue the other is better, but IMO vertical biamping is better for you.

When you vertically biamp, one amp powers a single speaker. The power supply of the amp handles the load of the highs and the lows. By contrast, Horizontal biamping lets the power supply of one amp playing the highs groove easily, while the other amp is beat to death trying to carry the load from the low sections of two speakers.

However, if you planned on using two different amps, say a tube SET amp for the highs and a Krell 1000W Class A amp for the lows, then horizontal biamping would make sense. But, it sounds like you are making two identical amps. You would gain more benefits from vertical biamping.

FYI, I no longer use two stereo amps for my speakers. Now, I have four monoblocks. It's the best of both worlds. Each channel is completely separated and each has its own power supply.

organ

Never heard of anyone using a resistor for the highs when bi-amping. It would change the gain and you'll get less highs than you should.

What tubes are you planning to use on the amps?

SolidSqual

Bi-amping your speakers with different amps is possible if you have a component in the chain capable of increasing the gain of one amp. Also, some amps, like the Halo Series from Parasound, actually come with gain knobs for each channel.

organ

Forgot about that too. My NAD amp has a variable input. Sounds like Merlot is building his own tube amps or have someone to do it for him.

Merlot

I am thinking of vertically bi-amping the speakers - sorry that wasn't clearer. One two channel amp on the left, the other on the right.

For the high frequencies I would be using the passive crossover in the speaker. Given it wouldn't be impedanced matched to the output transformer of the tube amp which will be wired at 8 ohms, my understanding is that is that the amp will not take kindly to it. The passive resistence is in excess of 30M ohm on my meter, the equivalent of an open circuit. The resistor across the inputs would bring it more into line with what the amp is expecting.

Needless to say I've been crusing the web and have found references to this, but not much detail...

The amps I'm thinking of are Bob Latino's ST-120 kits. Prior to ordering I want to ensure I understand the consequences of the resistor across the terminals... Output tubes could be 6550 or KT88. I build his ST-70 with KT88s and am very happy...

Thanks for all your feedback...

organ

Did you measure the resistance by just placing the meter on the x-over inputs? It shouldn't be a fixed number. It should rise and fall depending on the frequencies being sent to the speakers.

Since you're building the amp, build terminals to accommodate both the 4 ohm and 8 ohm windings. I find that if the speakers have a dip below 8 ohms, the 4 ohm output usually sounds best.

Did you have to change anything from the stock configuration on the ST-70 to run KT-88's? So far I've ran EL34, KT-77(EL34 sub), KT-66 and 6L6GC with no mods and got excellent results on all of them.