Do any of you have the old Beveridge 'White Paper'?

[Lampie519]

I tried this little amp on my Acoustats as these are my main speakers at this moment. The standard direct drive amp delivered the needed high voltage for the membrane (7KV). The sound was very clear and dynamic until clipping. I will try a more beefier output tube the next time. I will keep you updated.

 

[Lampie519]

Actual Zotl technology is great here as the "step up"can deliver very high voltages and there is almost no current load (i had to load the amp on the low impedant side to keep it stable though with a resistor load). The output tubes i used were PL81 as these can handle the high voltages without complains. The buffer was a E180F as it can deliver some current. There is no phase inverter or driver as the signal from my preamp is more then enough to drive the output tubes into class A2 plus it is already ballanced from the source (D/A converter is ballanced as well).
The other advantage is that only 2 output tubes are required as it is not an SRPP. And even if PL519 tubes are used it will still be much smaller and will be less power hungry .

 

[Lampie519]

To get to the high voltage i cascaded several HF transformers. This also will keep the parasitic capacity value low and prevent the cores from saturating.

 

[Lampie519]

Actually David Berning is driving his own ESL's directly already using his ZOTL amp:

DIY Audio - YouTube

This is what i did as well but i still need to build a more powerfull version. I am now building a new ZOTL amp for standard speakers but in doing so i am trying some new input stages with phase inverter that i could use in the HV ZOTL later on.

You can check the progress here:

ZOTL and ferrites

 

[AdotL]

Hi,


thanks for all the exciting news! The video showing Berning's ESLs is quite nice, especially the energizer box producing 2600V if I understood correctly. I didn't know about this video. I reminded me when I once asked him for advice for direct coupled amps for ESLs and he recomended the ZH270. Do You also use this circuit? Beveridge speakers need 3200V, isn't it?

Are ZOTLs very hard to build? I see some handmade transformers in Your fotos....
Thanks for all and my wishes You'll succeed!
Adrian

 

[Lampie519]

Hello Adrian,
All transformers are handwound by me as these can not be purchased "off the shelf".
The input/phase inverter stage works fine but can better be used as line driver or headphone amp. Not suitable as HV gain driver in my case as the voltage swing is just too low (the transformer ratio can be changed but this will require higher DC voltage and then it doesn't make sense to use Zotl technology).
The HV used in the Beveridge amps is of no concern if Zotl amps are used so we only need to have a bias voltage like the one David is using (that is not difficult to create).
Funny thing about the Beveridges that even a single ended amp can work here making the amps even cuter, not sure how much gain will be lost by doing so.
As i would like to replace my monster HV amps in the future (they work really well so i am not in a hurry) i will continue with this and keep you updated.

Best regards, Frank