Got it...now I remember...this is definitely the way if you want to make place for alternate components...I went ahead with the 5K trimpot and offset DC to around 0.2mV, worked pretty well..
It's still one channel, but I like the sound...its as astonishing as F6, slightly different signature, but unfortunately this time I don't have great speakers to test...and quite inefficient ones (82 dB) as they claim...doesn't go louder compared to how I experienced with Klipsch, but still decent music to hear...
I'm just building the Aleph J.
I have read threads that discuss setting R7 to 68K before assembly and adjusting it after 30 mins for 0.4V across the source resistors.
I have read that R7 adjusts the DC output to 0V.
I can't find any reference to the setting of R8 LTP bias ?
I have read threads that discuss setting R7 to 68K before assembly and adjusting it after 30 mins for 0.4V across the source resistors.
I have read that R7 adjusts the DC output to 0V.
I can't find any reference to the setting of R8 LTP bias ?
Because we have access to J74, (something that was in doubt when the PCB were laid out years ago...) that is the best course - leave the LTP pot open (R8 pot) and just use a 1K resistor in R8 and move on. 😀
I was measuring all the E96 resistors as I was installing them, they seem to be within the E48 range. That might be down to my multimeter but are they really that critical ?
The schematics on the first page shows R8 as 1K fixed or 2K variable.
If you installed a 500 ohm R8 variable the front end current will be somewhat
higher. If you absolutely cannot remove it you might consider lowering D1 to compensate.
If you installed a 500 ohm R8 variable the front end current will be somewhat
higher. If you absolutely cannot remove it you might consider lowering D1 to compensate.
Removing three pin variable resistors is actually fairly straightforward. The pins can be bridged with a large blob of solder while the part is pulled out of the board with a pair of pliers from the other side. The excess solder is removed afterwards with solder wick.
Minor damage to the holes isn’t much of a problem. The holes for the fixed R8 location bridge across the variable footprint.
Minor damage to the holes isn’t much of a problem. The holes for the fixed R8 location bridge across the variable footprint.
The BOM on the DIY store page shows R8 as a 500R variable pot ??
I will attempt to remove it.
OK, VR8s came out OK without any damage, now replaced with R8 = 1K0.
On my boards R8 is in series with R6 (560R), so I now have 1K6 in series with the emitter of Q2.
Q2 looks like a constant current source to me, now set to approximately 5.5mA.
On my boards R8 is in series with R6 (560R), so I now have 1K6 in series with the emitter of Q2.
Q2 looks like a constant current source to me, now set to approximately 5.5mA.
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10mA would require approx. 8.44V across R8+R6. R6 is already 560R.
R8 + R6 needs to be about 844R.
Thanks guys, I now need to remove the 1K0 resistors. I could have just adjusted VR8 to 280 Ohms.
R8 + R6 needs to be about 844R.
Thanks guys, I now need to remove the 1K0 resistors. I could have just adjusted VR8 to 280 Ohms.
On reflection, keeping VR8 as a 500R variable resistor, maybe it should be adjusted for 5.6V across R6, that would equate to 10mA through the CCS.
If you have a 9.1V zener at D1, then leave the 1k resistor in place at R8 and replace R6 with a jumper. Or simply jumper across R6 on the underside of the board if you would rather not remove it. I like to use a 200 Ohm resistor at R30 for easy measurement of the total current through the diff pair.
It's obvious what to do, I'm just making the point that the DIY store boards need a bit more advice for the novices.