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.
Regards
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/attachment.php?attachmentid=707877&stc=1&d=1538854004
https://www.diyaudio.com/forums/attachment.php?attachmentid=707878&stc=1&d=1538854004
I haven't installed the RCA jacks on the second one, that's how it looks on my coffee table.
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/attachment.php?attachmentid=707877&stc=1&d=1538854004
https://www.diyaudio.com/forums/attachment.php?attachmentid=707878&stc=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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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
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
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?)
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?)
probably lesser THD prior to clipping point is less disturbing
NB that (voltage) clipping point is the same in normal and parallel mode ; benefit is exactly in first sentence
so, clipping is on same level , you are just more surprised
IDss = Inter Dimensional shape shifter, but I do know the difference between a resistor and a capacitor.
Now my electronics pedigree is established.
I will claim to be to be an adequate assembler as I recently completed a pair of ACA's that worked perfectly straight off the bench.
Therefore, with enough guidance, there is hope of success for me from other diyaudio firstwatt amp projects.
Considering the next step up from the ACA's. To that end I'm compiling a BOM for an F4. Let the newb questions begin!
1. Are the Matched pairs LSJ74/LSK170 available from the store direct replacements for the 2SJ74/2SK170 input pairs on the F-4 schematic?
2. Store F4/BA-3 Trans Kit states that MOSFETS are matched at 22Vdc rail voltages. Store V3 Power Supply with 18-0-18Vac tranny delivers 24Vdc to the rails, correct?.
Any problem here that requires steps be taken to provide 22Vdc to the rails?
3. Having trouble gleaning from F4 thread and various other web sources how to ascertain the amount of gain in db is needed from a pre amp to properly drive the F4 from a standard 2v source voltage (DAC).
Reference to appropriate source materials, or known parameters specific to the F4 would be appreciated.
Calling that good for now, but surely there will be more to come.
Thanks in advance for your attention and assistance to come; Y'all seem to be really great at patiently helping folks along.
Now my electronics pedigree is established.
I will claim to be to be an adequate assembler as I recently completed a pair of ACA's that worked perfectly straight off the bench.
Therefore, with enough guidance, there is hope of success for me from other diyaudio firstwatt amp projects.
Considering the next step up from the ACA's. To that end I'm compiling a BOM for an F4. Let the newb questions begin!
1. Are the Matched pairs LSJ74/LSK170 available from the store direct replacements for the 2SJ74/2SK170 input pairs on the F-4 schematic?
2. Store F4/BA-3 Trans Kit states that MOSFETS are matched at 22Vdc rail voltages. Store V3 Power Supply with 18-0-18Vac tranny delivers 24Vdc to the rails, correct?.
Any problem here that requires steps be taken to provide 22Vdc to the rails?
3. Having trouble gleaning from F4 thread and various other web sources how to ascertain the amount of gain in db is needed from a pre amp to properly drive the F4 from a standard 2v source voltage (DAC).
Reference to appropriate source materials, or known parameters specific to the F4 would be appreciated.
Calling that good for now, but surely there will be more to come.
Thanks in advance for your attention and assistance to come; Y'all seem to be really great at patiently helping folks along.
1) Yes.
2) Store transistors will work great. 0-18/0-18 v transformer makes about 22v rails under load.
3) Build an Aikido linestage from Tubecad. Can be configured for as much gain as needed, which in your case is about 17db or a voltage gain of 7ish
(You want to take 2v rms, which is 5.6v pk-pk, into about 40V pk-pk, so 5.6*7 = 39.2, which is close enough)
2) Store transistors will work great. 0-18/0-18 v transformer makes about 22v rails under load.
3) Build an Aikido linestage from Tubecad. Can be configured for as much gain as needed, which in your case is about 17db or a voltage gain of 7ish
(You want to take 2v rms, which is 5.6v pk-pk, into about 40V pk-pk, so 5.6*7 = 39.2, which is close enough)
You'll still need a resistor across the Flea Amp's transformer, so it has a load to look at, but aside that, yes.
Start with a 20ohm 3W across the biggest (most ohms) secondary.
Big currents will flow only if needed. (...well, "big" for a Flea amp, but you know what I mean.) It's about the voltage swing from the transformer coupled triode into the F4. That you are attaching a "power amp" into another "power amp" doesn't actually mean anything in this case.
Start with a 20ohm 3W across the biggest (most ohms) secondary.
Big currents will flow only if needed. (...well, "big" for a Flea amp, but you know what I mean.) It's about the voltage swing from the transformer coupled triode into the F4. That you are attaching a "power amp" into another "power amp" doesn't actually mean anything in this case.
Still need a loading resistor across the outputs?
Roger that.
TPA 3110's are supposed to sound very nice, but only 3 w/ch into 8ohms, so not widely used as power amps.
Exploring options for my step up from the ACA build.
Aleph J was 1rst choice, but input JFET's too much hassle to get lined up.
F4 - Transistors needed are at the diy store, but I've got a 0 gain pre amp.
Not sure if I'm ready to build a pre amp (Aikido) just yet.
Using a low power integrated amp as pre seen in this thread and Papa's F4 manual has me thinking along that line.
With a TPA3110 driving the F4 you'll get about 9 watts out of the F4, assuming the TPA has a 24v supply. So it will work, but it's really not ideal. And your F4 will sound like a $2 class-D chipamp, since the F4 takes on what sonic characteristics it's preamp has.
If you use a 12v supply, which seems the recommended value for typical TPA3110 designs, you'll get 2.5W from the F4. The F4 needs voltage swing on it's input, not power.
Of course you could build a 24v Whammy, that would drive the F4 to full and you'll have a wonderful headphone amp as well.
Aleph J is easy - wait until Punkydawgs is back, (after Thanksgiving) buy the J74 pairs, and build an Aleph J. It's an incredible amp. No hassle.
I really like the F4, as it's totally and completely neutral. The hitch is you basically need a dedicated preamp to run it. But the community has provided over the years - Impasse, XRK audio ASKA Lender preamp, BA-3 preamp, Aikido, Zen Mod's 'Pumpkin', and lots of 70's-90's commercial preamps have tons of gain and output voltage as well.
Welcome to DIY. This rabbit hole doesn't end, and there's lots and lots of amazing stuff here.
If you use a 12v supply, which seems the recommended value for typical TPA3110 designs, you'll get 2.5W from the F4. The F4 needs voltage swing on it's input, not power.
Of course you could build a 24v Whammy, that would drive the F4 to full and you'll have a wonderful headphone amp as well.
Aleph J is easy - wait until Punkydawgs is back, (after Thanksgiving) buy the J74 pairs, and build an Aleph J. It's an incredible amp. No hassle.
I really like the F4, as it's totally and completely neutral. The hitch is you basically need a dedicated preamp to run it. But the community has provided over the years - Impasse, XRK audio ASKA Lender preamp, BA-3 preamp, Aikido, Zen Mod's 'Pumpkin', and lots of 70's-90's commercial preamps have tons of gain and output voltage as well.
Welcome to DIY. This rabbit hole doesn't end, and there's lots and lots of amazing stuff here.