This was my first big project with the training wheels off, meaning no comprehensive build guides, no parts kits, no official support. This was also my first foray into vacuum tubes and high voltages so I made the decision to move slowly and work methodically. The result was a pair of transparent and flexible vacuum tube preamps that worked nearly perfectly the first time I powered them on (nervously, fire extinguisher in hand).
How does it sound? Surprisingly clean. I haven’t had the opportunity yet to run it through its paces. I wanted to expand my repertoire of preamps and I settled on this particular design owing to some very positive experiences with the Universal Audio 610. The 610 has a pronounced distortion at high gain which can be really pleasing and I expected something similar from the G9. Not so. The G9 is remarkably clear, low-noise and low distortion through the range of gain settings. If you want a hint of crunch in your signal you can pad the input and drive the preamp stage a little harder. The output pot makes it easy to reign in a signal that’s a little too hot before it exits the circuit.
Jakob Erland of Gyraf Audio in Denmark designs and builds boutique studio gear. I haven’t had the opportunity to toy around with any of his commercial products, but he’s opened a number of his circuit designs for public, non-profit use on his website. Documentation is brief but adequate. However, Jakob is a regular on the GroupDIY forums and he is very supportive and forthcoming with newbies. The G9 Help Thread was an invaluable resource on this project and I doubt I would have gotten it so right the first time without the direct support of Jakob himself and other pioneering DIY obsessives.
The G9 circuit board is cleverly designed to accommodate the much lauded and costly audio transformers from Lundahl in Sweden as well as more affordable ones from Oxford Electrical Products in England. Initially, I hoped to invest in some fine Swedish steel but financial realities meant compromise. Still, the OEPs sound fine (rich and responsive low-end), though I haven’t had the opportunity to compare the two. Some builders have opted for variety: Lundahls on one channel, OEPs on the other; Lundahl inputs/OEP outs, etc. I doubt the difference in tonality is very substantial.
Project Specific Components:
Chassis & Front Panel – $260CAD incl. shipping from Collective Cases
PCB – £24 from pcbgrinder.com
Lorlin Rotary Switches – tot. $30CAD from Newark
Input/Output Transformers – 4 @ $23CAD/ea from Newark
Transformer Screening Cans – 4 @ $11.50CAD/ea from Newark
ECC82/12AU7 Preamp Tubes (JJ brand) – 4 @ $11CND from thetubestore.com
9pin Ceramic Tube Sockets – 4 @ ~$3CAD from thetubestore.com
Nearly every other component came from Mouser, save for a capacitor or two that was out of stock.
Total cost was around $1050CAD + various shipping charges + hookup wire. Not cheap, but significantly less than Jakob’s commercial version ($1800USD from Vintage King) or something like Manley’s single-channel unit ($1980USD from Vintage King).
4 Comments
Matt
2018-11-08 - 05:26that looks great! If you don’t mind me asking, how much soldering/DIY experience did you have before taking this on? I would really like some of these pres, but all I’ve done is a stagebox, a small patch bay, and a 500 series rack kit with very detailed instructions (from Total Audio Control).
Do you think this would be way out of my depth at the moment?
Evan Desjardins
2019-01-04 - 13:53Before taking this on, I had put together a couple Hairball 1176 kits. You can do this, but plan to spend a lot of extra time sourcing parts and teaching yourself new practical techniques.
Kenny Sacks
2022-08-26 - 22:18I would love to try this but my experience is limited to a few CAPI kits. I am mainly worried about electrocuting myself having zero experience with mains/high voltage. Can you share what you learned about that and what one should know about mains/HV before taking this on?
Evan Desjardins
2022-08-27 - 13:09Hi Kenny. I hope my post has been instructive in some way.
I haven’t dabbled in electronics much in the past few years because I’ve been busier mixing but if you’re feeling nervous about approaching a project with exposed mains or high voltage rails then I would suggest a) reading up more on the principles of electronics and electricity, and b) advancing to another kit project where you have to wire up mains. Before attempting this project I assembled a few of the Hairball 1176 kits and this was useful for building my confidence and manual skill.
And if you’re going to work on a tube project like this one, remember to keep one hand well clear of the work when you’re powered up and probing around inside. If you’re going to get zapped, you don’t want to allow the current to flow from one arm, through your chest and out the other (likely to the chassis on the other end).
Hope this helps. Try the GroupDIY forums for more thorough advice.