Vertical wires from C1 looks like a convenient way to roll capacitors. So given my power supply is in order i should not have any DC gain issues? I am using the rectifier on the universal power supply. Is there anything else i need to do to accommodate for the jumped C1?
Nice build Boky, i have many of your posts bookmarked
Yes, check the DC offset of your preamp before you hook things up. It is a DC blocking cap. I recommend running it for a little bit and when things are going well, try removing it.
C1 is there to ensure the gain drops to 1 as the input signal approaches 0Hz (DC).
With C1 bypassed, the DC gain of Aleph J will be the same as with other input signal frequencies.
You have to make sure that your source will not let any DC out.
You could build the Aleph J with a capacitor soldered to those vertical wires. Make sure it is all good first (you can set the Iq and output offset correctly; the amplifier is working correctly), and then:
1. Check the DC out of your source component(s)
2. If there's no DC coming out of your source, remove the C1 and short the vertical wires
ok thats making more sense to me now. Thanks for the explanation Boky. My preamp has multiple gain functions, Schiit Freya plus. Am i correct in thinking all the functions need to be tested for DC leak?
The DC leak as you call it, is the function of the pre-amp output circuit. There's either a DC blocking capacitor at the pre-amp output, or some other means of ensuring the DC component is not present at the output (OPAmp servo).
The best would be to ask Schiit. That is a valve preamplifier (I think)... ultimately, the decision to use C1 or remove C1 is yours to make.
I have only one source that I use with Aleph J, with no pre-amps or any other "boxes" in between. I am very confident that my source will not produce any DC at its output.
The best would be to ask Schiit. That is a valve preamplifier (I think)... ultimately, the decision to use C1 or remove C1 is yours to make.
I have only one source that I use with Aleph J, with no pre-amps or any other "boxes" in between. I am very confident that my source will not produce any DC at its output.
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Quick question about JFETs for pass amps. I thought I had a matched wuad of J74 but one of the 3 pieces is not matched. They are BL grade. Could I get away with buying a single pair of matched J74 and it not be a problem as long as it’s the same grade? Or do I need a matched quad?
With Nelson’s recommendation. I made a little breadboard jig and 12V.
To measure a JFET:
To measure a JFET:
- Get a 5 to 13 volt supply and a DC voltmeter (we used 12V)
- Connect the +V to the Drain
- Connect the Gate and Source together to a 100Ω resistor
- Connect the other lead of the resistor to ground
- Measure the voltage across the resistor, which gives the Idss (1 volt = 10 mA of current)
- Try to measure all devices under the same conditions, temperature, and duration of test
That's good. I was worried the readings might be from a Peak using low and non-constant Vds voltages.
Were the numbers from a quad from the diyaudio store? If so, you might try contacting it with your measurements since they seem to not meet the expected Idss spread.
Were the numbers from a quad from the diyaudio store? If so, you might try contacting it with your measurements since they seem to not meet the expected Idss spread.
Not from DiyAudio. I got them another way a long time ago and had tested them before using them on my Alpeh J.
I can order a matched pair from Punkydawgs on eBay for less than $25.
I can order a matched pair from Punkydawgs on eBay for less than $25.
Ah...then getting a pair from Punkydawgs is a good way to proceed. Hopefully he can supply a pair in the same range as your existing one.
Good luck with your build.
Good luck with your build.
Thanks for the help everyone and mr Pass. Very happy with the Aleph J. My other amp may be moving out soon 😉
Well? When your Aleph J is finally exuisitly built with love, skill and truck loads of money. Finally, adjusted, Up and running. The mighty all out awesome velvet musical sledge: The Aleph J…🥰
Well?
Thats the: Truely Good times! 😎👍👍👍
So. Crank it up!!🙂
https://tidal.com/track/311636
I have a lonely J74 that measures 9.9mA. Could be a good companion for your 9.72. Let me know if you want it.
What static resistance of 2SJ74 should be expected? I have values between 30 and 34ohms for 4 pieces. I also have values of around 105ohms for other 4 pcs. Could the other 4 be fake?
JFETs have sort of a capacitive barrier between the gate and the source and/or drain. They can not be tested with an ohm meter, which could coincidently damage that barrier, due to static discharge and render them unusable.