Build This MoFo!

[mindutis]

Has any of you tried a simple transformer with a rectifier and a cap bank instead of a power brick? Is a power brick a better solution?

Nice amps you have built here!

 

[chansiukwing]

Can I use 24V smps for the supply of Hammond 193T ( bias set to around 1.7A )?

 

[MEPER]

I use a 300VA trafo with LCLC filtering for each channel. It works very well. But has not compared with a SMPS brick. I run 3A bias. The ripple of the supply is in the mV area.

 

[MEPER]

…..and I use a custom choke for the MoFo than can handle many amps…...therefor 3A is no problem for the choke.

 

[PRR]

Can I use 24V smps for the supply of Hammond 193T ( bias set to around 1.7A )?

The ratio V/I should be similar to your load impedance.

24V 1.7A suits a 14 Ohm load. On 8r, about 10V of DC is just waste heat and cost.

24V 3A would suit 8 Ohms. But 24V*3A+ 72 Watts of idle heat and this is a LOT, even if you get maybe 24 Watts of audio out.

 

[MEPER]

Yes, it generates some heat at 3A bias. My PSU delivers 25-26 VDC which is approx. 80W of heat. The relative large heatsink I use gets around 54 C. I could probably go to 3.5 A if I want. Then voltage will probably drop to about 24 VDC because of voltage drop over the filter chokes. In the moment I am very happy with how it sounds. I don't need more power. The big choke stays 100% cool. It can handle more than 20A.

 

[jostwid]

Preamp with autotransformer for Mofo

I tried to use Pete Millets NU-Hybrid headphone amp (Korg triode with buffer)
combined with an Edcor PC600-15k in autoformer mode for driving the Mofo.

The voltage gain of the autoformer is 4.75 times but distortion rises a lot (more than 10db and mainly 3rd harmonic)

My question: Is the Edcor PC 600-15k suitable for this application as it is for instance in the M2?

The Edcor is wired as per attached picture.

Many thanks in advance for your replies

 

[PRR]

What are you driving the Edcor PC 600-15k with? And what frequency are you testing with?

The 600r side will be lower than 600 Ohm impedance at the bottom of the audio band. The distortion will be minimized with a VERY low source impedance. Possibly well under 60 Ohms is wanted, while many hi-fi sources are higher.

 

[jostwid]

Preamp with autotransformer for Mofo

Many thanks for your quick response

The Edcor is driven by Pete Millets Nuhybrid headphone amp.
The OPA551 can drive 32Ohm Headphones very decently. Thus i think the output impedance is adaequate to drive the Edcor.

Test frequency was 1khz

 

[jostwid]

The input impedance of the Mofo is about 50k Ohm.
If the Edcor is driven by a source of less than 50 Ohm then the distortion should not rise to the extent i experienced?

I continue to think that the Edcor is suitable for the purpose.

I will look for possible errors i could have made

 

[xrk971]

Yes, it generates some heat at 3A bias. My PSU delivers 25-26 VDC which is approx. 80W of heat. The relative large heatsink I use gets around 54 C. I could probably go to 3.5 A if I want. Then voltage will probably drop to about 24 VDC because of voltage drop over the filter chokes. In the moment I am very happy with how it sounds. I don't need more power. The big choke stays 100% cool. It can handle more than 20A.

You can run an IRFP240 at 80w?

 

[MEPER]

I use IRFP250 (as in the schematic) and it goes fine...….as far I as remember from the specs…...I am safe…...as long as I can keep the temperature at a reasonable level.

 

[Eric]

My MoFo runs each IRFP240 at about 60w. This is the highest I've ever run one of these. My giant Aleph-X amps run the mosfets at about 36w each. The MoFo mosfets are mounted directly to the sink (using only thermal grease) and the sink exhibits thermal rise of ~28-30c. Don't know about long term longevity, though, as the amp is still pretty new. Due to the simplicity of the build, I'm really not concerned about a burned mosfet - unless a dead one dumps rail voltage into my speaker as a result.

 

[MEPER]

I think the specs for IRFP250 (Vishay) says max. 190W but of course you want to have a good safety margin. The 3A current is no problem it can handle 19A at Tc = 100 C.

 

[jostwid]

The input impedance of the Mofo is about 50k Ohm.
If the Edcor is driven by a source of less than 50 Ohm then the distortion should not rise to the extent i experienced?

I continue to think that the Edcor is suitable for the purpose.

I will look for possible errors i could have made

Found
Culprit was a burnt protection diode of the Mofo channel connected.
Now the Edcor is performing as expected.
Never have come across a component that delivers that much for so little money

 

[Eric]

Glad to hear that you found it! Those diodes are pretty fragile critters sitting next to that big transformer if you don't handle your power supply "properly" as I discovered a short while ago...

 

[noviygera]

What will I need to drive the MoFo properly?

 

[drpro]

Try the Aksa Lender preamp, really rocks with this amp and it is modular in you can build the daughter boards for different gain allowing use with other amps.

 

[Soundhappy]

What will I need to drive the MoFo properly?

BA-3 as preamp is fantastic and flexible Mr Pass design with no feedback

 

[Vunce]

+1

Totally agree with drpro!
AKSA Lender pre/MoFo combo is sweet