A&H Spectrum Mixer Refurb 2

Overview The A&H Spectrum finally arrived on 20th January 2020, very well packed and at 59 Kg! After some serious unpacking the refurb can now begin, with the PSU being the first to be looked at, so that I can power on the Master/Group section initially then add the Channel sections.

PSU Refurb The power supply is an Allen & Heath RPS3 from 1991 (serial number 7) and is a 3A linear power supply based on tried and trusted LM723 chips. Whilst the metal chassis has some rust patches rusty and the PCB is old, it looks in ok shape, although the 48V rail power cap is either bulging or has a dome! After carefully checking the power supply components I switched it on; +16.3V, -0.8V and +48V. So looks like we need to replace a component!

The original reservoir capacitors are 10,000uF 35V with 85 degree temperature rating. I want to fit large capacitor values at 105 degree rating, but I am limited to a 30mm diameter as that is the size of the mounting. I located some 15,000uF 35V 105 degree capacitors made by EPCOS and fitted them. This will reduce the ripple voltage into the regulators down to 100mV.

The LM723 chips have date codes from 1988, so these were replaced and I added IC sockets, then all the smaller power capacitors and the original MJ3001 power transistors and bridge rectifiers. One of the bridge rectifiers had failed, hence no -15V rail. Remarkably the 723 has become obsolete, so it is was a good time to buy some before they get expensive. All the wiring to the rectifiers had become heat damaged and brittle (greaking off at the solder joints), so it all needed replacing with thicker gauge wire and the same colour coding.

The original transformer is a traditional open frame model at 225VA. It provides two secondary circuits at 21.5V for the 16V rails and one for the 48V phantom power. I am keen to switch in a toridial transformer for the main rails and it has to be 225/250VA which means a diameter over 100 mm. I will have to mount this on the inside of the front panel, as that is the only space big enough. Alternatively I could just buy a cheap secondhand RPS11 which has 5A rails and a toridial transformer – lets see what eBay offers!

Fader Cleaning The high quality Alps K-series 100 mm faders are in generally good condition but they needed a deep clean as the action was not smooth. I started with the Group and Master section and took them apart, cleaned them with IPA, then Dexoit Fader cleaner, and finally put some fader lube on the lower brass rail. Each slider was cleaned so that it would slide from one end to the other on gravity alone, once apart. Sometimes steel wool was needed to remove corrosion on the brass rail.

I may buy two new Alps faders for the Master section but lets see how well the cleaning has worked. At £15-20 each I don’t want to replace all 26. I will clean the Channel faders as part of the Channel refurb once I see what issues there are in each of the channel cards.

Fader Knobs The black slider caps are nice and chunky but well worn with the white line disappearing, however I do have all 26 in place and I will have to keep them. Modern caps are too short and stand proud of the panel or mean dropping the fader down by 4 – 5mm is not possible as there is no room in the chassis.

Panel & Knob Cleaning Whilst I waited for parts to arrive to get the RPS3 working, I cleaned the front panels with surface cleaner and deep cleaned every knob and switch cap (after removing them). This was a very long, but worthwhile task. A small number of knobs were broken or missing, as were some caps. I ordered 8 new knobs, so I could fit them in one row in the Group section, thereby releasing some original knobs and minimizing the colour change from new to old. The dark green caps for PAN are not available, so I ordered 30 light green caps and a couple of red and blue caps were also needed but I am hoping these colours match the originals.

Group Channel Refurb The eight Group PCB’s are in good condition but could do with an electrolytic recap and the Mylar film capacitors in the power conditioning replaced with modern MLCC. The HF/LF circuits really need Wima 2.5% polypropylene capacitors (2 x 15nF and 1x 2n7F). However the most important upgrade is to replace the balanced output drivers (NE5532 with trimmers) which live on a separate PCB attached into the Master section, with THAT1646’s. I will design a replacement PCB.

Roland CSQ-100 Refurb

My CSQ-100

Overview In November 2017 I bought a little Roland CSQ-100 in good working condition for a £150, with a plan to swap out the 2114 RAM memory and upgrade with more memory and the ability to store sequences when powered off.

My CSQ-100 has a serial number of 183628, which dates it to May 1982 and probably one of the last made, as by the end of 1982 you could buy a Roland SH-101 with a sequencer built in. Then in 1983 with the arrival of MIDI Roland moved onto MIDI sequencers such as the MSQ-100. With over 3500 sold this little sequencer was a big hit for Roland at the time.

CSQ100 History  Roland released the basic single track CSQ-100 Digital Sequencer with CV and Gate inputs and outputs in May 1979 and made over 3500 before introducing the more power 4 track memory CSQ600 a year later.

The CSQ-100 is micro processor based using an 8-bit Intel 8048 with a tiny 2k byte operating system, which went through 2 revisions. It was usually paired with Roland’s new mono synths of the time such as the SH-09, SH-1 and SH-2.

The CSQ-100 has no lithium or nicad battery, as there is no memory retention for the single 2114 RAM chip, so your sequences are lost at power off. However with no battery to leak, many have survived in good condition.

The CSQ-100 has two memory channels of up to 84 notes which can be played separately or in sequence. one after the other.   There are start and step pulse inputs but no DIN SYNC or wider interfacing capability. MIDI was over four years after the CSQ-100 was launched, but DIN SYNC was a standard in the early 1980’s. I plan to add DIN SYNC in to my CSQ-100 so it can play in sync with my Roland SBX-1 and Cubase.

Recap Whilst in physically good condition the PSU board needed a recap after 37 years. All the electrolytic and 100nF bypass capacitors were replaced with high quality modern replacements. Testing the power rails revealed the +15V was ok but the +5V had dropped down to +4.85V. So the 7805 regulator chip was replaced and the rail went back up to +5.00V. The electrolytics on the main board were also replaced. I use Panasonic and Nichicon capacitors.

Slider Dust Covers These had perished over the years and a new set were cut from 1mm black EVA sheet. It is important to do this as the old covers break into little pieces that drop into the switches and sliders. Using black EVA rather than a grey means that the hole around the slider or switch blends into the background of the panel cover. I also replaced the front panel screws with either new Philips head M3 at 6 and 8mm or hex cap M3 at 6mm to improve the look of the sequencer. A lot of the old screw heads had been damaged or were rusty.

Testing With the sequencer refurbished it was time to turn in on and check everything worked ok.