Hi!
I'm (very slowly) building a pair of crippled bridged F4:s to act as a output stage for my (balanced) iron pumpkin. I'm now at the stage where I need to make a PSU (I have tested them to work with a +/- 28V psu, but this leaves little thermal headroom to crank the bias), and I would like to ask what the lowest reasonable rail voltage for bridged F4 is.
I have efficient speakers, and 4 V RMS is loud enough. A bridged F4 is really silly for me, but this is what I am building=)
I'm (very slowly) building a pair of crippled bridged F4:s to act as a output stage for my (balanced) iron pumpkin. I'm now at the stage where I need to make a PSU (I have tested them to work with a +/- 28V psu, but this leaves little thermal headroom to crank the bias), and I would like to ask what the lowest reasonable rail voltage for bridged F4 is.
I have efficient speakers, and 4 V RMS is loud enough. A bridged F4 is really silly for me, but this is what I am building=)
Note that bridging doubles both power and distortion. (Unfortunately I can't help with your question about reasonable rail voltages.)
Bridging 'doubles' output Voltage which in the case of the F4 quadruples max rated output power into 8R. 25W => 100W give or take.
In the case of the F4, sure, theoretically HD can double when run bridged. However, I would not necessarily be too concerned. In a balanced configuration, as in torb's use case, I think most H2 cancels, so ... in practicality... I'm not so sure how it would all pan out with regard to distortion numbers. As always, I may have it incorrect. Valid concern... maybe, but nothing that would stop ME from trying it, and I have.
Lowest reasonable... ??? I think I've seen some posts from trusted people say perhaps 18-20Vdc has produced acceptable results. However, why not try the 'factory' 24V first? If you're running the 'factory' Iq now at 28V, and your goal is to crank it and/or have a bit of headroom for hot days... that might get you there.
Would love to see them!
With 28 V, it gets uncomfortably warm somewhere above 200 mA bias.
Transformers are expensive for me, so I would like to go for a reasonable low voltage from the start.
Sure🙂
Attachments
Use a cap MX with MOSFETs as the pass elements. That will drop 4 volts so you are down to 24 VDC.
Or build the cap MX with zeners and that can eat even more volts.
Or build the cap MX with zeners and that can eat even more volts.
A cap multiplier is a good idea, but my 28V psu is for the diy vfet part 2, which i love and want to keep operational.
Also, that psu is not quite up to the load of two channels of this.
Thus my need to build a new one (like dual mono 600va or something, toroidy goes much more expensive at 800va).
Also, that psu is not quite up to the load of two channels of this.
Thus my need to build a new one (like dual mono 600va or something, toroidy goes much more expensive at 800va).
Attachments
Makes perfect sense. I'm sure you know this, but the dissipation drops with the square of the voltage, so you may not have to go too far... If you drop 4V on the rails, that gives you 'quite a bit' of room to play with Iq, IMO. As @Stanislav suggested above, maybe you can experiment by dropping a few volts prior to making a commitment.
Is there anything I'm missing that prevents you from dropping the voltage on the bench PSU in the photo to test how you like the particular sound / measurements of lower voltage / higher Iq?
That is a fantastic design! Beautifully done.
I made the incorrect assumption that there would two separate chassis. Even with the relatively large heatsinks, I can imagine that those do get warm at your existing settings. Thanks for posting the photo.Thanks! I was going for the same general shape as the yamaha vfet monoblocks. There are two cases, I tried to post more pictures, without covers, but fail for some reason.
I did not know that dissipation drops with the square of the voltage, I thought it was somehow first degree linear, sweet and thanks!
And of course, you are correct in that I can just test it with the bench PSU. Stupid me again =)
I did not know that dissipation drops with the square of the voltage, I thought it was somehow first degree linear, sweet and thanks!
And of course, you are correct in that I can just test it with the bench PSU. Stupid me again =)
Power dissipation is usually the power that is physically dissipated by the amplifier at rest. In a Class A amplifier, that amounts to the power supply voltage times the idle current, with most of it dissipated by the heat sinks.
Power output is the power outputted to the speakers. That is determined by the output voltage (AC) times the output current. The output current is determined by the output voltage divided by the speaker impedance, giving:
Pout = Vrms x A = Vrms x (Vrms/R) = (Vrms)(Vrms)/R
Note that power supply current capacity is also a factor in maximum amplifier power output.
Power output is the power outputted to the speakers. That is determined by the output voltage (AC) times the output current. The output current is determined by the output voltage divided by the speaker impedance, giving:
Pout = Vrms x A = Vrms x (Vrms/R) = (Vrms)(Vrms)/R
Note that power supply current capacity is also a factor in maximum amplifier power output.
Currently in the background there are two bridged F4s driven by a very cool FE and an Iron Pre Pro. Into the little AN speakers.
Amazing sound...
It took almost four years to get here... and yes, the A5s are next to the F4s. They are hooked up SE into a pair of 1.7 Maggies.
If only the Iron Pre Balanced had TWO sets of balanced outputs.
Anyhow, the sound, even from here, my home office, is awesome. The bass is very powerful. I'm not sure if it's a bass bump or something else, but I noticed this when I first hooked up the system to the sacrificial El Cheapo Elacs: lots more deep end response.
Listening to Kiss Unplugged right now... and I really can CRANK it if I want... this set up really outshines the CJ preamp with a single F4...
Amazing sound...
It took almost four years to get here... and yes, the A5s are next to the F4s. They are hooked up SE into a pair of 1.7 Maggies.
If only the Iron Pre Balanced had TWO sets of balanced outputs.
Anyhow, the sound, even from here, my home office, is awesome. The bass is very powerful. I'm not sure if it's a bass bump or something else, but I noticed this when I first hooked up the system to the sacrificial El Cheapo Elacs: lots more deep end response.
Listening to Kiss Unplugged right now... and I really can CRANK it if I want... this set up really outshines the CJ preamp with a single F4...
If you wanted two sets of balanced outputs.... why didn't you build it with two sets???
Because I didn't think of it.
I thought I was going to finally simplify my audio life. ( Hint.. FAT chance ).
I made the mistake of trusting ZM... if he only thinks we need a single balanced output... Used the nice boxes that Gianluca provided ( nice boxes BTW ).
But, have no fear... I have TWO Iron Pre Bal... maybe I just need a Y connector of sorts. It does a great job of taking a SE input and outputting a balanced signal.
Oh wow... YES! I could drive the A5 and F4s all balanced with two preamps in the chain...
The caboose can be a fun place to be... while the locomotive goes off the rail, hopefully you stay on the track.
I thought I was going to finally simplify my audio life. ( Hint.. FAT chance ).
I made the mistake of trusting ZM... if he only thinks we need a single balanced output... Used the nice boxes that Gianluca provided ( nice boxes BTW ).
But, have no fear... I have TWO Iron Pre Bal... maybe I just need a Y connector of sorts. It does a great job of taking a SE input and outputting a balanced signal.
Oh wow... YES! I could drive the A5 and F4s all balanced with two preamps in the chain...
The caboose can be a fun place to be... while the locomotive goes off the rail, hopefully you stay on the track.
OK... so I guess I don't know where to post this... because it's all a combination of factors.
Right now I got Synchronicity by The Police playing... and it's incredible.
Now, I'm 65, had my first "stereo" when I was 14. So, I've been at this rodeo quite a few times...
wait... gotta go listen...
songs went by.
So Lonely....
The only things that are static from before is the AN speakers (little ones) and the Burson Swing DAC (V7 classic opamps) with Chromebook driving Tidal.
The sound is different from before. The bass is extended, punchy, fast, but not dry nor "wet".. It just is. The top end is extended, not closed in but not "tizzy"... just is, and the midrange is there. Voices are layered, the drum kit is natural sounding, the bass lines are clear, just like a bass guitar through a stack in the garage sound. The sound is simply there, noise level is subterranean.. notes are fast... as HP over at TAS, "I can hear the darkness between the notes"... There is no "note smearing"... none.
Sure, I must say I miss a bit of the "richness" of the CJ ET3SE, which is gorgeous sound, but this is now accurate sound.
I feel like I can really hear the Iron Pre (or rather not hear it)... and the F4s have been unleased to unheard of power... I still have to try this on the Maggies. Right now I'm just digging this, A LOT....
It's so FUN.
Might have to start selling stuff I may just not need after all?
??
( NOTE: Rozanne is putting out the red light )...
Naw..... just joking....
But folks, this sounds really good. The bridged F4s with the BA3 and the Iron Pre (Bal) are one heck of a proposition.
Should I try the Harbeths now?
Right now I got Synchronicity by The Police playing... and it's incredible.
Now, I'm 65, had my first "stereo" when I was 14. So, I've been at this rodeo quite a few times...
wait... gotta go listen...
songs went by.
So Lonely....
The only things that are static from before is the AN speakers (little ones) and the Burson Swing DAC (V7 classic opamps) with Chromebook driving Tidal.
The sound is different from before. The bass is extended, punchy, fast, but not dry nor "wet".. It just is. The top end is extended, not closed in but not "tizzy"... just is, and the midrange is there. Voices are layered, the drum kit is natural sounding, the bass lines are clear, just like a bass guitar through a stack in the garage sound. The sound is simply there, noise level is subterranean.. notes are fast... as HP over at TAS, "I can hear the darkness between the notes"... There is no "note smearing"... none.
Sure, I must say I miss a bit of the "richness" of the CJ ET3SE, which is gorgeous sound, but this is now accurate sound.
I feel like I can really hear the Iron Pre (or rather not hear it)... and the F4s have been unleased to unheard of power... I still have to try this on the Maggies. Right now I'm just digging this, A LOT....
It's so FUN.
Might have to start selling stuff I may just not need after all?
??
( NOTE: Rozanne is putting out the red light )...
Naw..... just joking....
But folks, this sounds really good. The bridged F4s with the BA3 and the Iron Pre (Bal) are one heck of a proposition.
Should I try the Harbeths now?
What resistor is needed to put a TU-8900 (from VK with Lundhall AM transformers / TCu Vcap) speaker out to input of F4? Looking for ohm value and type, if there is an recommended choice what would be a good example?
Speakers are 4 ohm, but I also have 8 ohm speakers, and 6 ohm.
I would be using the 4-6.3 ohm winding of the output transformer for 4 ohm and 8 ohm for 8 ohm. Have been using RCA 2A3, and when I possible, would like to try WE 300b.
Any other tips on cable are appreciated. I keep the F4 monoblocks next to the speakers with a 3 meter run of interconnect from the preamp.
Speakers are 4 ohm, but I also have 8 ohm speakers, and 6 ohm.
I would be using the 4-6.3 ohm winding of the output transformer for 4 ohm and 8 ohm for 8 ohm. Have been using RCA 2A3, and when I possible, would like to try WE 300b.
Any other tips on cable are appreciated. I keep the F4 monoblocks next to the speakers with a 3 meter run of interconnect from the preamp.
copied from another user with a similar setup:
"Mills 15 ohm 12 watt non-inductive resistors" across binding posts for "Elekits taps to 8-16 ohms", but not knowing what speakers he is driving.
another user : "12R, 15R, 20R, 22R, all Mills 5 watt resisitors" who thought 20R and 22R sounded best.
The main concern is I don't want to stress the TU-8900. It's sounded wonderful this summer as parts broke in, while living in a condo where loud volume was rarely permitted. Now back home I would like to put it in front of the F4's for more muscle.
The two non-inductive resistors that I can purchase through Mouser are:
Vishay:
NS00522R00FE12 : 22R 5W
MRA-1215R00FE12 : 15R 12W
"Mills 15 ohm 12 watt non-inductive resistors" across binding posts for "Elekits taps to 8-16 ohms", but not knowing what speakers he is driving.
another user : "12R, 15R, 20R, 22R, all Mills 5 watt resisitors" who thought 20R and 22R sounded best.
The main concern is I don't want to stress the TU-8900. It's sounded wonderful this summer as parts broke in, while living in a condo where loud volume was rarely permitted. Now back home I would like to put it in front of the F4's for more muscle.
The two non-inductive resistors that I can purchase through Mouser are:
Vishay:
NS00522R00FE12 : 22R 5W
MRA-1215R00FE12 : 15R 12W
Last edited: