About linear vs SMPS noise, if we place a linear PSU trafo away (remotely) from the amp, like most people connect it's SMPS bricks (I don't see many people using these bricks inside of their amps), it will have less mains noise, for sure... so the dual chassis mafia wins again 
That said, good SMPS have strong feedback at mains/harmonics frequencies, so it supresses mais ripple very well. Put some LR-C filters and the high frequency noise is out! But for RF interference, the only solution for a bad one is the parts bin...
About the linear PSUs...: toroidal trafos is not a panacea for low noise like much people think (XRK reported a lot about it, for example...). If toroidal trafo have voids in the windings or crossed turns, will 'spray" induction outside, and all trafos will have this at some extent due to practical methods to wind it. Even the start/stop band in the core will mess at some directions. The E-I counterpart "sprays" the magnetic fields in a more predictable way (stronger in some directions and almost null for others). Toroidals simply don't have "null" position for leakage fields. The ones that achieve this are very expensive to wind.
C-cores are more like E-I in the variability of leakage fields.
That said, good SMPS have strong feedback at mains/harmonics frequencies, so it supresses mais ripple very well. Put some LR-C filters and the high frequency noise is out! But for RF interference, the only solution for a bad one is the parts bin...
About the linear PSUs...: toroidal trafos is not a panacea for low noise like much people think (XRK reported a lot about it, for example...). If toroidal trafo have voids in the windings or crossed turns, will 'spray" induction outside, and all trafos will have this at some extent due to practical methods to wind it. Even the start/stop band in the core will mess at some directions. The E-I counterpart "sprays" the magnetic fields in a more predictable way (stronger in some directions and almost null for others). Toroidals simply don't have "null" position for leakage fields. The ones that achieve this are very expensive to wind.
C-cores are more like E-I in the variability of leakage fields.
Quick update. It is definitely the SMPS adapter that I was using that caused the Vdc dropped to 2V. As an experiment, I swapped out to the "working" SMPS AC adapter that I used for ACA amp and VOILA, the power supply voltage to MOFO is set correctly at 19 V and I was able to bias the amp correctly around 1.1 V across L1 as per manual.
Thank you all for the pointer. I definitely look into upgrade the powersupply to something better down the road if I like the sound of MOFO like the Power supply with full-wave rectifier that I am using for my other Pass Amps such as Aleph J and M2.
Regards,
Tom
Thank you all for the pointer. I definitely look into upgrade the powersupply to something better down the road if I like the sound of MOFO like the Power supply with full-wave rectifier that I am using for my other Pass Amps such as Aleph J and M2.
Regards,
Tom
One channel down!
I wanted to share the completed build of one of my Big MoFo channels.
I'm using a 250w 24-26v chassis mount SMPS (VF-S250-24A CUI Inc. | Power Supplies - External/Internal (Off-Board) | DigiKey) and an adjustable single rail capacitance multiplier which I laid out at and has been discussed at http://www.diyaudio.com/forums/soli...sy-capacitance-multiplier-48.html#post5508260. Binding posts are a Cardas CPBP that I got for a "good" deal on eBay. Mundorf MCap EVO aluminum / oil for the input cap.
I designed and machined the case based around a heatsink extrusion with a similar profile to the original one used by Michael. The entire build uses pop rivets, lock nuts, and t-slots to avoid all tapping - I hate tapping... Heat at a 2.5A bias seems to be handled sufficiently, raising to around 51c on the base of the heatsink after a few hours of use. I think it helps that the entire chassis is a mix of 1/8 and 1/4" 6061 aluminum which helps dissipate some of the heat as well.
I've only listened in mono, but even so, I've been super impressed so far. There is a slight mechanical / electrical hum from the SMPS, but none of it seem to be reflected at the speaker output. That said, the mechanical and speaker hum is less than the power transformer / output hum of my M2. I am also surprised by the volume I could get out of my ZRT 2-ways with the MoFo and a Salas DCG3 set with 3x gain. After building this channel's twin, I plan on building the Aksa Lender to get the full voltage swing needed.
I'll post more details and impressions once both channels are completed, but until then, I've attached are some pictures of the finished channel.
I wanted to share the completed build of one of my Big MoFo channels.
I'm using a 250w 24-26v chassis mount SMPS (VF-S250-24A CUI Inc. | Power Supplies - External/Internal (Off-Board) | DigiKey) and an adjustable single rail capacitance multiplier which I laid out at and has been discussed at http://www.diyaudio.com/forums/soli...sy-capacitance-multiplier-48.html#post5508260. Binding posts are a Cardas CPBP that I got for a "good" deal on eBay. Mundorf MCap EVO aluminum / oil for the input cap.
I designed and machined the case based around a heatsink extrusion with a similar profile to the original one used by Michael. The entire build uses pop rivets, lock nuts, and t-slots to avoid all tapping - I hate tapping... Heat at a 2.5A bias seems to be handled sufficiently, raising to around 51c on the base of the heatsink after a few hours of use. I think it helps that the entire chassis is a mix of 1/8 and 1/4" 6061 aluminum which helps dissipate some of the heat as well.
I've only listened in mono, but even so, I've been super impressed so far. There is a slight mechanical / electrical hum from the SMPS, but none of it seem to be reflected at the speaker output. That said, the mechanical and speaker hum is less than the power transformer / output hum of my M2. I am also surprised by the volume I could get out of my ZRT 2-ways with the MoFo and a Salas DCG3 set with 3x gain. After building this channel's twin, I plan on building the Aksa Lender to get the full voltage swing needed.
I'll post more details and impressions once both channels are completed, but until then, I've attached are some pictures of the finished channel.
Attachments
Excellent design congratulations !Attachments
Pass DIY Addict
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Thanks all for the kind words!
At a 2.5A bias, the SMPS is set to put out 26.7v, output from the cap mx to the mofo is at 24.2V. I am showing 0.16mV of AC on output of the cap mx at the mofo.
Sigh, I too have a collection of boxes per project organizing the BOMs, PCBs, and various components that are just awaiting free time.
It is the 300mm length version of the extrusion at http://www.wakefield-vette.com/Portals/0/resources/datasheets/392.pdf. I found one used on eBay for $50. I brought it to a local metal shop and had it sawed in half, so about 150mm high each.
No more playing around in mono, I need to go clean and organize the workshop and get building the second channel for that last 1/2 of a fugly!
No feedback preamlifier is sonically better for the MoFo.
For example BA-3 pre is interesting
Kindest regardshttp://www.firstwatt.com/pdf/art_ba_3.pdf
http://www.diyaudio.com/forums/pass-labs/258022-ba-3-preamp-build-guide.html#post3968063
Pass BA-3 Preamplifier - Audio Society of Minnesota
