Actually - if available, I will take 2 board sets. I have left my Paypal address in a PM. Thanks!
ALPHA 20 with SMPS / DC-DC / Cap Mx / CRC
I pulled the linear 400VA trafo and F6 PSU out of my case and installed the SMPS and DC-step-up PSU with cap multiplier. Well it is a lot smaller, lighter, and easy to install. I have it running at +/-26.0vdc rails and bias is still 1.3amps as governed by thr 0.47R on the source resistor/sense resistor fot the Aleph CCS. I am using a small heatsink from a Class AB LM3886 amp as the heatsinks for the cap Mx (about 10w dissipation per side). These are about the right sized heatsinks. The DC step up boards get warm and are aluminum so expect to be mounted to a heatsink.
It works ands plays music and sounds great when playing music, however, when no music playing I hear some noise and hum. I am chasing a small ground loop (about 1mVrms at the output). I like to see it below 0.2mVrms.
The cap Mx board has separate star grounds for the left and right channel. I bonded the separate two grounds per CRC together at the cap Mx output. I am not sure if that is the problem. The star point on the cap Mx
Here is a photo of the setup with +/-26v rais:
Closeup of the cap Mx:
I have the star ground connected to a CL60 NTC between the cap Mx and the chassis ground.
When I figure out the ground loop problem, this could be a very nice adjustable voltage Class A PSU.
I am wondering if the cap Mx should be split as in dual monoblocks? I am using the same SMPS and isolated cap Mx on the MoFo and it has no groundoops and is dead quiet. The ground loops drive me crazy.
I pulled the linear 400VA trafo and F6 PSU out of my case and installed the SMPS and DC-step-up PSU with cap multiplier. Well it is a lot smaller, lighter, and easy to install. I have it running at +/-26.0vdc rails and bias is still 1.3amps as governed by thr 0.47R on the source resistor/sense resistor fot the Aleph CCS. I am using a small heatsink from a Class AB LM3886 amp as the heatsinks for the cap Mx (about 10w dissipation per side). These are about the right sized heatsinks. The DC step up boards get warm and are aluminum so expect to be mounted to a heatsink.
It works ands plays music and sounds great when playing music, however, when no music playing I hear some noise and hum. I am chasing a small ground loop (about 1mVrms at the output). I like to see it below 0.2mVrms.
The cap Mx board has separate star grounds for the left and right channel. I bonded the separate two grounds per CRC together at the cap Mx output. I am not sure if that is the problem. The star point on the cap Mx
Here is a photo of the setup with +/-26v rais:
Closeup of the cap Mx:
I have the star ground connected to a CL60 NTC between the cap Mx and the chassis ground.
When I figure out the ground loop problem, this could be a very nice adjustable voltage Class A PSU.
I am wondering if the cap Mx should be split as in dual monoblocks? I am using the same SMPS and isolated cap Mx on the MoFo and it has no groundoops and is dead quiet. The ground loops drive me crazy.
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Hi JP,
Thanks for offering the diagram - this is really helpful. What I see is that the amp is floating relative to earth gnd, but that's ok - the MoFo was the same way. When I connect the chassis gnd (even though floating relative to earth gnd) to the star hub, the noise is substantially less but Fluke 101 mV scale shows 1.1mV. I can hear slight hum and some HF white noise. Almost like there is some noise being generated in the Cap Mx. I ran out of 1uF film caps so using 0.1uF and 2R2 for Cap Mx snubber vs recommended 1uF and 1R5. Maybe that might be source of noise?
The CRC uses a 12 gauge solid copper wire bus for the ground in "U" shape. Should CRC been kept separate gnd for each rail? But then when it reaches amp it is one (0v) GND wire.
Attached is my marked up diagram. For my CRC I have 6k8 2W bleeder resistors from each rrail to 0v and 0.1uF 100V film caps bypass at the output.
Thanks again.
X
Btw, I moved it off the bench and into the listening room and it works to power the speakers very well (apart from noise if one presses ear to the speaker cone). Neat to see such a compact lightweight PSU compared to 12lb 400VA trafo.
Attachments
Hi xrk,
How is signal gnd connected on amp pcb. Is there a 10ohm lifter?
Try to follow Bonsai recommendation for grounding.
Spk grnd to crc gnd or cap MX ground, to see if that's the case.
If everything fails put just the proper cap MX w/o crc and also check all individual blocks to see the problem source. Eg transformer and just cap MX as per bom supplying 2 channels and all gnds connected on cap MX output . It's the way Juma desIgned if I am not mistaken.
Regards
Prasi
How is signal gnd connected on amp pcb. Is there a 10ohm lifter?
Try to follow Bonsai recommendation for grounding.
Spk grnd to crc gnd or cap MX ground, to see if that's the case.
If everything fails put just the proper cap MX w/o crc and also check all individual blocks to see the problem source. Eg transformer and just cap MX as per bom supplying 2 channels and all gnds connected on cap MX output . It's the way Juma desIgned if I am not mistaken.
Regards
Prasi
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Thanks, Prasi. Ok I will try without CRC and put all grounds from Star hub. Does that include putting the signal GND from RCA to star hub and skipping negative frommRCA to PCB. No 10ohm ground lift on PCB. Only CL60 thermistor to isolate chassis and 0v.
Here is Juma’s Schematic.
I am sure you already seen this link by former brilliant member Bonsai. here it is anyway
Ground Loops: How to Wire-up an Audio Amplifier for Zero Hum and Noise
Also I always include 10ohm resistors and anti parallel diodes on amp for input if you remember my designs, whether or not amp designer includes them in the sch. These are nothing but HBRR and HBRL lifts as promulgated by D. Joffe and repeatedly suggested by Andrew T.
See Honey Badger sch too..
I request you to try to understand the problem block by block...Its helped me a lot before... I have a stereo LM1875 with integrated PSU and a separate tone control ckt fed by the same simple CT trafo and it works with absolute zero noise.
I have built it for sprite boombox in the kitchen for its owner
. Full Range Speaker Photo Gallery
Hi x,
you could try either way, but proper way is connect signal gnd to amp PCB gnd via lifter at the local decoupling star gnd as given by Bonsai in the link (page 29) and as suggested by AKSA..
Is the hum still present when signal is unconnected/shorted. then problem is somewhere else.
was this problem not present when you tested earlier with regular psu +trafo set up?
regards
Prasi
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I had the same issue when i connected to my audio interface,you remember we discussed the issue i had with my FH9, after that i used thermistors in series with L,N power lines and also i used the f6 power supply after boost and cap MX and it's almost gone, but it finally went away completely when i start using input transformers.
i m trying to separate the USB power source from the DATA line for my audio interface, and use a separate filtered and clean power source for USB 5v, see if that take care of the hum problem when connected to anything powered from USB. ( i had the same issue with my miniDSP when i powered it through my computer ).
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F6 PSU with CL60’s works very well to reduce hum for linear trafo application. However, I am not sure if it is compatible with the DC outputs of the dual channel cap multiplier here. I am thinking my problem may be two parts: use of too small as snubber film cap (0.1uF vs 1uF) and the ground from the amp needs to go back to the star hub vs the GND on the CRC.
Awesome. It’s a quick build if you have all parts. Do you have the UMS heatsink? That made things go much much faster.