*Soundgas Type 636P 2 - Twin Grampian 636 Preamp

Deposit or full payment. 'Soundgas-in-a-rack.' Transformer balanced twin channel germanium preamp based on the Grampian Type 636. 

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Preorders now open for the latest: secure yours with a deposit (or payment in full). Shipping April 2024.

Rackmount evolution of our Grampian 636 preamp circuit. A two channel Type 636 mic preamp with Carnhill transformer balanced outputs for greater versatility and extended sonic palette.


Update April 2024: we have now incorporated phantom power into the design (photos will be updated soon).

The Soundgas Type 636P2 is the latest incarnation of the Soundgas Type 636 and desktop Type 636P which both feature our evolution of same hairy mic preamp circuit as the original Grampian Type 636. However this is far more than two 636Ps in a rack: the addition of the Carnhill transformer balanced output option massively increases versatility and offers a wider sonic palette. From subtle sweetening and widening of audio signals passing through with very little gain applied through to maximum filth and gnarl via the original unbalanced input/outputs. The 636P2 brings the 636 preamp into contention for more subtle bus/mix sweetening as well as wilder germanium fuzz and drive. 

How does it sound? At higher gain settings the transformers smooth out some of the wildness of the 636 to deliver a classy – yet still harmonically rich – sound. We have been blown away by how different these sound with the balanced outputs, and by how much we want to use it on everything. And if you want the full original 636 preamp magic, untamed by those beautiful red transformers? Simple – just plug into the 1/4″ jack ‘punch out’ socket – this bypasses the transformer circuit and gives you that hairy (out of phase) direct output as found on the 636 and 636P.

What is it? Based on the Grampian Type 636 – famously used and abused by Lee ‘Scratch’ Perry and Pete Townshend – and many others since. This circuit is designed and built absolutely in the spirit of the original vintage units – no surface mount components in the audio path or tone sapping DSP. Designed, developed and assembled in our workshops in Crich, England. In an era of mass production, these builds are a throwback to a bygone era when small manufacturers made everything themselves.

This is a labour of love and represents the culmination of our collective experience of – and love for – the 636 circuit. It is not the modern way: the expense of working like this means these particular units are not for everyone, but this does mean we are able to control every aspect of the process and build something of which we are all justifiably very proud. The time and outlay just to source and test NOS transistors that perform to our specification is slightly terrifying: the vast majority of OC45s we have found do not meet our criteria.

Can I hear it? Yes, there are various demos below featuring a variety of sources. Scroll down to see the demos.

Here’s a stem-by-stem video demo of an earlier unit (you can also check out Hainbach’s encounter with this circuit).

What’s inside? Two boards from the Type 636P inside a 1U rack case with added Carnhill transformer balanced outputs. The two sides are independent circuits using a common power supply (on a standard IEC socket, internally switchable voltage). Each channel has a 1/4″ jack input, input level control pot (gain), Grampian specification mic transformer, overload lamp and input impedance switch (select between guitar/line use, or adjust to taste).

Staying true to the original Grampian 636 design, the mic preamp ‘punch out’ output is unbalanced on a ¼” jack socket and is out of phase – plugging into this output will disable the XLR outputs on the rear.

As with our original 636s, we have put tonal considerations ahead of all else. I was originally skeptical that we’d see a real benefit in using germanium transistors in the buffer section: all our original prototypes had used silicon and sounded great. However Dr Huw insisted that we build an all germanium version for comparison which blew all the earlier versions out of the water; this became the 636P which has now evolved into the 636P2.


I’ve been using Grampian 636s for getting on for 30 years having ‘discovered’ one entirely by chance back when they languished unappreciated and unrecognised (it cost me around £70 and needed a fair bit of work – even then it was very noisy and more than a little unreliable). I knew nothing at the time of their history and use by Pete Townshend and Lee Scratch Perry, nor what it was that made these unprepossessing grey boxes so very special. They reacted to liberal overload abuse with such unbridled (and unequalled) ferocity that I was immediately hooked and thus began my infatuation with the Grampian Type 636. I now know, thanks to Huw, that this germanium transistor based circuit is of a slightly odd design (which explains why so few people seem able to figure out how to fix them well).

To say I am proud and humbled by our team’s endeavours over the past three tumultuous years is an understatement. It all began when “Doctor” Huw rebuilt a Grampian Type 636 for our much-missed friend Philippe Zdar for his Motorbass studio. That unit had been stored on its side for 20-30 years with the battery at the top and was almost completely destroyed by acid leakage. I mentioned that as he’d almost built a new one in the process might that in fact be possible?

We’d never manufactured anything (Huw had custom built guitar pedals and synth modules). The new design had to be as authentic as possible but with lower noise and more low end: Huw triumphed and we cautiously set out to make ten replica Type 636s using refurbished vintage Gibbs tanks.

As soon as Huw had designed the 636, we discussed whether the mic preamp alone could be built in a standalone unit, and one appeared pretty quickly on my bench soon after (built into an old Binson Echorec faceplate we had lying around). Covid-19 played havoc with our plans and with Huw’s health, and what would eventually become the 636P had to wait.

In the meantime we continued building small batches of Type 636s to satisfy demand and keep our newly-employed studio engineer Ben busy during lockdowns. There are now around 80 Soundgas Type 636s in existence and while we’ve no plans to make more using vintage tanks, we do have a new 636 reverb project in mind.

The 636P preamp-only prototypes duly came along. In classic Soundgas style, what was intended as a prototype became the production version – the no-nonsense, minimal, aesthetic seemed fitting for our monstrous sonic wolf in sheep’s clothing. Plaudits started coming – ‘the only drive/fuzz I need’ and ‘this is the sound I’ve been searching for my whole life, thank you’ are two that have stuck in my head. Again, what started as a low key project has ballooned and we continue to hand assemble small batches of Type 636Ps in our workshops.

At present, all 636 units are entirely built by our team here in Crich, England in the grand tradition of old school British audio manufacturing: made by hand by talented people who obsess over – and focus on – sonic detail above all else. My thanks and appreciation go out to our dedicated tech team who have created – or helped in the creation of – these units.

More info on the build of the original Type 636P including photos and demos.


The units were originally intended as mic pres: using a SM 58 through them never sounded so fat. Alternatively using a Grampian Ribbon mic provides creamy delicious sonics, or the Grampian DP4 mics ensure a frazzle that is compelling. We have used the unit to mic up snares with a ribbon mic piped through the rear balanced, in phase output and then a DP4 for the snare bottom through the unbalanced out of phase “Break Out” output. (other mics are available)

The 636P2 is also a great tool for reamping, enriching or toughening up stems with that wonderful Germanium texture. If you tickle the input and find that sweet spot of gain stems will sound super rich with analogue warmth. Alternatively if you so desire absolutely annihilating your sonics with that lush harmonic distortion that Germanium delivers then drive the input and the gain til your heart’s content.

Whilst the units are intended to be dual mono there is a definite pleasure in using them as stereo units with similar gain and frequency response. Though due to the nature of the Germanium crystal and its atmospheric reaction there will be subtle variations in gain and frequency responses.eIf you use the 636P2 as an instrument DI it is absolutely crackers on drum machines and synths, from clear solid analogue warmth to absolute frazzled distorted crunch and fuzz.

As Pete Townshend discovered back in the sixties, you can plug in your electric guitar and crank the gain to max and achieve the most compelling distortion fuzz you’ve ever heard.



Brand new.

Voltage Information

Will be set up for either 120 or 240v operation before shipping.


For sales in UK the price will include 20% VAT. Buyers elsewhere may incur VAT or other local taxes on import.

More video

Type 636P2 Demo

Running different stems through the beast...

Prototype 636P2 in action

Early version without Carnhills!


*Soundgas Type 636P 2 – Twin Grampian 636 Preamp

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