The PSU filter is CRCLC and the last C is a 4-pole cap. I use 2x18V secondary. The chokes are Hammond 2.5 mH as far as I remember (159ZL). It has low DC resistance (10A type) so not much voltage is wasted. I also simulated the PSU on computer and ripple is down in mV level at 1.5A.
I shielded the Edcor up front as I had heard many stories about hum and relative high noise levels caused by "pick-up" from Edcor. The measurements showed that my M2X has very low noise levels so I am sure the shielding works and also keeping the PSU transformer at a distance also helps.
The LC filter is there to filter the ripple after the CRC filter. It is quite effective even with a relative low mH value. I have attached the result after simulation in PSU designer tool. The big toroid has more like 2x19V output at idle. The curve shows the ripple at output 2.3A. Simulation shows 1.3 mV ripple at that current. It is 42 mV after the CRC. But one thing is simulation.....it is difficult to know all parameters of diodes, transformer inductance etc. But it can give a good indication of what to expect.
I got a delivery from Farnell today, and I replaced RV1 and R6. Now it was easy to adjust DC offset to 0!
The amplifier is hooked up to my main speakers. I can barely hear any hum, even with my ear close to the speakers, so I won't bother with any additional shielding. And most important, it sounds really good!
The amplifier is hooked up to my main speakers. I can barely hear any hum, even with my ear close to the speakers, so I won't bother with any additional shielding. And most important, it sounds really good!
@MAPER
Thanks for the info on the chokes. I forgot about Hammond! The ESR is very low indeed!
CRC with 0.2ohm res shielded toroidal the edcor are ~8 inches from the shieding with altecs 103dB no audible hum, but I am still working on more shielding for the edcors. I want to get to the next level of shielding.
Thanks for the info on the chokes. I forgot about Hammond! The ESR is very low indeed!
CRC with 0.2ohm res shielded toroidal the edcor are ~8 inches from the shieding with altecs 103dB no audible hum, but I am still working on more shielding for the edcors. I want to get to the next level of shielding.
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My M2X was completed a few days ago and is playing the music nicely (see below)!
Thanks a lot for everyone who helped me with the comments, and especially @ItsAllInMyHead for the initial encouragement on my first "real" amp build after the ACA and for his excellent Noobs Watt M2X thread.
I have to admit I tried my luck (inadvertently) at the end of the process, so I think I'll share this (perhaps some less lucky future builder could be saved by reading this).
Yes, I did build the very nice Light Bulb Tester (see picture), and I used it when first time powering the transformer without the PSU board yet connected. The bulb did not even flash (made me a bit suspicious). Then I connected the PSU and tested again. No flash. Very suspicious. Anyway, measured the output voltage nicely at + and - 24V DC, so I connected the amp boards and there was to smoke - as we all expect, because we are careful builders, aren't we? Only then I tried it with the bulb tester again. As the was no flash of light, I decided to carefully check some points on the tester itself. And it measured weirdly. Then I shorted the L and N on the output cord of the tester - and the bulb did not glow anyway. Only then I found out that the bulb holder contacts were not touching the bulb... So - test your tester before using it on your precious creation.
Next. Adjustment process. As everything looked fine, I shorted the inputs (had to Google how this has to be done - short the signal pin with the ground sleeve of each input terminal making a special plug for that - I sacrified an old RCA cable for this (see picture) - not shorting the left and right input terminals with the cable as I initialy imagined - well, I "was" a total noob, you know). Then I connected the multi-meter on the output and started to adjust the RV1. I was surprised it was not making any difference on the voltage I saw. Well, I shruged my shoulders and connected the loudspeakers. It played music nicely. And only then I resorted to reading and found these posts:
M2X OFFSET ADJUSTMENT PROCEDURE
About frying the Mosfets without the dummy load resistor
Only then I noticed my multi-meter was set to AC, not DC...
Well, I was lucky. I did not melt my loudspeakers with DC on output, and I did not fry my Mosfets by turning the RV1 ("non-biblical" modification) to all extremes and leaving it there for any arbitrary time.
Your luck can be less permissive. So, take care
Thanks a lot for everyone who helped me with the comments, and especially @ItsAllInMyHead for the initial encouragement on my first "real" amp build after the ACA and for his excellent Noobs Watt M2X thread.
I have to admit I tried my luck (inadvertently) at the end of the process, so I think I'll share this (perhaps some less lucky future builder could be saved by reading this).
Yes, I did build the very nice Light Bulb Tester (see picture), and I used it when first time powering the transformer without the PSU board yet connected. The bulb did not even flash (made me a bit suspicious). Then I connected the PSU and tested again. No flash. Very suspicious. Anyway, measured the output voltage nicely at + and - 24V DC, so I connected the amp boards and there was to smoke - as we all expect, because we are careful builders, aren't we? Only then I tried it with the bulb tester again. As the was no flash of light, I decided to carefully check some points on the tester itself. And it measured weirdly. Then I shorted the L and N on the output cord of the tester - and the bulb did not glow anyway. Only then I found out that the bulb holder contacts were not touching the bulb... So - test your tester before using it on your precious creation.
Next. Adjustment process. As everything looked fine, I shorted the inputs (had to Google how this has to be done - short the signal pin with the ground sleeve of each input terminal making a special plug for that - I sacrified an old RCA cable for this (see picture) - not shorting the left and right input terminals with the cable as I initialy imagined - well, I "was" a total noob, you know). Then I connected the multi-meter on the output and started to adjust the RV1. I was surprised it was not making any difference on the voltage I saw. Well, I shruged my shoulders and connected the loudspeakers. It played music nicely. And only then I resorted to reading and found these posts:
M2X OFFSET ADJUSTMENT PROCEDURE
About frying the Mosfets without the dummy load resistor
Only then I noticed my multi-meter was set to AC, not DC...
Well, I was lucky. I did not melt my loudspeakers with DC on output, and I did not fry my Mosfets by turning the RV1 ("non-biblical" modification) to all extremes and leaving it there for any arbitrary time.
Your luck can be less permissive. So, take care
Attachments
I enjoy listening to my M2X, but there is one small (and common, I suppose) problem - small hum. It is very small, but still a little bit audible even about a meter away from my very small low sensitivity DIY Overnight Sensations desktop speakers. It's really minor (for my understanding), but I would still want to get rid of it.
I do not have an osciloscope, but even with my privitive mobile phone app spectrometer I can see that the hum is 50Hz and harmonics (100Hz, 150Hz) (see picture). Does it help to identify the source of hum? Is it from not ideal grounding scheme? Or is it from the toroid EMI? Or could 50Hz be because of both reasons? Or other reasons?
Neither my toroid (audio grade from Toroidy) nor Edcors are shielded.
My output ground goes directly to the star ground on the PSU.
Star ground is "lifted" from the safety ground by the CL60.
I am going to experiment, but first I would like to identify the source and the reason of the hum, if this could be told from the frequency itsetf. Could anyone be kind to share their thoughts?
Thanks.
Alvis
I do not have an osciloscope, but even with my privitive mobile phone app spectrometer I can see that the hum is 50Hz and harmonics (100Hz, 150Hz) (see picture). Does it help to identify the source of hum? Is it from not ideal grounding scheme? Or is it from the toroid EMI? Or could 50Hz be because of both reasons? Or other reasons?
Neither my toroid (audio grade from Toroidy) nor Edcors are shielded.
My output ground goes directly to the star ground on the PSU.
Star ground is "lifted" from the safety ground by the CL60.
I am going to experiment, but first I would like to identify the source and the reason of the hum, if this could be told from the frequency itsetf. Could anyone be kind to share their thoughts?
Thanks.
Alvis
Attachments
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Shielding the input transformers has helped several builders. As has shielding the power transformer.
Your wiring is functional, and esthetically pleasing. I try to minimize the lengths of my input wires, and bend them as far away from the AC carrying wires. Less important, to me are the output wires, but it still can help to move then away from AC currents.
I am currently in favor of grounding speaker out to the star ground, but my opinion carries very little weight.
I did shield the input transformer with copper tape and mu metal. I do adjust wiring to avoid input/output to be near AC. I have just a minimal hum with ears close to my 95db speakers. I can't hear it a foot away, and certainly can't when music is playing.
I have shielded Toroidy transformers on order.
Your wiring is functional, and esthetically pleasing. I try to minimize the lengths of my input wires, and bend them as far away from the AC carrying wires. Less important, to me are the output wires, but it still can help to move then away from AC currents.
I am currently in favor of grounding speaker out to the star ground, but my opinion carries very little weight.
I did shield the input transformer with copper tape and mu metal. I do adjust wiring to avoid input/output to be near AC. I have just a minimal hum with ears close to my 95db speakers. I can't hear it a foot away, and certainly can't when music is playing.
I have shielded Toroidy transformers on order.
Thanks Bones13 and avdesignguru.
I made the input wires a bit shorter and rewired output ground from PSU to the amplifier boards. Nothing changed - same small hum. It's really small and barely hearable in one meter from the speakers, so I will live with it for now. Next step would be isolation of the toroid and/or Edcors, and I am not so much into this as the hum is not big.
Although, I am contemplating exchanging the Audio grade Toroidy transformer to the Supreme Audio grade one later if I decide to make another FW clone. Therefore, your experience with it, Bones13, when you get it, would be very interesting to hear - how big difference does it make?
Or perhaps someone else can share their experience with Audio and Supreme Toroidy transformers on M2X?
I made the input wires a bit shorter and rewired output ground from PSU to the amplifier boards. Nothing changed - same small hum. It's really small and barely hearable in one meter from the speakers, so I will live with it for now. Next step would be isolation of the toroid and/or Edcors, and I am not so much into this as the hum is not big.
Although, I am contemplating exchanging the Audio grade Toroidy transformer to the Supreme Audio grade one later if I decide to make another FW clone. Therefore, your experience with it, Bones13, when you get it, would be very interesting to hear - how big difference does it make?
Or perhaps someone else can share their experience with Audio and Supreme Toroidy transformers on M2X?
I've shared this a few times in this thread—I used a regular 'ol Antek, internal shield (purple wire), no outer case for it—though the steel cases Antek makes are awesome—and I'd certainly have used them if I had the room in my otherwise optimized and tightly packed builds. Toroidy wasn't an obvious source for me being in the USA—so you are fortunate to have easy access to them—very nice stuff.
I plugged headphones into my speaker jacks (inputs shorted) and listened to all sorts of things to determine sources of noise—just with my ears—no official scope measurements.
- Shielding the Edcors with mu-metal—required as far as my opinion is concerned
- Ferrite core on primaries
- Rotating the transformer while listening to the amp (headphones/speaker jacks) and tuning it for lowest noise, very real.
- And—each daughter board had different noise levels. Lowest was Norwood—by half compared to Mountain View.
AND I can HIGHLY recommend Mark's latest boards. 7s are still installed in my monoblocks! Go figure (I'm skeptical?). Something about them with single OPA134s. Rev2 of those boards are on deck with dual OPA1611 installed—my fav in Whammy—just to try them out. Otherwise Norwood is killer—and anyone that is afraid of SMD work would be very very happy building Mark's new #6—in my setup extremely complimentary/similar to Norwood's vibe, if not indistinguishable (Mark did tell me that they are very alike on paper AFTER I didn't really hear much of a difference! So cool.).
I plugged headphones into my speaker jacks (inputs shorted) and listened to all sorts of things to determine sources of noise—just with my ears—no official scope measurements.
- Shielding the Edcors with mu-metal—required as far as my opinion is concerned
- Ferrite core on primaries
- Rotating the transformer while listening to the amp (headphones/speaker jacks) and tuning it for lowest noise, very real.
- And—each daughter board had different noise levels. Lowest was Norwood—by half compared to Mountain View.
AND I can HIGHLY recommend Mark's latest boards. 7s are still installed in my monoblocks! Go figure (I'm skeptical?
). Something about them with single OPA134s. Rev2 of those boards are on deck with dual OPA1611 installed—my fav in Whammy—just to try them out. Otherwise Norwood is killer—and anyone that is afraid of SMD work would be very very happy building Mark's new #6—in my setup extremely complimentary/similar to Norwood's vibe, if not indistinguishable (Mark did tell me that they are very alike on paper AFTER I didn't really hear much of a difference! So cool.).
I did not ground the mu-metal edcor shields. I kapon taped them so they weren't in contact with anything—I also attached them to the board post right below the autoformer, which was nylon to the sink—basically I made them completely inert and floating. Didn't occur to me to ground them... hmmmm....
I'll let someone who's more competent weigh in about the rail voltage. I think I was getting in the 27s on mine, unloaded... didn't question it but I used 3218s, admittedly larger than required, but I had them laying about.
I'll let someone who's more competent weigh in about the rail voltage. I think I was getting in the 27s on mine, unloaded... didn't question it but I used 3218s, admittedly larger than required, but I had them laying about.
Hi,
Do you still hear the hum when inputs are shorted or when the input terminals are open (no RCA plug in) for both channels?
If not, have you tried moving the amp away from the preamp or other devices during normal operation?
I am gathering parts for the build and I am in awe on how sensitive the Edcor trafos are (600:15k or 1:25 ~ 28dB?) from what you described. Looking at the internal pic of your amp, it seems to me that you have adequate distance from the PT and rail PSU to me. But I guess you will never know.
Abe
@amandarae, yes, the hum is still there when pre-amp is disconnected.
Also, I made some measurements with my mobile phone Spectrum app (the best I can do, so please take these numbers for what they worth). When pre-amp is connected and is on, or when it's dissconnected, the hum level next to the speaker is:
50Hz -95dB, 100Hz -85dB, 200Hz -95dB
Actually, the ambient noise in the room measured at the level of about:
50Hz -95dB, 100Hz -98dB, 200Hz -99dB
So, the only problem I see is on the 100Hz. And in 1m distance, the hum is on the ambient level when measured on the phone, though ears can still hear that the amp is on.
Interestingly, when pre-amp is connected but is off, this adds quite loud noice at 50Hz (on the level of -81dB, very audible). But when you turn the pre-amp on, this disappears. The pre-amp is Shiit Magni 3+.
@pfarrell, thanks for sharing again. My thoughts about your conclusions are as follows:
- shielding Edcors would definitely help, but in my view shielding Edcors is like saying that Papa's design has a flaw; if Papa put them there, they should be able to do their job without the shield; power transformer is different - Papa did not tell you how good your power transformer has to be
- ferrite on primary; as far as I've read, ferrite helps to fight high frequences, so I doubt it can help on 50-100Hz.
- rotating the transformer - definitely a way. I think Papa himself commented somewhere that this is his way to go.
- changing daughter boards - interesting. I would be surprised if it makes a difference on the 100Hz hum, but I will definitelly try this. I have only MV and Tucson made now, but I have all the parts for the others, and surely I will make and try Norwood first then.
Thanks everyone!
Alvis
Also, I made some measurements with my mobile phone Spectrum app (the best I can do, so please take these numbers for what they worth). When pre-amp is connected and is on, or when it's dissconnected, the hum level next to the speaker is:
50Hz -95dB, 100Hz -85dB, 200Hz -95dB
Actually, the ambient noise in the room measured at the level of about:
50Hz -95dB, 100Hz -98dB, 200Hz -99dB
So, the only problem I see is on the 100Hz. And in 1m distance, the hum is on the ambient level when measured on the phone, though ears can still hear that the amp is on.
Interestingly, when pre-amp is connected but is off, this adds quite loud noice at 50Hz (on the level of -81dB, very audible). But when you turn the pre-amp on, this disappears. The pre-amp is Shiit Magni 3+.
@pfarrell, thanks for sharing again. My thoughts about your conclusions are as follows:
- shielding Edcors would definitely help, but in my view shielding Edcors is like saying that Papa's design has a flaw; if Papa put them there, they should be able to do their job without the shield; power transformer is different - Papa did not tell you how good your power transformer has to be
- ferrite on primary; as far as I've read, ferrite helps to fight high frequences, so I doubt it can help on 50-100Hz.
- rotating the transformer - definitely a way. I think Papa himself commented somewhere that this is his way to go.
- changing daughter boards - interesting. I would be surprised if it makes a difference on the 100Hz hum, but I will definitelly try this. I have only MV and Tucson made now, but I have all the parts for the others, and surely I will make and try Norwood first then.
Thanks everyone!
Alvis
@pfarrell, I changed MV to Tucson. Wow, it made instant difference with the hum!
The hum on 100Hz went down from -85dB with MV to -91dB with Tucson!
What a difference! That means the hum almost disappeared!
So, I definitely confirm that the daughter board makes a difference on the 100Hz hum.
Very inviting to build and try Norwood if you say it was the quitest for you!
Thanks, @pfarrell!
The hum on 100Hz went down from -85dB with MV to -91dB with Tucson!
What a difference! That means the hum almost disappeared!
So, I definitely confirm that the daughter board makes a difference on the 100Hz hum.
Very inviting to build and try Norwood if you say it was the quitest for you!
Thanks, @pfarrell!