Archive for vintage

Ampex 601 Tube Preamp & DI Mod

Posted in Modded, Restored with tags , , , , , , on March 22, 2013 by AnalogAudioRepair

This was a fun project that involved removing some tape deck electronics and modding the remaining circuit into a tube mic preamp with DI.  As you can see, several of the tubes are not needed when using this as a preamp.  A whole bunch of other parts came out too which cleaned up the crowded underside of the chassis a good bit.  The headphone jack is now the DI input and the Input/Tape switch selects either the mic or DI.  The Line Rec Level pot is now the DI level control and an XLR output jack has been added on the side.

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Telefunken V72S Transformer Replacement

Posted in Repaired with tags , , , , , on February 26, 2013 by AnalogAudioRepair

This is a rare Telefunken V72S – the “S” is a higher gain version.  Unfortunately this one had a bad input transformer.  The frequency response of the transformer looked like this: /   A rebuilt original was too costly for my client, but Sowter offers a replacement that works just fine.  The hard part is removing the original and mounting the new one!

RCA BA-2C Tube Preamp

Posted in Restored with tags , , , , on February 26, 2013 by AnalogAudioRepair

This vintage RCA vacuum tube preamplifier was missing it’s power transformer.  Fortunately I had the schematics and a transformer that would fit the bill.  A couple power resistors were required to get the voltages spot on, but in the end it worked out well.  The unit got a full re-cap and a fresh set of New Old Stock vacuum tubes.  The new owner even received an original manual!

GATES Discrete Microphone Preamps

Posted in Racked Modules, Restored with tags , , , , on December 29, 2012 by AnalogAudioRepair

This is a pair of Gates broadcast discrete transistor mic pres.  These microphone preamplifiers were used in Gates radio boards and have transformer balanced inputs and outputs.  They have 37 dB of gain and I racked them with a level control ranging from 20-37db.  The position of the level control is immediately after the input transformer so there is no need for a pad on the input unless you are overloading the transformer!  These units were re-capped and wired for 150 ohms in and 600 ohms out.  This was a super simple and clean rack job so they only have XLR in and out, level control, and a power switch for the outboard +30v power supply.

CBS Volumax Limiter Mods

Posted in Modded with tags , , , , , , on December 29, 2012 by AnalogAudioRepair

This was a project for a client from Brazil – modding a CBS Stereo Volumax discrete transistor limiter.  The Volumax is a two band limiter with transformers in and out.  You can do fun stuff like turn off the high or low frequency limiting, vary the HF level, change the release times, and much more.  This was a pretty standard mod that also included XLR in and out.  Amazing units when you do a bit of work to them!

DuKane 2A81 Compressor Mods

Posted in Modded with tags , , , , , , , , on November 28, 2012 by AnalogAudioRepair

Here are a pair of vintage DuKane compressor/limiters.  They use an all discrete transistor circuit path with a FET for gain control.  They come stock with a (useless) noise gate, two inputs, and some controls on the rear panel.  These mods remove the noise gate, move the ratio and bypass to the front, and add release time settings.  Everything gets cleaned up and boards are re-capped if needed.  The results?  “A super smash box” according to one user!

Altec Coke Bottle Mic PSU

Posted in Repaired with tags , , , , , , on November 28, 2012 by AnalogAudioRepair

A client sent me a vintage Altec M11 “Coke Bottle” tube microphone that needed re-capping.  The 518A power supply has a lot of caps, but the new ones are much smaller.  After re-capping and a new tube the mic sounds great!

Acoustic 126 Bass Amp

Posted in Repaired with tags , , , , , on October 15, 2012 by AnalogAudioRepair

This is a vintage Acoustic Control Corp. model 126 bass amplifier.  I received it non-functioning with no power cord or fuse cap.  Replaced two output transistors, re-soldered an inductor in the EQ section, and cleaned the heck out of the pots and sliders.  Added a new power cord and fuse cap and it fired right up.  These ’70s Acoustic heads really sound good!

Allison Labs 2ABR

Posted in Modded with tags , , , , , , , , on October 15, 2012 by AnalogAudioRepair

This is a vintage Allison Labs passive filter / equalizer with custom mods.  It has UTC input and output transformers and XLR connectors added as well.

Universal Audio 1108 & 508

Posted in Racked Modules, Restored with tags , , , , , , , , , , , , , on October 7, 2012 by AnalogAudioRepair

This is a set of vintage Universal Audio (UA / Urei) 1108 discrete transistor microphone preamplifiers with matching 508 passive equalizers.  The preamps are transformer in and out and sound amazing.  The EQs use passive capacitors and inductors for simple but smooth EQ.  Restored and racked with phantom power and gain pots.