CT1 REVIEW

Following here, you may read a 100% complete review of the DACT CT1 audio attenuator review published in the Audio Electronics magazine, issue ONE: 2000.

The review is reprinted, with permission, from Audio Electronics, Issue 1, 2000, p.p. 42-45, of Audio Electronics magazine. © Copyright 1999 by Audio Amateur Corporation, P.O. Box  876, Peterborough, NH 03458, USA. All rights reserved.

Danish Audio ConnecT CT1 Audio Attenuator

Reviewed by Fred Gloeckler

(His conclusion):
...........With its clear, natural sound, superb specifications, compact size, and high quality standard, I highly recommend the CT1 for consideration when you need a volume control. After listening to it, I'm compelled to upgrade my system. Now, if they'd just provide a high-resolution means to adjust balance...
 

Danish Audio ConnecT CT1 Audio Attenuator

Reviewed by Fred Gloeckler

Danish Audio ConnecT Ltd., Rm. 1501/3 Ban Chang Glas Haus Bldg., 1 Sukhumvit Road Soi 25, Bangkok 10110, Thailand; (+66 2) 260 6072, FAX (+66 2) 260 6071, E-mail: vifadact@loxinfo.co.th, website: www.dact.com. Prices: CT1 mono attenuators, US $105; CT1 stereo attenuators, US $138.50; CT2 stereo attenuators, US $126.20.



The Danish Audio ConnecT (DACT) CT1 Audio Attenuator is a compact, 24-step switched attenuator. It uses surface mount (SMT) resistors In a series configuration and is available in one (mono unbalanced), two (stereo unbalanced or mono balanced), and four (stereo balanced or quad unbalanced) deck configurations (Photo 1).
It offers standard controls with total resistances of 10, 20, 50 and 100kOhm. Custom versions will be considered. The nominal attenuation at each of the 24 steps is: 0, -2, -4, -6, -8, -10, -12, -14, -16, -18, -20, -22, -24, -26, -28, -30, -32, -34, -38, -42, -46, -50, -60 and -infinite dB.
The SMT resistors are soldered to a circuit board, which, in turn, is soldered directly to the switch deck pins. The layout is very compact, and is said to minimize inductance and stray capacitance. Both the circuit board and switch contacts are gold-plated. The switch source appears to be ELMA.
Figure 1 shows the outline dimensions of the two-deck version (also see Photo 2). The front of the switch has a locating tab that fits in the notch in the mounting-panel hole. The header pins allow you to make connections by hardwire, a header socket, soldering to a circuit board, or, I suppose, a wirewrap (Photo 3). The CT1 takes up little panel space and is suited for "slim-line"enclosures that can't accommodate larger switches or potentiometers. Danish Audio ConnecT's model CT2 (not tested) is slightly more compact.
The switch has a positive mechanical detent at each step. While the turning torque is light, the detents can be felt and heard. The 6mm-diameter shaft accommodates knobs with standard 0.25" shaft holes. If panel space is at a premium, you can use a relatively small-diameter knob and still turn the shaft without using excessive force.
Danish Audio ConnecT has a comprehensive data sheet for the CT1. Key electrical characteristics are listed in Table 1. You can find more specifications on the DACT website.
My shop isn't equipped to confirm many of the electrical specifications. I checked attenuation accuracy, channel balance, frequency response, and channel separation with the outputs of a 20kOhm stereo CT1 feeding unity-gain buffers.
This setup simulates the loading an attenuator might see in real life. The CT1 was mounted in an aluminum box with its inputs connected to the input jacks via shielded cable. The attenuator outputs were connected to

TABLE 1: KEY ELECTRICAL CHARACTERISTICS Parameter Value Total resistance accuracy (new) 0.1% DC attenuation accuracy (new) ±0.05dB DC matching accuracy (tracking) (2 wafers) ±0.05dB Contact resistance (new) Max. 0.01Ohm Contact capacitance (adjacent contacts) 1pF Series inductance (10kOhm version, pin 1 to 3) Max. 0.2µH Bandwidth (10kOhm version, A=-6dB, deltaA=-3dB) 50MHz Noise voltage (10kOhm version, pin 1 to 3) 12.8nV/sqrt(Hz) Total harmonic distortion (A=-6dB, f=1kHz) Max. 0.0001%

the inputs of a pair of Borbely tape buffers¹ by short, unshielded wires. The buffers isolate the attenuator from the loading effects of cables and test equipment and have a 1MOhm input resistance.

Measurements
Measurements were made with a Fluke 8050A digital multimeter² using the Morrey version of a Heath IG-18 audio generator as a signal generator³. In addition to measuring the control resistance, I measured attenuation for each control step at frequencies of 1, 10, 20, 50, and 100kHz using the relative measurement capability of the 8050A. I then analyzed the measurements to extract attenuation, channel-balance, and frequency-response errors.
The total resistance errors for the two channels were -0.1% and -0.075%, which meet the tight specifications.
Because the CT1's performance is at or better than my instrumentation's measurement capability, I debated how to present the results, or even, whether to present them. I finally decided to just list the attenuation, channel balance, and frequency-response errors tabulated in table 2.

TABLE 2: CT1 ATTENUATION ERROR, CHANNEL BALANCE, AND FREQUENCY RESPONSE Nom. atten . (-dB) Attenuatio n Error (dB) Channel Balance (dB) Frequency Response Error (dB) Front Rear (Rear - Front) Front Deck Rear deck 1kHz 1kHz 1kHz 10 kHz 20 kHz 50 kHz 100 kHz 10 kHz 20 kHz 50 kHz 100 kHz 10 kHz 20 kHz 50 kHz 100 kHz 0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -2 0.00 -0.01 -0.01 0.00 0.01 0.00 0.03 0.00 -0.01 -0.01 -0.02 0.01 0.01 0.00 0.02 -4 0.01 0.01 0.00 0.00 0.01 0.01 0.05 0.00 0.00 -0.01 -0.04 0.00 0.01 0.00 0.01 -6 -0.01 -0.01 0.00 -0.01 0.01 0.03 0.04 0.01 0.00 0.00 -0.02 0.00 0.01 0.03 0.02 -8 0.01 0.00 -0.01 -0.01 0.00 0.03 0.04 0.00 -0.01 -0.01 0.00 0.00 0.00 0.03 0.05 -10 -0.02 -0.02 0.00 -0.01 0.01 0.03 0.04 0.01 0.00 0.00 0.02 0.00 0.01 0.03 0.06 -12 -0.04 -0.04 0.00 -0.01 0.01 0.02 0.03 0.01 -0.01 0.01 0.05 0.00 0.00 0.03 0.08 -14 -0.02 -0.02 0.00 -0.01 0.01 0.02 0.02 0.00 -0.01 0.01 0.08 -0.01 0.00 0.03 0.10 -16 -0.04 -0.04 0.00 -0.01 0.01 0.01 0.01 -0.01 -0.02 0.00 0.08 -0.02 -0.01 0.01 0.09 -18 -0.05 -0.06 -0.01 -0.01 0.01 0.02 0.01 -0.01 -0.03 -0.01 0.09 -0.01 -0.01 0.02 0.11 -20 0.01 0.01 0.00 0.00 0.01 0.02 0.02 0.01 0.00 0.01 0.01 0.01 0.01 0.03 0.03 -22 0.00 -0.01 -0.01 0.01 0.00 0.02 0.01 -0.01 0.00 0.01 0.02 0.01 0.01 0.04 0.04 -24 0.01 0.01 0.00 0.01 0.01 0.02 0.01 -0.01 0.00 0.02 0.03 0.00 0.01 0.04 0.04 -26 0.00 0.00 0.00 0.01 0.01 0.02 0.01 -0.01 0.00 0.02 0.04 0.00 0.01 0.04 0.05 -28 0.02 0.01 -0.01 0.01 0.02 0.02 0.01 -0.01 -0.01 0.01 0.06 0.01 0.02 0.04 0.08 -30 -0.01 0.00 0.01 0.01 0.01 0.02 0.02 -0.01 0.00 0.02 0.06 -0.01 0.00 0.03 0.07 -32 -0.05 -0.05 0.00 0.01 0.01 0.02 0.01 0.00 0.00 0.02 0.08 0.01 0.01 0.04 0.09 -34 -0.02 -0.03 -0.01 0.00 0.00<