synthetic
Well-known member
Here's my latest project, a mic pre based on the API 312. I borrowed pieces from several pres to come up with this circuit:
http://www.jefflaity.com/misc_pix/forsell_api_preamp.gif
Here's the parts list so far:
http://www.jefflaity.com/misc_pix/forsell_api_parts.xls
I'm using a Luhndahl 1636 for the input transformer and a Forsell JFET992 as my discrete op amp. The output cap is a massive 40uF Polypropylene cap. I don't have an output transformer yet, I'm just going unbalanced for now.
I used a 10k linear pot for the gain instead of the 25k rev audio pot that the API uses. I don't get a lot of gain out of the preamp yet, and I'm not sure if this is a design flaw or a build flaw. I suspect the latter.
The power supply is a Peter Green preamp supply. I used 24V regulators to make it into a 24 volt supply.
Once I get this up and running I hope to create a web page about the construction. It seems like a nice project for a beginner (of which I definately categorize myself). For now, here's a picture of the project in process:
More pics here:
http://www.jefflaity.com/gallery/API-Forsell-Preamp
Let me know what you think, -jl
http://www.jefflaity.com/misc_pix/forsell_api_preamp.gif
Here's the parts list so far:
http://www.jefflaity.com/misc_pix/forsell_api_parts.xls
I'm using a Luhndahl 1636 for the input transformer and a Forsell JFET992 as my discrete op amp. The output cap is a massive 40uF Polypropylene cap. I don't have an output transformer yet, I'm just going unbalanced for now.
I used a 10k linear pot for the gain instead of the 25k rev audio pot that the API uses. I don't get a lot of gain out of the preamp yet, and I'm not sure if this is a design flaw or a build flaw. I suspect the latter.
The power supply is a Peter Green preamp supply. I used 24V regulators to make it into a 24 volt supply.
Once I get this up and running I hope to create a web page about the construction. It seems like a nice project for a beginner (of which I definately categorize myself). For now, here's a picture of the project in process:
More pics here:
http://www.jefflaity.com/gallery/API-Forsell-Preamp
Let me know what you think, -jl