FT15K mosfet power amp

[Flavio88]

Sorry, i'm italian and my english is terrible
Futura Elettronica FT15K mosfet amp.
Some opinions about this power amplifier?
For me this is a very good amp.:

 

[Leolabs]

Any pictures????

 

[Flavio88]

I attached the original pdf.
Sorry is in italian 😀

 

[Flavio88]

Some questions:
Can you recommend me some transistors to replace the MPSAs? They are too much noisy.

I have replaced the input electrolytic cap with a mkt cap,there is others upgrades that i can do?

Here is the MPSA92 datasheet

 

[Leolabs]

A quite traditional circuitry.Nothing special but reliable.

I did use the 2SA872 for the input pairs,2SB647/2SD667 for the driver stage,and the obsolute 2SK135/2SJ50 for the output stage.U can try them if u want🙂

 

[Flavio88]

Thanks for your advise. I'll do my best.

I need a special help... At first in one of the two channels the zobel network resistor (R17)went up in smoke, after changing it everything went OK, but now happens the same problem to the other channel, in your opinion it could be a problem due to the substitution of the input capacitors? Or due to an anomalous high frequency oscillation? If yes, what can I do to compensate this oscillation?

Tanks...

 

[Leolabs]

I havent encounter such problem,so really cant make any correct statement on this one.

To me,possibly the quality of the component itself or maybe like what u have said😱scillation.

If u really worry about the oscillation,try to increase the value of C2 to 470pF,will limit the input bandwidth to around 150kHz,seems enough to me for audio application🙂

 

[ilimzn]

Thanks for your advise. I'll do my best.

I need a special help... At first in one of the two channels the zobel network resistor (R17)went up in smoke, after changing it everything went OK, but now happens the same problem to the other channel, in your opinion it could be a problem due to the substitution of the input capacitors? Or due to an anomalous high frequency oscillation? If yes, what can I do to compensate this oscillation?

Tanks...

This would almost certainly be caused by HF oscilation...

 

[Flavio88]

Thanks to everybody but I have resolved the problem:
It was only a grounding error, I didn't have connected the chassis to ground.😀 😀 😀

Leolabs, can i use also the 2SA872/2SC1775 instead of the
MPSA92/MPSA42 for the entire circuit?

The collector current rating of 2sa/2sc is more less of the mpsas,
does it change something?😕


sorry for the english
Thanks...

 

[Leolabs]

The 2SA/2SC pair u suggested is normally for input stage,if they are used at driver stage,i dont think they will drive the MOSFETs.

 

[palesha]

Leolabs say " the obsolute 2SK135/2SJ50 for the output stage"

What to use new one to replace this outdated evices. Any chance of using IRF devices with some modifications?

 

[richie00boy]

Exicon and Magnatec make replacement devices. IRF types are not really suitable unless you incorporate a proper thermal tracking system.

 

[Flavio88]

Thanks, but exactly, where do I have to use the 2SA872 and the 2SB647/2SD667?
example:
T1 = 2SA872
T2 = 2S...

And which benefits done really hand the substitution of the resistors with others of the "metal film" type?

Thanks a lot🙂

 

[Leolabs]

T1=T2=2SA872

T3=2SB647

T4=T5=2SD667

Metal film??Well i havent try.Still to normal stuff😀

 

[UltimateX86]

A quite traditional circuitry.Nothing special but reliable.

I did use the 2SA872 for the input pairs,2SB647/2SD667 for the driver stage,and the obsolute 2SK135/2SJ50 for the output stage.U can try them if u want🙂

Hi

you produced this amplifier?

thx

 

[esoes]

FT15K Schematic rev