Has anybody tried (matched) parallel IRF240? I've got some interesting chassis that have 2 sinks each, so monoblock would have to have the devices split to give the heat somewhere to go.
The other challenge is an inductor that will fit in said chassis, but I think Jack at Electra-Print can help with that...
The other challenge is an inductor that will fit in said chassis, but I think Jack at Electra-Print can help with that...
I double posted, then deleted my second post.
I dunno. Do electrons flow from ground to positive?
There's always some rule I miss, so wait for a better answer.
But, common sense tells me to put an isolator on that TO-3.
Believe me I know the temptation to not use an isolator if not needed.
Just buying them seems like a hassle.
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say that two mosfets are having common node at sources (ignore another common node at drains , due to impedance there)
to have equal current distribution between them , they need to be twins ... which is hard
way of making lookalikes behaving as twins is to introduce helping elements , to equalize current contribution ...... and that are source resistors
price is somewhat lesser xconductance , comparing to two naked mosfets , but you have function ...... and xconductance is way greater than with just one
say that you're good with just 0R22 in source
or - just take IRFP150 , split it in two halves and mount on two sinks
I double posted, then deleted my second post.
I dunno. Do electrons flow from ground to positive?
There's always some rule I miss, so wait for a better answer.
But, common sense tells me to put an isolator on that TO-3.
Believe me I know the temptation to not use an isolator if not needed.
Just buying them seems like a hassle.
IF drain is grounded , be free to mount mosfet without isolation on sink
but!! :
- isn't better to have audio GND isolated from chassis?
-I can't see GND up in MOFO schm ...... and I'm pretty sure that there is no benefit in making it that way
Interesting concept. Does it sound good?
Are the pink resistors Takman Rex carbon film resistors?
I got a stepped attenuator with those for BA3-pre.....but difficult or probably impossible to hear difference between quality resistors.
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Autox,
Just use your Schiit headphone output for the preamp. They should swing enough for a few watts. But to get the circa 11w possible with the standard MoFo, you need a pretty powerful (voltage wise) and low distortion preamp.
I am not sure why you would want to scale it down as a buffer preamp. It is a buffer (no gain) as is. It needs a Preamp or more specifically, a voltage gain amp that has outputs high enough to drive the power output you need in voltage. The MoFo takes care of the current.
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XRK,
I'm assuming a typical source stepped up to mofo voltage with a bare transformer won't have the current to drive the mosfet gate. All the favored pre's for the mofo provide adequate current at their output voltage, but none of them do it with a single transistor. It's my (limited) understanding that a transformer with a buffer can do it, and a mini mofo could do it with a single transistor.
And there are plenty of other applications for a buffer pre.
My root curiosity is to what degree scaling a mofo's power down to pre levels eases sourcing of sink and choke. Or if it's just a foolish endeavor and there are good reasons to use more complex pre designs.
I'm assuming a typical source stepped up to mofo voltage with a bare transformer won't have the current to drive the mosfet gate. All the favored pre's for the mofo provide adequate current at their output voltage, but none of them do it with a single transistor. It's my (limited) understanding that a transformer with a buffer can do it, and a mini mofo could do it with a single transistor.
And there are plenty of other applications for a buffer pre.
My root curiosity is to what degree scaling a mofo's power down to pre levels eases sourcing of sink and choke. Or if it's just a foolish endeavor and there are good reasons to use more complex pre designs.
Autox,
The gate of a MoFo is a MOSFET, and they take very little current compared to a BJT. You can drive with any opamp that can drive a few kOhms. The Aksa Lender Preamp for axample, was designed to drive a 7kohm load. It’s close sibling, the Melbourne is designed to drive the Edcor transformer used in the M2, which is 600ohms. But many opamps drive 600ohms just fine. It’s when you ask the Preamp to drive the voltage needed for 25w into 8ohms, it’s challenging for opamps most can’t do +/-20v with low distortion.
For MoFo you want circa 10w into 8ohms or 25vpp. If your Schiit Vali headphone amp can do that, you are set. Headphone amps can drive 30ohm headphones no problem. So the MoFo should not be an issue.
Looking at specs for Vali, it says 115mW rms max into 600ohms and this is equivalent to 23.5vpp. That will do about 8.6wrms in the MoFo with 8ohm speakers. So looks like Schiit Vali May be just the ticket for your MoFo amp. Look no further as that’s plenty of power.
You could actually take the Edcor (only 600ohm load) from the M2 and drive it as an autoformer with your Vali and get about 6x gain. You would have an MOFOMM.
The gate of a MoFo is a MOSFET, and they take very little current compared to a BJT. You can drive with any opamp that can drive a few kOhms. The Aksa Lender Preamp for axample, was designed to drive a 7kohm load. It’s close sibling, the Melbourne is designed to drive the Edcor transformer used in the M2, which is 600ohms. But many opamps drive 600ohms just fine. It’s when you ask the Preamp to drive the voltage needed for 25w into 8ohms, it’s challenging for opamps most can’t do +/-20v with low distortion.
For MoFo you want circa 10w into 8ohms or 25vpp. If your Schiit Vali headphone amp can do that, you are set. Headphone amps can drive 30ohm headphones no problem. So the MoFo should not be an issue.
Looking at specs for Vali, it says 115mW rms max into 600ohms and this is equivalent to 23.5vpp. That will do about 8.6wrms in the MoFo with 8ohm speakers. So looks like Schiit Vali May be just the ticket for your MoFo amp. Look no further as that’s plenty of power.
You could actually take the Edcor (only 600ohm load) from the M2 and drive it as an autoformer with your Vali and get about 6x gain. You would have an MOFOMM.
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I do not know what Rin of MOFO is but i guess that it is similar to the one of M2
Consequently the Edcor 600/15k when driven by a buffer should work for the MOFO?
say that , for easier calc , Rin of MoFo is in vicinity of 50K
600:15K is having forward voltage ratio (as autoformer) of 1:6 (6 V/V)
50K is transformed back to source as 1/(6^2) , so source needs to be capable of driving 50K/36=1K39
(impedance ratio is square of voltage ratio)
which is easier than 600R , in any case
again, with xformers - when you read impedances , they're given as declared ones , while you need to do your math whenever you are moving from declared figures
600:15K is having forward voltage ratio (as autoformer) of 1:6 (6 V/V)
50K is transformed back to source as 1/(6^2) , so source needs to be capable of driving 50K/36=1K39
(impedance ratio is square of voltage ratio)
which is easier than 600R , in any case
again, with xformers - when you read impedances , they're given as declared ones , while you need to do your math whenever you are moving from declared figures
That was my original thought about the input section for the MoFo, make a mini-M2 using the Edcor 600/15k. It does work very well. Here's about where the discussion starts:
Earlier Cinco MoFo posts
However, after bouncing some ideas off the board and some experimentaion, I found that I didn't need that much gain (the +14dB of the Edcor). Most of my listening was at -21dB or -18dB attenuation with Edcor.
Further talks with ZM and reading his Iron-preamp and Iron Pumpkin threads and now I'm working on building an Iron Pumpkin (poor man version) with Slagle autotransformer volume control in place of ZM's Iron Turtle AVC. Now I listen at -6dB or -3dB with the Poor-man Pumpkin and I can go up to +6dB. I've been listening to bread-boarded version for a while... pretty sweet sounding.
For party levels I just hook up my M2 clone.
It all depends on the cajones of your source(s) and sensitivity of your speakers so your milage may vary. More clarity to be had without an extra buffer and transformer... just saying.
Cinco
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"For MoFo you want circa 10w into 8ohms or 25vpp. If your Schiit Vali headphone amp can do that, you are set. Headphone amps can drive 30ohm headphones no problem. So the MoFo should not be an issue."
So would a normal pre supply enough voltage to make a watt or two? Don't need much power at all for my horns....
So would a normal pre supply enough voltage to make a watt or two? Don't need much power at all for my horns....