Becomming...
Here is a new pair of MoFo monoblocks in progress. These are being built with a mix of available parts, along with some new ones. I already had a pair of 27V MeanWell RSP-150 SMPS and Mini Dissipante 3U chassis on hand from a set of ACA monoblocks that are being re-directed. These will use the store PCBs as a platform for the amp, and a new pair of Hammond 195T5 chokes. I will be building new veroboards for a CapMx and input gain stage.
The target power rail voltage is 25V, with a quiescent current of 3A. I have enhanced the power dissipation capacity of the heatsinks usng 1/4" copper plates. With these, the heatsinks should be good for about 0.41 °C/W temperature rise. Given my normal ambient room temp of 22 °C, heatsinks will hopefully stay below 55 °C. That's going to be hotter than my other FW clone amps, but still reasonable.
Here are a couple pictures of the main components and trial fitment. The veroboard locations are still being studied.
Here is a new pair of MoFo monoblocks in progress. These are being built with a mix of available parts, along with some new ones. I already had a pair of 27V MeanWell RSP-150 SMPS and Mini Dissipante 3U chassis on hand from a set of ACA monoblocks that are being re-directed. These will use the store PCBs as a platform for the amp, and a new pair of Hammond 195T5 chokes. I will be building new veroboards for a CapMx and input gain stage.
The target power rail voltage is 25V, with a quiescent current of 3A. I have enhanced the power dissipation capacity of the heatsinks usng 1/4" copper plates. With these, the heatsinks should be good for about 0.41 °C/W temperature rise. Given my normal ambient room temp of 22 °C, heatsinks will hopefully stay below 55 °C. That's going to be hotter than my other FW clone amps, but still reasonable.
Here are a couple pictures of the main components and trial fitment. The veroboard locations are still being studied.
Attachments
MoFo monoblocks
When I tried the RSP-150 SMPS as a substitute PSU for one of my Hafler chassis ACA builds, I found that it needed better support for the lower octave or so. To that end I'm planning to use a capacitance multiplier on the output of the SMPS. In addition to lowering the ripple, the CapMx will be used as a softstart for 24,000 uF of capacitance at the power input to the MoFo PCB. I chose the MrEvil version for its low dropout capability. This is important with 3A as the target current. The adjustments on both the CapMx board and the SMPS will let me dial in an exact voltage. I expect this may also be helpful to find the "sweet spot" for the IRFP250 Mosfets. I also plan a second pair of MoFo PCBs with the FQH44N10 Mosfets for comparison.
An input stage is needed to provide some gain, as neither of my preamps are particularly happy driving 20V p-p. For solid-state, I've put together a Juma style gyrator loaded Son of ZV9. It's nice and small, and will hopefully complement the MoFo well. It will also give me some time to enjoy the basic amp while I'm planning and building an octal tube based gain stage. More on that later.
When I tried the RSP-150 SMPS as a substitute PSU for one of my Hafler chassis ACA builds, I found that it needed better support for the lower octave or so. To that end I'm planning to use a capacitance multiplier on the output of the SMPS. In addition to lowering the ripple, the CapMx will be used as a softstart for 24,000 uF of capacitance at the power input to the MoFo PCB. I chose the MrEvil version for its low dropout capability. This is important with 3A as the target current. The adjustments on both the CapMx board and the SMPS will let me dial in an exact voltage. I expect this may also be helpful to find the "sweet spot" for the IRFP250 Mosfets. I also plan a second pair of MoFo PCBs with the FQH44N10 Mosfets for comparison.
An input stage is needed to provide some gain, as neither of my preamps are particularly happy driving 20V p-p. For solid-state, I've put together a Juma style gyrator loaded Son of ZV9. It's nice and small, and will hopefully complement the MoFo well. It will also give me some time to enjoy the basic amp while I'm planning and building an octal tube based gain stage. More on that later.
Attachments
i bought these from hong kong together with 16n50d, and you know what? they tested as enhancement devices.....bummer, laser marking seems legit looking...
You don't really gain any headroom, but of course it can be done. You can do a MoFo with no input coupling cap or bias circuit at all, if you're brave. You might have to pick through a few IXTH6N50D2's to find the exact bias point you want for your particular chokes. I've found that IXTH6N50D2 and Hammond 159ZC bias up nice for an 8 ohm or 16 ohm load.
This is a stereo version, with all the iron cut off after I listened to it for a few months. I'm more of fabbed PCB kinda guy usually, but this was a fun evening's work.
Thanks zen mod!. This is as much as i can find:
some notes from farnel listing:
The NTE4 is a professional Audio Transformer, 1:4 turn ratio, 200R primary, 3.2kR secondary impedance with free wires and chassis mount. This transformer features very low distortion, excellent frequency response, cost effective cable version for free wiring, fully perm alloy-shielded studio versions.
and the attachment
If its no good might you know of a reasonable alternative? If its jensen pricing i may as well build another preamp just for the MOFO
There must be a mistake in the datasheet?
some notes from farnel listing:
The NTE4 is a professional Audio Transformer, 1:4 turn ratio, 200R primary, 3.2kR secondary impedance with free wires and chassis mount. This transformer features very low distortion, excellent frequency response, cost effective cable version for free wiring, fully perm alloy-shielded studio versions.
and the attachment
If its no good might you know of a reasonable alternative? If its jensen pricing i may as well build another preamp just for the MOFO
There must be a mistake in the datasheet?
Attachments
Last edited:
dunno
can't extract enough info about NTE4 itself , confused with that pic -can't connect NTE with NTL and NTM , to have some meaning
though , one thing maybe will help you in final decision- remember that Rout after xformer is square of voltage ratio
if you have 30R as Rout of buffer in front of xformer , then xformer connected as 4V/V gain device , final Rout is 30R * 4^2 = 480R
can't extract enough info about NTE4 itself , confused with that pic -can't connect NTE with NTL and NTM , to have some meaning
though , one thing maybe will help you in final decision- remember that Rout after xformer is square of voltage ratio
if you have 30R as Rout of buffer in front of xformer , then xformer connected as 4V/V gain device , final Rout is 30R * 4^2 = 480R