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About alexcp

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  • Location
    FL, USA


  • Location
    FL, USA
  • Interests
    DIY audio
  • Headphones
    Grado GS1000i; Beyerdynamic T1; Sennheiser HD800
  • Headphone Amps
    Musical Fidelity X-CANv8 and assortment of DIY headamps
  1. alexcp

    krell ksa5 klone

    50C is normal for power semiconductors, you don’t need to make it cooler.
  2. alexcp

    krell ksa5 klone

    A CRC filter is something along these lines: In that diyAudio post, both capacitors were 4700uF and the resistor was 4ohm. Have a look e.g. here: http://www.learnabout-electronics.org/PSU/psu12.php for the theory behind it.
  3. alexcp

    krell ksa5 klone

    FIf you are working with the "new" power supply, the one with opamps, then each opamp compares the reference 12V voltage (supplied by D1 or D2) with the portion of the output voltage from the R8/R7 or R9/R10 voltage divider. If the voltages differ, the opamp drives the pass transistor so that the voltages become equal. With the 511/750 ohm divider, V(out) = 12V * (511+750) / 750 = approx. 21.2V. If you want a lower output voltage, you can reduce the value of the top resistor in each divider (R8 and R9). For example, 499ohm instead of 511ohm would give you 12V * (499+750) / 750 = approx. 20V, 475ohm would give you 19.6V, and so on. Paralleling 2kohm with the 511ohm gives you 1/(1/511+1/2000) = 407ohm and approx 18.5V. However, if you bias is too high, a better thing to do may be to carefully tweak resistors around V(be) multiplier (Q14) in the amp itself. Reducing R19 from 825ohm and/or increasing R18 from 221ohm would decrease bias. Be careful though - should R19 be missing, your bias current would be very high.
  4. alexcp

    krell ksa5 klone

    Thank you Kevin!
  5. alexcp

    krell ksa5 klone

    Hello, Another build in progress: The amp proper is built (see photos) and tested; the sound with Grado GS is wonderful! Thank you Kevin for sharing the design! No power supply yet; I use my desktop lab supply for now The caps are Samwha RD; perhaps not in the spirit of the thread, but I just had them The output transistors are D44H11 and D45H11 (I could not match MJFs, so I used what I could match; had to add some insulation though) Resistors are RN55/RN60 and Panasonic ERX3 No case yet, plan to use one from modushop/HIFI2000 Question: I want to use a high resistance volume control pot (50k or 100k). Would it be ok to increase the resistance between the gate of the input JFET and the ground so as not to load the pot too much? What would be a practical limit on this? 1Meg? Thank you!