A question for SIT Mofo. The high frequency ripple of the bias voltage from SMPS can be reduced with one of those small filter? Or should I consider something else (or just ignore it)?
TDK Filter
SLF7045T-471MR22-PF TDK | Mouser
SIT Mofo
https://i1.wp.com/blog.audiomaker.tech/wp-content/uploads/2018/03/sitmumosimp.png
TDK Filter
SLF7045T-471MR22-PF TDK | Mouser
SIT Mofo
https://i1.wp.com/blog.audiomaker.tech/wp-content/uploads/2018/03/sitmumosimp.png
Hi guys,
Just got around to planning a Mofo build. Quick question. Would a 160VA 2x 0-15v (5.3A each) torroidal be enough for a lower power Mofo (19v-20v) stereo in a single chassis? Its a parts bin find looking for a use together with the diyaudiostore's PS boards I have left over from my F4 build. Thanks.
Just got around to planning a Mofo build. Quick question. Would a 160VA 2x 0-15v (5.3A each) torroidal be enough for a lower power Mofo (19v-20v) stereo in a single chassis? Its a parts bin find looking for a use together with the diyaudiostore's PS boards I have left over from my F4 build. Thanks.
meanies posts about transformers moved into its own thread....
to jervill
My first try was exactly that transformer voltage and power rating with 10Tmf in
CLC configuration for both channels. Sedlbauer- Conrad (Blue Drugstore 😀)
The 10mH,5A 179ZJ Hammond choke was build in between.
Maximal Bias was tested to 2,8A each channel with the lower priced Hmd chokes on source.
Thermaly limit but proper working conditions.
Driven by differnet Tube gain stages to experiment with.
Not finished yet but will move forward next time- winter is diy time 🙂.
My choice is now 17VAC 160VA and Bias arround 2A should work fine.
My first try was exactly that transformer voltage and power rating with 10Tmf in
CLC configuration for both channels. Sedlbauer- Conrad (Blue Drugstore 😀)
The 10mH,5A 179ZJ Hammond choke was build in between.
Maximal Bias was tested to 2,8A each channel with the lower priced Hmd chokes on source.
Thermaly limit but proper working conditions.
Driven by differnet Tube gain stages to experiment with.
Not finished yet but will move forward next time- winter is diy time 🙂.
My choice is now 17VAC 160VA and Bias arround 2A should work fine.
Fellow Audionauts,
My MoFos keep blowing up.
I'm not sure what's going on, but after listening to them for a while, something gives and the power supplies start cycling in reset mode.
I built my MoFos to specifications in MichaelR's original PDF, with IRFP250 MOSFETs, and Hammond inductors model 193T (50mH @ 2A DC). My DMM reads DCR=0.6R for each inductor.
Power supplies are, admittedly, no-name laptop types that claim to output "19V == 4.75A". My DMM reads 19.5V and 19.4V respectively.
When biasing them, I assumed the published resistance 0.8R (because I don't trust the DMM reading), and so set the voltage across the inductor to 1.02V. If anything, I would think this to be a "conservative" setting if the measured inductor resistance is to be believed.
I just now labelled them "A" and "B" so I can tell them apart, so I can't tell for sure if the non-functional one is the same one each time.
I suppose I could have ordered or received the wrong part in my original order; I didn't check the resistance on each component before installation. And I don't know how to check capacitance or inductance without an LCR meter.
Can anyone help diagnosing what to look at next?
Kind regards,
Drew
My MoFos keep blowing up.
I'm not sure what's going on, but after listening to them for a while, something gives and the power supplies start cycling in reset mode.
I built my MoFos to specifications in MichaelR's original PDF, with IRFP250 MOSFETs, and Hammond inductors model 193T (50mH @ 2A DC). My DMM reads DCR=0.6R for each inductor.
Power supplies are, admittedly, no-name laptop types that claim to output "19V == 4.75A". My DMM reads 19.5V and 19.4V respectively.
When biasing them, I assumed the published resistance 0.8R (because I don't trust the DMM reading), and so set the voltage across the inductor to 1.02V. If anything, I would think this to be a "conservative" setting if the measured inductor resistance is to be believed.
I just now labelled them "A" and "B" so I can tell them apart, so I can't tell for sure if the non-functional one is the same one each time.
I suppose I could have ordered or received the wrong part in my original order; I didn't check the resistance on each component before installation. And I don't know how to check capacitance or inductance without an LCR meter.
Can anyone help diagnosing what to look at next?
Kind regards,
Drew
use inline Ameter or known 0R1 resistor to check Iq
use proven supply , not anonymous and unknown quality
use proven supply , not anonymous and unknown quality
I found my MoFo voltage drop goes up as the unit fully heats up. It might start at .8 volts and rise to 1 volt or more after an hour. I ended up doing some listening tests and my MoFo still sounded good when set to a max rise to .9 V after 1 hour of cooking. When cold, it read about .7 volts.
FYI I am using heat sinking at the bottom of the recommended range with 18.5 volt 100 watt supplies. IR gun thermometer readings are about 60 degrees C at the Mosfet plastic case when fully hot.
Thanks to all for the replies!
I realize now that my previous post was unclear. Only one of the channels has died, but it has happened twice.
@Zen Mod, I can get my DDM in series with the inductor, but I feared it would affect the bias current, especially since the inductor DCR is so low already and the DMM reports 14% lower resistance than the manufacturer lists (0R6 vs 0R7). I had similar qualms about using the low resistor.
Unfortuately, I am unsure what qualifies as a "proven supply". Mine appear to be the "NANTO" brand, model SK90190474. I've seen the brand "Meanwell" mentioned hereabouts, but in both the 'pro' an 'con' columns. Any suggestions of models for Reliable PSUs would be appreciated. I'm considering a single PSU capable of handling both channels.
@avdesignguru, I have been re-setting bias as the units heat up as indicated in the original article. I reset at 15 min, 30 min and 60 min. Perhaps I should try dropping to 0.9V and see if that helps.
@vdi_vienna Good question; unfortunately I'm not sure it's the same one, as I didn't mark them. Lesson learned. I replaced the pad with new. I bought what were claimed to be "thermally conductive silicone" material, 30mm squares.
Waiting for replacement parts, so it'll be a while before I can get Channel B back in service.
Kind regards,
Drew
I realize now that my previous post was unclear. Only one of the channels has died, but it has happened twice.
@Zen Mod, I can get my DDM in series with the inductor, but I feared it would affect the bias current, especially since the inductor DCR is so low already and the DMM reports 14% lower resistance than the manufacturer lists (0R6 vs 0R7). I had similar qualms about using the low resistor.
Unfortuately, I am unsure what qualifies as a "proven supply". Mine appear to be the "NANTO" brand, model SK90190474. I've seen the brand "Meanwell" mentioned hereabouts, but in both the 'pro' an 'con' columns. Any suggestions of models for Reliable PSUs would be appreciated. I'm considering a single PSU capable of handling both channels.
@avdesignguru, I have been re-setting bias as the units heat up as indicated in the original article. I reset at 15 min, 30 min and 60 min. Perhaps I should try dropping to 0.9V and see if that helps.
@vdi_vienna Good question; unfortunately I'm not sure it's the same one, as I didn't mark them. Lesson learned. I replaced the pad with new. I bought what were claimed to be "thermally conductive silicone" material, 30mm squares.
Waiting for replacement parts, so it'll be a while before I can get Channel B back in service.
Kind regards,
Drew
Hmmm..
3” tall does seem a bit light.
Do you have an IR thermometer to get an idea how hot the sinks get?
3” tall does seem a bit light.
Do you have an IR thermometer to get an idea how hot the sinks get?
