To get more information contact me at: firstname.lastname@example.org
Amplifier End version
started in the 2021
After the good
experience made using
Circlotron I immediately thought about their use in this project.
These companies have supported this project.
interstage transformer is used to reduce the output impedance of the vacuum tube
and to create a differential signal to drive the mosfet with opposite phase as
required by the Circlotron design.
It is necessary a good 4 : 1+1 with a minimun inductance of 50H to have a good low frequency response.
Ft(-3dB) = R / ( 2 * 3.14 * L ) = 3000ohm / ( 2 * 3.14 * 50 ) = 9.55Hz
LL1671/30mA in ALT Q configuration have 35H so the version with an air gap for only 20mA will have about 35H * 30mA / 20mA = 52.5H.
Using a 4 : 1 instead of a 2 : 1 + 1 the mosfet grid will be driven with low impedance and more current so there is a better high frequency response and faster slew rate.
Using a CLC power supply in a normal amplifier you can reduce the noise but in this case the mosfet gate is isolated from the high current power supply so there is no benefit and it is possible to use a single 22000uF or 10000uF + 15000uF like in my case.
Following the experince of my last amplifiers I have used Schottky Fast Soft recovery diodes in any section of the power supply but you can use normal 36A diode bridge like the IRF 36MB60 and for the anodic voltage a diode bridge made with 4 x UF5406.
To create a fast diode bridge with these TO220 and large SMD chips I have created 2 simple pcb.
For this design you can use normal transformers produced in stock but my choice is 2 custom made on my specifications:
Transformers in the world
external size 125x65mm, core type M0, flux 80% than normal (13000 gauss instead of 17000 gauss).
There are some choice for the power supply capacitors:
All the resistors on the signal path have 2 positions on schematic because ...
otherwise to get a slightly better result using the MK132 Caddock.
The my choice is the HiFi-2000 mod. Pesante dissipante
5 units with 10mmm frontal panel.
On paper each lateral heat sink of this chassie have a capacity of 0.25 °C/W so it will keep the output devices in a good safe area also when the environment condition are terrible 35 °C.
The total cost to create this amplifier is not very low
but you are building a reference amplifier without compromise.
You can reduce the cost using only 4 x 22000uF 50V KG for the high current power supply, another attenuator and standard transformers.
|Qty||model||brand||unit price (euro)||total price (euro)||shop|
|4||10000uF 50V||Nichicon Super Through||15||60||www.partsconnexion.com|
|4||15000uF 50V||Nichicon Super Through||20||80||www.partsconnexion.com|
|4||2.2uF 250V MKP||Solen||2||6||www.solen.ca|
|1||LM317 soft start||-||10||10||ebay.com|