Once the bias trimpots are soldered in the board, it is difficult to measure their setting. I doesn’t know where they ended at. I needed to make quite a few turns of adjustment to get to 1.6A.
It looks like you have a jumper wire in place of a 0.22 Ohm resistor. I would recommend having the 0.22 resistor there.
I have a 0.1 uF Polycarbonate cap at C1, just in case I can use the amp with a balanced input. My preamp is single-ended, so I ground -IN with the jumper position. Yes, the cap isn’t needed, but I found a good supply of them a while back.
I do recommend installing 10 Ohms at the HBR location. I think that is one reason why my build has no hum.
It looks like you have a jumper wire in place of a 0.22 Ohm resistor. I would recommend having the 0.22 resistor there.
I have a 0.1 uF Polycarbonate cap at C1, just in case I can use the amp with a balanced input. My preamp is single-ended, so I ground -IN with the jumper position. Yes, the cap isn’t needed, but I found a good supply of them a while back.
I do recommend installing 10 Ohms at the HBR location. I think that is one reason why my build has no hum.
I’m building my Aleph with the Semisouth jfet at Q9, I’m fallowing some recommendation from Nelson earlier in this thread I think. Do you suggest to have a 0.22 ohm resistors even with the SS jfet?
Do you actually have a 0.1uf at C1 or was it a typo? It’s a 1uf on the original aleph schematic. 0.1uf must reduce the sub bass quite a bit.
Do you actually have a 0.1uf at C1 or was it a typo? It’s a 1uf on the original aleph schematic. 0.1uf must reduce the sub bass quite a bit.
In post #12 Nelson talk about the offset trimpot that need to be of lower value for this configuration. The final value is about 350ohms instead of 1k for a standard aleph.
The recommandation for removing the source resistance for the ss jfet is on post 82. Related to the difference in tempco vs the usual mosfet I think
The recommandation for removing the source resistance for the ss jfet is on post 82. Related to the difference in tempco vs the usual mosfet I think
From my memory Cody tried and without source resistor for SS he always had 2H positive. Later he could achieve 2H negative by playing with a gain pot. But this boards is alteration of original Aleph J schematic, so no dedicated gain pot.
I started stuffing my DIYstore Aleph J boards for my SemiSouth version of the Amp. I notice that the Aleph J illustrated build guild schematic has resistors in parallel with 2 pots. R7 (2k pot and 1k resistor) effectively making it 666 ohm pot; R27 (100K pot with a 68K resistor) = 40.5K pot; I notice that Codyt in post 81 and Rainfallsky post 156 does not have those resistor in parallel . With the resistor in Parallel in R7, the pot the value closer to what ZenMod suggest in Post 366. What about R27, should I install the parallel resistor or it does not really matter ? Also R8(1k) is missing a 2K pot, does that matter ? Am I being too neurotic ?
They are not in parallel, those values are estimate. They are either trimpot or fixed resistor. Idea is to first use trimpot, find values you need for exact dc offset and preferred bias. Then desolder trimpots, measure them, and solder exact same values of fixed resistors.
So the powering up of the first channel is a success. Everything is rock stable at 1.45A at this moment. I’ve decided to follow Tungsten advice and put back in the 0.22 source resistor for the SS Jfet. I will listen to this configuration before trying mods. I have also replaced the 100k bias pot with a 20k one since it seem to be enough to bias up to 2A with this Aleph J Semisouth/Irfp150 configuration. I also have a 600ohm resistor parallel with the 2k bias pot.
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I have been really enjoying the sound of this amp. I still have the IRFP048 and FQH44N10 in place. Since listening to several albums over the last few days, I have made a couple small tweaks. The gate stopper resistors, R9 and R10, have been increased to 220 Ohms. C2 has been changed to an Elna Silmic II, bypassed by a Wima Polypropylene 0.1 uF. C3 remains a Nichicon FG series, bypassed by a 0.47 uF Polyester film.
I made similar capacitor choices with my first Aleph J. The amp seems to benefit from mixed cap selection.
I made similar capacitor choices with my first Aleph J. The amp seems to benefit from mixed cap selection.
What difference did you heard by doing this or did you have some oscillation?
I thought I detected a trace of oscillation on some recordings with a lot of high frequency content. Increasing the value of the gate stoppers ended this. I also used Shinkoh tantalum film resistors at the gates of the FQH44N10 devices.
The combination of tweaks has both improved the quality of detail in recording ambiance and left the sound remarkably smooth. It is the sort of change that makes me want to listen to lots of my old favorites to hear what they sound like with this setup.
The combination of tweaks has both improved the quality of detail in recording ambiance and left the sound remarkably smooth. It is the sort of change that makes me want to listen to lots of my old favorites to hear what they sound like with this setup.
My pair of Aleph mono blocs have been playing music now for maybe 12 hours and they sound great. I’m running them at 1.6 amps with 0.22 ohm up and down and everything else as original schematic. I have been running some test too to confirm that everything is ok, distortion at one watt is really low and negative second harmonic it is.
Prior to this amp I have been listening to the vfet lottery 2sk82 amp for a year maybe. The Aleph sound a little bit darker/less bright and less 3D compared to it at this time. For those who have built this amp, how do you find that the bias change the sound? Or what is your bias sweet spot
Hubert
Prior to this amp I have been listening to the vfet lottery 2sk82 amp for a year maybe. The Aleph sound a little bit darker/less bright and less 3D compared to it at this time. For those who have built this amp, how do you find that the bias change the sound? Or what is your bias sweet spot
Hubert
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I ended up using codyt recipe after experimenting with different source and ALEPH resistors.
1K8 for the ALEPH resistor
0.1 5w for the IRFP150
jumper wire for the SemiSouth
Bias between 1A6
Bias at 1A5 was slightly brighter which is what I ended up with my F6 SemiSouth amp.
1K8 for the ALEPH resistor
0.1 5w for the IRFP150
jumper wire for the SemiSouth
Bias between 1A6
Bias at 1A5 was slightly brighter which is what I ended up with my F6 SemiSouth amp.