Ok, I think I see it now. It creates the voltage drop to control the AC gain of CCS.
As the speaker current increases, so does the voltage drop, which in turn opens the Q4 more. As a result, at high speaker currents, the quiescent current through MOSFETS will drop.
Am I wrong, ZenMod?
Ok, the little voice in head connected with "good sleep" is telling me "cut the trace, cut the trace".........while practical side is saying "this amp is dead quiet, dont mess with it." I hate that little voice, good sleep not withstanding.
I used the back plate parts kit from store with brass standoffs.....
Russellc
Just measured my Aleph J boards recently purchased from the diyAudio store and none of the mounting eyelets are at ground potential. One looks like it could be, but looking closely, it has been isolated from the ground plane. Just FYI before you cut.
I doubt, short of some reason I dont see, (and there could be many!) that I will bother. My boards are from a while back when 6L6 had a parts group buy for the Aleph J.
Unless a compelling reason, safety or sound improvement I am not going to mess with it whether the brass standoff goes to ground or not.....
Russellc
Thanks for that intel.
I've got a couple of tweaks in the pipeline, so I'll see what my DMM has to say when I get the chance.
As with others commenting similar thoughts, my Aleph J doesn't sound broke - so there's no immediate fix needed.
Based on the board layout from the design thread at Post #48, the trace that appears to come closest to an eyelet is V+ at the bottom left corner:
Is this the eyelet you're concerned about? If not, then which one?
Feel free for anyone to correct me if I've picked out the wrong board layout pic.
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I have checked the PCB again, only this time with an extra pair of glasses so that I can see little things properly. Well, I owe an apology to everyone for a false alarm. I am getting too fricken old... sorry guys!
The area with ground fill is very small, resembling T ground topology, and is done properly. All good.
I had an ACA PCB on my mind when I looked at the AlephJ PCB; ACA PCB does have an eyelet that is a part of the ground track and this is correct for the ACA amp because there are no thermistors / any other ground connections.
The area with ground fill is very small, resembling T ground topology, and is done properly. All good.
I had an ACA PCB on my mind when I looked at the AlephJ PCB; ACA PCB does have an eyelet that is a part of the ground track and this is correct for the ACA amp because there are no thermistors / any other ground connections.
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Dear Aleph J builders,
I just finished my Aleph J build - first real electronics project since 25 years.
I have chosen Aleph J as it has an opinion of mellow, gentle amp - exactly what I was looking for. Unfortunately I am quite unhappy with the sound. I do not speak audiophile lingua but will do my best to describe my problem:
The sound seems to be congested - all instruments together - no separation. A lot of details but no soundstage - everything is garbled together. Also fatigue comes after just couple minutes of listening - seems to be related to high frequencies which are quite tiring. No hum, no noise abut definitely not mellow. My (very) old HK 630 delivers a great soundstage and instruments isolation - I can listening it for hours - not so with Aleph J, unfortunately...
Well, as so many happy builders cannot be all wrong - I assume a problem must be with my build. I would appreciate any suggestion about how I could improve a sound quality of my Aleph J.
Thanks in advance!
I just finished my Aleph J build - first real electronics project since 25 years.
I have chosen Aleph J as it has an opinion of mellow, gentle amp - exactly what I was looking for. Unfortunately I am quite unhappy with the sound. I do not speak audiophile lingua but will do my best to describe my problem:
The sound seems to be congested - all instruments together - no separation. A lot of details but no soundstage - everything is garbled together. Also fatigue comes after just couple minutes of listening - seems to be related to high frequencies which are quite tiring. No hum, no noise abut definitely not mellow. My (very) old HK 630 delivers a great soundstage and instruments isolation - I can listening it for hours - not so with Aleph J, unfortunately...
Well, as so many happy builders cannot be all wrong - I assume a problem must be with my build. I would appreciate any suggestion about how I could improve a sound quality of my Aleph J.
Thanks in advance!
Ah, right.
- DAC/preamp: RME ADI-2 DAC
- Speakers: vintage Canton Quinto 520
PCBs are all from diyaudio shop, matched Mosfets from reputable German seller, matched Jfets from eBuy seller recommended on on one for the forums here. Transformer from Toroidy. The rest of the parts is from Mouser.
Bias, DC measurements are correct.
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Can you post the photos? Input wiring, RCA's, PCB wiring.
How did you ground the PCB's? Show us the PCB grounding arrangement - power supply negative, speaker negative, XLR shield.
Are you using Aleph J in balanced input mode (your DAC has balanced out XLR's...)
Did you try swapping the hot and cold on XLR's?
Toroidy has a large number of static shielding wires... how did you connect those?
Are you sure the JFET's are of a correct grade? Measure the voltage drop across R8 and then calculate the current, I think it should be around 8mA. Then, measure the Vgs at each JFET - i think it should be 0.2V.
I think the voltage drop across R7 should be close to 4V to open the MOSFETs.
Check the components in the output CCS, especially the AC gain components and confirm they are correct. Vce on Q4 should also be close to 4V
Make sure that you did not swap the resistors R1 (R3) and R2 (R4)
If you have an oscilloscope, load the Aleph J channels with something like 10ohm / 50W resistors and check the symmetry and clipping at 20Hz, 10Khz, 20kHz
Also, make sure the MOSFETS are not oscillating !!!! Use 1:10 on probes
How did you ground the PCB's? Show us the PCB grounding arrangement - power supply negative, speaker negative, XLR shield.
Are you using Aleph J in balanced input mode (your DAC has balanced out XLR's...)
Did you try swapping the hot and cold on XLR's?
Toroidy has a large number of static shielding wires... how did you connect those?
Are you sure the JFET's are of a correct grade? Measure the voltage drop across R8 and then calculate the current, I think it should be around 8mA. Then, measure the Vgs at each JFET - i think it should be 0.2V.
I think the voltage drop across R7 should be close to 4V to open the MOSFETs.
Check the components in the output CCS, especially the AC gain components and confirm they are correct. Vce on Q4 should also be close to 4V
Make sure that you did not swap the resistors R1 (R3) and R2 (R4)
If you have an oscilloscope, load the Aleph J channels with something like 10ohm / 50W resistors and check the symmetry and clipping at 20Hz, 10Khz, 20kHz
Also, make sure the MOSFETS are not oscillating !!!! Use 1:10 on probes
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Just a note on the fatigue. Mine was measuring perfectly but the highs were extremely fatiguing for the first month compared to my other amps. It eventually settled in nicely and now sounds very smooth. I never had the soundstage issue you describe. Maybe the speaker impedance is not ideally suited to the Aleph J.