Just got my Big MoFo mkII put together.
I used the chassis and psu’s from my original build to speed up the process.
This version uses Lundahl 2733 chokes and Dell cpu coolers/Noctua fans with a PWM fan controller. Since the MoFo boards are mounted upside down, I flipped the connectors and trim pot to the backside to help make wiring and bias adjustments MUCH easier.
As ZM would say....Fugly!!
Fired up without a hiccup and producing wonderful music
The MoFo is still the quietest amp in my stable, background noise is not audible with 99dB speakers.
Thanks again Michael Rothacher for sharing this design with us
I used the chassis and psu’s from my original build to speed up the process.
This version uses Lundahl 2733 chokes and Dell cpu coolers/Noctua fans with a PWM fan controller. Since the MoFo boards are mounted upside down, I flipped the connectors and trim pot to the backside to help make wiring and bias adjustments MUCH easier.
As ZM would say....Fugly!!
Fired up without a hiccup and producing wonderful music
The MoFo is still the quietest amp in my stable, background noise is not audible with 99dB speakers.
Thanks again Michael Rothacher for sharing this design with us
Attachments
Thanks for the positive feedback fellas.
JW,
Yes and yes.
I’m using a wall wart to power the fans right now, but I’m going to try a 12v linear voltage regulator tapped off a filter capacitor. That will eliminate the separate power plug and potentially forgetting to turn the fans on.
I have a few versions of daughter boards to plug into my Aksa Lender pre depending on the amplifier used. It’s really a sweet combo!!
Cheers,
Vunce
JW,
Yes and yes.
I’m using a wall wart to power the fans right now, but I’m going to try a 12v linear voltage regulator tapped off a filter capacitor. That will eliminate the separate power plug and potentially forgetting to turn the fans on.
I have a few versions of daughter boards to plug into my Aksa Lender pre depending on the amplifier used. It’s really a sweet combo!!
Cheers,
Vunce
Just to retreive this nice project.
Is-it possible to add a peamp stage with BF862 (maybe more than one paralleled), to give little gain (6dB) to the MoFo and an easier input impedance...
Something like this:
http://www.diyaudio.com/forums/attachments/group-buys/616921d1495124663-xrk971-pocket-class-headamp-gb-pocket-class-schematic-v8-voltages.png
Is-it possible to add a peamp stage with BF862 (maybe more than one paralleled), to give little gain (6dB) to the MoFo and an easier input impedance...
Something like this:
http://www.diyaudio.com/forums/attachments/group-buys/616921d1495124663-xrk971-pocket-class-headamp-gb-pocket-class-schematic-v8-voltages.png
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I hope someone can point me to the right direction for my MOFO build.
- Double check all the values make sure they are matching BOM when soldering onto the board.
- Used a laptop AC adapter that output 19VDC 4.74A. I'm using 193T for my build.
- Checked the Voltage DC at 19.74V from the adapter before connecting to +/- supply on the MOFO board.
- I also use Z1 (Optional) 20V Zener for my MOFO build
When connecting the adapter to power supply on MOFO board, the DC voltage at the power supply +/- measured only at 2.07 VDC at the board and Voltage across L1 is 0 Vdc.
At this point, I only connect L1 and power supply on the board to test out and check for biasing, I do not connect anything to input and output. Could it be the reason why the power supply voltage get pulled down to 2.07V instead of 19V ?
Thanks,
Tom
- Double check all the values make sure they are matching BOM when soldering onto the board.
- Used a laptop AC adapter that output 19VDC 4.74A. I'm using 193T for my build.
- Checked the Voltage DC at 19.74V from the adapter before connecting to +/- supply on the MOFO board.
- I also use Z1 (Optional) 20V Zener for my MOFO build
When connecting the adapter to power supply on MOFO board, the DC voltage at the power supply +/- measured only at 2.07 VDC at the board and Voltage across L1 is 0 Vdc.
At this point, I only connect L1 and power supply on the board to test out and check for biasing, I do not connect anything to input and output. Could it be the reason why the power supply voltage get pulled down to 2.07V instead of 19V ?
Thanks,
Tom
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Unless I botched the math (very possible) a 60 W incandescent light bulb should have the correct resistance to test the power supply.
put a 1 ohm 5 watt resistor in series with the bulb and test the PSU.
If you measure ~ 2 V across 1 ohms and the supply measures 19 volts, its not your supply.
put a 1 ohm 5 watt resistor in series with the bulb and test the PSU.
If you measure ~ 2 V across 1 ohms and the supply measures 19 volts, its not your supply.
Thank you DougL for the pointer, I will try this out. I will post some photos and pictures later in case I can't figure out what's wrong. MOFOs seem to be fairly simple circuitry with very minimal component count. I believe it might have something to do with the PSU laptop adapter.
Thanks,
Tom
Other thing about strange low voltages:
Some SMPS have difficulty to start with external capacitances (or incandescent bulbs, or valve filaments), and some of these have latching or very strong fold back protection, so it stops with a intermediate voltage, or simply turn off.
For these high current supplies is not very common, but it can occur eventually.
Is worth checking this also.
The PSU will start normally without load if it is the problem, and will power resistive loadings, but will die when try light bulbs (or capacitor banks).
Perhaps someday someone here get a SMPS with this behavior, so is worth mentioning.
Some SMPS have difficulty to start with external capacitances (or incandescent bulbs, or valve filaments), and some of these have latching or very strong fold back protection, so it stops with a intermediate voltage, or simply turn off.
For these high current supplies is not very common, but it can occur eventually.
Is worth checking this also.
The PSU will start normally without load if it is the problem, and will power resistive loadings, but will die when try light bulbs (or capacitor banks).
Perhaps someday someone here get a SMPS with this behavior, so is worth mentioning.
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