音響制作工藝 DIY Audio Craft

hi
After that 211 se amp for audio physics speaker …I started to make pse project for quad electrostatic speaker . output should be 40 w . we have 6 box !
2 for power output …2 for power supply….one for pre amp and last is power supply for pre amp . ...... solve mechanical noise in this plan .

I didn't have any experience in 1000 v and 2 x 50 ma of 211 .so before to start main project …I connect the power supply to parallel 211 …and see the bias – voltage and current. I decided to use more oil capacitor.

211 have a grid-plate capacitance 14pF and mu 12 times. That make the driver are hard to design. Parallel 211 even more worse.

If you set the high frequency F3 roll-off at 30kHz, you need the total loading on driver stage less than 28k (14k for parallel 211). So, typical driver tube cannot drive 211 well. Say, 6SN7, internal resistance is 7.7k, if we used 30k loading, the F3 frequency cut off at 22.5kHz. For parallel 211, it would be 11.3kHz. That consider un-acceptable!!

So, You need a driver with internal resistance below 3k and have good enough power to well control the parallel 211. It also need high swing (voltage) to driver 211 to maximum output. That need a power tube as driver!! But, power tube always do not have enough gain. You need additional input/gain stage. That tube need have enough power to drive the driver (Power tube driver) too!!

Chung

Hi
Thanks for your advise .but as you know audionot has parallel 211 in expensive model …how abut design ?

Here is the AudioNote Ongaku 211 PP's diagram.

Hi
This schematic is SE 211…..and has just single 211 in one channel .

Oh! ... Yes ...
My mistake ...

F2A,

I don't dis-agree commercial amplifier use parallel 211. But, on DIY point of view, I prefer SE 211 or even push-pull to get more output power.

You need high swing, low impedance tube to drive parallel 211. You may use 211SE to drive 211PP

Chung

http://tdsl.duncanamps.com/dcigna/tubes/sheets/misc/vt4c-1h.gif
Refer to Ge data for vt4c ….we can see 3 points for 211 in class a audio amp :
• 750 v -46……. Need 41 grid swing cur 34 ma
• 1000v -61 need 56 grid swing cur 53 ma
• 1250v -80 need 75 grid swing cur 60 ma

211 need high voltage for good sound.
What I did before is 1100V B+, 70V self-Bias. So, the plate voltage around 1030V

211SE at 1250V could output 19.7W. So, Parallel 211SE cannot get more than 40W.

I prefer run 211 at Class A2 mode, it can have 35W. It is not big different with parallel 211.

Chung