Geeky tube stuff - expect BS engineer talk within

[Hemisaurus]

So I've been using the Tube Data mirror on tubedata.milbert.com for ages, and I never bothered to visit milbert.com until today, and I see they are doing OTL tube amps, which seems like a kick, so I poked about and read the patent and stuff, figured I'd share it.

http://davidberning.com/technology/patent5612646

and the guys own blurb

The Berning ZH amplifiers take advantage of new technology in order to eliminate the audio-output transformer. These amplifiers use radio frequency to change the voltage-current transfer characteristics of the output tubes from their normal impedance-plane to one suitable for driving a dynamic loudspeaker. The radio frequency re-mapping is implemented using special high-frequency power conversion techniques. The high-voltage, low-current tube impedance-plane is re-mapped to the high-current speaker impedance-plane through a special transformer at a constant RF carrier frequency of 250 kHz. Because the audio signal is riding on a carrier, it is not subject to parasitic elements of the transformer that would otherwise distort the audio signal. There is no low-frequency limit for this impedance conversion, and these amplifiers are dc-coupled, with the exception of a small, high-quality, dc-blocking capacitor at the input of the amplifier to prevent the amplification and application to the speaker of any dc that might be present at the input.

The impedance matching in the ZH amplifier is precisely determined by the effective turns ratio of the RF conversion transformers. Both the push and pull portions of the amplifier are handled in a symmetric fashion, as they are in a conventional transformer-coupled amplifier, and negative feedback is not required to force the positive-output current capability to be similar to the negative-output current capability.

Audio-output transformers have a limited impedance conversion range imposed by the parasitic elements. Audio-output transformers also have limits imposed by voltage breakdown between primary and secondary, and required insulation also affects the parasitic elements adversely. It is difficult to make a high-fidelity transformer with much more than a 25:1 overall primary-to-secondary turns ratio for the above reasons. These restrictions are eliminated in the ZH amplifiers, and larger effective overall turns ratios are applied to use the tubes more efficiently than they can be with the smaller ratios. One implication of this change is that the reflected plate resistance of the output tubes is lowered, making the tubes appear more like triodes to the speaker. The Quadrature Z, like the ZH270, uses a special triode-connected screen-drive arrangement (Berning patent no. 3,995,226) that offers greatly enhanced reliability and also improved linearity at low idle currents.

Another implication of using a higher-effective turns ratio is that the output tubes operate at lower current and higher voltage than they otherwise would. As tubes become weak with age, the current capability is reduced, but the voltage capability is not affected. Longer useful tube life is expected because less current is required for a given output power. The opposite situation applies to the traditional OTL amplifier.

The higher effective-turns ratio also means that distortion is reduced for a given amount of negative feedback because the current loading of the output tubes is reduced. The higher-voltage, lower-current tube operation afforded by the higher effective-turns ratio operates the tubes with sufficient efficiency so that the Quadrature Z can deliver high power with only four modest-sized output tubes.

Audio-output transformer-coupled amplifiers should not be operated without a load connected because the inductance of the transformer's primary can cause the plate voltage to reach a sufficiently high voltage to break down insulating materials, resulting in amplifier failure and even fire. Some amplifiers are even unstable without a load. Unlike output-transformer-coupled amplifiers, the ZH amplifiers can be operated safely without a load, as the voltage cannot exceed its normal designed-in operating voltage.

[dunwichamps]

i have looked at some OTL designs but nothing as engineered as this, Quite interesting.

Using a carrier frequency reminds me of AM radio scheme. 

[Hemisaurus]

Yeah, with low powered output tubes you can maybe find a MOSFET in the voltage range, though looking now I guess they're making MOSFET's in the KV range. It is AM modulation, though too low for a standard receiver to pick it up, wonder if it interferes with shortwave radio?

[Mr. Foxen]

Is this a bit like SMPS for changing up current and voltage? Can the two be cooupled is the next technical challenge, it help back combining class D and SMPS for a fair while, Peavey already did a SMPS valve amp.

[Hemisaurus]

Was that the VB-3, they had a terrible time getting that launched. It uses a switched mode supply, and I think a toroidal output transformer. I'm surprised more people don't use toroids, Traynor did in the YBA200, and Plitron or is it Piltron? make a variety of tube transformers up to 400W for KT88 octets.

SMPS uses PWM to control the output voltage not AM, so it looks like a different process, and note they are still using transformers here for output, so it's not completely transformerless either.

Anyway guess I can't fault Peavey, Matamp couldn't build a 400W model either, and they were using transformers

[dunwichamps]

amps often follow "tradition" whether that be good or bad. Seems to be what happens, That why a majority of say LTPI all have the exact same component values. Like the designers didnt bother to see if it can be adjusted or tweaked just copy and pasted it really

[Hemisaurus]

Well it all stems from the application notes, which does make rolling your own easier, take a bit of Marshall, a bit of Orange and a bit of Fender, adjust to suit.

Toroids though, lighter, take up less space, still look damn cool , create less EM interference which keeps your circuit quieter, why not. I imagine if they were used enough the prices would come down.



Here's what they use in the Traynor, yeah it's PCB, not my fault

[Mr. Foxen]

Anyway guess I can't fault Peavey, Matamp couldn't build a 400W model either, and they were using transformers

They have, Julian Cope uses it. Uses transformers by John Chambers, bunch of trouble with the other ones they had.

I heard there is some property of how a toroidal saturates that makes them sound not like the familiar saturated amp tone, but it might be BS. I would guess its more to do with the little tweaks to spec that come from experience. not being available to them.

[Hemisaurus]

Yeah, Chambers pretty much showed them how to build it, wish I had his transformer winding capabilities.

I doubt 90% of players couldn't hear the difference, like the old Orange 50's (80's whatever) that looked like they were wound on the same core as the 100's, you had twice as much iron in there before you'd hit saturation.

[dunwichamps]

yes toroids would be quite superior as PTs, I think players would still prefer stand up style OTs as they color sound due to restricted bandwidth. The only thing that should be considered using toroids is that they have large inrush current

[Hemisaurus]

I'm sure you could make a toroid with a restrictive bandwidth, funny the things that people like

Tying it back to the original post, if they claim to have cleared up all the phase issues and distortions introduced by tubes, who is going to buy their amps?

[dunwichamps]

I'm sure you could make a toroid with a restrictive bandwidth, funny the things that people like

Tying it back to the original post, if they claim to have cleared up all the phase issues and distortions introduced by tubes, who is going to buy their amps?

put some demoes up, all that i ever did to sell amps

[Mr. Foxen]

Restricted bandwidth is good if you don't like the sound of cabs farting. People should go nuts with high pass filters, there'd be so much more loud available.

[dunwichamps]

you can always just push a OT past its rated bandwidth to shrink the low end limit. more power and small bandwidth

i can see that the Axis of Nerdom is solely compromised by Hemi, Oli and Me

[Hemisaurus]

Told you, there's moose23 as well I think, but keep it to regular talk in other threads. It's like walking into a store, and everyone else is speaking Urdu,  you feel a little out of place, maybe a bit paranoid.

[Mr. Foxen]

It's like walking into a store, and everyone else is speaking Urdu,  you feel a little out of place, maybe a bit paranoid.

That is pretty standard where I live.

Also, I'm a total hack when it comes to techy stuff, I'm good at getting my hands on interesting amps.

Only C-cores are TRVE

[dunwichamps]

ill keep the techobabble to the builders thread i started

[Hemisaurus]

ill keep the techobabble to the builders thread i started

You mean Dunwich Porn Thread #6?

[dunwichamps]

ill keep the techobabble to the builders thread i started

You mean Dunwich Porn Thread #6?

truth, but i tried to consilidate my shit into one area so atleast i wont gum up the board with tons of crap, plus I hope other builders post in there 2, atleast Moose does

[moose23]

I understand what you guys are talking about but don't really have anything to contribute as I don't spend much time around amps bar playing them and it's a long while since I finished college.

And yeah I'm trying to get stuff into the builders thread but that means taking pictures of everything I do which doesn't really happen. Hopefully we can encourage more people to post and build their own gear.

[Hemisaurus]

I understand what you guys are talking about but don't really have anything to contribute as I don't spend much time around amps bar playing them and it's a long while since I finished college.

I'm 19 years out, you?

[moose23]

I understand what you guys are talking about but don't really have anything to contribute as I don't spend much time around amps bar playing them and it's a long while since I finished college.

I'm 19 years out, you?

11 since I finished my Electronics diploma/degree, did a degree in Oceanography and Computing a few years after that and managed to work as furniture fitter all through both. That sort of thing died with the end of the Celtic Tiger so unemployment had me building my own effects and very soon after I was building for others. Did a year and a half as cycle messenger but quit that at the start of this year.

[Hemisaurus]

Ooh, I dipped in once, and that was it. I've thought about going back once or twice, but thankfully never had to.

Furniture fitter, you should build your own amps, as you could build your own head cabs as well.

[El Zombre]

There's this guy http://www.youtube.com/watch?v=3293JPYNOM8 whose amp I found got to from this thread:

http://www.audioasylum.com/cgi/t.mpl?f=otl&m=33380

There are also examples of full range speakers used for guitar amps that sound quite nice, so that begs the question whether or not limited bandwidth is beneficial, or if it just masks the effects of the cheap power supplies (compared to hifi amps) most guitar amps have.

[RacerX]

Toroidal, my ass.

Restricted bandwidth? pft.

Gimme big iron & tubes with all the inherent limitations. Class A or A/B ftw!