You guys are all very Eagle eyed!
A quick update, JPS64 is close to finishing up the Aksa Lender front end board for the LuFo. It will have its own dedicated 55v DCDC step up voltage booster on the bottom and the preamp itself will be all through hole. However, we could not make the DCDC step up through hole. The lower power supply board however has a massive cutout to allow clearance for a large 2.2uF 250v MKP axial film cap for the input of the Aksa Lender. The output coupling will be taken care of by the LuFo’s on board cap (which can be a large boutique Mundorf etc). This board is in the usual M2X/Yarra bolt pattern.
The Aksa Lender is probably my favorite preamp of all time. Hugh Dean designed it at my request because I was looking for a good preamp to drive the F4. It can be used for any 0dB gain power stage like F4, MoFo, LuFo, etc. It will drive 50Vpp cleanly, and with a superb harmonic distortion profile. It will be set up for 22.4dB gain so should be quite compatible with most preamps and sources.
A quick update, JPS64 is close to finishing up the Aksa Lender front end board for the LuFo. It will have its own dedicated 55v DCDC step up voltage booster on the bottom and the preamp itself will be all through hole. However, we could not make the DCDC step up through hole. The lower power supply board however has a massive cutout to allow clearance for a large 2.2uF 250v MKP axial film cap for the input of the Aksa Lender. The output coupling will be taken care of by the LuFo’s on board cap (which can be a large boutique Mundorf etc). This board is in the usual M2X/Yarra bolt pattern.
The Aksa Lender is probably my favorite preamp of all time. Hugh Dean designed it at my request because I was looking for a good preamp to drive the F4. It can be used for any 0dB gain power stage like F4, MoFo, LuFo, etc. It will drive 50Vpp cleanly, and with a superb harmonic distortion profile. It will be set up for 22.4dB gain so should be quite compatible with most preamps and sources.
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LuFo progress update
The LuFo Amp lives!!
Powered up drama free without any magic smoke
Bias easily adjusted to 3A with a couple turns of the trimpot. (1.65v across the MOT with a DCR of 0r55 ohms)
Set up my AKSA Lender preamp and a single Speedster (Paul Carmody design) speaker. Using an iPhone as the source I gave the volume knob a twist and noticed a strange behavior. The bias current was moving when increasing/decreasing the volume pot. After chatting with X, I checked for voltage at the JFET gate, almost 1vdc was present. I removed the zener diode (V161) and the issue was solved, near 0vdc at the JFET gate.
Clear sailing from there, no turn on/off plops or noises, no background hum, super quiet amp. Even with just a single speaker playing the music has an effortless presentation. Running for over two hours and the heatsink is 54°C, it’s a bit toasty but I expected temps would be a bit high because of the not ideal horizontal fins. I believe a 4U 400mm chassis would be perfect for cooling duty.
Time to get working on the second channel for stereo listening, and try adding the ACP+ as a front end. Lots to play with here.....
The LuFo Amp lives!!
Powered up drama free without any magic smoke
Bias easily adjusted to 3A with a couple turns of the trimpot. (1.65v across the MOT with a DCR of 0r55 ohms)
Set up my AKSA Lender preamp and a single Speedster (Paul Carmody design) speaker. Using an iPhone as the source I gave the volume knob a twist and noticed a strange behavior. The bias current was moving when increasing/decreasing the volume pot. After chatting with X, I checked for voltage at the JFET gate, almost 1vdc was present. I removed the zener diode (V161) and the issue was solved, near 0vdc at the JFET gate.
Clear sailing from there, no turn on/off plops or noises, no background hum, super quiet amp. Even with just a single speaker playing the music has an effortless presentation. Running for over two hours and the heatsink is 54°C, it’s a bit toasty but I expected temps would be a bit high because of the not ideal horizontal fins. I believe a 4U 400mm chassis would be perfect for cooling duty.
Time to get working on the second channel for stereo listening, and try adding the ACP+ as a front end. Lots to play with here.....
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Nice work, Vunce. Thanks for verifying the prototype board. Sorry about the Zener diode on the LU1014D. I forgot that we can’t put it there if the source pin is connected to a choke which generates a reactive back-emf greater than 0.6v. 54C is par for the course with a big Class A amp. Looking forward to what you get with stereo. I was not able to get anywhere with building the OPA454 front end board tonight. Another night...
The LuFo Amp lives!!
Powered up drama free without any magic smoke
Bias easily adjusted to 3A with a couple turns of the trimpot. (1.65v across the MOT with a DCR of 0r55 ohms)
Set up my AKSA Lender preamp and a single Speedster (Paul Carmody design) speaker. Using an iPhone as the source I gave the volume knob a twist and noticed a strange behavior. The bias current was moving when increasing/decreasing the volume pot. After chatting with X, I checked for voltage at the JFET gate, almost 1vdc was present. I removed the zener diode (V161) and the issue was solved, near 0vdc at the JFET gate.
Clear sailing from there, no turn on/off plops or noises, no background hum, super quiet amp. Even with just a single speaker playing the music has an effortless presentation. Running for over two hours and the heatsink is 54°C, it’s a bit toasty but I expected temps would be a bit high because of the not ideal horizontal fins. I believe a 4U 400mm chassis would be perfect for cooling duty.
Time to get working on the second channel for stereo listening, and try adding the ACP+ as a front end. Lots to play with here.....
Sounds great! With that power output and that damping factor, this SE amp will rock!
Just for the interest I contacted a guy i know with a question:
Specifications:
Nominal current 5A minimum
DCR max 0,5 Ohm
Inductance: min. 100mH
Silicon Steel plate laminate
Unpainted side covers (end bells)
EI-core
Air gap
And got an answer:
The unit price for 2pcs is 50Euro + VAT 24% and for 50 pcs the unit price is 42 Euro + VAT 24% .
The size will be 12 cm x 10.5 cm x 15cm ( width x height x depth ).
If you add all the shipping costs, time put in, etc... the total price might be much closer to Hammonds.
But the custom vintage look and a possibility to mount a choke outside an enclosure might be rewarding
I contacted Kevin Carter (US distributor of Lundahl) and he has told me that the Lundahl LL2773/3.5A is $145 each; LL2773/5A is also the same price.
As a recap, the inductances are 95mH and 65mH (respectively) with the coils in series, and DCR should be about 0.44 ohms. The saturating currents are 5.6A and 8A respectively. Max ripple voltage is 70Vrms @ 100Hz or 14Vrms @ 20Hz.
It will take until September to get them though.
Best,
Anand.
As a recap, the inductances are 95mH and 65mH (respectively) with the coils in series, and DCR should be about 0.44 ohms. The saturating currents are 5.6A and 8A respectively. Max ripple voltage is 70Vrms @ 100Hz or 14Vrms @ 20Hz.
It will take until September to get them though.
Best,
Anand.
Hi Anand,
That’s just me not thinking through the fine details and designing based on past similar situations. It’s great that Vunce does these verification builds and works out all the bugs in advance so that everyone out in the wild can expect an amp that will build up easily and and have an uneventful first power up.
Thanks for checking on price of Lundhals. That’s a fair price for the extreme quality and luxury item that it is.
That’s just me not thinking through the fine details and designing based on past similar situations. It’s great that Vunce does these verification builds and works out all the bugs in advance so that everyone out in the wild can expect an amp that will build up easily and and have an uneventful first power up.
Thanks for checking on price of Lundhals. That’s a fair price for the extreme quality and luxury item that it is.
i want to play around with ACA and then build my dusty M2 pcb....i have to start with this amp....now i see other amps....
Guys you are awesome !!!
Hi Chermann,
Thanks for the kind words. Glad you want to try this amp out. We are close to releasing the new Gerbers soon once we verify it all works in stereo. The other PCB is not identical as this is a mirror image left/right board set so must be verified.
I think we are getting closer everyday to a choke GB to make this truly affordable for everyone.
Cheers,
X
Some good news - my big dual mono chassis has been delivered (but not yet assembled). It’s very well made with 12mm thick front panel, 245mm x 200mm x 40mm fins heatsinks, nice CNC solid billet aluminum handles, machined aluminum feet, all hardware like IEC inlet, power switch, VU meter and driver board. I’m very happy with it.
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Nice mono bloc chassis XRK, is this what you got it - 1PCS All aluminum amplifier chassis / Preamplifier case / AMP Enclosure /DIY box (320 *200*300mm)|Amplifier| - AliExpress
Or its bigger brother - 1 pair MC2620 All aluminum chassis Mono audio case Split amplifier Housing Class A power amp box 260*200*363MM|Amplifier| - AliExpress
Or its bigger brother - 1 pair MC2620 All aluminum chassis Mono audio case Split amplifier Housing Class A power amp box 260*200*363MM|Amplifier| - AliExpress
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