Build This MoFo!

What will I need to drive the MoFo properly?

you will have to answer two questions to yourself:

"How many volts input into Mofo do i need to get the listening volume i like out of my speakers"

"What kind of distortion would i like to add to the Mofo sound (which is rather neutral..)"

Myself i use the following 4
BA3
LuminAria

NuHybrid (Korg triode with buffer by Pete Millet) in two versions:
without step-up transformer (for high efficiency speakers and low volume)
with step-up transformer
 
I am building the BA-3 pre because it has a lot of gain. It is made for power amps that has no voltage gain. In the moment I use a preamp which has max. 10 dB of gain. This is fine for MoFo with 94 dB speakers. It is only low level recordings where I am close to the 10 dB the preamp can deliver. If I want to play very loud I may need a bit more than 10 dB but I also build BA-3 because of other qualities…..
 
Hi All,

First of all a big thanks to Michael for sharing this great design. I have completed my build of the 24V version of the MoFo and I like the sound very much. Unfortunately, something went wrong this morning. I have built it with a very low priced inductor that claims to be rated at 3.0A (and I am suspecting this is the problem). It has a DCR of 1.3 ohms, so I biased it at a voltage of 3.25, i.e. 2.5A.

Anyway, it has been running for 2 weeks, and this morning while playing some music I heard a pop on the left channel, and after that no more music, leaving a low frequency hum on the speaker. The right channel is still fine. When I touched the surface of the inductor casing, it seems to be much warmer than that of the right channel. I have not started any troubleshooting / measurements yet. My questions:

1. What are the recommended steps to troubleshoot?
2. In case the inductor is found to be faulty, will this be a good replacement? https://my.element14.com/hammond/195s4/choke-70mh-15-chassis/dp/2893269?st=hammond inductor

Thanks & Best regards
Liu
 
An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.


Hi Zen Mod,

Thanks for the reply. I have done the following:

1. On the faulty channel, measured the voltage across the inductor, V=9.5-11.0 increases with time, does not change much when I turn P1 anti-clockwise (many turns). Iq=6.9-8.5 A.

2. On the good channel, measured the voltage across the inductor, V=3.25, Iq= 2.5A

3. Swap the inductor or the normal channel to the faulty channel, V=9.5-11.0, same as step 1.

So I can now conclude that the problem does not seem to be caused by the inductor. So how should I proceed? Attached are pics of the finished chasis and the faulty channel mounted to the heatsink. Visually I can't detect any burnt component. The colour of the solder on the transistor does appear slightly charred as compared to the normal channel though. Could I have burnt the transistor?

Best regards
Liu
 
Last edited:
OK. Another go at attaching the pics.
 

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