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New 2A3 PSE
by Andrea Ciuffoli - starting in the November 2007

INTRODUCTION

The targets of this project are the following:

COMPONENTS

All the audio transformer used in this project are Mars products got at VT4C.
 
  • Japan Audio Grade Z11 (0.35mm) Lamination;
  • Traditional Look with Silvery Cover;
  • Air-gapped to prevent magnetic Saturation (Interstage or Output transformer only);
  • Layered for Perfect performance;
  • Excellent Quality but very competitive price.;
  • Only large and experience factory can have that large production line!;
     
    		•
    LM-2013U
    2.5k SE Output transformer
       
  • Single Ended Output Transformer Recommend for 2A3, 6A3, 6B4G
  • Frequency Respond: 10Hz - 37kHz(-3dB), 10Hz - 25kHz (-1dB)
  • 2.5k primary.
  • 0-4/8/16ohm secondary.
  • Large 100W core!!
  • Primary 15H, DC resistance 189ohm.
  • Max. 140mA
  • Max. 750V
  • Made in China
  • Weight :1750 (gram/Each)
  • Size (mm): 79 x 65 x 89H
  • Brand : 45
  • Power: 20 Watt
    		•
    Item No: LM-2013U
    Quantity (Each) Price (US$)
    1 - 3 45.00
    4 or more 40.00
     

     
    LM-130D
    150W Hi-end quality transformer designed for 2A3 SE.
         
  • High quality Z11 Lamination import from Japan
  • Designed for 2A3 or 45
  • Could be use for Self or Fixed Bais
  • 250-0-250 150mA
  • 0-CT-5V 3A,
  • 0-6.3V 2A,
  • 0-CT-2.5V 3A,
  • 0-CT-2.5V 3A,
  • Primary 0-110V and 0-110V (Serial connect for 220V, parallel connect for 110V)
  • Made in China
  • Weight :3300 (gram/Each)
  • Size (mm): 98 x 83 x 102H
    		•
    Item No: LM-130D
    Quantity (Each) Price (US$)
    1 - 3 53.00
    4 - 9 50.00
    10 or more Call

     
    LM-5H-2C
    5H power choke
         
  • 5H on full-loaded
  • 12H unloaded.
  • Max. 200mA
  • Max. 750V
  • DC Resistance approx 105 ohm
  • Made in China
  • Weight :1450 (gram/Each)
  • Size (mm): 79 x 65 x 89H
  • Brand : Mars
    		•
    Item No: LM-5H-2C
    Quantity (Each) Price (US$)
    1 - 3 35.00
    4 - 9 30.00
    10 or more Call

    Follows the table with the materials cost to create my version using the best components

    items models description price (euro)
    2 LM-2013U Output transf. 60
    2 LM-130D Power supply transf. 80
    2 LM-5H-2C Inductances 40
    2 Siemens D3A Driver tubes 20
    4 Shuguang 2A3C  Output tubes 100
    2 Golden Dragon 5AR4 Vacuum tues 30
    2 100uF + 100uF 500V Jensen Electrolityc Dual 70
    2 0.22uF 600V Jensen Copper film paper-in-oil 70
    2   Chassie corner 30
        Varies components + connectors 100
        Total price about 600

    but probably it is possible to create it using low cost components but reducing the sonic performances.

    2 LM-2013U Output transf. 60
    2 LM-130D Power supply transf. 80
    2 LM-5H-2C Inductances 40
    2 Siemens D3A Driver tubes 20
    4 Shuguang 2A3 standard Output tubes 70
    2 GZ34 or 5AR4 Vacuum tues 20
    4 100uF + 100uF 500V Any electr. + MKP bypass 20
    2 0.33uF Any MKP 10
        Chassie 30
        Varies components + connectors 100
        Total price about 450

    SIMULATIONS

    To check the performances of the circuit I have used the SE Amp CAD simulator by GlassWare.

    In the previous screen shot are visible the low performances using a single 2A3 output tube:

    In the previous screen shot are visible the better performances using a pair of 2A3 as output tubes to create a PSE (parallel single ended):

    In the previous screen shot are visible the performances using a pair of 2A3 as output tubes at max range.

    In the previous screen shot is visible the operating point using a pair of 2A3 as output tubes at max range.

    DRIVERS

    First test with a basic circuit

    This basic circuit have very good sonic performances but it need a not common vacuum tube to be used in a integrated amp.

    The target gain of this tube should be about 70-100, the anode resistance no more than 7-8k and low distortion until 50-60Vrms.

    I know only one tube with these characteristic, found in my PF2007 project. the D3A Siemens.

    The SRPP (Totem pole) has been skip because the power supply transformer have a single 6.3v output and also
    because the sonic performances of SRPP are never very good.

    It is possible use 2 stage driver with a circuit similar to the Herb Reichert (Audio Note) 300B but in this case the
    cost will increase for the second interstage capacitor.

    Another 2 stage driver without the second interstage capacitor is this following circuit used in my AV amplifier but
    I suggest it only if you will create a stereo amp. and not a monoblock because it use only half of the tube sections.

    An idea got from Alan Kimmel (http://www7.taosnet.com/f10/mustage.html) to get the highest possible load impedance
    to obtain more gain, low distortion and more voltage swing is show in the following circuit.

    The RJM Audio have published a headphone version on http://www.geocities.com/rjm003.geo/rjmaudio/diy_twi.html.

    The my first modification

    The my second  modification

     

    MEASUREMENTS

    Here are some plots generated with my Clio system by Audiomatica.

    THD of the basic driver stage created with a D3A Ra=10Kohm and Rk=100ohm at Vin=0.77Vrms

    THD of the basic driver stage created with a D3A Ra=10Kohm and Rk=100ohm at Vin=0.97Vrms

    THD of the Alan Kimmel modified driver stage created with a D3A Ra=10Kohm and Rk=100ohm at Vin=0.77Vrms

    THD of the Alan Kimmel modified driver stage created with a D3A Ra=10Kohm and Rk=100ohm at Vin=0.77Vrms

    THD with a pair of 2A4 at 60mA with the D3A basic driver to 8ohm load and input = 0.5Vrms

    THD with a pair of 2A4 at 60mA with the D3A basic driver to 8ohm load and input = 0.6Vrms

    Frequency response

    FINAL SCHEMATIC

    After the measurements is clear that the Alan Kimmel modified driver have more gain and low distortion but the final result on speaker output is quite the same.

    The sonic performances since to be compromised using the Alan Kimmel modified driver because the basic driver give a more natural sound so this is my final choice.

    The power supply has been optimized by the software PSU Designer II in few minutes.

    It use a single 5AR4 Golden Dragon vacuum tube and a single 100+100uF 500v Jensen electrolytic buy both at Audiokit online shop.

    If you use high efficiency loudspeakers near to 95db you can ear 50-60Hz noise.
    In this case you can use dc filaments with a 36A diode bridge and 33000uF 16v.

    RESULTS

    It give a good power and high sonic performances.

    The output power respect the simulations done and It is enough to drive any high sensibility loudspeakers like Apostrophe', AER, Lowther and some Fostex.

    The parallel compensate the low inductance value of the output transformers and it give a good low freq. band.

    Like all my vacuum tube amp. also in this project the damping factor is high so it give solid dry bass and no colorations.

    The temperature of power supply transformer is acceptable after long time playing.

    Off course if compared to the my new 845 amp. are clear some limits at high level power.