Your onto it. With shorting plugs in power amps inputs you eliminate anything upstream. So if amp is quiet with plugs, problem is upstream. Preamp or source. I had 2 different pre amps do the exact same thing. Unlikely they are both defective .
This wasn't typical 60 hz him....some fizzy sounds coming through Tweeter sections. So I catagorize it as noise.
Very slight, ear must be close. Typically this test is done for hum, and it would eliminate hum if power amp is ok. If amp hums with inputs shorted, problem is in amp.
Next I will switch leads to see if noise follows, which will confirm noise is up stream "somewhere. Will then substitute different D/A converter. If not that, somewhere with laptop I guess.
Russellc
There is some hum from woofer, but seems a little higher than hum @ 60 hz. Plus there is a little noise from tweeter as well. Again it is so low level you have to put ear very, very close to hear it.
Both preamps do this, so it seems unlikely that both units have same problem. I am going into work today, but will narrow down where it is coming from.
I will trade various parts of system around, and move sources to other systems in other rooms. Also, I can narrow down things by switching cable coming from source and so forth making sure this noise changes channel with switch, or doesn't. One good thing about having multiple systems set up in different rooms!
Russellc
Both preamps do this, so it seems unlikely that both units have same problem. I am going into work today, but will narrow down where it is coming from.
I will trade various parts of system around, and move sources to other systems in other rooms. Also, I can narrow down things by switching cable coming from source and so forth making sure this noise changes channel with switch, or doesn't. One good thing about having multiple systems set up in different rooms!
Russellc
Some thoughts:
- Is it really 60Hz hum? This would point to a ground loop picking up AC mains noise.
- Is it maybe more like 120 Hz? This would point to noise coming from the PSU (rectified 60 Hz gives 120 Hz). This could come either directly via the PSU rails, or via EMI pickup within the amp.
- What happens if you disconnect the sources, and ground the amplifier inputs? Does the noise go away?
- What happens if you swap the input wires (left / right)? Does the noise stay in the same channel, or does it change to the other channel?
See post 5019 above, shorting inputs leaves both speakers dead quiet. As I said, I don't know if it is 120 hz, but seems higher and a little fizz from tweeter area. 60 hz hum that I have experienced didn't sound in the tweeter. as to switching cables etc., I just brought that up in post 5023 but wont have a chance until after work.
I think you may be right about 120 hz? But don't know if that would sound through tweeters. Sort of reminds me of some noise you might hear on an ancient AM radio between stations, not the white noise but as you get closer to station.
Please note, this is very subtle, and to hear it ear must be right next to drivers, Bass and high frequency drivers. One or two feet away you wouldn't hear it. ("Well, I don't anyway!)
will report back once some cable swapping is done. It seems I am drifting out of the "Aleph J" topic category as I believe amp is exonerated, being dead quiet on both channels with inputs shorted.
Thanks for the thoughts and ideas,
Russellc
I think you may be right about 120 hz? But don't know if that would sound through tweeters. Sort of reminds me of some noise you might hear on an ancient AM radio between stations, not the white noise but as you get closer to station.
Please note, this is very subtle, and to hear it ear must be right next to drivers, Bass and high frequency drivers. One or two feet away you wouldn't hear it. ("Well, I don't anyway!)
will report back once some cable swapping is done. It seems I am drifting out of the "Aleph J" topic category as I believe amp is exonerated, being dead quiet on both channels with inputs shorted.
Thanks for the thoughts and ideas,
Russellc
back with an odd question that I dont think I've seen asked here at all.
The aleph output to the speakers itself is dead quiet for me, but im now just noticing a high frequency whine near 12khz (according to a cheap0 spectrum analyzer app) coming from the chassis. Is this normal? Any component I should focus my attention toward?
Didnt notice it till now because i just moved the amp somewhere it's easier to see/hear/reach and I fixed some loud buzz on a different component.
The aleph output to the speakers itself is dead quiet for me, but im now just noticing a high frequency whine near 12khz (according to a cheap0 spectrum analyzer app) coming from the chassis. Is this normal? Any component I should focus my attention toward?
Didnt notice it till now because i just moved the amp somewhere it's easier to see/hear/reach and I fixed some loud buzz on a different component.
Attachments
Last edited:
and hmm.....
since ive posted this I've noticed that the 12khz whine stopped but then came back, at least on two different occasions. When it goes away I can more clearly hear a more typical? 60/120hz noise that one might associate with transformers and rectification. I'm assuming this mechanical noise coming from the chassis is somewhat normal. That right?
still a little unsure about the 12khz whine though. Just to be clear, this noise is unrelated to the signal amplification at my speakers and is noise at/from the physical object itself. Was expecting the unit to be more or less mechanically quiet.
since ive posted this I've noticed that the 12khz whine stopped but then came back, at least on two different occasions. When it goes away I can more clearly hear a more typical? 60/120hz noise that one might associate with transformers and rectification. I'm assuming this mechanical noise coming from the chassis is somewhat normal. That right?
still a little unsure about the 12khz whine though. Just to be clear, this noise is unrelated to the signal amplification at my speakers and is noise at/from the physical object itself. Was expecting the unit to be more or less mechanically quiet.
The 12kHz noise comes (and then disappears <- a common symptom / common issue) from the mains supply; try using the IEC connector with an RF Filter, or make one (the filter) yourself. The transformer snubber (I think it is called Quasimodo around here...) can help as well.
It is unlikely that the oscillations come from the PCB (MOSFET's), but this can be confirmed with an oscilloscope whilst the input RCA's are "shorted" to ground.
The 120Hz buzz: a 10-20ohm ground-break resistor is required to stop this buzz; see post #4909.
It is unlikely that the oscillations come from the PCB (MOSFET's), but this can be confirmed with an oscilloscope whilst the input RCA's are "shorted" to ground.
The 120Hz buzz: a 10-20ohm ground-break resistor is required to stop this buzz; see post #4909.
Last edited:
You may already have taken care of this, but if that mounting arrangement is going to be permanent, I'd put a good layer of thermal grease between the main chassis and the plate that the board is mounted to. You want to make sure you have good thermal contact between the 2 pieces.
Yes, already taken care of.
Attachments
Input snubber is already in place per quasimodo.
Will look at an RF filter for the mains. Likely have no room for the IEC's with the built-in filters I've seen so it would have to be a ferrite bead or something. How do I go about selecting the right one? I briefly looked into this during my build but was overwhelmed with the options so figured I'd delay it until it ever became a need.
Here ya go. (credit: 6L6)
I interpreted the ground break to solve issues of 120hz buzz coming out of the speakers. This is buzz coming from inside the chassis. It's not too annoying. Am I misinterpreting the purpose of this ground break?
I can hear the buzz of the transfo with ear to chassis—quieter with lid on. Don't hear that same buzz with ear to speakers (My F5 transfo has less "buzz" with ear to chassis than AJ, go figure). I did turn the transfo and "tune" the "buzz" to a minimum—quite significant—before installing HBRs, however.
Since that time—I have realized that my issues were related to power cable vs. signal routing. HBRs were fun to do though, just cause. Now, system is virtually silent—and sounds simply incredible with ZM Iron Pre in front. I've had to fight not to leave my body (would have have been inconvenient at the time) twice when listening to the SP-10MK2.
All transfos Quasimodo-ed. Thank you MJ.
Since that time—I have realized that my issues were related to power cable vs. signal routing. HBRs were fun to do though, just cause. Now, system is virtually silent—and sounds simply incredible with ZM Iron Pre in front. I've had to fight not to leave my body (would have have been inconvenient at the time) twice when listening to the SP-10MK2.
All transfos Quasimodo-ed. Thank you MJ.
Last edited:
Common Mode RF chokes: Common Mode Choke | Coilcraft. Chose the choke for 3-4 amps nominal current (which is plenty). Aim for 4mH inductance - see if the choke will fit inside the amp.
NOTE: The RF filters will change the sound of the amp.... this is a purely personal thing - some like it - some don't. The sound will become cleaner and vague at the same time. It's difficult to explain... You have to try and see if you like it. You may not!
The RF Suppressor internal construction/parts' values- see attached pdf.
NOTE: The RF filters will change the sound of the amp.... this is a purely personal thing - some like it - some don't. The sound will become cleaner and vague at the same time. It's difficult to explain... You have to try and see if you like it. You may not!
The RF Suppressor internal construction/parts' values- see attached pdf.
Last edited:
thanks. have a couple of things to consider.
I'm relatively confident in the q-modo as it was implemented per the thread with a bias towards slightly over damping.
Interaction with the surroundings is highly possible since I have 2 toroids crammed into a 4U. The toroids seemed to be free of mechanical vibration during the initial build powerons. Have felt transformer noise before. To me it definitely seemed to be coming from the amp boards as I dont recall any noise during the individual PSU checkouts.
I'm relatively confident in the q-modo as it was implemented per the thread with a bias towards slightly over damping.
Interaction with the surroundings is highly possible since I have 2 toroids crammed into a 4U. The toroids seemed to be free of mechanical vibration during the initial build powerons. Have felt transformer noise before. To me it definitely seemed to be coming from the amp boards as I dont recall any noise during the individual PSU checkouts.
The PSU checks you carried out were probably done with no load.... toroid transformers will perform differently under the load - inside the amp.
In general, the 2 toroid transformers' axes have to (should...) meet at 90deg.
gotcha and yea, using 2X Antek AS-2218's
the only way i could fit them in the chassis was side by side with their axes aligned.
build pics here
You can mount toroid transformers one on top of the other; the only thing to take care is a sudden "acceleration" .. due to a large amount of mass mounted quite high from the anchor point, and then only if you'll be moving the amp from one place to another. Case height permitting, of course.