Square wave perfomance of 303

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23-Nov-2017 04:05 PM

Iang

Iang

Posts: 2

I have just been checking a 303 for a friend who thinks the amp is far to bass heavy. Took a look inside and all looks in order and it is evident that a full set of new capacitors have recently been done. Ran a sweep from 10Hz to 30KHz and seems very linear level output, sine and triangular waveforms look very good but with a square wave not so. The rising edge is good with no overshoot but then the waveform droops down before the falling edge. Response does not alter at any level running into 8 ohms so suspect it is not power supply droop. Any pointers as to where to look ?

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26-Nov-2017 08:51 AM

Joost Plugge

Joost Plugge

Posts: 943

The 303 was designed in a age with sensible frequency limits. For producing a good square wave you need the basic frequency and a infinite number of harmonics. Not possible in a 303, so test only the bandwidth with a sinus and check the -3dB points.

Joost Plugge

DaDa Engineering

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27-Nov-2017 04:24 AM

EJP

EJP

Posts: 1412

The 303 was designed, like all prior and subsequent Quad power amplifiers, with a 15Hz lower pole and a 55kHz upper pole. It is not intended to reproduce square waves perfectly, or medium-wave transmissions either.
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27-Nov-2017 06:39 PM

Iang

Iang

Posts: 2

That is good to know. The sine performance looks excellent and is certainly linear in amplitude within accepted bandwidth. So I think that the amplifier is not at fault in my friends system. He is using a Carver pre with a very high output level, something like 7v at full output so maybe some mis matching, but I did lend him a 33 to try out and he didn't think that improved things. Maybe he needs a hearing test :)

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