45W@8R 70W@4R CLASS B SO LOW DISTORTION.

[drowranger]

ok then ...here is some fast food details ...

----amplifiers are not RF devices nor power supply there is a serious chance that the ground plane you made causes trouble

----if you decide to stay with a ground plane after all as seen from your pictures proximity of ground plane between traces is way too close ... that might cause inductunce or capacitance with other traces and drive the amplifier to oscilation


---- next option will be to have a star ground on board

---- you have missed decoupling and bypass of rails on the pcb .... for this type of amplifier that might help a lot ...

---- " curent source" for LTP Q3 need to be as close is possible

--- since you made the pcb with LTP tansistors close enough you might as well bring them even closer so thermal coupling and matching will also add some quality more to the amp

---- C3 feedback capacitor is not MKP cap ...its an electrolytic ou have used the wrong part

---- Finally thermals is a quiet serious issue on this amplifier since no output resistors are used ...beyond serious heatsinc the needs to be used ...idle is supposed to be monitored properly and the diode string of 1N400X has to be properly attached on the heatsink


---- use of better transitors than 2955-3055 combo is recomended and choise of make and quality will make the amp more thermally stable ( pcb has to be able to use TO247 devices also )

----On this configutration with 33+33 volts belive it or not i think that is marginal i wouldnt go more than 30+30 with 2955-3055 combo better transitors might stand up to 35 or 40 volts

----even though vas transitor Q5 is excelent freq and perfomance whise i could as well make pcb that could feature BD139-140 family also just in case BC is marginal ...

my 2 cents

 

[drowranger]

i made mistakes on c3 should be polarized capacitor.about decoupling capacitor on rail i think that is for pssr.i move the driver transistor so it can accommodate the aluminum bar between the power transistor and the driver trans.and for the diode 1n4148 ived copied that from leach amp.

thanks for the correction.

 

[drowranger]

Modification

i made mistakes on c3 should be polarized capacitor.about decoupling capacitor on rail i think that is for pssr.i move the driver transistor so it can accommodate the aluminum bar between the power transistor and the driver trans.and for the diode 1n4148 ived copied that from leach amp.

thanks for the correction.

removed R14 and change c3 with electrolytic capacitor

 

[AndrewT]

a very important point.
LEARN BY DOING.
I.e let him find out for himself why the design has shortcomings.

It is never a good idea to rely only on what others say

As a teacher, I am not allowed to "contact" a pupil.
I was standing beside one of my 11year old pupils instructing the class on Safety with their soldering irons.
While explaining "this eejit" had switched on and was proceeding to melt/burn through the mains cable of the soldering iron.
Did I wait for his experiment to show the lesson that had to be learned?
You are damn sure I did not wait. I swung out rapidly to move/remove his arm hand/ away from the danger. It was almost a slap but was interpreted as appropriate action to ensure safety of my charges.

Instructing is necessary. Instruction can be informative. Instruction can save lives.

Some hours later while teaching the next set of 11year olds, one girl jumped and screamed out.
She had touched a bared Live wire in a cable that that been burned through accidentally. Another chance to "instruct" on safety. Mistakes can happen, but don't ignore. Take appropriate action, in this case report the accident and teacher can then make safe. Her peers got the message. The subject was very lucky she only brushed against the bared wire.

Before anyone jumps on the bandwagon, the school were asked to install 24V irons and when refused asked for high temp cables, again refused. Budgets ruled and I was under instruction to proceed with the lessons.