Archive for EQ

Calrec PQ 1161 Mic Pre & EQs

Posted in Repaired with tags , , , , , , , , , on September 29, 2013 by AnalogAudioRepair

I have always been interested in Calrec modules.  They are touted as being “as good as Neve”, “built to BBC specs”, and on and on.  Recently I found myself with a few modules on my bench from two different clients.  The first two were racked and powered but the second unit was noisy.  The other module came from a larger rack with 1181 and 1161 modules.  It had a different problem which I will get to later.  Besides the beautiful construction of these units, the first big thing I noticed was that the pair had all discrete amplifier cards, while the single unit had ICs (chips) on the cards!  It seems Calrec changed over at some point between the serial numbers in the 450 range and those in the 600 range.

The discrete amplifier cards are easy to pull out and swap for quick troubleshooting.  That was good because it allowed me to pinpoint the output amplifier as the noisy board.  Then probing with the oscilloscope tracked the noise down to the first transistor on the card.  Replaced the part, and it spec’ed just like the good channel again.

Thankfully the module with ICs had a much simpler problem, though one to watch out for!  These modules were sold with no light bulbs in the EQ and phase reverse switches.  The owner bought bulbs, put one in the EQ switch and watched smoke come pouring out!  Fearing the worst, he brought me the module.  Thankfully, there is a current limiting resistor which gave it’s life (and gave up the magic smoke) to save the day.  The problem was the way that the bulb socket mounts on the switch.  It is a plastic holder that straddles the switch and is soldered to the first pin on either side.  However, on this one module the other pins were not bent down for some reason (as they were on all the other modules) so pushing in the bulb caused it to short against the second pin!  Replacing the 100 ohm resistor and bending the pins was all it took to get things back to normal.

Image

Calrec PQ 1161 Preamp & EQ

Calrec PQ 1161 Preamp & EQ

Calrec chip amplifier cards B202/205/210

Calrec chip amplifier cards B202/205/210

Calrec chip amplifier cards B202/205/210

Calrec chip amplifier cards B202/205/210

Calrec discrete amplifier cards B202/205/210

Calrec discrete amplifier cards B202/205/210

Calrec discrete amplifier cards B202/205/210

Calrec discrete amplifier cards B202/205/210

Calrec discrete amplifier card B202/205/210 PCB Front

Calrec discrete amplifier card B202/205/210 PCB Front

Calrec discrete amplifier card B202/205/210 PCB Back

Calrec discrete amplifier card B202/205/210 PCB Back

Neve 5316 Diagrams

Posted in Uncategorized with tags , , , , , , , , , , , on July 21, 2013 by AnalogAudioRepair

I have been working on some modifications to the Studio G Neve 5316.  The board came from BBC Scotland and did not have any schematics.  While it is certainly possible to figure out a lot of the signal flow without block diagrams, it is sort of like driving across country without a map – you know where you start and end, but you have to find signs in between.

I posted on Geoff Tanner’s vintage Neve forum at http://auroraaudio.net/forums/ and frequent contributor Mr. Blake Devitt was able to provide some helpful documents.  The forum did not handle large images well, so I volunteered to host them here for anyone who needs them in the future.

Block Diagram

Block Diagram

Circuit page 1

Circuit page 1

System Diagram

System Diagram

Telefunken ELA V624 Discrete Preamp & EQ

Posted in Repaired, Restored with tags , , , , , , , , , , , on June 29, 2013 by AnalogAudioRepair

Bad packing, or should I say NO packing, is to blame for the damage this preamp suffered.  It was shipped to me in a small flat rate Priority Mail box with nothing to protect it.  As you can see, the frame was bent and one of the circuit boards was broken into six pieces!  The frame was easy enough to bend back, but the PCB was like a little jigsaw puzzle that required epoxy and jumper wires to make it structurally and electrically sound again.  While I had it open, I replaced the electrolytic caps and added XLR ins and outs as well as a power jack with regulation.

The ELA V624 is a nice little module from later Telefunken mixers.  It has a mic pre with 60dB of gain, high and low EQ (I believe at 60Hz and 10kHz), and a line input as well.  Both the mic and line have transformer balanced inputs and I wired the unit with an impedance balanced output.  The circuit is fully discrete transistor and runs on +24v DC.  They are not as huge sounding as the earlier discrete modules (V672 Pre, W695 EQ, etc.) but very useable on a variety of sources.  Certainly worth the time spent repairing such unnecessary damage!

Bent Frame

Bent Frame

Broken PCB

Broken PCB

Broken PCB 2

Broken PCB 2

Before

Before

Fixed Frame

Fixed Frame

Fixed PCB

Fixed PCB

Recapped

Recapped

XLR Box

XLR Box

Completed, Front

Completed, Front

Completed, Back

Completed, Back

Sphere 1014 and 910 Equalizers

Posted in Racked Modules with tags , , , , , , , on May 3, 2013 by AnalogAudioRepair

This is a rack full of vintage Sphere equalizers.  My client made the wooden case from zebra wood and walnut.  I wired and mounted the EQs and transformers and built the power supply.  The 1014s are IC based parametric EQs with high and low cut filters.  The 910s are fully discrete graphic EQs with inductors for each band.  We used transformers from Orphan Audio – Quad Eight inputs and Reichenbach outputs.  Unfortunately the Reichenbachs were PC mount so I had to attach them to some perfboard.  The Quad Eights mounted right below the input jacks on the back panel.  Power requirements were +/- 24VDC for audio and +5VDC for logic.  It was a lot of wiring to fit in the box, leaving length for servicing.  They are pretty fantastic EQs, especially the graphics!

Sphere On

Sphere Back

Sphere Back

Sphere Wiring

Sphere Wiring

Sphere Xfmr Board

Sphere Xfmr Board

Sphere PSU

Sphere PSU

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.

Yamaha PM1000

Posted in Modded, Racked Modules with tags , , , , , , , , , , , on September 19, 2012 by AnalogAudioRepair

Yamaha PM1000 discrete transistor console strips cut down, recapped, modded, and racked as mic pres with EQ.