What about Staving Student II as preamp?
It have tube as input and MOSFET as output (single ended).
Gain is 17 - 20 dB depending on CCS or Resistor mode to drive the tube.
Kit is available in the moment but not the chassis which is sold out (as far I could see).
It is a fine amp and I think good for MoFo where some gain is needed.
It have tube as input and MOSFET as output (single ended).
Gain is 17 - 20 dB depending on CCS or Resistor mode to drive the tube.
Kit is available in the moment but not the chassis which is sold out (as far I could see).
It is a fine amp and I think good for MoFo where some gain is needed.
principally - you can connect any amp in that way - two channels in parallel, that way doubling current capability, ref. to sole channel
can't see why you can't do the same with MoFo; though - will it be enough and of SQ you're expecting, only you can tell, after trying it
My MoFo's where driving a 3 Ohm load without any issues; it's 22V and biased at 3A.
Thank you for each of your responses, this is very helpful
That tube schematic looks interesting but why the funky secondary's on the B+? Is that because of the wall voltage being higher?
I think this is a solid approach, if it's not broken then don't fix it. What makes a mosfet suitable in this application / what bigger mosfet would you pick?
I have considered building a Starving Student as a headphone amp in the past, I saw it in your profile picture. I have a dedicated tube amp for HD 650's so since I don't need another amp I would prefer something just for speakers. I've built a bottlehead crack so I have built something point to point before and I think I could get a metal top plate fabricated and work through it with some help, but if i have to I'm open to high gain solid state designs.
I only mentioned putting two in parallel because in the story/guide pdf he writes you can get close to 100 W with two big mofo's bridged, and maggies want that kind of power.
That tube schematic looks interesting but why the funky secondary's on the B+? Is that because of the wall voltage being higher?
I think this is a solid approach, if it's not broken then don't fix it. What makes a mosfet suitable in this application / what bigger mosfet would you pick?
I use SSII 99,99% just as preamp. There are RCA out as standard if using the dedicated chassis. If another chassis is used the headphone jack could be omitted so it is made as a preamp only.
I started using a BA3-Pre amp for MoFo as BA3-Pre also has a lot of voltage gain as the power part of BA3 does not have voltage gain (as I remember). BA3-pre is a very nice solid state preamp but takes a little patience to adjust offset and distortion. As MoFo has some 2nd harmonic a good starting point using BA3-pre is to set distortion to a minimum so only a small amount of 3rd harmonic is present.
When I build the Korg preamp I found out that this worked very well also (I have 94 dB speakers). I was surprised how well it worked with MoFo.
I started using a BA3-Pre amp for MoFo as BA3-Pre also has a lot of voltage gain as the power part of BA3 does not have voltage gain (as I remember). BA3-pre is a very nice solid state preamp but takes a little patience to adjust offset and distortion. As MoFo has some 2nd harmonic a good starting point using BA3-pre is to set distortion to a minimum so only a small amount of 3rd harmonic is present.
When I build the Korg preamp I found out that this worked very well also (I have 94 dB speakers). I was surprised how well it worked with MoFo.
Would it be possible to build a MoFo using this big Mosfet and let a preamp drive it directly or is the energy required too large so a dedicated driver circuit is needed?:
https://docs.rs-online.com/d331/0900766b80a3b4c7.pdf
It could be driven at 20-40 Vds and 10-15A Ids?
https://docs.rs-online.com/d331/0900766b80a3b4c7.pdf
It could be driven at 20-40 Vds and 10-15A Ids?
YEAH! I like the idea. Something like a BAF2015 but a follower. Maybe a Singing Bush Follower. Not even sure how you'd implement schade feedback, or if you could. My guess is something would have to be put in front of the big fet to get proper drive out of it. Been playing with source followers lately (FAOW, SEWA, MOFO)...I think its near perfect, needs a decent pre of course, plenty of those around here.
Input capacitance of IXFN140N30P can be near 20,000pFd. At 20kHz this is 417 Ohms reactance. Quite a heavy load for nominal 10k interfacing. And like a Half Watt of drive energy (not power) so a single-ended driver must be large.
Against that: nobody wants full-power 20kHz. But peaks to full power do happen at 6kHz on some tracks.
Is that Ciss at fig. 11 in data sheet?
That is the capacitance a preamp will look into when connected to the gate (like MoFo schematic)?
I wonder how an amp like Whammy would handle this if you connected the headphone out directly.....SSII and Wayne linestage 2018 with the large output transistors may handle this also?
That is the capacitance a preamp will look into when connected to the gate (like MoFo schematic)?
I wonder how an amp like Whammy would handle this if you connected the headphone out directly.....SSII and Wayne linestage 2018 with the large output transistors may handle this also?
That input capacitance may not be as bad as it first looks. If you look at Nelson's old article about the Citation 12 he talks about fet input capacitance. To paraphrase what he said --- in a follower the majority of the input capacitance is gate to source which sees only a small amount of the voltage swing and the effective input capacitance may only be
10 to 20% of the ciss .
10 to 20% of the ciss .
Perhaps a better choice: IXFN140N20P
Much lower input capacitance: Ciss 7500 pF
https://www.mouser.ca/datasheet/2/240/Littelfuse_Discrete_MOSFETs_N-Channel_HiPerFETs_IX-1856167.pdf
Much lower input capacitance: Ciss 7500 pF
https://www.mouser.ca/datasheet/2/240/Littelfuse_Discrete_MOSFETs_N-Channel_HiPerFETs_IX-1856167.pdf
I'm working on a MoFo project and have a high quality power supply that can deliver 6A at 25VDC. Apart from more heat is there a downside to running with the Hammond 193T, biased to 1.7A, with this slighty higher supply voltage (higher than 19VDC as per MRs MoFo dream story)?
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