Balanced SET? North Audio

Their amps can only be used with a fully balanced pre amp. They take the + and - and amplify individually. They come together at the output transformerwhere and the noise cancelling happens. This is not push-pull. Any tech nuts out there that might have better understanding of this. If anybody is really interested contact www.northaudio.com . I am not any way connected to North Audio. I just got very sold on the idea when I met him on the phone. He was doing some work on my pre that I just bought. I haven't listened to them either. They are located just out of Ottawa. I am in Vancouver. Is there anyone in the Ottawa area that would be interested in checking them out. The owner Steve sounds like a nice guy and has a showroom at his house. He was also telling me about his new proto type 45 balanced monoblocks. He sounds very proud of them and says with the right speakers that nothing can touch them. Let's not rule out something new before someone gives it a chance.

12-15-06: Sdrsdrsdr They come together at the output transformer where and the noise cancelling happens. This is not push-pull”

Actually, that is exactly push-pull is. Push-pull or single ended refers to the output of an amplifier. That amp as a push-pull output. Period.

A SET and all other SE tube amps uses a single ended output transformer. In short, the one primary tap will have a + bias source from the power supply, the other tap will be coupled to the anode of the output tube.

This is not the case for North Audio – their amp clearly uses a push-pull output transformer, as do each and every push pull transformer coupled tube amp.

And if you think what they are doing is new, unique or special, I suggest you have a look at Cary’s V12 series of amps. They are also pairs of 100% single ended amps (also EL34, 6550 or KT88) wired into a push-pull configuration via a single push-pull output transformer. And I believe V12s have been around for 10 years. You’ll probably see many other manufacturers with similar designs if you care top do a bit of research.

“Any tech nuts out there that might have better understanding of this.”

I have built amps (tube and transistor, single ended and push-pull) for more than 10 years, although I do not consider myself a nut of any kind. What I am not, is totally naïve.

“[Steve] sounds very proud of them and says with the right speakers that nothing can touch them.”

I would be surprised if he didn’t. That is exactly what I think of the amps I build.

“Let's not rule out something new before someone gives it a chance.”

Of course not. But then the design has to actually be new, which this clearly isn’t. At best it is a slight variation on a design that is more than 50 years old.

BTW, I am not saying North Audio are frauds, or that the owner is a bad guy or that their systems sounds bad. However, they won’t be the first audio site to sell vaporware. Particularly funny are their “feedback less“ mosfet amp and their “balanced” (i.e. un-rectified) HT supply. (tip, rectified HT power is better in tube amps)

Kind regards
Paul

I know North Audio, have met Steve a number of times, heard some of his equipment and have been to his home/store. He is actually a service tech for an elevator company who eventually realized he could turn his expertise to designing and building audio equipment (absolutely nothing wrong in this). He is very opinionated on some subjects (eg. the cheapest Dale resistors are far superior sounding than Vishays etc.). I have not had any of his equipment in my own system, although I have heard several pieces in other high quality systems and thought they sounded okay. All of his equipment is expensive (by my standards, anyway). There are several people living in this area (Ottawa) who think very highly of his stuff.

When stereo was new there was a brief interest in converting mono amps to stereo, without adding any output tubes or power supply. (Yes really). My memory of the circuit details is a bit dim, but it involved connecting the center tap of the output transformer through the primary of another transformer. One channel drove the output tubes in common mode, and came out of the auxillary transformer. The other signal drove the output tubes differentially, and came out of the original transformer. The signals involved might have been L+R and L-R instead of L and R. Certainly the rig would work better with the relatively small A-B being the common mode signal.

Anyway, such an amp might be described as push-pull and single-ended at the same time!!

sdrsdrsdr, not only is your analysis of these amps incorrect but now that I look at it, North Audio's analysis is also severely flawed.

BTW, I read the manual and he never claims it is not push-pull.

Their amps can only be used with a fully balanced pre amp. They take the + and - and amplify individually

This has nothing to do with being push-pull or not. Push-pull amps that can accept a single ended signal must do the inversion inside the amp. His amp simply omits the inverter and thus can only accept a preamp that has done it already or passed through a balanced signal from a source.

They take the + and - and amplify individually. They come together at the output transformerwhere and the noise cancelling happens. This is not push-pull. Any tech nuts out there that might have better understanding of this.

I have been involved with electronics for about 30 years including teaching it at the AAS degree level for 10 years which included amplifier circuit theory. This is as push-pull as you can get.

It is a bit unusual in that it appears the output tubes are biased class A where-as most use class AB, but VAC uses a similar scheme with 300Bs and I assume others do too.

His analysis is way off.

He talks about it takes 4 times as much power to be twice as loud because power is a squared relationship, and then tries to use the P = (V squared) divided by R formula to prove it. That makes no practical sense. The formula is correct, doubling voltage does quadruple power, but this does not prove in any way that it takes four times as much power to be twice as loud.

These statements from his manual are also wrong

The distortion from each single-ended power amplifier is identical in shape, magnitude and in phase in relation to each single-ended amplifier AND the distortion and noise which are kept on the same phase because the two amplifiers are identical AND Everything got cancelled out!

This is simply not true.

The only thing that cancels is noise that is picked up identically by the + and - input signals, and even this can only happen if everthing in both phases is EXACTLY the same as everything in the other phase. It will cancel the majority of this noise but not everything.

The noise generated by a particular tube or other component is completely random in nature, so the noise from the two output tubes cannot be equal amplitude and in phase and therefore will not cancel.

The output tubes are also being fed music signals of opposite polarity. The distortion components will have a phase relationship determined by the polarity of the input signal so the distortion will be out of phase just like the music signals are and will not cancel.

In other words, this guy is either a BS artist or doesn't understand his own circuit. It may sound fine but it doesn't do what he claims.