Simple question,
I had a F4 built as a dual mono, two 230VA (if I recall correct) transformers to feed the whole thing, got proof 25W not enough to feed my speakers and I am sure if I sell those to buy more sensitive ones I won't buy again anything this big in size (and $$$) thought I might have another F4 built and use them as mono blocks, what would it take to convert the already made one into it?
Grazie
I had a F4 built as a dual mono, two 230VA (if I recall correct) transformers to feed the whole thing, got proof 25W not enough to feed my speakers and I am sure if I sell those to buy more sensitive ones I won't buy again anything this big in size (and $$$) thought I might have another F4 built and use them as mono blocks, what would it take to convert the already made one into it?
Grazie
You could set them up in bridge mode I surpose. That would more than double the output power, if suitable.
A clue as to what an "F4" is may help you get an answer.
A clue as to what an "F4" is may help you get an answer.
https://www.diyaudio.com/community/threads/f4-power-amplifier.97540/
High power output stage using multiple parallel n and p pairs as source followers. Requires high gain preamp.
@Giovanni: It would be relevant to know what speakers you are driving...
See also this thread further down the page...
High power output stage using multiple parallel n and p pairs as source followers. Requires high gain preamp.
@Giovanni: It would be relevant to know what speakers you are driving...
See also this thread further down the page...
F-5T V2 and planars R3
@BeardyWan I have been following the F4 thread for quite a while before deciding to have one built, next there is a BA-3 based preamp to find out if with some 7-8 extra db gain over my Audio Research SP9 the F4 can better drive the 90dbW/m my JBL L220 sensitivity, so far they 25W out of the F4 can't make it, as much as I tried to like it right yesterday I switched back to the KT88 amp and you can tell there is way more juice but way more.
I know SS and Tube sound totally different and can tell after a few months with the F4 but it seems it just can't make it so the option is change speakers, change amp or build another one and use them as bridged so I can have 50W per channel.
Technically the question is should I build another F4 would I go again for dual mono to have them exactly the same or is that a waste (two transformers etc)? Also, to make of the existing one a bridged one what does it take?
Grazie
I know SS and Tube sound totally different and can tell after a few months with the F4 but it seems it just can't make it so the option is change speakers, change amp or build another one and use them as bridged so I can have 50W per channel.
Technically the question is should I build another F4 would I go again for dual mono to have them exactly the same or is that a waste (two transformers etc)? Also, to make of the existing one a bridged one what does it take?
Grazie
Giovanni,
The F4 manual describes the mono parallel (for more current) and mono balanced (for more voltage swing) operations. See page 7 and on:
https://firstwatt.com/pdf/prod_f4_man.pdf
You'll need a balanced output from theamp for the latter operation.
I think you need to first identify what is lacking with your DAC+SP9+F4. If the F4's +/-20V swing is not enough for you then building a higher gain preamp won't solve the problem. I suggest again that you do this test with your tube amp: https://www.diyaudio.com/community/...h-voltage-power-do-your-speakers-need.204857/ . This will let you know how much voltage swing you need and help you decide how to proceed.
Has your F4 been repaired? Please ask your friend to verify the bias current since at one point you had described it as cool running.
The F4 manual describes the mono parallel (for more current) and mono balanced (for more voltage swing) operations. See page 7 and on:
https://firstwatt.com/pdf/prod_f4_man.pdf
You'll need a balanced output from theamp for the latter operation.
I think you need to first identify what is lacking with your DAC+SP9+F4. If the F4's +/-20V swing is not enough for you then building a higher gain preamp won't solve the problem. I suggest again that you do this test with your tube amp: https://www.diyaudio.com/community/...h-voltage-power-do-your-speakers-need.204857/ . This will let you know how much voltage swing you need and help you decide how to proceed.
Has your F4 been repaired? Please ask your friend to verify the bias current since at one point you had described it as cool running.
I'm a little surprised that the BA-3 / F4 falls short for you. Lot of work and more $$, but a second amp for dual mono would give you 100W into 8 ohms (by running balanced / bridged). NP shows how to convert the BA-3 gain stage into a balanced version at this link. A possibilty if you like the sound otherwise, but truly just need more power.
BA-3B
This can be used with an SE input where you just ground the other input. But a balanced input would be preferred, if possible.
BA-3B
This can be used with an SE input where you just ground the other input. But a balanced input would be preferred, if possible.
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BA3B is an excellent idea; that will run things balanced and should give all the voltage swing needed. I think Giovanni should still do the voltage test to confirm what he needs for voltage swing.
I will give that thread you suggested a look @Dennis Hui in the hope I can perform the test with my tube amp and find out how much voltage it takes to run the big and old JBLs, hopefully a multimeter will be all it takes...
I had the F4 repaired, my tech made a soft start to slowly charge the caps then a relais to open the circuit (sorry I dunno how to explain), he also added coolers on the diodes which were running warm, I don't think he checked the bias but will ask him next time (I don't remember how this is performed) but the amp never got any warm, not even after hours being turned on, I could keep the hands onto it for the whole time
If the amplifier never gets warm, bias is not set properly. Amplifier heatsinks should be 30-40C
Also, what preamp are you using to drive F4? The F4 amplifier has zero voltage gain, and unless you have a high gain preamp, you will get only small power from it.
EDIT: I see you have an Audio Research SP9. It has 20db gain on the linestage, which is a voltage gain of 10.
Assuming you have a source that outputs 1Vrms average for typical music, this means the SP9 will output 10Vrms to the F4.
10Vrms input to F4 will output 10Vrms to the speakers.
Power is V^2/load
Assuming 8ohm speakers,
10^2 = 100
100/8= 12.5w
If your volume knob is all the way up, you are getting approximately 12W to your speakers. (With some higher peaks depending on your source.
Also, what preamp are you using to drive F4? The F4 amplifier has zero voltage gain, and unless you have a high gain preamp, you will get only small power from it.
EDIT: I see you have an Audio Research SP9. It has 20db gain on the linestage, which is a voltage gain of 10.
Assuming you have a source that outputs 1Vrms average for typical music, this means the SP9 will output 10Vrms to the F4.
10Vrms input to F4 will output 10Vrms to the speakers.
Power is V^2/load
Assuming 8ohm speakers,
10^2 = 100
100/8= 12.5w
If your volume knob is all the way up, you are getting approximately 12W to your speakers. (With some higher peaks depending on your source.
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Trick question:
is that something in 'Talian water, so Greedy Boyz living in area to which all roads are leading, are so amused to post ooomphteen threads related to F4?
this one is at least 3rd one from Giovanni1968, practically being about exact same issues - what to do with F4 and how much oomph it needs for that and is it possible with puny AR SPwhatever
is that something in 'Talian water, so Greedy Boyz living in area to which all roads are leading, are so amused to post ooomphteen threads related to F4?
this one is at least 3rd one from Giovanni1968, practically being about exact same issues - what to do with F4 and how much oomph it needs for that and is it possible with puny AR SPwhatever
Unfortunately I think the whole process was messed from start, I should have probably gone for a higher output amp given my speakers, reading here and there and following members advise I went for the F4 also because, as far as I recall, a sound which won't make me miss tubes with the benefits of low distortion bla bla bla
Second mistake was to have a person far from my to build it and as such couldn't follow the process.
Now the BA-3 is gonna be built locally and it is an advantage, fingers crossed.
I am sorry I am ripping space off the forums @Zen Mod but I won't know who to ask neither I want to contaminate the F4 thread with my doubts.
@6L6 I will make a test to check the preamp output, I did it already and I think I did report the results, will do it again along with the other test suggested by @Dennis Hui I will also look at how to check the bias of the F4 as even tho the temperature here has been like North Pole it was nowhere near 40C
Grazie
Second mistake was to have a person far from my to build it and as such couldn't follow the process.
Now the BA-3 is gonna be built locally and it is an advantage, fingers crossed.
I am sorry I am ripping space off the forums @Zen Mod but I won't know who to ask neither I want to contaminate the F4 thread with my doubts.
@6L6 I will make a test to check the preamp output, I did it already and I think I did report the results, will do it again along with the other test suggested by @Dennis Hui I will also look at how to check the bias of the F4 as even tho the temperature here has been like North Pole it was nowhere near 40C
Grazie
there is no problem with Forum space you're filling ..... (space is cheap and web is fast, nowadays)
problem is that Old Geezers as I am, can't fathom is it just Deja Vu, or you're asking same questions, again?
If thinking of final outcome, it could be much clever keeping things in one thread (you already started, not someone else), solving detail by detail
I mean, I can't help when I'm lost
If you're asking new questions, fine with me
If you're asking same questions again, again fine with me - I lost track what was replied and what not (even if I have faint feeling that you already got thorough details how to and when)
problem is that Old Geezers as I am, can't fathom is it just Deja Vu, or you're asking same questions, again?
If thinking of final outcome, it could be much clever keeping things in one thread (you already started, not someone else), solving detail by detail
I mean, I can't help when I'm lost
If you're asking new questions, fine with me
If you're asking same questions again, again fine with me - I lost track what was replied and what not (even if I have faint feeling that you already got thorough details how to and when)
Never mind, thanks for your support, I will find out how to check the bias and how to eventually turn it into a parallel mono just in case I go that route.
keep questions in one thread, and you'll get replies
work on replies you got, and guys spending time to give them will not have impression of their time being wasted
that's not just necessary netiquette, it's also confirmed as most effective strategy
bunch of necessary knowledge is already on F4 origin page
https://www.firstwatt.com/f4.html
https://www.firstwatt.com/pdf/prod_f4_man.pdf
work on replies you got, and guys spending time to give them will not have impression of their time being wasted
that's not just necessary netiquette, it's also confirmed as most effective strategy
bunch of necessary knowledge is already on F4 origin page
https://www.firstwatt.com/f4.html
https://www.firstwatt.com/pdf/prod_f4_man.pdf
Giovanni, I’m a little surprised that you’re finding the 25w/channel is not enough (assuming that the bias and actual 25w per channel is being output) for your L220’s. I’m currently running my L150’s (88db sensitivity) with my Aleph J in a room 14’Wx22’Lx8’H and it is plenty loud for me. I’ve also powered them with an M2 and was again impressed with how they handled the 150’s.
Ciao @JSA1971 I don't know what's wrong with mine, my suspect is the bias is not correct as I mentioned above the brick never gets any warm, true that the room is colder than outside (...) but still my guess is it doesn't even reach 40C with an ambient temp of 27-28C and even back then end of summer when here gets really warm it never gets to any uncomfortable degree of heat when touching it.
I will review the constructions notes to find out how to measure the bias and if that can be done with one multimeter I will try and check it just for the sake of it, maybe adjusting would bring more juice to the speakers.
Grazie
Hello Giovanni,
you can measure this yourself with a normal DMM (digital multi meter). Set your DMM to V.
Put the red probe of DMM to one leg of a bias resistor and the black probe to the other end / leg of this bias resistor.
Now measure the voltage - you should get a value of circa 0,2 V (=200mV) over one of the bias resistors.
Work slowly and careful! Be careful that no probe of the DMM is slipping uncontrolled into the amp switched on!
Don't touch the transformer and the AC-input during this 'operation'.
Cheers
Dirk
you can measure this yourself with a normal DMM (digital multi meter). Set your DMM to V.
Put the red probe of DMM to one leg of a bias resistor and the black probe to the other end / leg of this bias resistor.
Now measure the voltage - you should get a value of circa 0,2 V (=200mV) over one of the bias resistors.
Work slowly and careful! Be careful that no probe of the DMM is slipping uncontrolled into the amp switched on!
Don't touch the transformer and the AC-input during this 'operation'.
Cheers
Dirk
Attachments
You can measure over bias resistors R16 / R17 7 R18 - write down the voltages and post them here.
Also measure over the bias resitors R19 / R20 / R21 - write them down and post here.
Then we can see / calculate, if your F4 is biased correctly.
DC-offset is measured at the speakeroutput (without any speaker connected!). Red probe DMM to + speaker out,
black probe of DMM to - speaker out. Measure in Volts (or mV).
Cheers
Dirk
Also measure over the bias resitors R19 / R20 / R21 - write them down and post here.
Then we can see / calculate, if your F4 is biased correctly.
DC-offset is measured at the speakeroutput (without any speaker connected!). Red probe DMM to + speaker out,
black probe of DMM to - speaker out. Measure in Volts (or mV).
Cheers
Dirk
Grazie @cubicincher so I just power it up, let it warm for an hour or so, no input signal, no load on the output and take the measurements, is that correct?
I will have to find out the resistors on the boards (they kept telling me for ages "ohhh, yeah, you'll see, all of a sudden your sight will drop..." it did happen even tho way later than they all predicted but, damn, viewing glasses!) and check it all out, maybe tomorrow while I bake the lasagna I assembled today, you know, here in the Vesuvio bay Sunday is mangia mangia day ;-)
Grazie ancora
edit: bottom of this the procedure seems pretty straightforward even for a nerd like me
I will have to find out the resistors on the boards (they kept telling me for ages "ohhh, yeah, you'll see, all of a sudden your sight will drop..." it did happen even tho way later than they all predicted but, damn, viewing glasses!) and check it all out, maybe tomorrow while I bake the lasagna I assembled today, you know, here in the Vesuvio bay Sunday is mangia mangia day ;-)
Grazie ancora
edit: bottom of this the procedure seems pretty straightforward even for a nerd like me
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