I'm using the the big 5U chassis. Be careful that you don't get too hot in the 4U chassis. What is the temperature of your heatsinks?
Running about .59V at the .47 ohm resistors, i have 20 deg C over ambient at the heatsinks (using remote laser scanner). That is with the amp running music for about 3 hours. I will up it a bit to .65V tomorrow while monitoring the temp. I do not want to risk blowing anything up and Nelson recommended the bias current at 1.3 amps or about .6V at the bias test point.
Also, I am running only 20v DC vs the 23v most have. Using a 16V transformer, as the 18v are out of stock. Not sure how much that affects things.
Also, I am running only 20v DC vs the 23v most have. Using a 16V transformer, as the 18v are out of stock. Not sure how much that affects things.
With the 5U chassis I am at .760 (1.6Aish). I can hold my hand on the heatsink forever. I have small kids and a curious cat so I think I will stop at 1.6A. And I am getting sick of having test leads sticking out of the amp all the time. One thing is sure though...every bump in bias (I've gone from .5V to .6V to .7V and now .76V) has sounded better with more dynamics, more control and a more precise soundstage.
I am building a BA-3 based preamp now...hopefully it will best the Jfet Boz. Next I am looking at maybe Toshiba Mosfets for the F5 or finding a way to mount the rectifiers directly to the caps upside-down with a heatsink on top. Maybe CLC filering. Also, bypassing the power caps with some 10UF polys was a good move. It never ends...
I am building a BA-3 based preamp now...hopefully it will best the Jfet Boz. Next I am looking at maybe Toshiba Mosfets for the F5 or finding a way to mount the rectifiers directly to the caps upside-down with a heatsink on top. Maybe CLC filering. Also, bypassing the power caps with some 10UF polys was a good move. It never ends...
Hi CRCook,
Here is the man himself's explanation on what it happening to the F5 and what you can do and not do,lol
Try this link and see if it will help! http://www.firstwatt.com/pdf/art_f5_turbo.pdf
Happy Listening!
NS
Hi crcook,
I have 2 f5's what do you want to know?
If you really want to know how hot you can run them it goes like this ,If you have big heat sinks,you can run the bias up till the heatsinks get up to 50 C,then you keep a eye on the transformer because if it's not big enough it will get hot and most of the time starts buzzing,Fans will help the transformer and the heatsinks,alot of folks run .6a and play music,some run 2.6A too ,It's just how much hardware you have and how well you can get rid of the heat,lol. I guess a balancing act so to speak!
I am running water cooled sinks ,I ran up to 3 amps bias but backed off to 1.5 my trans former started getting warm,My F5 sounds good there ,so I am happy,I also have 2 F5c they give the bass a new name ,lol. I read all the F5xxx threads 2 ,,,takes a while,(weeks)might double up your Jfets too! If you have a variact ,try dropping the rails to 18v and reset your bias and then your DC offset,
A different sound there also and putting 5 R in the J74 changes things a bit too!Better curve tracking,
Have fun I do! Best to you!
NS
I have 2 f5's what do you want to know?
If you really want to know how hot you can run them it goes like this ,If you have big heat sinks,you can run the bias up till the heatsinks get up to 50 C,then you keep a eye on the transformer because if it's not big enough it will get hot and most of the time starts buzzing,Fans will help the transformer and the heatsinks,alot of folks run .6a and play music,some run 2.6A too ,It's just how much hardware you have and how well you can get rid of the heat,lol. I guess a balancing act so to speak!
I am running water cooled sinks ,I ran up to 3 amps bias but backed off to 1.5 my trans former started getting warm,My F5 sounds good there ,so I am happy,I also have 2 F5c they give the bass a new name ,lol. I read all the F5xxx threads 2 ,,,takes a while,(weeks)might double up your Jfets too! If you have a variact ,try dropping the rails to 18v and reset your bias and then your DC offset,
A different sound there also and putting 5 R in the J74 changes things a bit too!Better curve tracking,
Have fun I do! Best to you!
NS
You can take a single pair of mosfets up to about 2 amps with 24v rails…assuming you have the heatsink. I’ve run a single pair f5 at 1.8A I. A 5U chassis for a long time. Higher than 2 amps you risk overstressing the devices even if the heatsink temps are reasonable.
If you have another pair of mosfets like the f5 turbo you can go higher. Currently running 1.8 amps with 32V rails with dual pair mosfets in a 5U Chassis.
If you have another pair of mosfets like the f5 turbo you can go higher. Currently running 1.8 amps with 32V rails with dual pair mosfets in a 5U Chassis.