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A guide to building the Pass F4 amplifier.
A guide to building the Pass F4 amplifier.
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Old 17th September 2018, 04:39 PM   #1081
albertli is offline albertli  Canada
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My F4 has been on for 16 hrs since last night. The temperature seems very stable @50c on MOSFET, 52c on heatsink at 200mV. Offset is within range.
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Old 17th September 2018, 04:55 PM   #1082
adason is offline adason  United States
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I like your washers!
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Old 17th September 2018, 08:24 PM   #1083
albertli is offline albertli  Canada
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I like your washers!
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Old 17th September 2018, 08:27 PM   #1084
albertli is offline albertli  Canada
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Sound exactly the same with mine which made some 10 years ago. Lovely sound. 😄😄
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Old 17th September 2018, 08:44 PM   #1085
mrdave45 is offline mrdave45  United Kingdom
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That's great to know albertli. I built one a couple of years ago and am thinking about another and I was slightly concerned they wouldn't be adequately matched so that I would have to use them biamped. I have the impasse to drive them balanced so want to try that. Although Im not sure I really need 100w per side, Im not sure whether 100w balanced per side with short speaker cables or 25+25 per side with long speaker cables and biamped will be better.
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Old 17th September 2018, 10:31 PM   #1086
albertli is offline albertli  Canada
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Originally Posted by mrdave45 View Post
That's great to know albertli. I built one a couple of years ago and am thinking about another and I was slightly concerned they wouldn't be adequately matched so that I would have to use them biamped. I have the impasse to drive them balanced so want to try that. Although Im not sure I really need 100w per side, Im not sure whether 100w balanced per side with short speaker cables or 25+25 per side with long speaker cables and biamped will be better.
I build this one for friend. I finished mine some ten years ago. All my speakers are over 90db so I don't need anything bigger than this. I presume you like your impasse pre, do you have tried other preamp to drive your F4? I have been using the Convergent SL1 signature and the MFA . Both are good but I like the MFA better with more power to drive my F4.
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Old 17th September 2018, 11:26 PM   #1087
mrdave45 is offline mrdave45  United Kingdom
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Yeah, using the impasse. What's the mfa? My open baffles are about 94db and go thunderous with just one f4. I think that biamping would probably be the better solution over the extra power but loss of damping factor.
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Old 6th October 2018, 07:25 PM   #1088
Jeffs is offline Jeffs  United States
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A guide to building the Pass F4 amplifier.
Default Finished second F4, how to parallel?

First of all, thank you to everyone who has helped and tolerated my questions over the years.
I basically finished the second F4 last night.
Photo's of first vs second build attached.
The second one biased up just as it was supposed to.
Yes, one F4 in stereo provides a high enough sound level for almost any sane listening.
Without getting into politics, I don't exactly feel sane these days.
My preamp for the F4's is using 6SL7's in the gain stage, just measured the output and it is hovering around 31-32 volt range. That's a couple of volts higher than expected. This week I built a passive pre with a 50k attenuator but I bypassed it for the test.
Speakers are... well, the data sheets found around the web are not consistent. The earliest versions I found said 88dB and "4 ohm nominal". I've recently found another version of the data sheet which states "4 to 8 ohm". When listening I sit 3 meters in front of the speakers which are just under 1 meter from the wall and there are about 6 meters behind me before the rear wall. The room is not set up ideally by any stretch of the imagination.
If I may ask one, two part question: how do I wire the input and output to turn these into parallel monoblocks - and can I use jumper wire to connect input / outputs if required? I'm down to less than two feet of wire suitable for output, still have plenty for input. Easy to order more, but if not required all the better.
https://www.diyaudio.com/forums/atta...1&d=1538854004
https://www.diyaudio.com/forums/atta...1&d=1538854004
I haven't installed the RCA jacks on the second one, that's how it looks on my coffee table.
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Last edited by Jeffs; 6th October 2018 at 07:27 PM. Reason: pictures did not appear in post
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Old 6th October 2018, 07:38 PM   #1089
Zen Mod is online now Zen Mod  Serbia
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A guide to building the Pass F4 amplifier.
for out-box paralleling of inputs , you need just Y RCA cable , or - if you installed input XLR (pin 1 GND , pin 2 Rch input , pin 3 Lch input) just put shortie in 2 and 3 holes of XLR then route RCA cable to any RCA jack on amp

for output paralleling - just put shorts between two hots , no need to short neg. outputs , considering that you're using common PSU for both channels
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Old 13th October 2018, 10:00 PM   #1090
Jeffs is offline Jeffs  United States
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A guide to building the Pass F4 amplifier.
They sound great as expected. Noise floor is lower than using a stereo F4, but I've been doing a lot of cable organization which may have helped.
Is there a reason why I'm driving them to clipping easier now than when using a single stereo F4?
The most significant recent change being that before the preamp I have installed a passive preamp with a 50K attenuator. (because I added a phono stage which needed volume control, and switching cables got old when going between MacBook and TV source) I also went from very inexpensive, very short interconnect to a pair of 3 meter interconnects (still inexpensive, using Gotham GAC-4/1 cable datasheet ). Previously, speaker wire was 18 gauge cheap hardware store type and fairly long (~5 meter). Now using very short speaker cable with the amps almost up against the backs of the speakers. Have tried short 14 gauge, and short braided 15 gauge equivalent.
Both amps go into clipping at the same time.
They are biased at 0.2v when hot, and they aren't running very hot but will climb in temp if listening too loud (going to class AB?)
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