A Directory of Apex Audio Amplifiers

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petr_2009

Banned
Joined 2009
Evheniy K. said:
Hi all!
I have a question about the APEX P30ZF preamplifier. Has anyone measured THD? What were the results?
What regulates a 1k ohm trimmer? In my case, I do not see any changes from the adjustment.
Thank you.
Click to expand...

In the model, this tuning resistor practically does not work.

With what signal sources is it necessary to use a preamplifier with a gain of more than 6?

The 10uF output capacitor prevents operation with inverting amplifiers with low input impedance.
 
S

stagekraft

Member
Joined 2021
Hey All,

I ran across this layout for an "Redesigned" Apex B250 online, looked like a nice build and I was wanting to try it.
I have this PCB artwork and a component layout/stuffing guide, but I can't seem to find a schematic that matches this layout.
1675382018099.png


Can anyone help me please?

JohnR
 
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Agus sugiono

Agus sugiono

Member
Joined 2018
petr_2009 said:
Many radio amateurs liked the APEX AX17 circuit and began to clone it. The disadvantage of the original circuit is a high cutoff frequency from below. Therefore, many radio amateurs began to increase the capacitance of capacitors: input capacito and in the negative feedback circuit. Due to the tracking power of the input stage, it is little affected by changes in the resistance of the signal source (volume control potentiometer). For those who are going to repeat it, I would recommend using a Baxandall pair in the voltage amplifier (as is done in the AX16 amplifier and others). A pair of Baxandall, due to the tracking power of input repeaters, has a lower input capacitance, and a voltage amplifier with a pair of Baxandall, due to deeper local feedback, introduces less distortion. The amplifier has a relatively high frequency of the first pole - above 20 kHz. Due to this, the output impedance in the entire sound band is constant. Using a servo control system allows you to remove the input capacitor and the feedback capacitor.

The amplifier has a relatively short signal propagation delay, 65 ns. Due to this, negative feedback copes well with both switching distortion and high-speed distortion. Due to the high frequency of the first pole, the amplifier has a short decay spectrum, the 7th harmonic and above is negligible.

Here are some tests of the modified circuit, maybe someone will be interested
Click to expand...
Excuse me sir, what kind of simulation do you use?
 
44250

44250

Member
Joined 2011
forum.yu3ma.net
graham355 said:
Hello,
Does anyone know the power requirement for Apex SB3.1 BJT preamp 47k ? My transformer is 180va 24-0-24 vigortronix toroid and it seems excessive. I was thinking or using 30va or 50va instead but I am not sure how much power it requires.
Thank you.
Graham
Click to expand...
even 10W transformer is ok. you really do not need more than 20W or 30W transformer. more is better - but too much is not needed.
 
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