Hi OllBoll,
likely that for the same bias not so much is happening.
Nelson wrote a few times, only total bias matters.
Of course, with half the mosfets, the remaining cook gently at twice the original dissipation (with same total bias current), which should be avoided due to reliabilty.
Lowering bias will certainly raise distortion, as will drain source voltages lower than 15 V or so.
Hannes
likely that for the same bias not so much is happening.
Nelson wrote a few times, only total bias matters.
Of course, with half the mosfets, the remaining cook gently at twice the original dissipation (with same total bias current), which should be avoided due to reliabilty.
Lowering bias will certainly raise distortion, as will drain source voltages lower than 15 V or so.
Hannes
If one instead of halving bias to halv lowered it to ~ 62.5 % thus increasing the bias of the pair left by 25 %, would this bias increase compensate for higher usage / mosfet or is it then a better idea to use other mosfets, for example use parallel Toshiba 2SK2013 with a lower rail voltage?
Quote:
Originally Posted by samoloko View Post
I would like also to thank Zen Mod
great guy
nope ;
he's dumb , lazy and mean ;
he's just acting nicely in public ..... sometimes
Hum on my Aleph J
My Aleph J started having hum coming out of the speakers, after fixing a perfectly working table top assembly into a chassis. Can't figure out why. I am using a standard papa's zen type power supply schematic with 4 x 15000uF on each rail and toroid at 2 x 18v, 600VA. When i disconnect the input wires from the pcb, there is absolutely no hum. But when i connect the inputs to the RCA socket and ground the -ve input for SE operation, there is hum, even without any input being connected to RCA sockets.
The hum is mild but audible. Amp works very well as far as sound output is concerned.
What could be the problem area. There are no ground loops. RCA sockets and speaker outputs are isolated from the chassis.
Any pointer to where I should look or add any small cap somewhere to suppress the hum?
TIA.
My Aleph J started having hum coming out of the speakers, after fixing a perfectly working table top assembly into a chassis. Can't figure out why. I am using a standard papa's zen type power supply schematic with 4 x 15000uF on each rail and toroid at 2 x 18v, 600VA. When i disconnect the input wires from the pcb, there is absolutely no hum. But when i connect the inputs to the RCA socket and ground the -ve input for SE operation, there is hum, even without any input being connected to RCA sockets.
The hum is mild but audible. Amp works very well as far as sound output is concerned.
What could be the problem area. There are no ground loops. RCA sockets and speaker outputs are isolated from the chassis.
Any pointer to where I should look or add any small cap somewhere to suppress the hum?
TIA.
To add, when I short the input at the RCA socket, the hum disappears completely. Leads me to believe that the amp in itself is pretty quite. Seems to me that the shielded input wire that I am using is picking up hum. I have also tried two thin wires twisted around as input wires. Still picking hum.
Is there a small cap that I should add at the input socket to stop the stray pickup?
Yes, ZM. The power earth is connected to the chassis and the chassis is connected to '0v' of the PS through 10ohms NTC as per Papa's schematic.
Anilva
As the only thing that changed is connecting to the Pre ..
Are both screens (L & R ) on the cables to the preamp connected both ends?
Only the preamp end need to be as maybe you got ground connection on the mains cable as preamp chassis is grounded.
Maybe just snip snip on one of them and then can alwayse solder back
As the only thing that changed is connecting to the Pre ..
Are both screens (L & R ) on the cables to the preamp connected both ends?
Only the preamp end need to be as maybe you got ground connection on the mains cable as preamp chassis is grounded.
Maybe just snip snip on one of them and then can alwayse solder back
Yes, the hum is present with or without the RCA inputs connected to a preamp. No big change in the hum levels.
My problem as mentioned above is not with a preamp connected. The amp on a standalone basis is having minor audible hum. I did everything as per the book. When the screen wire (which is connected to the RCA input connectors) is disconnected from Aleph J PCBs, there is no hum. There is also no hum, when I short the input to the ground. So the screen wire is picking up hum along the way. The length of the screen wire is quite short (6 inches) and is away from the transformer (which is mounted towards the front of the chassis). Amp in itself sounds terrific. But I am getting bugged with this hum. My F5 is dead quite, with exactly the same wiring topology.
Seems worth the try. I will turn the toroid and check. I did add a 0.33uF cap to the ground tab of the RCA socket. No difference.
Thanks to all for the help. BTW, what is the input impedance I need to take if I need to calculate a RC filter for blocking any DC from the preamp?
Cheers.
Tried all the suggestions to eliminate the 50Hz hum. Wouldn't go away. Got fed up. Closed the cover of the chassis and stopped further attempts in disgust. While I was connecting the preamp back to the amp, i noticed the hum dropped as soon as I connected one channel. As soon as I connected the 2nd channel, the hum went back up and increased. Must be two grounds from the preamp are forming a loop. Will try again tomorrow with few other attempts.
Two questions: firstly does it make a difference if i add a power supply filter in between the amp and the power socket? secondly what is the fuse rating that I should use for the fuse in the primary of my transformer. The voltage rating i my country is 220v. Couple of 2A fuses blew on startup.
Thanks.
Two questions: firstly does it make a difference if i add a power supply filter in between the amp and the power socket? secondly what is the fuse rating that I should use for the fuse in the primary of my transformer. The voltage rating i my country is 220v. Couple of 2A fuses blew on startup.
Thanks.
OK - 'till now we are crawling in dark ; please - switch the light on , and post few pictures ...
regarding filter - some amps do not like filters ....... try and listen ;
fuse - it really depends of actual xformer , rectifier and caps used
in any case - if your xformer is rated at 600VA , why using fuse which will not allow full A potential of it ? divide 600 with 220 and add 20% ; so - 3A15 fuse is good for start
regarding filter - some amps do not like filters ....... try and listen ;
fuse - it really depends of actual xformer , rectifier and caps used
in any case - if your xformer is rated at 600VA , why using fuse which will not allow full A potential of it ? divide 600 with 220 and add 20% ; so - 3A15 fuse is good for start
Thanks. Will try and post some pictures. I am using 2 x 18v, 600VA toroid with 4 x 15000uF, 63v capacitors on each rail using rc network as per zen amp psu. Also use a 10 ohms NTC to the chassis from the 0V ground. The bridge rectifiers are the the metal package, 50amps, 1000v types mounted to the chassis.
Cheers.
Hum is gone
Thanks everyone for the advice and help.
Finally managed to get rid of the hum, by applying brute force. I changed the power supply board with a another one (which I used to test the Aleph J on the workbench). The difference between the two ps boards is the replacement board has 4x22000uF on each rail instead of 4x15000uF on the earlier one. Though I don't believe the value per se made the difference, may be there is a problem with one of the electrolytics. I don't have a LCR meter to test the electrolytics.
Anyway, finally put the lid on the chassis not to be opened for at least few days. BTW, I added a 0.47uF in the input to block any unwanted dc creeping into the amp. Amplifier sounds terrific. Very happy at the end of the day for all the efforts of the last few months.
Overall a very different experience building a Aleph J compared to F5. Building F5 was a breeze compared to Aleph, which also seems to run lot hotter.
Now on to the F5 with paralleled Toshibas....
Thanks once again.
Thanks everyone for the advice and help.
Finally managed to get rid of the hum, by applying brute force. I changed the power supply board with a another one (which I used to test the Aleph J on the workbench). The difference between the two ps boards is the replacement board has 4x22000uF on each rail instead of 4x15000uF on the earlier one. Though I don't believe the value per se made the difference, may be there is a problem with one of the electrolytics. I don't have a LCR meter to test the electrolytics.
Anyway, finally put the lid on the chassis not to be opened for at least few days. BTW, I added a 0.47uF in the input to block any unwanted dc creeping into the amp. Amplifier sounds terrific. Very happy at the end of the day for all the efforts of the last few months.
Overall a very different experience building a Aleph J compared to F5. Building F5 was a breeze compared to Aleph, which also seems to run lot hotter.
Now on to the F5 with paralleled Toshibas....
Thanks once again.