Searching for the perfect project

[hcaw]

Hi all,

I'm currently building a ribbon microphone from scratch and am searching for the perfect pre-amplifier project to accompany it.
I've searched high and low on the net but have been left slightly confused by the range of options available, and am hoping someone out there can point me in an interesting direction. I am looking for the following:

>=60dB clean gain
>=1.5kΩ input impedance
IC based (Could be persuaded to use valves)
Option for phantom power
Standalone system (ie. not a 500/51x design)
Power supply design included
Not decided on transformer/transformerless
Ideally I want to find a project with pre-existing single layer PCB designs that I can print myself.

Many thanks,

Hcaw

 

[okgb]

You may also look at the " pre " preamp that people are using to make active ribbons , that may
give you more latitude on the preamp itself

 

[hcaw]

Could you post a link, as pre preamp is a hard thing to search for!

 

[okgb]

I agree the search function is not the best , though try searching ribbon preamp or active ribbon

 

[alexc]

Sounds like a job for Expat Audio's 'Eden Preamplifier'

http://groupdiy.com/index.php?topic=50419.msg639081

Probably about as high performance in diy preamp as I can imagine.

Masses of gain in a 'straight wire'.

You do the simple packaging into a unit with bipolar psu, phantom and i/o connectors.

And do several of them in that box for a very attractive price.

I think tube would be difficult to achieve that level of gain with the desired clean/quiet -ness.
Certainly would cost a lot more.

Good luck

 

[bruce0]

How about a differential path preamp.  In this type of preamp the "balanced" connection is maintained throughout the signal path in the preamp.  This can contribute to lower noise, and tends to produce high gain preamps.

I believe this has been done in several contexts, some pretty well baked plans that you could carefully self etch.

1) The amek desk mic pre
2) The green pre which seems to be a copy of the amek desk
3) The lola preamp
4) Some of the THAT corp preamps ( I think the eden is based upon one of those chips).

The green pre has some nice layouts that have traces wide enough to self etch.  I will post what I have but you may find better. Someone may have boards.

The lola you can get a kit, throw away the front panel (maybe hairball would sell you a PCB) and mount it in a 1 U case (many folks do this with 500 gear), or buy or make a 1U 500 rack that holds 2 modules.

The Amek layout is posted here as well.  Looks like the green to me.

The That chips seem like a good idea, some very nice low noise high gain preamps are possible, some nice eval boards available.  Some folks have cloned and were selling the eval boards on ebay.  I think the eden might be a THAT based design, not sure.  One advantage of the THAT design is that they are EXTREMELY well documented, with power point presentations and data sheets and design notes fully thought out and explained like they really want to sell them.  I have read that they do good customer support too.




The That chips have layouts for eval boards available, and you can buy the eval board (or try to etch one ... don't know how touchy that would be in terms of trace size, and some of the that chips are only available in surface mount but some are dip).

I have not made a green or any differential preamp yet, but I want to.  Unfortunately I am going to do it in 500 format.  So I may be wrong in what I have put forth here, but I am SURE someone will correct me if I am blowing smoke up your flux vent.

The documentation is very spread out the green pre... the project seems to have been abandoned.. but people say they like them, and my read of the schematic is that they are differential.  Some of the nice versions of this folks have put common mode chokes on the front end (see the amek) which I like.

Attached is amek schem, green schem to follow.
The reason I like it is that I think it has a balanced architecture (symmetrical) although you may disagree, like the Amek input modules and the Lola.

 

[bruce0]

Here is a green pre schematic, which seems very similar to the amek

 

[bruce0]

And a board layout, may be sized correctly for etching I just don't know.

This was once a very well documented project but a lot of the files are on some dead server.  You should be able to find most of it somewhere.

 

[hcaw]

Apologies for the delay, just got back from holiday! Thanks very much for all your responses, the Eden preamp looks like a good solution, as do the circuits posted by bruce0.
I like the idea of building a 2 x 500 series modules into a 1U rack case, I will also do some research into THAT corp preamps as it could be really handy that they are so well documented.