F5 power amplifier

[osscar]

thanks for the advice Master! This definitely helps.

 

[acold7dusta]

has anyone built zobel networks for their F5, or is it not necessary for this topology? I'm running higher capacitance CAT5 cables (10ft)

bump

 

[tinitus]

Output is stable
But you may have to be careful with source and interconnects

 

[bobodioulasso]

bump

If this cable does not work, try an ordinary one instead of adding a zobel.

 

[carlomar]

bump

I try a high capacitance speaker cable and fuse blow up.

 

[acold7dusta]

thanks for the replies, I'll try ordinary 12ga and see if runs any cooler (couldn't hold my hand to 5 seconds, zobel wasn't helping)

without load, i can hold it comfortable for over 20 seconds

 

[tinitus]

quote from F5 manual

A caveat is in order here – this is a very wide band amplifier with a high input
impedance. In order to prevent the output voltage from bleeding back to the
input at very high frequencies (thus making a fine power oscillator), keep the
input and output cables separate, and don’t externally connect the speaker
ground to the input ground. Good ground shielding on the input cables is
important, and caution is called for in using Litz and other specially low
inductance / high capacitance cables. I have not seen a specific example of a
problem, but historically it is to be expected when an amplifier’s bandwidth
exceeds 200 KHz. If the amp makes funny noises, runs extra hot, or blows
fuses, this might be an indicator of such an issue.

quote from above

and don’t externally connect the speaker
ground to the input ground.

I suppose speaker ground(power supply) and input ground(chassis) is seperated by thermistor

 

[acold7dusta]

quote from F5 manual

A caveat is in order here – this is a very wide band amplifier with a high input
impedance. In order to prevent the output voltage from bleeding back to the
input at very high frequencies (thus making a fine power oscillator), keep the
input and output cables separate, and don’t externally connect the speaker
ground to the input ground. Good ground shielding on the input cables is
important, and caution is called for in using Litz and other specially low
inductance / high capacitance cables. I have not seen a specific example of a
problem, but historically it is to be expected when an amplifier’s bandwidth
exceeds 200 KHz. If the amp makes funny noises, runs extra hot, or blows
fuses, this might be an indicator of such an issue.

quote from above

and don’t externally connect the speaker
ground to the input ground.

I suppose speaker ground(power supply) and input ground(chassis) is seperated by thermistor

I've read that, but after all the countless hours I put into those cables I just REALLY wanted to make them work...

 

[acold7dusta]

amp's running much more stable (cooler and less noise), and sounds much more "relaxed", with an increase of upper midbass...interesting

 

[Nelson Pass]

I've read that, but after all the countless hours I put into those cables I just REALLY wanted to make them work...

Some capacitance across the 100 ohm feedback resistors will
stabilize that. Start with .001 uF and work up to .01uF.

 

[udailey]

amp's running much more stable (cooler and less noise), and sounds much more "relaxed", with an increase of upper midbass...interesting

What did you do to get this gain in sound quality and stability?

 

[serious_lee]

I finally got my FETs in and I am wondering how you guys go about matching (or if you bother). I have 20 of each JFETs and 6 of each MOSFET. I read somewhere that there were many more needed (1000 comes to mind) to get a good match. Please reply back with methods, circuits, links etc. so that I can compare what I've read to experienced guys. There's a lot of information out there for a newbie.

Thanks,
Everett

 

[Electrolastic]

I am building a F5. However, I have problem with thermal drift. I use 5K NTC thermistors. Output DC swings up to 100mV and idle current swings up and down too.

I attach the thermistors to the power MOSFET with glue. What is the proper way to mount/attach the thermistors? Would some one help. Thanks.

 

[Bidoux]

I have to apologize, I didn't read the whole thread, but it is quite obvious, seeing it's lenght. So maybe my question has already been asked.

Here, on figure 15 we can see an amp that looks like a F5 with bipolar instead of fets. The author says it is a design to avoid.
Is the F5 so much different that the topology is no longer a problem ?

 

[gaborbela]

Hello
Please use the melting type of glue . That has great conductivity .
In case if the mosfet and the thermistor has different temperature .
Greeting

 

[acold7dusta]

What did you do to get this gain in sound quality and stability?

It was a matter of not sounding right, vs. sounding normal. I removed my zobel network (cap & R in series), and swapped out my high capacitance cat 5 speaker cables, with normal 12ga wire, and tweaked the bias. I'm now at .685V on the left with <1mV dc offset, and .687V on the right with ~1mV dc.

The right channel still gets very hot after about 2 hours, so i definitely need to give it more air to breathe (open rack is on the left of my speaker)

 

[acold7dusta]

Some capacitance across the 100 ohm feedback resistors will
stabilize that. Start with .001 uF and work up to .01uF.

Thanks, what kind of effect will I look for on a scope? still new to scopes

 

[Marra]

Has anyone used transformers from Toroidy.pl. I seem to remember that someone said they were going to try them and post results but I havent come across any more posts. I still have another 100 pages to read so maybe I havent found his results yet.

 

[acold7dusta]

there's one on page 696, from doing a simple search

 

[Marra]

Thanks for the pointer