ESP P3A Mods/Upgrades

[kalmara]

My guess about the orientation of that cap is because the constant current load in the original circuit (bootstrap) is on the negative rail and most of the times resulting in negative offset in the output. But that's not the question.

 

[sudhir kumar]

how to modify p3a as quasi npn output i.e 2n3773 ? please help with graphical representation.

 

[dadod]

Hi kalmara,
If you have not solved oscilation problem yet, try to insert 100 ohm resistors to Q5 and Q6 bases. CFP is prone to oscilation and you included CM and with it more gain.
dado

 

[effebi]

Hi kalmara,
If you have not solved oscilation problem yet, try to insert 100 ohm resistors to Q5 and Q6 bases. CFP is prone to oscilation and you included CM and with it more gain.
dado

This was already suggested by AndrewT in post 55, at the end. I believe base stopper are always a good idea, EF or CFP.
I also would like to see if kalmara could solve, and in case the updated schematics. Long time ago I also was doing something like that ....
bye
effebi

 

[dadod]

I simulated something similar and 33ohm diriver base stopper were not enough. Oscilation stops with 100ohm.
dado

 

[dadod]

100pF base collector for Q5 or Q6 or both could help, you have to try what stops oscilation, but base stoppers are still necessary.
dado

 

[grunf]

I replaced the original P3A transistors with these transistors

BC546B - 2SC2362 input stage
BD140 - KTB1369 VAS
BD139/140 - 2SC4793/2SA1837 driver
for output I use C5242/A1962

suplly voltage is +/- 25V

sound is much better than with the original scheme transistors

 

[grunf]

I forgot to write that all Capacitors are Panasonic FC and the Black Gate on negative feedback and bootstrap.
Input capactiors is Polypropylene.

 

[PauloPT]

Phase lead capacitor

Sorry to ressurect this old thread. I built a P3A and I'd like to take the most out of it. I was wondering about the phase lead capacitor - the cap between VAS colector and LTP feedback base. I don't have a scope. What would be the optimum value for this cap? Is there any way to calculate it?


Thanks.

 

[AndrewT]

Start small. Adjust Cdom and listen.
Go around this try, adjust, listen loop as many times as you have patience for.

 

[PauloPT]

I did some simulations and I got slightly higher distortion with phase lead cap than without it. Shouldn't be the oposite?

Thanks.

 

[sgrossklass]

Nope. Remember that output stage distortion tends to dominate, and that increasing Cdom reduces open-loop GBW - so there's less open-loop gain to suppress output stage distortion. But obviously low distortion is of no use if the thing oscillates like mad in real life.

Given the flexibility in power devices, it is to be assumed that the default value of C4 is chosen to be on the safe side. If you don't have a scope (or even an RF probe), it is best left at the standard 100 pF.

 

[AndrewT]

He is adding feedback with the extra cap. That allows the Cdom to be reduced slightly and yet maintain at least the same stability margins, i.e. the open loop gain at >=20kHz is very similar.
This can lead to slightly improved distortion, not necessarily worse.

 

[kp93300]

Power supply caps on the Rod P3A Rev B board

sorry to resurrect an old thread.
I am now populating the boards and notice that there is a long distance between the 100uF power suppply caps and the 100nF bypass caps.I would like to seek answers to these
1) Is there any advantages in using 480 Uf caps?
2) Can i solder the bypass caps on the underside of the power supply caps ?
3) In the place of the bypass caps , i am thinking of placing 47 Uf caps that i have lying around. Can i use higher value and is there any trade off ?
4) Is the value of the bypass caps critical? which is better --l ceramic bypass caps or mkp caps ?
thanks

kp93300

 

[AndrewT]

do not attach the HF decoupling caps to the MF decoupling.
It is the high impedance between to cap connections that reduce the tendency to ringing.
The HF decoupling goes to the Power device Power input pin and returns to the Power Ground.

 

[Adi_007]

Hi, the schematic of P3A is very similar with P101...is it posible to modify the P3A with the input from P101?....what value Ra and Rb should have?....thanks

60-80W Power Amplifier
Project 101 - High Power, High Fidelity Lateral MOSFET power amplifier

 

[AndrewT]

Rb has the same voltage as Vbe of Q11.
In that location Rb defines the current out of the tail of the LTP.

Ra feeds Q11 so that Q11 can operate as an amplifier.

Q1 & Q2 could work as inputs (there are two inputs) with as little as 100uA and as much as 10mA. you choose a value that gets good performance of the transistor AND gets adequate amplification of signal to feed into the second stage.

Q11 ca work within a similar range of current for it's Ic.


But look at the quiescent power of these devices and at the peak power.

 

[gorex69ers]

The value of Rb 280 ohms, for Ra 22 k