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Old 16th August 2018, 06:06 PM   #1371
jwjarch is offline jwjarch  United States
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Nice work Vunce! Do you have the fans/PWM on a separate power supply? I noticed you scavenged the CLC board from your AKSA Lender Preamp as well. Is that what you're using to drive the MoFo?
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Old 16th August 2018, 06:48 PM   #1372
Vunce is offline Vunce  United States
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Thanks for the positive feedback fellas.

JW,
Yes and yes.
Iím using a wall wart to power the fans right now, but Iím 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. Itís really a sweet combo!!

Cheers,
Vunce
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Old 28th August 2018, 08:49 AM   #1373
marconi118 is offline marconi118  Germany
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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/attac...8-voltages.png

Last edited by marconi118; 28th August 2018 at 08:51 AM.
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Old 28th August 2018, 08:51 AM   #1374
marconi118 is offline marconi118  Germany
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in case of need R3 could be replaced by a CCS or a BS170 mosfet gyrator.

Some ideas but my design knowledge is too low to design it myself....
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Old 28th August 2018, 08:07 PM   #1375
tommydoan84 is offline tommydoan84  United States
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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
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Last edited by tommydoan84; 28th August 2018 at 08:11 PM.
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Old 28th August 2018, 08:28 PM   #1376
Vunce is offline Vunce  United States
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Hi Tom,

Could you post some pictures? That would help troubleshoot your MoFo.
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Old 29th August 2018, 01:55 PM   #1377
marconi118 is offline marconi118  Germany
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I suppose PSU is not strong, it collapses at 2V
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Old 29th August 2018, 03:31 PM   #1378
DougL is offline DougL  United States
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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.
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Old 29th August 2018, 04:33 PM   #1379
tommydoan84 is offline tommydoan84  United States
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Quote:
Originally Posted by DougL View Post
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.
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
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Old 29th August 2018, 05:07 PM   #1380
DIYBras is offline DIYBras  Brazil
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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.
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Last edited by DIYBras; 29th August 2018 at 05:11 PM. Reason: Added info: ...(or capacitor banks)
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