Let me see what I can get out of a LuFo-Lite simulation. So let’s make rail 20v and skip the cascode. I think bias current circa 2A should be good. Same MOT - typical 55mH and 0.55ohm DCR.
Let’s assume a cap multiplier is used so supply is 24vdc and 3.5v drop across the cap Mx, and another 0.5v drop across the CRC.
PSU is 24v 5A SMPS brick.
Let’s assume a cap multiplier is used so supply is 24vdc and 3.5v drop across the cap Mx, and another 0.5v drop across the CRC.
PSU is 24v 5A SMPS brick.
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I'm interested in this too. I asked Michael Rothacher about a different schematic using chokes he posted some time ago in the FAOW thread. Mostly because I picked up a pair of Hammond 193S cheap on ebay, and I'm thinking about trying something lower powered using them. Inductance is high (1 H) but the max current (1 A) is low, so maybe not ideal for a LuFo-lite, though.
I tried it with a 20v rail and you can theoretically get 20w out of it. But wait, ... without the cascode, the LU1014D is limited to a maximum of 20Vpp swings or it will self destruct. So to keep things safe, let’s say 19vpp. With that, only a 12v supply is needed and max power is 5.6W. However, the amp is very simple and has a great harmonic profile. Should be a fun fleawatt amp or a superb and very powerful headphone amp. The 12v lends itself to battery usage schemes for very low noise PSU's. Or certainly there are some very capapable low noise 3A 12v supplies floating around. Total dissipation is only about 15w so not a big heatsink. Bias current is automatically set at around 3A based on DCR of your choke. If you have 1ohm DCR choke, this can work well too as the bias current will drop to about 1.5A and heat output will drop in half.
The Hammond chokes will work well for this I think. As you can see there are no bias current adjustments - this is an adjustment free amp. Turn it on and it should stabilize. At 1.0ohm DCR, bias current is 1.65A, but the dissipation in the LU is still about the same, the dissipation in the choke is less, and the THD actually goes down to 0.06%.
The Hammond chokes will work well for this I think. As you can see there are no bias current adjustments - this is an adjustment free amp. Turn it on and it should stabilize. At 1.0ohm DCR, bias current is 1.65A, but the dissipation in the LU is still about the same, the dissipation in the choke is less, and the THD actually goes down to 0.06%.
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Thank you for doing this X, it's really appreciated.
I think I might just give this a go and have some ideas for a build with some bits and pieces I've accumulated. Apart from a MoFo comparison, albeit with the output power difference, it will also be interesting to see how it sounds against my current SE-OTL amplifiers driving my 15ohm Lowther horns.
With a 12V supply requirement, albeit at 3A, linear regulated power supplies become a realistic option too.
I think I might just give this a go and have some ideas for a build with some bits and pieces I've accumulated. Apart from a MoFo comparison, albeit with the output power difference, it will also be interesting to see how it sounds against my current SE-OTL amplifiers driving my 15ohm Lowther horns.
With a 12V supply requirement, albeit at 3A, linear regulated power supplies become a realistic option too.
I finally found some time to assemble the LuFo amp boards. I will need to build the other channel of the OPA454 front end board. Then drill and tap holes in a heatsink.
This is a really roomy board with not so many parts to solder. It went pretty easily and quickly.
This is a really roomy board with not so many parts to solder. It went pretty easily and quickly.
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Nice work X!
I looked over my build notes, the polarity labeling for H111 is reversed. Anode should face R111. Do not populate V121/V161.
My LuFo, driven by an AKSA Lender preamp, has been the main amp for past few weeks and has logged close to 100hrs. Other than the issue playing the Hey Now song, the LuFo has been a stellar performer. The soundstage is impressive, this was immediately noticeable when LuFo replaced the previous amplifier (TPA3255). The MOT inductor option is a great budget friendly choice, but I’m hopeful one of the “custom inductor” inquiries out there turns out to be a gem!
I looked over my build notes, the polarity labeling for H111 is reversed. Anode should face R111. Do not populate V121/V161.
My LuFo, driven by an AKSA Lender preamp, has been the main amp for past few weeks and has logged close to 100hrs. Other than the issue playing the Hey Now song, the LuFo has been a stellar performer. The soundstage is impressive, this was immediately noticeable when LuFo replaced the previous amplifier (TPA3255). The MOT inductor option is a great budget friendly choice, but I’m hopeful one of the “custom inductor” inquiries out there turns out to be a gem!
Hi X, regarding the LuFo-Lite simulation you posted, I have a pair of Lundahl LL1694 filament chokes, with the windings paralleled they are good for 3A with an inductance of 40mH and static resistance of 0.45ohms. Any chance of you substituting those values into your simulation with 8 and 15ohm speaker loads? Output cap values can probably be halved with 15ohm load.
Apart from trying a LuFo-Lite with my 15ohm Lowther horns, I think I'm going to try a LuFo-Lite build to drive a high-efficiency full-range driver in an open baffle. In that context bandwidth limiting becomes an option too, a suitably smaller input capacitor will roll-off the FR curve at the bottom end, avoiding the need for a crossover. Hmmm...
Apart from trying a LuFo-Lite with my 15ohm Lowther horns, I think I'm going to try a LuFo-Lite build to drive a high-efficiency full-range driver in an open baffle. In that context bandwidth limiting becomes an option too, a suitably smaller input capacitor will roll-off the FR curve at the bottom end, avoiding the need for a crossover. Hmmm...
Hi Vunce,
Thanks for the build notes! I think I got them all. I took a Sharpie and made notes on the board and X-out the Zener on the JFET and also caught the A vs K error on the LED. There is also a misplaced + sign on one of the inductor terminals. One thing that needs to be changed is how close one of the 0.1ohm resistors is the pot on one channel. Literally 1mm away and that thing might get warm. The painful process of drill and tap on the heatsinks is near. I still need to assemble the second channel front end and assembled the second channel monoblock chassis.
Good to hear that it’s been getting a long run in your main system.
Cheers,
X
Thanks for the build notes! I think I got them all. I took a Sharpie and made notes on the board and X-out the Zener on the JFET and also caught the A vs K error on the LED. There is also a misplaced + sign on one of the inductor terminals. One thing that needs to be changed is how close one of the 0.1ohm resistors is the pot on one channel. Literally 1mm away and that thing might get warm. The painful process of drill and tap on the heatsinks is near. I still need to assemble the second channel front end and assembled the second channel monoblock chassis.
Good to hear that it’s been getting a long run in your main system.
Cheers,
X
Hi Nautibuoy,
I think if you want to use this at low power for your Lowther horn or a small full range OB, there’s no need to run at 3A. So let’s use a single Lundhal at 90mH and 0.9ohm and see how that works. I will simulate for 8ohm and 16ohm load. Note that 16ohm load needs more voltage to get power out. You may be better off with at least a single cascode to get more voltage swing. Otherwise 19vpp into 16ohms is only 2.8w rms.
I think if you want to use this at low power for your Lowther horn or a small full range OB, there’s no need to run at 3A. So let’s use a single Lundhal at 90mH and 0.9ohm and see how that works. I will simulate for 8ohm and 16ohm load. Note that 16ohm load needs more voltage to get power out. You may be better off with at least a single cascode to get more voltage swing. Otherwise 19vpp into 16ohms is only 2.8w rms.
Here is the LuFo Lite sim for the Lundhal inductor, for 8ohm and 15ohm load. FFT plot for 15ohm load - I think the Lowthers would sound good. This is 11Vpp so there is still 19Vpp max for some headroom. 96dB is quite loud at 1w.
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I'm gonna have a go at a LuFo-Lite.
With a 12V power supply, even with a hefty bias current, the heat dissipation requirements of a LuFo-Lite are pretty manageable. I've bought some heatsinks on ebay and I'm sketching out how to make use of them - the basic circuit is so simple that it can all be squeezed into quite a small arrangement around the TO247 adaptor board so plenty of scope to be a little creative.
With a 12V power supply, even with a hefty bias current, the heat dissipation requirements of a LuFo-Lite are pretty manageable. I've bought some heatsinks on ebay and I'm sketching out how to make use of them - the basic circuit is so simple that it can all be squeezed into quite a small arrangement around the TO247 adaptor board so plenty of scope to be a little creative.
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