I got the transformers, boards and mosfets from Frank. Mine is not as elegant, but I have heard it playI unfortunately had to go abroad for some weeks, so thorough listening will be later..
A nice thing about this is that it does the amplification so no need for a special preamplifier..
Now it is in a nice working mode. Together with the SALs and two 15" Monacor, electronic x-over it is marvellous. The mofo substituted a tube amp, and it beats it being natural and distinct at one and the same time.
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If you get a custom made choke for the MoFo what would the specification be for such a choke? if we go for the high bias version 2.5A. Would this be a choke that can handle at least 3A DC, 50 mH and then as low DC resistance as possible? ...is there any requirements for the DC resistance?
Hi MEPER,
Well my transformer is a bit different since I have voltages gain in my design. I use a 350-400VA double C-core transformer, the induction is 10mH/80mH with a total dc resistance of less that 0.15 Ohm. This means that if one can tolerate a DC offset that is about 150-200mV, you can leave out the output capacitor.
Also, you should se how the induction is over the frequency range, mine work as a perfect inductor to about 14 KHz.
Well my transformer is a bit different since I have voltages gain in my design. I use a 350-400VA double C-core transformer, the induction is 10mH/80mH with a total dc resistance of less that 0.15 Ohm. This means that if one can tolerate a DC offset that is about 150-200mV, you can leave out the output capacitor.
Also, you should se how the induction is over the frequency range, mine work as a perfect inductor to about 14 KHz.
Interesting with the possibility to not use an output capacitor. How low could the value for the inductor be? it would hurt the low frequencies if it is too low I guess. So a 50 mH that has 1 mOhm DC resistance and can work to 20 kHz and handle up to 3A would be nice. Then there will be 2-3 mV DC at the output. I could live with that. It may require a lot of iron and thick cupper wire.
proper chokes (OK, it is split load , so Donut is possible) - Donut a' la overkill - Solid State - diyAudio.rs
That is a big choke. DIY opens up a lot of possibilities that is not possible with commercial products. I was not able to open the attached picture. Is the PCB for the MoFo for sale somewhere? Could be a fun project during the winter season…..should work with the Korg Nutube preamp which I plan to build.
OK.....and 50 mH is large enough to give low frequency performance I assume. I have a contact at Overgaard transformers. I got some nice trafoes from them recently so I will hear want they can offer. They make a lot of high end audio stuff which I did not know until I was at a visit picking up some "heavy stuff".
Think I did something "crazy". Ordered a pair of chokes at the local "transformer pusher". I asked what was possible below 25 kg (50 mH, 3A DC, 20 kHz). I got these options:
Type str. EI 120/60 50mH, 50 mOhm weight 5,5 Kg
Type str. EI 150/50 50mH, 30 mOhm weight 7,7 Kg
Type str. EI 180/60 50mH, 16 mOhm weight 14 Kg
Type str. EI 180/92 50mH, 8 mOhm weight 20 Kg
I went for the big one…….then I will have 20 mV DC at 2.5A bias. This should be OK without output capacitor. Think it could be a fun project during the Autumn. I asked once again to have confirmed that the choke works at 20 kHz. They makes fine output transformers so I think they know what they are doing.
Are these MoFo's made as commercial amps by someone?
Type str. EI 120/60 50mH, 50 mOhm weight 5,5 Kg
Type str. EI 150/50 50mH, 30 mOhm weight 7,7 Kg
Type str. EI 180/60 50mH, 16 mOhm weight 14 Kg
Type str. EI 180/92 50mH, 8 mOhm weight 20 Kg
I went for the big one…….then I will have 20 mV DC at 2.5A bias. This should be OK without output capacitor. Think it could be a fun project during the Autumn. I asked once again to have confirmed that the choke works at 20 kHz. They makes fine output transformers so I think they know what they are doing.
Are these MoFo's made as commercial amps by someone?
Yes, when I get them. The factory closes 3 weeks for summer vacation. I expect to get them in about a month or so. Think they have about 3 weeks of delivery time. I can ask for the dimensions and maybe a drawing. Maybe I will change the name from "MoFo" to "MoFu" when the amps are finished
