Friday, September 9, 2016

Pioneer SPEC-1 Pre Amplifier

Pioneer SPEC-1 Pre Amplifier

Today were showing off a recent Pioneer SPEC-1 we restored.  The SPEC-1 was introduced in 1977 and available due to demand as reported into early 1980’s+ designed to be paired with the SPEC-4 amplifier. The SPEC-1 featured an impressive all function 3-staged CLASS-A SEPP topology incorporating a robust 4 gang Alps stepped potentiometer with the addition of the Mic Mixing circuit. The SPEC-1 sets itself apart in a almost totally linear flat response!

To read up on our Pioneer SPEC-4 Power Amplifier Restoration click the link below!

Power Supply AWR-094 & Fuse AWX-091
The power supply is into two stages feeding -/+B 48V rails split output for each tone/RIAA stage. A soft start input circuit shunt is employed to enable power muting.  A separated fuse PCB AWX-091 is populated with the smoothing stage 1000MFD caps.

The AWX-091 was populated with new high temp (105C) long life rated Nichicon PW’s increased to 1000MFD/100V and 63V capacitors.  The AWR-094 was populated with high temp (105C) long life 
rated PW’s and Panasonic FC’s. The voltage regulated TO-220 devices were replaced with modern MJE1503# TO-220 devices and new thermal compound applied to the sinks.  Each soft-start speaker coupled relays were removed and brandished. 

Input Circuit RIAA EQ AWF-017 & Mixing Amp AWM-083
The input circuit utilizes the Class-A SEPP buffer amplifier design to provide the output impedance required by the precision ALPS and the EQ RIAA Stage. A PA application designed microphone mixing circuit involves a 2-stage complimentary NPN/PNP gain stage.

Below is the only published RIAA Curve Response/Deeviation online to date, we performed this closely monitoring the 2.5mV input sensitivity and an ultra low distortion source (.0022 % dB THD)

The electrolytic here were replaced with Nichicon PW’s and the initial input films replaced with high grade MKP polypropylene film capacitors.  Initial differential pair BJT’s were updated with 1% match 992 TO-92 devices to replace the failure prone 2SA726 devices. All small signal BJT’s were replaced with 1845/992 TO-92 devices in the mixing circuit and 2473 diodes replaced with modern 4148 type.  The original relay was replaced with a low noise variant Omron MY-4 relay.

Tone Amp AWG-035 & Filtering AWM-082
The RIAA and Tone amp stages again use a Class A SEPP topology. The RIAA is boasted with the -/+ B 48V rails to accommodate varying input levels and high output cartridges. The sub-sonic and high frequency tone controls enable a possible 5900+ combinations for variable attenuation including a bypass switch for the filtering stage.

All of the electrolytic on these assemblies were replaced with audio grade Nichicon KA and PW low impedance capacitors, Bi-Polar caps replaced with Nichicon VP type electrolytics. the .47MFD films were replaced with a high grade MKP polypropylene film capacitor.   The tone differential pair’s were replaced with 1% matched 992 T0-92 devices replacing the original 2SA726, remaining BJT devices were replaced with low noise 1845/2383/1013 compliments. 2473 diodes were replaced with modern 4148 type diodes. 

Audio Notizen

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