Expat Audio Eden Preamps

Hi!

I have just finished cobbling together a pair of Expat Audio's Eden preamps. Expat is run by Rochey and Keith (SSLtech) from this forum, and with their experience and expertise I have high hopes.

The preamps are based on a INA163 chip, and come part-built with surface mount things, so most of the work is already done. All I had to do was wire up XLR ins and outs, a 5K gain control, and a ±15V power supply.




The boards were much smaller than I had expected, so the rack i ordered from Farnell is far to big! One could easily fit four or even eight of these in a 1U unit. I've ordered a shorter case for this and will do a transplant when it arrives. For now all the leads are left long until I know where everything will sit in its final home.



You can use a 5K pot for the gain, but I had a pair of nice Elma rotary switches, so made up some attenuators to give roughly 2 to 3 dB steps up to +54 dB from the INA163 preamp chip.  It is a bit fiddly but a bit of tape helps keep the resistors in place whilst you solder. You can do this with Lorlin switches too.





The PSU board also came from Expat and has a regulated bipolar supply, and also a 48V output. I've built this for ribbon mics so I don't need that option. That also allows me to skip putting capacitors at the input. Overall it is a very simple build indeed.

So, how does it sound?

Well, so far I am VERY impressed. It has oodles of clean gain - in fact +60dB in total.. I did a couple of quick tests with some ribbon mics and their is no audible hum or hiss even at full gain. The sound is rather neutral and uncoloured in character - I'll try to post a frequency sweep next week but I expect it to be flat. It is a good option for ribbons where clean quiet gain is essential. It will certainly get used in our studio.

Rochey and Keith have done a really good job on this. Thanks guys! Here's their website...

http://expataudio.myshopify.com

I'm thrilled to see this write up, and pleased that your getting the promised performance!

Your wiring is so much cleaner than mine!!!!

/R

:blush:

Really pleased that you like it, Stewart!

They're certainly a VERY quick 'build', with everything connectorised.

Actually the 163 is capable of even higher gain, but I found that there's a point above 60-something dB at which it stops sounding so good, so we took the decision to limit the gain, in favour of purest sonic performance. -It's a VERY sudden 'corner', and the range which we settled on is one which is absolutely clean at ALL settings.

Of course, you KNOW you're going to be hassled for a resistor value table now, don't you! ;-)

Hi Keith & Dafydd, great work on this!

It is a VERY easy build and I certainly spent more time with the drill than the iron.

Had a slight hiccup with the power supply in that I forgot that the top of the 7915 is NOT at 0V like the 7815!
So I advise other builders NOT to heat sink both regulators to the chassis.  :

>Actually the 163 is capable of even higher gain, but I found that there's a point above 60-something dB at which it stops sounding so good, so we took the decision to limit the gain, in favour of purest sonic performance. -It's a VERY sudden 'corner', and the range which we settled on is one which is absolutely clean at ALL settings.

I spotted that and checked with Rochey about removing the on-board resistor. But 60dB is pretty handy anyway!

>Of course, you KNOW you're going to be hassled for a resistor value table now, don't you! ;-)

Got one at the workshop which I will share in a day or two. It is slightly skewed in that I adjusted it for nearest 'in stock' resistors.

I also have a spreadsheet that I could share but is in a mac format (numbers). If I can translate to Excel then I will upload and post it here. But it is a very simple calculation.

Very tempted to knock together a phantom version with the other pair.

Hi.

zebra50 said:

I also have a spreadsheet that I could share but is in a mac format (numbers). If I can translate to Excel then I will upload and post it here. But it is a very simple calculation.

Click to expand...

Numbers will save as Excel, or use the share menu to save/email as excel. If you have an old version that doesn't, or can't find menu, you can pm me and I can convert it and email it to you.

The Gimmer

Thanks!

So, by request, I calculated these values for the resistors....



Note that there is a 12 ohm resistor on board, so everything is in addition to that. Also note that a second gain stage on the preamp adds a further 6dB to the total, so my calculated 54 gives an overall gain of +60dB.

Having worked that out, I then went to the resistor stash and used 'near enough' values. Here's what I actually used...



As you can see the gaps are not very even, but mostly around 2dB steps in the middle.

Here is the spreadsheet in a couple of formats, errors and omissions quite likely! The spreadsheet calculates both ways, so resistance from gain, and gain from resistance. I haven't checked the XLS version.

http://www.xaudia.com/omnip/Other/EpatEden/EdenPreampCalcs.numbers
http://www.xaudia.com/omnip/Other/EpatEden/EdenPreampCalcs.xls

Cheers!

Stewart

Unless you're recording heartbeats 10 ' away 60 db is plenty for almost anything  ,
even with a quiet string part you're going to have to set the gain for the louder section anyway ,
what are things where people find themselves needing 70 db ? [ just curious ]

Greg, I think the issue is microphone sensitivity.

Ribbon mics (I'm told) have pretty poor sensitivity.

that's true , but it's still a matter of recording something that is very quiet and then your choice
may not be a ribbon ,  and more gain [ & room ] makes for a different sound .
Anyone have practical example of where they needed & used 70db of gain  ?

Where did you get the awesome knobs? (They look like Empirical Labs??)

Yes! About 4 or 5 years ago we had a big group buy of Distressor knobs. I would guess that almost everyone who was here at the time has a few stashed away somewhere. Drop me a PM if you want a couple in exchange for a donation to the forum.

I don't think I've ever used 70dB, or had the facility to do so.

But if I want to use a 1930s  ribbon mic and don't want to use a +20dB Fethead style thingy, then having up to 60dB is welcome.

Putting 4 of these in a 1U case would be nice.  What's the chances they have a HPF on them?

okgb said:

Anyone have practical example of where they needed & used 70db of gain  ?

Click to expand...

I've recorded some indie pussy voices where they want "that vintage thing". 70dB is needed when they quietly wail away the performance with a ribbon mic, think Thom Yorke only on the quiet bits. Noise isn't always such a big issue and it's worth a try for the effect. Also classical acoustic guitar sounds strangely good with a ribbon if the noise can be tolerated (bury it in a mix if possible).

At least this Eden circuit doesn't at any of its own noise, unlike some of the tube stuff I've used.

Here is a design we have been working on for a 4 channel 1U set up of Eden pres.  I would love some feedback if there is any interest or thoughts on changes.



The grey holes above and below the 48v's are mounting holes for the Eden control PCB's.  There is another set under the Gain knob.

Well, looks great, and not a lot else you can do with the spacing already fixed by the control boards.

Could you use a smaller on/off switch and create some more space between the channels? Maybe a small push button? Just a thought.

I don't know of any good push buttons for Mains power.  Do you have a part # for one?

dandeurloo said:

Here is a design we have been working on for a 4 channel 1U set up of Eden pres.  I would love some feedback if there is any interest or thoughts on changes.

The grey holes above and below the 48v's are mounting holes for the Eden control PCB's.  There is another set under the Gain knob.

Click to expand...

These are now available at www.collectivecases.com !!!