2 questions about my quad 405 clone

[iceman]

I built a chinese quad 405-2 clone, powered by +/- 25V
There's no speaker attached, i have 100W 4Ohm resistor instead, where the probe is connected.
I have 2 questions.
Q1.) Why isn't the squareWave the same on pic #2 as on pic #1 ?
Pic #1 is the signalgenerator -> Oscilloscope, no amp involved at all
Pic #2 : I have a 100k pot as volumeControl , Signalgenerator -> volumeControl -> lineIn on the Amp.
The probe connected after VolumeControl.
Are there better potentiometers to find ?

Q2.) Is there anything i can change/replace on the amp to make it better ?

 

[ejp]

Q1.) Why isn't the squareWave the same on pic #2 as on pic #1 ?

Because the 405 was never designed to behave like a medium wave transmitter, as the designers emphasised repeatedly. The bandwidth is 55kHz or less, and this is never going to reproduce square waves accurately.

Q2.) Is there anything i can change/replace on the amp to make it better ?

Given the above, define ‘better’ in such a way as to conform to the original design intent.

 

[arjen6t8]

My experiences with these Chinese Q405 clones are not all that positive, but if you want to tinker with them, there's a lot of information here on DIYaudio already. Otherwise have a look here: Keith Snook Quad-405 modifications or do a Google search for the 'Bernd Ludwig Quad-405 paper'.

 

[jxdking]

I don't know the clone. However, in the origianl Quad 405, there is a low pass filter at the output of opamp that limits the bandwith around 40KHz as I recall.