F5 power amplifier

[Renron]

No aversion here, I prefer it! Aikido 6sn7.

 

[tinitus]

What is the aversion to running a pre-amp with the F5 ?

I suppose none
Tho being a buffer, B1 is a preamp too, right

But if you have speakers with a bit "pronounced" top, you might be in luck that a passive attenuator rolls off the top a bit, if using longer interconnects
A tube pre with higher output impedance might do that too

 

[a.wayne]

I have never heard a system that didn't benefit from a pre-amp , wouldn't leave home without one ...

 

[labjr]

Some sources have have sufficient gain and output impedence built-in and don't need any additional preamp or buffer.

 

[cviller]

But a preamp with gain will sound louder, which is appealing until you turn down to the level you had before...

 

[a.wayne]

But a preamp with gain will sound louder, which is appealing until you turn down to the level you had before...

Christian,

When using your boards , shouldn't there be more gain than standard F5? There are a few questions on your F5 blog in need of some attn.......

regards,

 

[acold7dusta]

Thanks to member Tea-bag, jazz, Cviller, A.wayne, Renron, and everyone that helped me along the way, I know have an operating amp! warming her up as we speak, and will fine tune in about 45 more minutes!

Thanks again guys- without your help I'd be going insane trying to figure it out. Don't get me wrong though-in the meantime I've learned so much more than if it would've went smoothly (take the good with the bad, ha)

 

[cjkpkg]

Update:

I FINISHED the F5...I am now running an Antek 600VA 18V toroid. The PSU caps are 4X33,000uF. Rail voltage is 23.9V on both sides.

I am running at 755mV for a bias of 1.61A - 800 was a little too warm. DC output is less than 10.

I am gaining much respect for the F5. At first I was disappointed with the gain but with the incremental improvements in the PSU and burn in time are turning this into a very respectable amp.

I broke down and ordered a B1 board and matched jfets from passdiy. It will be interesting to see how this combination works. I complain of gain issues but honestly I NEVER listen to music that loud.

Once I get the B1 built the next step may likely be some larger uber-efficient speakers for the living room. Unfortunately I am relegated to bookshelves. BIB's are not an option at this time.

Looking at the Fostex FE167s maybe...drivers need to be <$100.

 

[cjkpkg]

getting some more time with the F5...been listening to XM jazz and XM chill line out to a homemade preamp - the UCP referenced in the chipamp forums. The speakers are diy Fonkens with fostex FE127E drivers eNabl'd(self).

I will post opinions when I complete the B1 build.

 

[kp93300]

DC offset of about 5 v !--help needed

I have been enjoying the F5 for the past 3 months.
Of late I notice that one channel has a high dc offset of 5 V and I am unable to trim it to below 4 V.
I can adjust the bias easily. I normally use .55V across the 0R 47 at R12 due to my small heatsink. .
After warming up for 45 minutes, I can adjust the dc offset to below 10 mv.
I have changed a new set of mosfet but problem persisted.
The other channel shared the same power supply and works well.
The thermister has been checked and Ok.
I need help to know where to troubleshoot.

thanks in advance .

kp93300

 

[kp93300]

problem solved

I changed R4, R3, R1, R2 , Q1 and Q2.
dc offset now is zero.

I think i fried one of the jfet by static discharge while changing interconnect.
kp93300

 

[Nelson Pass]

Usually it takes quite a zap to damage a Jfet. They don't have
the delicate Gate insulators of Mosfets.

 

[markofka]

Hi there,
Just built my first F5,standart PCB but with toshiba sk1530,sj201 transistors. 8x47000 caps,24V-1.1A.
First impression it's too smooth,like diy member Bear mentioned in "F5 listening" impressions" thread. But didn't find solution to solve this out.
Amps is very stable,with wide soundtage,great detail but too smooth at the top end,no simbiliance at all.
What could i do to improve resolution performance?
1.Bypass big electolytic caps with MKP?
2.Increase current to 1.3A?
3.Change Tosh's to IRFP's? (Teabag said tosh's smooth things)
4.Burn in amp ,since it's working only two hours or so?
5.Change resistors at PCB, meaning i have Toshiba instead IRFP?

Thanks

 

[AudioSan]

Hi there,
Just built my first F5,standart PCB but with toshiba sk1530,sj201 transistors. 8x47000 caps,24V-1.1A.
First impression it's too smooth,like diy member Bear mentioned in "F5 listening" impressions" thread. But didn't find solution to solve this out.
Amps is very stable,with wide soundtage,great detail but too smooth at the top end,no simbiliance at all.
What could i do to improve resolution performance?
1.Bypass big electolytic caps with MKP?
2.Increase current to 1.3A?
3.Change Tosh's to IRFP's? (Teabag said tosh's smooth things)
4.Burn in amp ,since it's working only two hours or so?
5.Change resistors at PCB, meaning i have Toshiba instead IRFP?

Thanks

try to burn in the amp for a good 100 hours.
my aleph 1.7 had the same sound at first.

 

[a.wayne]

100 Hrs, that would take a Yr ... LOL...........


Markofka wrote : Amps is very stable,with wide soundtage,great detail but too smooth at the top end,no simbiliance at all. What could i do to improve resolution performance?

So it has detail but need better resolution


Toshiba's or IRFP's ?

.

 

[markofka]

My F5 has quite good detail,but lacks resolution (detail) at the top end. Dont know how to describe better. I have Hiraga's le monstre and le class too and they both performs better,except "bass tightness" area.

Now i rewired my PSU ,increased bias,things got a little better.Will wait for another sugestions while amp is burning in...

 

[wingman65]

Nelson, thank you for your contributions to this community and for sharing your work. I keep reading your articles over and over and I'm starting to get it What is "New Class A"??? I have a Technics amp that is New Class A


Tony

 

[kp93300]

My F5 has quite good detail,but lacks resolution (detail) at the top end. Dont know how to describe better. I have Hiraga's le monstre and le class too and they both performs better,except "bass tightness" area.

Now i rewired my PSU ,increased bias,things got a little better.Will wait for another sugestions while amp is burning in...

I suggest bypass of the power supply caps.
regards
kp93300

 

[etoiledusoir]

Hi everybody,

I'm in the first step to build a f5. I know that a lot of question have been made concerning heatsink. But I found some surplus stock of heatsink made for power rectifier on the web and I really don't know if they are ok for the project. The dimension is 6 1/4" X 6 1/4" X 9" Long.

Aluminum Heat Sink 6 1/4" X 6 1/4" X 9" Long. - eBay (item 7607693627 end time Apr-15-10 09:31:06 PDT)

I plan to make a vertical amp, the trafo and psu on the bottom and the heatsink on top with two channel pcb on the same surface. Is this heatsink fit for the job ?

 

[jackies]

Those heatsinks are commonly used, you'd need 4 of these I reckon.