F4 power amplifier

[jleaman]

F4

Ok, so after a week of listening then putting al together, I LOVE THIS AMP, very VERY good detail. It is dead A$-$ Quiet, I have to admit it, they are quieter then my aleph mini's ) I'm talking about noise ratio and humms : there is literally NONE!

Pure sound, I should build another.

The one bad thing, DAM THEY GET HOT.

 

[carpenter]

Another reason to try water cooling?

 

[jleaman]

Another reason to try water cooling?

Not going to happen

i just turned bias to 300mv tho so shes a little cooler

 

[carpenter]

I'm considering the possibility of separating the power rails to the Mosfets from the jfets, and running the Mosfets at higher voltages than the jfets--about twice as much voltage, actually. Water cooling will be useful.

 

[jleaman]

I'm considering the possibility of separating the power rails to the Mosfets from the jfets, and running the Mosfets at higher voltages than the jfets--about twice as much voltage, actually. Water cooling will be useful.

would be good, however loud and just a pain for me..

 

[Jaac]

Re: F4

Ok, so after a week of listening then putting al together, I LOVE THIS AMP, very VERY good detail. It is dead A$-$ Quiet, I have to admit it, they are quieter then my aleph mini's ) I'm talking about noise ratio and humms : there is literally NONE!

Pure sound, I should build another.

The one bad thing, DAM THEY GET HOT.

Do you have any idea how hot ? Firt my aleph 5's where hot but then i touched the sinks of a pair of xa100 at my work, they where even hotter so no problemo ! around 60 degree. Nice amp btw

 

[lykkedk]

i just turned bias to 300mv tho so shes a little cooler

Hmm... why don't you just set bias to 200 or 250mV (schm. related)... I can't hear any sonic difference if i crank mine up to e.g. 300 (schm. i used is the 250mV bias) Later changes's in F4 schm. the gate resistor's (among other canges too) change and bias go down to 200mV.

You really have to have the F4 turned on, for some time, and adjusting the DC-offset, when she is thermic stable (mine 2... are 1,5hour to become 100% stable), having at this time a temperature of ~40-45 C - with 250mV bias meassured on pwr. resistors.

All this is vere important i think. I leaved mine two monoblocks playing when having a party not so long ago, for around 12hour's ... still having the same temperature... Jleaman, i think that its your'e real goal for now (judging by the size of your'e heatsink's i don't think you should go further than the described bias)

Jesper.

 

[skseah]

Hi,
Here is my F4 with Conrad Heatsinks..bias set at 200mV..hot but seems OK for the hot temperature in Singapore.

 

[skseah]

Hi,
Here is my F4 with Conrad Heatsinks..bias set at 200mV..hot but seems OK for the hot temperature in Singapore.

An externally hosted image should be here but it was not working when we last tested it.

 

[carpenter]

Hi,
Here is my F4 with Conrad Heatsinks..bias set at 200mV..hot but seems OK for the hot temperature in Singapore.

Handsome amp!

 

[DaveM]

Help?

I fired one channel of my new F4 up this afternoon and I can't seem to get the bias up into range. With P1 maxed out I am only able to get about 55 mv across the bias resistors. I checked the value on P1 (5k) and the components around it and everything seems to be correct. The DC offset is easily set, and the amp is passing a signal just fine. Ideas of where to look first?

DaveM

 

[carpenter]

Dave, which version did you build?

 

[DaveM]

I built the Peter Daniel boards.

 

[carpenter]

I retrieved this quote from a prior, saved, post:

....."If you can’t reach 200mv replace R9 with lower value ~6K
zero the output offsets again
let the chassis warm up and adjust for 200mv, or 250mv and zero the output offsets again."

Enjoy

-Mal................

Maybe this will help, keep us posted. John

 

[DaveM]

Thanks Carpenter. I will give it a shot.

DaveM

 

[DaveM]

Well with a 5k resistor in R9 i am able to achieve my bias, but then the DC ofsett goes through the roof. I was thinking that if I drop the value of r22 to 375 I should be able to get my DC offset in line. Is there any harm in this?

DaveM

 

[audiorasp]

Dave, double check the grounding. See my post # 1347.

Geo

 

[DaveM]

Grounding... Been there done that. Yes I double checked it and I have the signal ground to the signal gnd and the power ground to the ground next to it.

 

[carpenter]

Well with a 5k resistor in R9 i am able to achieve my bias, but then the DC ofsett goes through the roof. I was thinking that if I drop the value of r22 to 375 I should be able to get my DC offset in line. Is there any harm in this?

DaveM

Have you been adjusting offset with P2? Is it twitchy, or just won't go anywhere near zero volts?

 

[DaveM]

When I bring the bias up to 200 mV, the DC offset is around 30 volts. When I drop the bias to about 170mV, I can get the DC offset down to about 30mV .