Thanks ZM! And is it OK also to not use 0.47 Ohm source resistors for a single pair of these Exicon lateral Mosfets, given their thermal stability vs. vertical ones?
That is a great learning, thanks ZM!
Just to confirm, that is the Iq/quiescent current right?
I was actually aiming for the usual 1.3 Amps over 24 V rails for a toasty ~30W heat dissipation per Mosfet. It is pretty cold here in the UK, that would do nicely.
Thanks Dennis, good call out!
Indeed, since I will use a normal CRC power supply, probably easiest for me to check the Iq from the "R" of the CRC during the biasing.
I did the calculations, ended up deciding that I will not need a front end/gain stage etc.
For broader context, I will build balanced monoblock F4's and drive them from a balanced source swinging 6 Vrms.
So 6x6/8 = ~5W for 8 Ohm load should be fine.
Thanks ZM!
For now, I am very much tempted to have the sound of that 2nd Harmonic cancellation through balanced operation.
Long time ago, when I tried that with ACA (moving from single ended to balanced mono), that was a pretty nice improvement.
Given ACA has a 2nd harmonic dominant distortion similar to F4, I think I will like that balanced setup. Will see..
For now, I am very much tempted to have the sound of that 2nd Harmonic cancellation through balanced operation.
Long time ago, when I tried that with ACA (moving from single ended to balanced mono), that was a pretty nice improvement.
Given ACA has a 2nd harmonic dominant distortion similar to F4, I think I will like that balanced setup. Will see..
Hello Friends!
The F4 channels are up and running MAGIC.
I only listened for 20 minutes, but wow this sound is completely naked. No filter over the sound, just complete see thru. Never thought this kind of sound was possible. I am amazed.
Some questions raised during the bias process. I was only able to bias to 0.06V max, so the F4 build guide advised to change R9 to 5K. However, I already reached my personal volume limit when the the preamp was at 0-dB. There is even a possibility to increase the gain of the preamp by +3db, +6db and +12db, but this will let my ears bleed probably.
1. Is it really needed (sound quality wise) to get up to 0.13V when cold or 0.2V when hot?
2. I have seen that distortion figures are better at 0.13V / 0.2V, but is there a downside as well compared to my 0.06V?
Please let me know your thoughts about increasing the biasing to 0.13V/0.2V or just leave it as it is at 0.06V
Thanks for your advise!
Koos
The F4 channels are up and running
MAGIC.I only listened for 20 minutes, but wow this sound is completely naked. No filter over the sound, just complete see thru. Never thought this kind of sound was possible. I am amazed.
Some questions raised during the bias process. I was only able to bias to 0.06V max, so the F4 build guide advised to change R9 to 5K. However, I already reached my personal volume limit when the the preamp was at 0-dB. There is even a possibility to increase the gain of the preamp by +3db, +6db and +12db, but this will let my ears bleed probably.
1. Is it really needed (sound quality wise) to get up to 0.13V when cold or 0.2V when hot?
2. I have seen that distortion figures are better at 0.13V / 0.2V, but is there a downside as well compared to my 0.06V?
Please let me know your thoughts about increasing the biasing to 0.13V/0.2V or just leave it as it is at 0.06V
Thanks for your advise!
Koos
Yes,it’s magic.
Surely you have seen the F4 build guide.
Se the four rules on the page.
Distortion figures vary with bias so it would sound even better with more bias with “sweet spot was closer to 300mV bias”
I have 0.27V bias with 5u-300 heat sinks.
You must have fantastic speakers to drive them with no gain? I have tried it but preferred to change pre to +6db.
Good luck tweaking.
Surely you have seen the F4 build guide.
Se the four rules on the page.
Distortion figures vary with bias so it would sound even better with more bias with “sweet spot was closer to 300mV bias”
I have 0.27V bias with 5u-300 heat sinks.
You must have fantastic speakers to drive them with no gain? I have tried it but preferred to change pre to +6db.
Good luck tweaking.
Enjoy the F4's, it's a pretty nice beast.Hello Friends!
The F4 channels are up and running
I only listened for 20 minutes, but wow this sound is completely naked. No filter over the sound, just complete see thru. Never thought this kind of sound was possible. I am amazed.
Some questions raised during the bias process. I was only able to bias to 0.06V max, so the F4 build guide advised to change R9 to 5K. However, I already reached my personal volume limit when the the preamp was at 0-dB. There is even a possibility to increase the gain of the preamp by +3db, +6db and +12db, but this will let my ears bleed probably.
1. Is it really needed (sound quality wise) to get up to 0.13V when cold or 0.2V when hot?
2. I have seen that distortion figures are better at 0.13V / 0.2V, but is there a downside as well compared to my 0.06V?
Please let me know your thoughts about increasing the biasing to 0.13V/0.2V or just leave it as it is at 0.06V
Thanks for your advise!
Koos
Which preamp are you using for driving F4 as it's a crucial piece of kit in that case?
Koos,
Increasing the bias will not have an effect on the volume you are getting. What it does, however, is increase your class A envelope.
Your current bias of 0.06V across the 0.47 ohm source resistors give you about 2.3W (RMS) class A into 8 ohms.
The standard bias of 0.2V across the 0.47 ohm resistors give you about 25W RMS class A into 8 ohms
In addition, increasing the bias lowers the distortion and changes the distortion profile. You can see these effects in Papa's article:
https://firstwatt.com/pdf/art_leaving_class_a_2019_redux.pdf
I don't know what output level you are currently using out of the amp, but I do suspect its distortion is somewhat higher than if it were at the standard bias level.
So disadvantage of higher bias? Heat. Right now you are running at less than 1/3 the dissipation of the standard bias.
I personally would make the change to allow for higher bias. If nothing else, you can then compare to see if you actually prefer one bias level over the other.
Cheers,
Dennis
Increasing the bias will not have an effect on the volume you are getting. What it does, however, is increase your class A envelope.
Your current bias of 0.06V across the 0.47 ohm source resistors give you about 2.3W (RMS) class A into 8 ohms.
The standard bias of 0.2V across the 0.47 ohm resistors give you about 25W RMS class A into 8 ohms
In addition, increasing the bias lowers the distortion and changes the distortion profile. You can see these effects in Papa's article:
https://firstwatt.com/pdf/art_leaving_class_a_2019_redux.pdf
I don't know what output level you are currently using out of the amp, but I do suspect its distortion is somewhat higher than if it were at the standard bias level.
So disadvantage of higher bias? Heat. Right now you are running at less than 1/3 the dissipation of the standard bias.
I personally would make the change to allow for higher bias. If nothing else, you can then compare to see if you actually prefer one bias level over the other.
Cheers,
Dennis
I agree with Dennis. I would increase the bias by stacking another 10k resistor on your current R9 to get the 5k value. No need to unmount pcb's and all that, in my opinion. Just a simple tack soldering job. Gain won't change, but the increased bias will allow the amp to function as designed and intended.
Hello sov,
Thanks for your help. I will raise it up to at least .2 then.
At this moment the F4 is driving Lii Silver 10’s and I have a small listening room of 4 by 4 meters.
Regards,
Koos
EDIT: I still have to measure the output voltage of the preamp (Gustard X20 Pro). I red somewhere that they have more gain than average preamps. Will share the values once I have measured it.