QUASI Amplifier for Beginners

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ariyanto

ariyanto

Member
Joined 2011
apexaudio said:
PCB size is 110x105mm, fit top layer in this size.
Regards
Click to expand...

Ok For indeed the same size but different picture mr ....... there are holes for the bottom layer and top layer to ga there, distinguishing it?
 

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wattaniya

Member
Joined 2009
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amptech

Member
Joined 2009
signal pair of trannies on that supply rail is asking for trouble.. it's a very basic amp using the diode system to set up the bias voltage..peavey old bass amps used same idea in there o/p amps.. it's better to use the amplified diode transistor tracking like so many amps out there..
 
nigelwright7557

nigelwright7557

Member
Joined 2008
murtonpikesystems.co.uk
amptech said:
signal pair of trannies on that supply rail is asking for trouble.. it's a very basic amp using the diode system to set up the bias voltage..peavey old bass amps used same idea in there o/p amps.. it's better to use the amplified diode transistor tracking like so many amps out there..
Click to expand...

Crossover distortion is only really audible at low volumes so you can get away with a couple of diodes if your not too fussy.

However I use a Vbe multiplier in my designs in case i want to listen at low volumes.
 
nigelwright7557

nigelwright7557

Member
Joined 2008
murtonpikesystems.co.uk
amptech said:
most of the amp's I've seen over the year's use the vbe multiplier design making setting up the amp much better... still it's all down one's choice...
Click to expand...

The Vbe multiplier isnt idot proof. Many years ago my first amp with Vbe multiplier blew up on power up as I had turned the pot wrong way.

After that disaster I always put a zener in parallel with the Vbe multiplier to stop it going too far.
 
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amptech

Member
Joined 2009
so your clamping the q setting voltage! some may set the vr adjustment to half way and check the reading across the emitter resistors. in the case of some mosfet stage's with no source resistors the quick way would be place the meter between the plus rail etc but we know this already...
some newbie's to the world of amp building will need some pointer's in the right direction and there are many of us that use our own style of setting up unit's..as they say 'there's plenty of way's to make a pot of tea and the out come is the same..
 
A

amptech

Member
Joined 2009
Hi AndrewT..

I would agree there as mistakes can be costly if something is wrong and all that hard work goes up in smoke when power is applied. I think most of us over the years have done that mistake of working on a peace of equipment thinking yep, it read's ok on cold check's then power up only to see something start to burn..oh **** quick pull the plug..

Regards A.
 
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yohnsee

Member
Joined 2010
A little help please

Hy! I am in a hurry, i quickly have to make a 120W/4ohm amplifier. This quasi one is just fine, but i have 2x50VDC rail voltages, and i cannot change it. Is it possible to get this 120W/4ohm from 1 pair of output devices? Or it can only be achieved with 2 pairs? And an other question: Is the 2SC3281 a good substitute for this job? Because i can only get these from the local dealer. And he said, it is nearly as good as 2SC5200's.
Please help me guys.
Thanks in advance.
 
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amptech

Member
Joined 2009
Hello Yohnsee, I've seen many designs over the years using just a pair of power devices to give up to 150w using +/-50v rails. so yes you can build your 120w design...the main reason for adding 2 pair's is for better current sharing with the o/p stage. check on the inter net for circuits within your amps power ratings there's plenty out there..

also the 2sc32181 and it's counter part matched device is also fine for amplifier power stages....
 
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yohnsee

Member
Joined 2010
amptech: Thank you for the answer. I am currently looking at the circuit described in this thread, because it is easy and quick to build, and needs only a few parts. I have to replace an active speaker's amp, because it can not be repaired. So i am on to build a new one for it, and i have to do it in 2 days, so that is why i hurry, and i only have npn transistors, i cannot buy their pnp pair, because the local dealer ran out of them. So i want to make this quasi with npn transistors.
And i cannot change the supply voltage.
Thanks for any help.
Bye!
 
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radio

radio

Banned
Joined 2009
Zdravo Mile!
Dali postoji neki tutorijal u vezi ovaj 550W pojacavac u klasi B, posto treba mi za maturski rad!!
Ili ako hoces detaljniji opis rada pojacavaca?!
Unapred veliko hvala!

Mile Hi!
Is there a tutorial on the 550W amplifier in class B, after graduation I need to work!
Or if you want a description of the amplifier?
A big thank you in advance!
 
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yohnsee

Member
Joined 2010
apexaudio said:
Quasi complementary amplifier based on old Dynacord. For begginers Class B without adjust.
Click to expand...

Excuse me, i may be tired this evening, but i am building this amp from the schematic (not from the pcb) and on the schema the MJE15031's emitter goes to OUT rail, but on the pcb it goes to one of the output trannies' collector.
Please say it is only my mistake, or i don't see something obvious.
Thanks
 
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