Tube OTL and Zotl amps

[Mr. Moscode]

The Beveridge amps are indeed direct coupled to the ESL’s and the other speakers are Acoustat Monitor 4’s. Also these have direct drive high voltage OTL’s designed by me about 20 years ago replacing the original ones as these were hybrids, an absolute nogo at the time for me.

Best regards,
Frank

I have a friend who is into rebuilding Acoustat amps and sent one to me and asked for a new circuit board. I ran into a bug with the damn op amps and haven't revisited it. He wanted to keep the op amps.

Could you share your DD otl design you use for the quads?
Of course that means I can't use my quads as test instrument with other amps. I'd have to be able to switch the wires between OTL and xfmer input.
What about arc over protection?

Happy Easter if you celebrate that holiday.

GK

 

[Lampie519]

Happy Easter !

Not sure if the amps are suitable for Quads as these are fragile. No protection whatsoever ..

Acoustats are different "beasts".

 

[thor.zmt]

Nice idea. Can it bypass the dsp? Not a fan of digital processing, simply because of the increased latency and the same reason you don't like switchers.

In this case, no. But the DSP in the Amp is very open. All dynamics bypass if there is no need to engage and the X-Over/EQ you directly enter coefficients, you can literally derive these to match an RC filter.

DS, like switchers, needs to seen nuanced. In the right environment, set correctly, it allows for things neigh on impossible with analogue. Like phasecoherent crossovers with steeper slopes than first order.

And let's not forget, the source is digital, the Amp is digital I put and in effect digital to the speaker terminals.

To control volume, apply EQ and crossovers they are best off in DSP. Any other option would be a compromise and degrade the system.

A system I'm working on the software control now contains 10 Channels of amplification (24W / 6 Ohm each), adjustable power supplies worth 240VA+, a DSP chip that is in effect the digital mastering Suite for Pro Tools created at the Power Station Studio New York on a chip (actually a 32 Bit ARM Cortex M4) and all the routing needed.

I am matching it with custom designed drivers. Specifically:

5.5" woven Carbonfibre long throw, bumped backplate, dual 6 Ohm voice coil Woofer/Subwoofer, two voice coils mean two amps per bass driver for 48W/3Ohm, official factory rating is 60W continous,

3" Midrange/Full range with a ceramic coated aluminum cone and a very low distortion neodymium magnet system, this is good for 180Hz - 18kHz with first breakup well beyond 10kHz, 15W continous rating or a 2" inverted dome unit for smaller systems

1" inverted, oxide coated titanium Dome with 20mm voice coil and low distortion neodymium magnet system

Combine them with the electronics PCB which is like less than half an A5 page.

Voila, 240W total, active 3 Way system digital end to end. Using my M/S derived single Box Stereo system allows a wall to wall soundstage with depth and hight.

Now, is it a match for (say) a Pair of Wilson Watt 5 Puppy 3's driven by a Moscode Hybrid (I know a system) and a good turntable frontend plus tube preamp?

Nope. It will also sell for less than a line cable in this system.

And it will handily beat the stuffing out of a typical modern streaming Class D amp plus pair of cheapish bookshelf speakers which in the end often still cost a lot more.

Anyway, the system is a bit like audio lego and allows high quality All in one, Satellite/Subwoofer Systems or even L/R speakers.

The largest system Towers with 4 Woofers, 8 Midranges (Line Array) and 8 Tweeters (Line Array) and 480W per side. Wireless, except for power.

So it is aimed at a higher level of quality than typical sound bars, Bluetooth speakers with a level of quality well past entry level "high end".

But in a modern style and package that works for modern mass market customers and aimed at mass market styling, pricing and volume.

Thor

 

[thor.zmt]

Funny i never had this "issue". the moment i heard electrostatic loudspeakers i knew this is the way to go (for me that is). Then i needed something to drive those (direct drive naturally and with tubes no silicon in the signal path). Now the next step is how to solve the bass ( almost wall to wall speakers?) that was solved as well.

Funny, while I never wanted such a setup myself, but I helped a friend, who sadly passed recently, to realize a similar system for his music room, where it shared space with a babygrand, a small organ and two Harpsichords and a nice minimalist recording setup based around ribbon and tube microphones with BBC spec tube electronic and a BBC spec Studer B-77. It was rehearsal and recording space for early music, as well as just listening room.

Speaker 2-Way ESL's ~2m tall, MF Panels down to ~ 100Hz, 5kHz crossover to HF panels, took my friend ten years of experiments to get them how he wanted.

300B PP Amplifier on the HF panels, capacitor coupled drive from 300B Anodes, balanced circuits, direct coupled

845 PP Amplifier on the HF panels, capacitor coupled drive from 845 Anodes, balanced circuits, capacitor coupled

2kW solid state Pro Audio Amp's with dual 18" Pro woofers in dipole "w" frame. Additional 18" woofers "infinite baffle" venting the basement for ultra low (< 44Hz) content

Passive line level first order LCR crossovers, balanced

WE437A "With output transformer" preamp, custom silver transformers, transformer based volume control

TDA1541 based non oversampling DAC or Audio synthesis DAX (essentially the DAC portion of Pacific Microsonic Model 2 pro audio AD-DA.

This system is certainly one of the most impressive and best I heard ever, literally sitting there and recording and immediately going to playback was incredibly impressive.

It took years to complete and is only practical if you live in huge Victorian house with an attached 2,000 square foot conservatory.

Amplifiers, preamp, TDA1541 DAC, line level X-Over with included attenuation were my designs.

No attempts were made to eliminate transformers or inductors, instead high performance custom designs were commissioned.

Thor

 

[thor.zmt]

> re: pwr amps on a chip.

There are many options. It's like saying "Burgers". You have McDonald's (who knows what is in that burger patty) and next to it at K11 Mall in Kowloon you have butchers club, with burgers made from fldry aged imported beef etc that only cost double McD.

Both are "Burgers" by name.

It's the top 2 octaves of detail that is screwed up. That's where the Futterman's shine.

That could be the drivers the Monitors used, or the voicing. A lot of studio monitors (and headphones) are very Midrange focused. For many good reasons.

You should know the Futterman's use 60 db or so of NFB, 90 db open loo gain but the input tube runs current starved so the top octaves run at much lower gain and thus NFB.

I know that, FWIW. It also results in rising distortion at HF, similar to what we observe in most solid state amps.

We probably have differing views and options there. To me that is very much "voicing" and that is whole other artform.

Which brings me to this. I hung a moscode output stage off a F-OTL just to hear it. you would think it would be the dream hybrid but it wasn't.

Not surprised. Do the Sziklai output with tubes and P-Fets, that will get a lot closer I think.

The trick is to make it be seductive so you don't want to turn it off.

Yup, precisely.

Here's another schem of what you are talking about.

View attachment 107662

It's simple enough and it has to do what the tube tells it to, to an extent. But it does it with a high NFB chip amp + an input xfmer neither of which I'm a fan of.

I warned that my point was the princple, not a specific schematic.

I start from principles and then move towards actual detailed implementations.

FWIW, this principle can used with such a variety of solid state circuits, nobody prevents you from using open loop designs (non-nfb) or designs with single stage feedback (eg Sziklai or inverted Darlington).

Again, personal signature, taste, voicing.

For a computer speaker chips are OK.

That simply is prejudice like "burgers can only be low end fast food". It is not a fact.

Have you compared these hybrids to the chip amp alone? Any improvement? I know we tend to stand on theory when we analyze a ckt by eye but how does it sound?

I have only ever used Chip Amp's or indeed other circuits for hybrids that sounded agreeable to great on their own.

It would be stupid to stick any old chip in unheard.

And I would never use the chips in John Broskies design you showed.

We have to stay objective but customers let us know what we've got.

Indeed. I hope you took the time to watch this video review of the "All in One" wireless hifi system I designed (industrial design by a good friend).

I for one are very happy with what this reviewer (and many others) found.

They expected a gimmicky Soundbar and came away go smacked that this thing was actually serious hifi...

Thor