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  1. A2029

    1101 Audio custom crafted headphone amps

    You can likely run the 6080 alone without the 6J5 tubes as the 6J5s would be pretty much idle when the 6080 is running (6080 tubes are so powerful that they do all the work when run as a combo with other tubes). Generally the most powerful tube (lowest anode/cathode resistance) will do most of...
  2. A2029

    L0rdGwyn's DIY Audio

    Beautiful! I really dig the grey chassis, reminds me of old school military gear. Congrats on the build Keenan!
  3. A2029

    The Reference 6J5 Thread (L63, 6C5, 12J5, 6P5, etc.)

    *Awesome job with the write ups! Some great reads :)
  4. A2029

    1101 Audio custom crafted headphone amps

    As long as the pins are secure I wouldn't worry about adding solder. Only if it develops noise down the road would you need to worry about it.
  5. A2029

    1101 Audio custom crafted headphone amps

    I'd recommend either a good rosin core 63/37 solder, or the 62/36/2 that bcowen suggested. Back in the day ROHS (lead free) requirements were not in place, so it's more likely that they were using a lead based solder (either 60/40 or 63/37). You don't want to mix a lead free solder into the lead...
  6. A2029

    1101 Audio custom crafted headphone amps

    Those are the Cinemag input transformers (optional for XLR input). They take the balanced XLR and convert it to a single ended signal for the amp to use.
  7. A2029

    1101 Audio custom crafted headphone amps

    Like this (quickly drawn in Paint, lol). Only one channel shown:
  8. A2029

    1101 Audio custom crafted headphone amps

    You can get away with using a super cheap 2 pole rotary switch. Number of positions will be your number of desired resistances to test. I.e. If you wanted a switch for 300, 150 or 120, 64 and 32 ohms, you would get a 2 pole, 5+ position switch.
  9. A2029

    1101 Audio custom crafted headphone amps

    For headphone amp measurements, even 2-3W metal film should be plenty. Stay away from inductive wirewounds if possible.
  10. A2029

    1101 Audio custom crafted headphone amps

    As long as the 4pin XLR and the 1/4" outputs are the same (i.e. you aren't trying to measure an amplifier that has separate balanced and summed single ended outputs), then either of these will be equivalent. If you plan to measure solid state amps that are inherently balanced but have summed...
  11. A2029

    1101 Audio custom crafted headphone amps

    Those are the S45's 45mm :)
  12. A2029

    1101 Audio custom crafted headphone amps

    That cable will work. On your amp you also need to provide a load similar to what the amp will see. An easy way to do this is if you have a 4pin XLR out as well as the 1/4" out on your amp, then you can buy a male 4pin XLR connector and solder in some 300 ohm resistors for each channel (to mimic...
  13. A2029

    1101 Audio custom crafted headphone amps

    M2 doesn't have line level inputs on the back, so has to go through the pre input on the front which I believe slightly reduces accuracy of the input and increases noise very slightly, but not a big deal unless you are doing sensitive measurements.
  14. A2029

    1101 Audio custom crafted headphone amps

    That's correct, USB with the Motu M4 acting as the ADC.
  15. A2029

    1101 Audio custom crafted headphone amps

    Quite simple setup: Schiit Modius DAC fed from a laptop, going into a Blue Halo amp. Output from the BH going into a Motu M4. REW running on laptop to capture the distortion plots. After tubes were in place, amp was turned on and given 20 mins warmup and volume set to produce 80dB volume...
  16. A2029

    1101 Audio custom crafted headphone amps

    This is quite interesting: EL34 tubes (Svetlana in this case) run in the BH have over 10X the 2nd harmonic distortion than a 6SN7 (Rogers branded Sylvania). This was at ~80dB into HD650's. The spikes at 8Khz and 16Khz can be ignored as they are from the switching power supply hooked up to the...
  17. A2029

    1101 Audio custom crafted headphone amps

    Sure thing, that would be appropriate with the red power button :)
  18. A2029

    L0rdGwyn's DIY Audio

    Nowhere near as costly as Duelund caps :wink: Much much smaller ones of these (0.47uF), haha
  19. A2029

    L0rdGwyn's DIY Audio

    @L0rdGwyn should slot in some of these little guys: 95mm D x 220mm L :stuck_out_tongue_winking_eye:
  20. A2029

    L0rdGwyn's DIY Audio

    This is awesome Keenan! Congrats on the build!
  21. A2029

    L0rdGwyn's DIY Audio

    That's very true, using the resistor trick with a lower ohm tap gives both of those benefits, but comes at the expense of lower power output for higher impedance loads. Fortunately these Sowter transformers are being paired with the LCD-4 as primary, so #2 isn't a problem due to the flat...
  22. A2029

    L0rdGwyn's DIY Audio

    Mental gymnastics complete :grinning: Here are the windings and impedances for your transformers @leftside Z/4Z/9Z/16Z 22/88/198/352 Six relays total per transformer (U1-U6 above). For 16Z, no relays are on. For 9Z, relays U1/U2 on, for 4Z relays U1-U4 on, for Z all relays (U1-U6) on.
  23. A2029

    L0rdGwyn's DIY Audio

    @leftside We are having custom transformers made, but unfortunately not individual windings for each output. Sowter uses the following scheme of parallel and series windings to extend the frequency response of the transformer. If wiring three secondary windings for a switch was hard as @L0rdGwyn...
  24. A2029

    1101 Audio custom crafted headphone amps

    Both the KT150 and the EL34 run off of ~475V in the variant of your amp. Bias current for the KT150 is close to double that of the EL34. Bias current for the EL34 can be set to preference based on percent of max tube dissipation. The higher the percent of max dissipation, the less distortion and...
  25. A2029

    L0rdGwyn's DIY Audio

    I believe plate resistance in the 1200 ohm range, so a 5K transformer would work well. Here is my idea for the top cap, crudely drawn in paint in about 10 seconds: Black is aluminum tubes, white would be high heat thermal epoxy in between the tubes. Innermost black tube could be copper instead...
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