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  1. According to their website, part nr. 5452258 has the following electrical parameters: Nominal current 13.5 AN Nom voltage 400 V Rated voltage (III/3) 250 V Rated voltage (III/2) 400 V Rated voltage (II/2) 630 V Rated surge voltage (III/3) 4 kV Rated surge voltage (III/2) 4 kV Rated surge voltage (II/2) 4 kV Edit: It looks like part nr. 1729131 has the same properties listed.
  2. With differential measurement - which better corresponds to what the membrane sees if I'm not mistaken - there should be some cancellation, right. Guess I'll be breaking out the analyzer over the holidays again, currently too busy listening when time permits
  3. I have now pulled some numbers from the circuit. And I took more pretty pics, which I‘ll start off with: Now for some numbers: PSU voltages: V_HV_pos=402V, V_HV_neg=-403V V_LV_pos=14.88V, V_LV_neg=14.88V Current sources: Right channel voltage drop over the RN60C 49R9: V_ccs_pos=857mV, I_ccs_pos=17.17mA V_ccs_neg=856mV, I_ccs_pos=17.15mA Left channel voltage drop over the RN60C 49R9: V_ccs_pos=862mV, I_ccs_pos=17.28mA (adjusted to 857mV/17.17mA) V_ccs_neg=856mV, I_ccs_pos=17.15mA On the left side the initial B+=20V current source adjustment was the following: V_ccs_pos=845mV, I_ccs_pos=16.93mA V_ccs_neg=847mV, I_ccs_pos=16.97mA So going from a B+ of 20V to full a 402V led to an increase in current of a meager 1%. Next up is gain, THD and clipping. Input is a single ended 0.1V at 1kHz from the Boonton 1121. The – input of the carbon is grounded through a 220R resistor (equivalent the output impedance of my preamp). The output is measured unloaded. L+: V_out_rms=42.5V, gain=52.56dB, THD=0.3% L-: V_out_rms=46.0V, gain=53.26dB, THD=0.095% R+: V_out_rms=41.9V, gain=52.54dB, THD=0.38% R-: V_out_rms=46.6V, gain=53.37dB, THD=0.09% The THD is higher than I would have expected (the Boonton‘s baseline is at 0.00085% btw). It‘s mostly 2nd harmonic though. Here’s how I took the gain and THD readings: And here’s what the THD spectrum looks like (notched out fundamental at 1kHz, peaks at 2kHz and 3kHz, and maybe even 4kHz): Here we see the output just before clipping: CH2 in purple is the input signal to the amp, 1kHz at like 1.5Vpp (518mVrms): CH1 in yellow is the output signal. 764Vpp. The probe is rated for 600Vpp at its 10x setting, so that was stretching it a bit… And here we see clipping with an input signal of 1.9Vpp (668mVrms): I also took temperature readings after the amp has been running for 2hrs or so. Ambient is at 24°C. Right behind where the SiC Fets are mounted, the heatsink temperature is 45°C (113°F). The corner the farthest away from where the bracket connects to the heatsink is as 41°C, so the heatsink gets utilized reasonably well. Inside the case it read 43°C. I realize that the brackets are not positioned ideally on the heatsink (too far up), which is why I have used chunky brackets, thinking that the thick material would conduct heat nicely. Seems to work well enough. Seeing the 21°C rise in temp makes me think I could try upping the current. Calling it a furnace was overstating it a bit perhaps, but the whole enclosure gives off an impressive amount of heat already. I also employed the opto servo btw, going up to 17.5V positive offset before putting in the jumper. The amp now comes on with like 1V offset, which goes down to a few mV after a couple of minutes. I don’t think I could hear any sonic difference between going raw vs. opto servo. So, two questions remain: Why is THD so high? I would have expected a lot less. Is it the frontend perhaps? And what's up with the gain imbalance? It’s consistent between polarities (single ended input, - input grounded). Could that be the cause?
  4. Input and output wiring in place: And I'm happy to report that the amp is working! No smoke, no arching, no shrapnel. After like an hour of warming up and fiddling with offset and balance, I gave it a listen with my 007mk1. Wow. I'm treating pin 1 as analogue ground btw, and circuit ground goes to the chassis earth ground point via a CL60 thermistor. Zero noise, zero hum - with my gear at least. Bias is still around 17mA for all channels, I'll get some more accurate numbers when I set up the optocoupler servo. Not sure if I'll go up to 20mA, this amp is a furnace at 17mA already.
  5. Thanks for the encouragement, y'all. Getting closer now:
  6. HV and LV wiring is now in place: Next up is input and output wiring.
  7. Progress is slow during the week, but thanks to home office I can get some soldering done over the lunch break. For connecting the HV and LV PSUs and the amp boards I'm going with a star ground, held in place by wire wrap and soaked with solder: Here's how the manifold looks like in circuit: There's good clearance too: Although the currents are substantially lower than what I'm used to from solid state, I took care to have equal lengths of fat wire for each of the HV and each of the LV supplies. I hope the grounding scheme is going to be quiet, I passionately hate ground related hum.
  8. Can you post a pic of the whole PSU so we can see cap and diode orientation and voltage references and so on?
  9. Goop: Bolted down: Fits like a glove: Good clearance: And the full monty:
  10. The amplifier boards are now fully populated, including the front end Jfets, for which I picked pairs of 2sk170bl from the same batch with an Idss of 7.3 and 7.4mA. Using a benchtop PSU supplying 20.00V DC I then set the constant current sources to 17.00mA: It's going to be interesting to see how much this will go up with the full B+.
  11. Okay, moving on. Here's how I wired up the transformer: And here we see the unloaded secondary voltages: Here the PSU boards are mounted to the front plate for heatsinking. The power resistors (500R and 16k) will be used to load the PSU for testing: And finally, the moment of truth: One more view from above: So far, so good.
  12. If I recall correctly, they are Molex Eurostyle Terminal Blocks UL certified for 300VAC, which would mean 425V DC peak. I'm not sure if there are terminal blocks rated for 600V with a 5.08mm pitch. Since I'm using the amplifier boards with a ground plane, i used a couple of layers of Kapton tape at the bottom of the terminals and used very little solder in order to avoid the arching that's been reported with these boards. Edit: I just realized that the terminal blocks aren't the Molex that I thought I had installed. I guess I should replace them, which is not going to be easy 😕 Mouser has some phoenix 5.08mm pitch terminals rated for 400V. What would be a good alternative to the screw terminals? I'm not their biggest fan either.
  13. Thanks, I'll be adding 10k resistors at the inputs then. I'm making good progress with my build after it lay dormant for over a year:
  14. Want impedance volume pot is everyone using? And those of you who aren't using a volume pot in their amp, are you terminating your inputs to ground with a resistors other than the 500k on the circuit board?
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