Original thread by Jonte Knif:
http://www.groupdiy.com/index.php?topic=38252.msg471585#msg471585
some tips from the drawing board
http://www.groupdiy.com/index.php?topic=42919.msg554436#msg554436
Jonte, I'd like to thank you very much indeed for making this great studio tool. It is a pre amp but in reality it is much more than that.
I have several other preamps but this one and my version of the 9K see the most use.
I use it for:
Gain make up after my 26ch passive summing mixer.
To process individual instruments (like software synths which really come to life through this thing).
Record various sources.
Re-record dead and sterile mixes through it.
Due to the I/O transformer configuration that I used, I have slight extreme bass and extreme highs roll off .
Hi pass filter is very useful as a creative tool not only as a band aid. I expanded original filter to 8 frequencies
(30-60-90-150-250-330-440-750Hz)
I'm planning the low pass as well, have to wind the inductor, soon I hope.
The preamp is very quiet in any setting and has a lot of gain.
I've added several features to the original design and my PSU is a bit different to the original design (6.3V- 338 regulated, 783 for the 48V, HV is the same as on Jonte's schematic, and 317 regulated for the relays and VU buffer).
I have the input transformer (OEP) relay switchable primaries and secondaries for series parallel winding configuration.
Everything apart from UL,P & T choices is relay switchable.
Build inside dead M1R case, TRS for ins-outs, was lazy to make bigger holes for XLRs.
PCB is huge, double sided.
Filter caps soldered on switches.
Russian pio in the sound path.
Russian 6n23p on the input
Mullard NOS E81L on the output.
I'll be building at least 4 more channels, this time with line input option only and different input and output transformers.
I'm having it for a couple months now and I'm using it every time I do music.
Cheers