LAB2104

Research IT Labratory

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Category: Tape Decks

Voltage measurement of balanced outputs

“dB”    It is common practice to measure balanced outputs with unbalanced voltmeter. This article discuss how it is the right way to do that. Lets start with several definitions about the output levels. Definitions decibel Abbr. dB Equal to one-tenth of a bel. [After Alexander Graham Bell.] 1. A measuring system first used in […]

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Otari MX55 – Improvement & Modifications

   The MX55 is one of the semi-pro reel-to-reel machines made by Otari. The machine implements robust construction but the signal path is very complicated full of op-amps. This article describe the required modifications for the improvement of the playback and recording. The preliminary work is based on: full rebuild of the mechanism – cleaning […]

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Nakamichi Dragon – Rebuild & Improvements

Introduction    The Dragon model made by Nakamichi is one of the top cassette decks and it is unique with its playback auto azimuth correction system which improves the high frequency loss due to the azimuth errors in the records. In the past several years we serviced around 10 machines and made full rebuild of […]

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Tandberg 3014A: 680mV vs 580mV – Myth or Reality?

   Some experienced technician claims that the reference level specified in the service manual was wrong listed for all the Tandberg 3014A models. The service manual specify 580mV at the Dolby chip test points (TP4) when using standard Dolby test tape like Teac MTT-150 (400Hz-200nWb/m ANSI). The Tandberg level test tape is based on 1kHz/250nWb/m […]

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Noise performance analysis of Op-Amps

I. INTRODUCTION    In a previous research we discuss the design and performance of J-FET discrete input ultra low noise preamplifier with voltage noise less than 0.3nV/ЦHz [1]. The circuit has significant benefits compared to the simple op-amp use but it is not suitable for some low scale and low power devices. Front transistor used […]

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Tandberg 3014A: rebuild & review

Part 1 – Introduction    It is a post commenting repair & upgrade process of one interesting cassette deck. I will make a detailed review of this model due to its unique circuit design (reduced use of negative feedback stages). The idea was to repair some problems, calibration, replacing the old parts that grow old and […]

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Time constant mod for the Revox B750 MK-II

   Revox B750MK-II is very interesting amplifier. It integrates nice RIAA EQ preamp for MM cartridges. After changing all of the capacitors and transistors, its sound is very impressive. First of all it is a current feedback amplifier. The power amps sound pretty at all. This post is purposed to the RIAA EQ of the […]

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LNA2104 – Ultra Low Noise Preamplifier

   The amplification of low signals from inductive transducers is not an easy task. Existing integrated amplifiers are good enough but in some applications the requirements are for better signal to noise ratio and high gain. For example the LT1028 / LT1128’s voltage noise is less than the noise of a 50Ω resistor. Here we […]

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Reel-to-Reel Project @LAB2104

   Engineers from the Laboratory of Embedded Systems (LAB2104) at Technical University – branch of Plovdiv,  started a new project for developing of contemporary Reel-to-Reel tape deck. The project includes partnership of some companies, like HWGroup (which have experience in development of smart MIDI mixers for Harman Kardon) and Technocity (one of the biggest new vinyls […]

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Phase compensation in tape recorders – stay close to the original

   Phase compensation is a method for correcting the time problems on spectrum in magnetic audio recording. These compensation networks are provided for the record amplifier circuitry, also for playback amplifier. These networks enable the circuit to be optimally compensated for group delay introduced by the record equalization circuitry with separate adjustments for both operating speeds. The result […]

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