ACL - Discrete Core Ladder Filter

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449,00 €
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  • Manufacturer: ACL - Audiophile Circuits League

The ACL 24dB Disrete Core Ladder Filter VCF is classic transistor ladder design. 
A fully discrete, low noise, low distortion audio path is used in the whole circuitry. 
Some special features provides loads of possibilities as described in the text below. 

The VCF ladder design consists of 4 stages, providing an buffered output for each of the 4 stages separately in order to 
get a 6dB, 12dB, 18dB and 24dB/octave -sloped filter output individually. 

The cutoff frequency of the VCF can be controlled manually using the knob named „CUTOFF“ and by 3 independent external control voltages, connected to the input jacks „1V/OCT“, „CV1“ and „CV2“, the latter two having attenuators. 
The VCF´s resonance can be controlled manually and by an external CV. 

When resonance is turned fully, up self oscillation will occur, enabling to use the VCF as a voltage controlled quadrature oscillator (a 90 degree shift occurs at every filter pole) 

In a very classic design of a lowpass adder VCF, the lower frequencies are damped more than higher frequencies, generating a loss of self oscillation at low cutoff frequencies. 
This behaviour can be achieved by switching „Q LIN“ to LOW“ or „MID“, assigning 2 different cutoff frequencies of high pass filter in the feedback loop of the filter. 
By switching „Q LIN“ to „HI“ the cutoff frequency of that high pass filter is lower than 1 Hz, enabling self oscillation even down to the LFO range of frequencies, 
The cutoff frequency is temperature stabilized and shows good tracking with 1V/Oct. to up to 5 octaves. 
3 audio signals can be connected, being summed together to one signal in order to enter the VCF. 
When approaching 8V PP, the ladder will start to saturate, creating a awesome creamy and compressed sound, to go into distortion if the input level is pushed further. 

In many ladder designs, the lower frequencies gets more attenuated (bass loss), when increasing resonance, approximating a bandpass behaviour at very high resonance settings. 
The „BASS BOOST“ control can be used to compensate for that effect. 

That way you can make very bombastic bass sounds, since the sound might got higher resonance settings and still kept it´s bass fundament. 
When not overdriven by input audio signals, the overall distortion of the fully discrete audio signal circuitry is quite low due to the use of low distortion discrete buffers, enabling a very clean sine wave when self-oscillating no too strongly, unlike some other designs. 
The use of matched components made it possible to keep the CV-feedtrough quite low.

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