SKU: 72003354785

Doepfer A-101-1 Vactrol Filter

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Description

Doepfer A-101-1 Vactrol FilterDoepfer A 101 1 Vactrol Filter Eurorack Module For Sale. This module is part of the extensive Doepfer A 100 Modular product line. We're a Doepfer dealer. If you're looking to buy a system, monster case, or large lot of modules, please contact us. This item is new in box, carries the manufacturer's warranty, and ships free within the continental US. All photos shown here were provided by the manufacturer, along with the following product description:

Doepfer A-101-1 Vactrol Filter Eurorack Module For Sale.
This module is part of the extensive Doepfer A-100 Modular product line.

We're a Doepfer dealer. If you're looking to buy a system, monster case, or large lot of modules, please contact us. 

This item is new in box, carries the manufacturer's warranty, and ships free within the continental US. All photos shown here were provided by the manufacturer, along with the following product description: 

This is the first vactrol based module in the A-100 system. A vactrol is a combination of a light depending resistor (LDR) and a LED (light emitting diode) both put into a small light-proof case. Increasing the LED brightness causes a decrease of the LDR resistance (e.g. the light controlled voltage module A-179 is an application of a LDR). This effect can be used in circuits that require variable resistors to obtain the desired function (e.g. VCFs, VCAs, VC phasers, VC trigger delays, VC slew limiters, VC Envelope Generators, VC LFOs, VCOs and many more). The advantage of vactrols compared with other solutions (e.g. OTAs, diodes, transistors or FETs as variable resistors) is that they behave like a normal Ohm resistor and can handle high voltages without causing distortion. This is probably the reason why the sound of vactrol-based circuits usually is described as soft or mellow. Disadvantages are theexpenditure and consequently the expenses and the not exactly defined coherence between LED current and LDR resistance. For each vactrol the LDR resistance decreases when the LED current increases but mechanical and electrical tolerances cause that each vactrol will behave a bit different (e.g. because of the differences in alignement and distance between LED and LDR, different brightness of the LEDs at the same current).

Module A-101-1 is a special multitype filter based on an idea by Nyle A. Steiner (published in Electronic Design, issue  25, December 1974, page 96 ff). The circuit uses the standard non-inverting amplifier filter design. Different filter types (low pass / LP, band pass / BP, high pass / HP) are realized by injecting the audio signal into different points of the circuit and using a common output for all filter types. One may feed three different audio signals into the filter simultaneously. Each signal is filtered correspondingly (LP resp. BP resp. HP) and the sum of the three filtered signals appears at the output. Of course it is possible to feed the same signal to all three inputs. In this case one obtains different combinations of LP/BP/HP according to the settings of the three input attenuators for LP/BP/HP. Even a Notch filter is possible (not available in the original design). The filter inputs are normalled, i.e. the BP input is connected to the LP jack socket provided that no cable is plugged into the BP socket (same applies for HP/BP inputs). 

In contrast to the original circuit vactrols are used instead of diodes as variable resistors for frequency control of the filter. Due to the"crooked" response of vactrols the filter has not an exact frequency control standard (like V/Oct). The inevitable tolerances between different vactrols will lead to an individual sound of each module and individual resonance behaviour. Even the resonance control is realized with vactrols. Consequently this parameter is voltage controlled, too. Resonance can be increased up to self-oscillation. Resonance and consequently self-oscillation may vary with the filter frequency because of vactrol tolerances.

A special feature of the module are the two audio outputs. Out 1 is the output of the original circuit. In the original circuit by Nyle A. Steiner the output level was distinctly dependent upon the resonance (higher resonance = higher output level). Out 2 compensates this behaviour by the usage of an additional vactrol that is connected in series to the vactrol that controls the resonance. This additional vactrol forms an attenuator (or simple VCA) that approximately compensates the level increase for higher resonance settings.

Two LED displays show the current frequency and resonance setting. The LEDs are connected in series to the LEDs inside the vactrols and show consequently the LED illumination inside the vactrols.

Width: 16TE / 16HP / 80.9 mm
Depth: 50 mm (measured from the rear side of the front panel)
Current:
+30mA (+12V) / -30mA (-12V)

 

 

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SKU: 72003354785

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Norman Shurtleff
Port Orchard, US
★★★★★ 5
Great ipad
Style: Wi-Fi, Size: 128GB, Color: Blue, Configuration: Without AppleCare+
I recently purchased the Apple iPad 11-inch with the A16 chip, and I couldn’t be happier with the performance. The speed and responsiveness are outstanding, whether I’m browsing the internet, streaming videos, handling work tasks, or using multiple apps at once. The 11-inch display is bright, crisp, and provides excellent color quality, making it perfect for watching movies, reviewing documents, and viewing photos. The battery life easily lasts throughout the day, even with heavy use. The A16 chip delivers smooth performance with virtually no lag, making multitasking effortless. Apps open quickly, and everything runs seamlessly. The lightweight design makes it easy to carry around, whether for business, school, or travel. The camera quality is impressive for video calls and document scanning, and the overall build quality feels premium, as expected from Apple. Overall, the Apple iPad 11-inch with the A16 chip is an excellent investment for anyone looking for a powerful, reliable, and versatile tablet. It combines speed, portability, and ease of use into one outstanding device. Highly recommended!
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Reviewed in the United States on June 6, 2026
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W. T. Traylor
Battle Creek, US
★★★★★ 5
It’s an iPad that works great
Style: Wi-Fi, Size: 128GB, Color: Silver, Configuration: Without AppleCare+
Super easy to setup using my wife’s older iPad. With a good case it is very durable and the unit was new.
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Reviewed in the United States on June 7, 2026
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John Jones
San Leandro, US
★★★★★ 5
Clear display
Style: Wi-Fi, Size: 128GB, Color: Blue, Configuration: Without AppleCare+
I got this to replace an old iPad Pro. It does everything my old pro did, except for having a smaller screen. Good value and set up and migration from old iPad was super easy. Good battery life and so far playing games on it haven't been an issue
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Reviewed in the United States on May 30, 2026
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Pug lover
Birmingham, US
★★★★★ 5
New Ipad
Style: Wi-Fi, Size: 256GB, Color: Yellow, Configuration: Without AppleCare+
Nice size with a nice clear picture. Replaced a very old iPad. Not all apps and things transferred like the iPhone. But very manageable with a little time. So far I am pleased with this iPad.
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Reviewed in the United States on June 6, 2026
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Mads
Waukegan, US
★★★★★ 4
Its Great! Except one tiny detail
Style: Wi-Fi, Size: 512GB, Color: Pink, Configuration: Without AppleCare+, Style: Wi-Fi, Size: 512GB, Color: Pink, Configuration: Without AppleCare+
Ipad works great, easy to set up and everything transferred from the cloud from a backup I had (thank god because my other ipad is completely dead). Everything is in order except they put the magnets in the wrong spot xD. It doesnt matter functionality wise and I feel its more hassle to exchange than its worth so I am going to keep the iPad. With the case its in it doesnt really matter because theres a spot already for the pen. 4/5 stars
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Reviewed in the United States on May 13, 2026

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