Fables of the Construction

After a month or more baby-induced hiatus the build at Sandpit is getting back up to speed, though I am still managing to fit in some sample making, recording and reviewing here and there. The outer timber frame for the control room is now up and feeling solid with the first order of mineral wool arriving tomorrow, though I really don’t know where it’s going to go as space is a little short during this build. I guess I’ll just have to wade into the job of wedging it all into place, a task reliant on the chicken wire I have ordered turning up in time; the chicken wire is to hold the mineral wool in place in the roof sections as well as to prevent slippage in some wall cavities. Here are a few photos from the last week or so.

Roger in the brace position

Control Room Outer Frame (door and window spaces in foreground)

There’s been a lot of this…

…and a whole load of this.

Renovations of the Midas PR mixing desk have also been on hold, but design work has started up again, i.e. I have started jotting stuff in my notebook and splurging lists and links all over Evernote. As an aid to this task I have managed to get a copy of The Handbook For Sound Engineers: A New Audio Cyclopedia edited by Glen Ballou. It’s a 1987 edition so doesn’t have many of the digital bits n bobs in the latest revision, but then again this cost me £11 costs instead of ~£80. The new one does have an excellent chapter on transformers by Bill Whitlock (of Jensen transformers), but this is available from the Jensen website as a PDF anyway. Amongst the audio gold (mostly acoustics and electronics) in this book is a chapter on mixing consoles with some great info and opinion on grounding issues, which are probably the most significant aspect with regard to sound performance and quality. It even mentions the use of the Dean Jensen designed 990 discrete op amp, a version of which that I am using in the mix-buss amplifier, as a method of getting much higher performance (lower impedance and noise ratios) though with the caveat that “this elegant device inevitably carries an elegant price tag”. Anyway, a f***ing great book which reaps rewards with every dip in, much like its predecessor The Audio Cyclopedia by Howard Tremaine which had it’s last revision in 1969; needless to say I have that too.

Awesome tomes of audio know-how – you won’t find this kind of quality on G***S***s!

And to prove how cool this book is and why you should get your own copy, here is an inspiring pictorial extract…wow…just wow…

The apex of sound engineer chic – it never got better than this.

Right, off to the Sandpit now to screw some shit together, then swear, take it apart, and screw back together how I originally had it…then splurge acoustic sealant all over it and make a cup of tea…and repeat…

March Movement

The build is now under way at Sandpit following a few weeks of prep (see previous post). Though some gear has gone to temporary accommodation and a basic rig is sat under the stairs at my house, including the 25kg-a-piece Event Opal monitors which may have rattled window frames a few streets away when I made a batch of bass samples at home!

The first major construction job has been the control room outer stud frame, which has meant filling the limited floor space of the studio with a not inconsiderable pile of timber, seen here accompanied by Roger and Brian who are voluntarily sharing construction duties…fools.

The photo to the right illustrates this initial space issue, which has now eased due to some of the gear pile being redistributed to houses and onto the temporary storage platform above. Now the stud frame for the outer shell of the control room is up we have some clear space to work in, until the mineral wool and plasterboard get delivered.
At the time of writing the control room outer shell stud frame looks like this – the 2″ x 8″ beams are just propped in place to select the best lengths of timber. The stud wall in the foreground shows where the window and door will go. Once the beams are in place the mineral wool, deadsheeting and plasterboard layers will be applied before the inner stud frame is constructed on a float of high density mineral wool. Work has come to a halt for a few weeks now as I am taking paternity leave, though still awaiting the arrival of the child at the time of writing.

In the mean time I have taken delivery of these two shiny new Carnhill transformers (VTB2281s) which will serve as the output bridge from the JFET992 based mix-buss amplifiers in the 70s Midas PR mixing console mentioned in previous entries. Can’t wait to wire ’em up and hear how they fit in. Having chosen the final modifications for the input and group channels there now remains the not-insignificant task of cleaning/lubing old pots and faders, cleaning some switches, recapping and making a few other circuit adjustments. The main monitor section has been designed and now requires final component selection and layout (buffers, multi-gang rotary switches, stepped attenuators, etc.) – this is obsessive’s heaven.

2012 Here We Go

I’m sure I started the year thinking ‘I shall post more often’, but as ever the juggernaut of time flattened that one. I find myself sat in an almost empty Sandpit Studio having spent the last couple of weeks packing away gear so the build can at last begin (building regulations approval was granted mid-January after I had submitted possibly the most over-detailed application for two soundproofed rooms ever created…the spreadsheets…oh the spreadsheets!).

Basic rig for the coming months

I have managed to make a 6U rack of essentials (mic pres, headphone amp, Lavry monitor/mix AD/DA, patchbay, RME HDSP and power distro) to keep recording over the coming months. There’s also a few cases filled with pedals, mics, cables, etc. And then there’s the monitors…


Possibly the hardest packing task was the expansive mess of electronics components, especially those associated with the Midas PR mixing desk renovation work. Everything had to be sorted, catalogued and boxed up. All done now and I may be able to squeeze that into my house for occasional fiddlings…this desk won’t build itself you know?!

This rather blurred photo (iPhone+strip lighting+evening+physical exertion=shit picture) is taken from the temporary storage platform I built to store gear/crap during the first part of the build, which is the control room. The boxing up exercise is in mid-flow, though ‘flow’ might be a tad inaccurate considering the amount of times I became paralysed by indecision (you never know when you want to get to a tape head de-magnetiser in a hurry!).
The prepping of the control room end of the unit has now begun and the first materials will hopefully get ordered within the next week. First up is the air conditioning unit and the air extraction fittings as the appropriate holes will have to be made in the external blockwork wall before the outer skin of the control room can be built up. Then it’s time for the timber framing. The whiteboards are out and the order of works is getting refined on them as I type this (I keep remembering details and going over to the board to put them on the list…maybe I just like the smell of the pens…).
Photos of the build and some attempt to explain them will follow soon.

The Midas (Re)Touch

Once upon a few years ago I was given two mid-70s Midas mixing desks that had been rescued from a slow death in a Wiltshire shed. They sat on the floor of my studio at the time (a roof space in an old malthouse in Bristol) and I would occasionally plug the bigger one in (a 36 module frame) and record various things through it for a different flavour. I became increasingly excited by the idea of restoring and modifying the desk to suit my own needs and whims as I found the raw sound very pleasing, especially the way it distorted – I have often turned it into a feedback synth as it produces rich oscillations. What particularly interested me was the potential for creating a studio centre-piece that would both inspire and limit my work so that a sonic character could be established and explored without investing the kind of session time that a large frame mixer can cost. The majority of the input channels are the PR003 type which have a simple three band EQ: fixed frequency high and low shelves and an inductor based mid-peaking EQ with three selectable frequencies (1.6kHz, 3kHz and 6kHz). There are two PR004s which offer more EQ options, but no sweepable parametrics. Each channels has two ‘foldback’ sends and two ‘echo’ sends and can be assigned to two of the four group busses…simple stuff.

The Midas PR series was constructed to custom orders and made from the premium components of the day: Penny and Giles faders (wirewound!), WIMA and Erie capacitors, Welwyn resistors, Sowter transformers, Plessey switches, Bourns pots and Ernest Turner VUs. The signal paths are short due to the simplicity of routing and EQ and the number of gain stages are few, which is all good news for audio quality. The only real negative aspect is the use of ICs for most of the gain stages, though the critical preamps and group summing amps are all discrete. In the mid to late 70s the quality of ICs was not what it is today and this Midas PR uses UA748s, which were superseded by the all-conquering NE5534 in the 80s and is still going strong today. The PR003 and PR004 input modules that make up 24 channels of the desk I am rebuilding use three ICs each for EQ buffering and final output (i.e. mostly unity gain roles) and are relatively innocuous in their effect. Nevertheless the UA748 is not neutral in tone and has some serious shortcomings. Having done a variety of qualitative tests I have decided to replace them all with On Semi NE5534ANGs, which significantly improves the frequency response and headroom. The aged electrolytic capacitors are being replaced and the final decoupling caps are being replaced with high quality poly film types, though I have yet to finalise the choice (there are a few listening tests to carry out yet).

As well as IC upgrades and new caps there are plenty of crusty pots and crunchy faders to restore or replace, but there are some more fundamental changes to make. This desk only has four group busses, though there are eight group channels (four have no faders are were probably some form of monitor send), and there is no mix summing buss (i.e. master mix – these desks were mostly spec’ed for live use, most famously Pink Floyd’s Dark Side of the Moon tour). With some rearrangement of the main chassis bussing and by changing the channel routing switches I have managed to make it into an eight buss console with a stereo mix-buss (I managed to get a set of matching Penny and Giles faders to re-equip the four faderless group modules). Of course this means I have had to make my own mix and monitor section which is currently in breadboard form. The mix buss is based around two JFET discrete op amps (DOAs) made by Fred Forrsell (JFET992) and offers masses of clear headroom and output level. Tests so far show a healthy +23dBu output into 600Ω before clipping.

Three of the nine VUs (8x group, 1x PFL) are damaged beyond repair and I have had no luck finding direct replacements (they are large Ernest Turners), but I happened to source four large Shinohara VUs that fit the chassis cutouts, and their different look gives the desk a wee bit more funk-junk factor!

Anyway, I shall no doubt write more (witter on) about this in future posts, so for now here’s some pictures of the Midas PR in various stages of disassembly…

Midas PR chassis

The Midas PR chassis with the four Shinohara VUs sat in position (new holes need to be drilled)


PR003 modules.

A selection of PR003 input channels. Less is more in knob world – just so long as they’re different colours.

Mix buss breadboard

The JFET mix buss and PSU on a breadboard during testing (just one channel). Two foldback/echo modules to the right with their dub-tastic ‘Spin’ knobs which feed the return back into the send…oh yeah!



Joining the 21st Century

Sandpit Studio is just over 10 years old and now, at long last, has its own web presence…hurrah! It’ll take a wee while to get up to speed, but soon enough there will be pictures, sounds, opinions (probably too many), ideas, stories and whatever else I can think of. There’ll be a wealth of technical jibberings about acoustics, electronics and recording as well as musings on artistic process, sonic experimentation and actually finishing a mix.

I’m Robbie and I run/staff/haunt Sandpit Studio. There’ll be some info on who on earth I think I am and what it is I do/have done at some point. Hopefully there’ll also be some contributions from those who regularly work in and support this cosy little hub of creative joy.

Until then…then.