I'm relieved to announce another PASS DIY F3 clone has entered the world.
After much angst and fussing and ultimately salvageable user error, an F3 using csample's amp boards and dual mono variant of the F1 PS has joined the fold. With LU1014Ds mounted direct to the boards, Aleph CCS bias of 21V, and a final R3, R4, R5 configuration of 2R7, 2R7 and 3R3, there is a relatively stable drop of ~2.1V between LU1014D drain and source (LH TP4 and TP3 of 3.46V and 1.36V; RH TP4 and TP3 of 3.49V and 1.37V). Under bench testing the LU's hit approximately 60degC. This may be on the hot side.
Bench listening tests on some rather unforgiving Klipsh bookshelf speakers suggested an amazing ability of this amp to clean up and render listenable some rather rough keyboard/synth heavy techno. Moving on to a finer system (Seas A26 with a passive preamp using Electra-Print 1:8 line level transformers) and music (Steely Dan's Aja, on an antique Sony CD player), revealed a richness and fullness of sound evident even over dinner in the next room. At least one listener felt like he was listening to some songs 'for the first time'. The bass may be a little less punchy than that from a pair of monoblock MoFos, but the detail, clarity, and evennness of volume across the frequency range more than makes up for it. On vinyl (Rega P3, Ortofon 2M Bronze cartridge, Rega Fono Mini A2D phono stage), the system now seems to push the limits of the recording medium, but overall the sense of hearing songs 'for the first time' persists (Jethro Tull's Stand Up, Crosby Stills & Nash (self titled), Pink Floyd's Dark Side of the Moon). A very interesting step up for this listener and his system.
Thank you to csample for these clone boards, to woofertester, wg46, and Mr. Pass for the LU1014D group buy, to this forum for tolerating and helping my troubleshooting efforts, and of course to Mr. Pass for such a wonderful amp design and such generous support of stumbling hobby enthusiasts like me. :3
After much angst and fussing and ultimately salvageable user error, an F3 using csample's amp boards and dual mono variant of the F1 PS has joined the fold. With LU1014Ds mounted direct to the boards, Aleph CCS bias of 21V, and a final R3, R4, R5 configuration of 2R7, 2R7 and 3R3, there is a relatively stable drop of ~2.1V between LU1014D drain and source (LH TP4 and TP3 of 3.46V and 1.36V; RH TP4 and TP3 of 3.49V and 1.37V). Under bench testing the LU's hit approximately 60degC. This may be on the hot side.
Bench listening tests on some rather unforgiving Klipsh bookshelf speakers suggested an amazing ability of this amp to clean up and render listenable some rather rough keyboard/synth heavy techno. Moving on to a finer system (Seas A26 with a passive preamp using Electra-Print 1:8 line level transformers) and music (Steely Dan's Aja, on an antique Sony CD player), revealed a richness and fullness of sound evident even over dinner in the next room. At least one listener felt like he was listening to some songs 'for the first time'. The bass may be a little less punchy than that from a pair of monoblock MoFos, but the detail, clarity, and evennness of volume across the frequency range more than makes up for it. On vinyl (Rega P3, Ortofon 2M Bronze cartridge, Rega Fono Mini A2D phono stage), the system now seems to push the limits of the recording medium, but overall the sense of hearing songs 'for the first time' persists (Jethro Tull's Stand Up, Crosby Stills & Nash (self titled), Pink Floyd's Dark Side of the Moon). A very interesting step up for this listener and his system.
Thank you to csample for these clone boards, to woofertester, wg46, and Mr. Pass for the LU1014D group buy, to this forum for tolerating and helping my troubleshooting efforts, and of course to Mr. Pass for such a wonderful amp design and such generous support of stumbling hobby enthusiasts like me. :3
It's funny you should mention that. When I was first testing the output, I was erroneously connecting speaker out to the opposite side of the cap boards, and all I got out of the amp was bias voltages cut in half and this noise like an out-of-tune AM radio. It took looking at pictures of other's successful builds here for me to realize that doing so meant I was connecting the speakers in parallel with the cap board, rather than in series as designed. One of the side photos above was taken while that error was still in effect.
Thanks for the congratulations, and congratulations to you as well, especially for your tiny bit higher operating point!
Ah, man. Unfortunately after my F3 warms up I get this sound like static in one channel. I tried swapping out the output caps and disconnecting the input, it's still there, and I can play music over it. The attached phone recording tracks first from woofer to tweeter. I'm going to doublecheck but I'm almost certain I don't get this on the other channel. Any ideas what might be causing this?
Google Docs link, hopefully this works: https://drive.google.com/file/d/1ISdqu6P3-YKY-a_4ZHxafsDGbNeh7YJD/view?usp=sharing
Google Docs link, hopefully this works: https://drive.google.com/file/d/1ISdqu6P3-YKY-a_4ZHxafsDGbNeh7YJD/view?usp=sharing
Poor LU. That's the second one I've killed then. I have such bad luck with these things.
ZM you were right, the LU was dying. I put his brother in & the amp is back to singing again. Was using my ACA in my main system in the interim and the F3 was sorely missed. It has sooooo much more presence and clarity. I really want this amp to keep working.
Nota bene: I honestly don't think these LU1014Ds can handle desoldering events. Whatever you put them on, be it the xrk mounting pcb, or direct mount to csample's F3 boards, it's one and done. At this point I've killed three, I'm so far successfully using two, and have a single spare.
Since your amp was working but the LU1014D were running hot (60°C per your post) I am wondering if the soldering killed it or if it was the heat during operation. As a reference the direct mounted LU's that I tested were running around 45°C using a solid copper heat bridge between the board and the heatsink. You may want to verify good contact between the heat bridge and the heat sink using a .001 inch feeler gauge to verify contact across the full face of the heat bridge and not just at a single point. A solid heat bridge with thermal transfer paste would also conduct more heat out. After I killed one LU with the surface mount soldering I mounted my final LU's using short wire leads and screwed/clamped them to the heat sink with a mica insulator. I think this approach is the best for heat transfer and is the least likely to damage the LU.
Attachments
Zen Mod - Thanks for sharing the document in post 1070. Would adjusting to get a 2.46Vds in operation be another way to get to the sweet spot for lowest distortion? Is adjusting the Aleph current source to achieve 13dB gain important for lowest distortion? Thanks!
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Yes. The heat bridge I've been using is a hollow brass bead, a 5mm cube, soldered to the vias on the back of the LU's drain pad, with a piece of keratherm between it and the heatsink. I knew it was a hack at the time but I couldn't source a solid cube, and I had trouble with the adapter boards as described below. With the amp playing music through my Seas A26's for a couple hours, I've been checking the LU temps relentlessly and it's been mid-50's or less, with an open chassis top, though just now I checked it and the LUs creeped above 60c, so now the amp is off.
I found these little glue-on/tape-on heatsinks for ICs, and ordered a few, and as soon as they get here I'll be taping them onto the top of the LU's, using a thermally conductive foil adhesive.
ICK SMD A 5 SA
WLFT 404 24.5 X 27.7
I was originally using the adapter boards with the first two LU1014Ds I got from the group buy. Unfortunately the pins that came with the adapter board are spaced too narrow and despite my best efforts at gently bending the pins to fit the TO-247AC mount holes on the board, they broke off the adapter PCBs, taking the traces with them. I couldn't get flying leads to solder in place as the pads were gone, and it's when I then tried to de-solder those LUs that I destroyed the first two. I think those adapter boards work fine as long as there's only one soldering event, and a flexible flying lead approach is used.
yup, seems 2V46 being magic number
setting gain of Aleph CCS - don't bother; as usual Pa made best overall choice
do it, only if you hope altering THD spectra to your specific needs