Amplifier upgrading!!!!!!!!!

psyche · 14th April 2006, 11:18 PM

Hi there,

My name name is Padelis and I am from Greece.I electronics here in Greece and I decided to build and amplifier for my home project studio.I bought a kit from a company here in Greece which is an 2x60watt amp.On the schematic the output transistors are bdw83 and the provided transistors are 2sd817(upgrade???).So what i want to ask you is what to do in order to make this amp better.I would like less distortion, more watts and be a little faster.I know that if i want to change the output transistors i will have to change the drivers too.So here i am to the more experts diyers asking for help and opinions!!!!

Thanx in advance
Padelis.

quasi · 14th April 2006, 11:35 PM

Can you please attach a schematic. It will be easier for people to offer advice.

Cheers

CBS240 · 15th April 2006, 12:26 AM

Maybe you could use a complementary design instead of quasi. Not that quasi is bad, it's just that there exists in these modern times some pretty good complementary output transistors.(no offense quasi

) You may not have to change the drivers, just use them in emitter follower darlington arrangment. Also wouldn't hurt to add small base resistors to those outputs. In doing this, you may also want to include a Vbe multiplier for bias and thermal stability instead of diodes as class AB emitter followers can be sensitive to temp. and bias changes. Loading the VAS with a current source might work also, however there are designs that don't use a CCS.

quasi · 15th April 2006, 01:21 AM

It seems as though you have already bought the amp kit.

The BDW83 is specified as a darlington and I cannot find information about the 2SD817. A more modern transistor would be a TIP142.

The number of changes required would not work well with the existing kit PCB so I would build as is and see what you think.

Use any upgrade money you have to build an excellent power supply using a 500va transformer with a seperate bridge and capacitor bank for each amp module. Use at least 10,000uf per rail (20,000uf total) per amp module.

Cheers

quasi · 15th April 2006, 01:24 AM

Offence? me?

None taken CBS240. I actually like complimentary transistor output stages. For high power I prefer quasi-comp because watt per buck it's hard to beat.

Cheers

darkfenriz · 15th April 2006, 01:27 AM

Looks like from early seventies. Not a nice idea to build an amplifier like this. Try something else, more worth bothering.
regards
Adam

AndrewT · 15th April 2006, 08:04 AM

Hi,
persist with the kit and get it working. I do not recommend spending extra money modifying this rudimentary quasi design.

As Quasi said build a good supply and case and allow for a new amplifier PCB to be substituted later.

Eva · 15th April 2006, 08:39 AM

psyche:

That circuit is really terrible (not due to the quasi output stage but due to the lousy rest) and probably from early seventies as it has ben already pointed out. Also, ECA book tells that 2SD817 is a Toshiba 1500V 1.5A TV horizontal deflection transistor, thus not suitable at all for an audio amplifier. Furthermore, Toshiba electronic components website does not contain any reference to that device (meaning that it was discontinued a long ago) and I couldn't find any other alternative manufacturer in google, so what you have are FAKE transistors, forgeries (very common in Southern European countries).

In my opinion you have been scamed, so it would be a good idea to return everything to the supplier and ask for your money back.

Also, remember that this forum is full of great projects to build, you just have to be patient and search. You should also search for threads on fake components and read them because I feel that local stores on your country are flooded of fake transistors and ICs (as it happens in Spain and Italy).

bogdan_borko · 15th April 2006, 09:59 AM

Oh man, who sold you that kit in 2006. ???

psyche · 18th June 2006, 02:52 PM

Hi there,

soryy for been away for soooooooooo long but i had completely forgot that thread.a few corrections:
the output transistors are 2sd718

I have built this amp a few months ago and it sounds simply good.I was just wondering if i could improve its performance, thats all! Now i am ready to build a new amp from the schematics that are posted here in the forum but i can't decide which one to build.These are all great.BTW what would you recommend me to build?Have in mind that i will use it in my studio.

Thank you guys you are great

Padelis

14th April 2006, 11:35 PM	#2
quasi diyAudio Member Join Date: Sep 2004 Location: Adelaide, Australia	Kalimera Padeli, ti kanis; Can you please attach a schematic. It will be easier for people to offer advice. Cheers __________________ http://sites.google.com/site/quasisdiyaudiosite/

15th April 2006, 12:26 AM	#3
CBS240 diyAudio Member Join Date: Aug 2005 Location: K-town	Maybe you could use a complementary design instead of quasi. Not that quasi is bad, it's just that there exists in these modern times some pretty good complementary output transistors.(no offense quasi ) You may not have to change the drivers, just use them in emitter follower darlington arrangment. Also wouldn't hurt to add small base resistors to those outputs. In doing this, you may also want to include a Vbe multiplier for bias and thermal stability instead of diodes as class AB emitter followers can be sensitive to temp. and bias changes. Loading the VAS with a current source might work also, however there are designs that don't use a CCS. __________________ All the trouble I've ever been in started out as fun......

15th April 2006, 01:21 AM	#4
quasi diyAudio Member Join Date: Sep 2004 Location: Adelaide, Australia	It seems as though you have already bought the amp kit. The BDW83 is specified as a darlington and I cannot find information about the 2SD817. A more modern transistor would be a TIP142. The number of changes required would not work well with the existing kit PCB so I would build as is and see what you think. Use any upgrade money you have to build an excellent power supply using a 500va transformer with a seperate bridge and capacitor bank for each amp module. Use at least 10,000uf per rail (20,000uf total) per amp module. Cheers __________________ http://sites.google.com/site/quasisdiyaudiosite/

15th April 2006, 01:24 AM	#5
quasi diyAudio Member Join Date: Sep 2004 Location: Adelaide, Australia	Offence? me? None taken CBS240. I actually like complimentary transistor output stages. For high power I prefer quasi-comp because watt per buck it's hard to beat. Cheers __________________ http://sites.google.com/site/quasisdiyaudiosite/

15th April 2006, 08:04 AM	#7
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, persist with the kit and get it working. I do not recommend spending extra money modifying this rudimentary quasi design. As Quasi said build a good supply and case and allow for a new amplifier PCB to be substituted later. __________________ regards Andrew T.


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15th April 2006, 01:27 AM	#6
darkfenriz diyAudio Member Join Date: Jun 2004 Location: Warsaw	Looks like from early seventies. Not a nice idea to build an amplifier like this. Try something else, more worth bothering. regards Adam

15th April 2006, 08:39 AM	#8
Eva diyAudio Member Join Date: Oct 2003 Location: Near the sea	psyche: That circuit is really terrible (not due to the quasi output stage but due to the lousy rest) and probably from early seventies as it has ben already pointed out. Also, ECA book tells that 2SD817 is a Toshiba 1500V 1.5A TV horizontal deflection transistor, thus not suitable at all for an audio amplifier. Furthermore, Toshiba electronic components website does not contain any reference to that device (meaning that it was discontinued a long ago) and I couldn't find any other alternative manufacturer in google, so what you have are FAKE transistors, forgeries (very common in Southern European countries). In my opinion you have been scamed, so it would be a good idea to return everything to the supplier and ask for your money back. Also, remember that this forum is full of great projects to build, you just have to be patient and search. You should also search for threads on fake components and read them because I feel that local stores on your country are flooded of fake transistors and ICs (as it happens in Spain and Italy).

15th April 2006, 09:59 AM	#9
bogdan_borko diyAudio Member Join Date: Nov 2005 Location: serbia, zajecar	Oh man, who sold you that kit in 2006. ???

18th June 2006, 02:52 PM	#10
psyche diyAudio Member Join Date: Jun 2005 Location: Athens	Hi there, soryy for been away for soooooooooo long but i had completely forgot that thread.a few corrections: the output transistors are 2sd718 I have built this amp a few months ago and it sounds simply good.I was just wondering if i could improve its performance, thats all! Now i am ready to build a new amp from the schematics that are posted here in the forum but i can't decide which one to build.These are all great.BTW what would you recommend me to build?Have in mind that i will use it in my studio. Thank you guys you are great Padelis

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