Flatpicker
Well-known member
Here?s a proto mic pre I?ve been working on for the last year.
http://mywebpages.comcast.net/flatpicker/Preamp1.jpg
http://mywebpages.comcast.net/flatpicker/Preamp2.jpg
Of course it didn?t take that long to layout and build - most of my time was spent waiting for money to come in that didn?t have to go right back out, if you know what I mean. Anyway, I finally managed to assemble one channel of it over the holidays, but my digital camera was broken so I could not post pictures until now.
My intention was to layout a board that allowed me to try different op amps, input transformers, and output configurations. The one in the pictures is configured basically like the ?JFET Mike Preamp using Jensen JE16 Input Transformer? circuit shown on Fred Forssell?s schematics page. The 12 position switch sets the gain in 5dB steps and the pot is a 5dB gain trim. The 3 switches are pad, phase and phantom power.
For the record, I am NOT using the API type output transformer in this configuration ? I just threw it in there for ?looks? while taking pictures. The chassis is from Par-Metal and I punched the holes using a manual press-punch at work.
Except for one or two schematic screw-ups (that ended up being pc board screw-ups, hehe) it works great. Sounds great too. I can crank the gain up to 70dB and it?s extremely quiet. In comparison the pres in my Aardvark Q10 sound muddy, and with the gain set to 70dB using the same monitoring levels, the noise sounds like Niagara Falls!
I wanted to try something different and put the transformer immediately after the XLR, hoping that the extra gain would improve the signals S/N a little before traveling across the board to the switches. Also, since I?m using the LL1538XL and plan to mostly record acoustic music, I reasoned that it couldn?t hurt to try it this way.
In hindsight, I should have kept the pad and phase switching on the primary side of the transformer using relays and silver DPDTs instead of 4P4T gold push buttons. The relay version would have actually been cheaper, plus you can?t find the needed make-before-break pushbuttons anyway. To be honest, I can?t remember why I was so hell-bent not to use relays. Ah well? learning ? that?s what it?s all about, isn?t it?
Needless to say, a new ?improved? version is in the works. Now, if I just had some more money? :wink:
http://mywebpages.comcast.net/flatpicker/Preamp1.jpg
http://mywebpages.comcast.net/flatpicker/Preamp2.jpg
Of course it didn?t take that long to layout and build - most of my time was spent waiting for money to come in that didn?t have to go right back out, if you know what I mean. Anyway, I finally managed to assemble one channel of it over the holidays, but my digital camera was broken so I could not post pictures until now.
My intention was to layout a board that allowed me to try different op amps, input transformers, and output configurations. The one in the pictures is configured basically like the ?JFET Mike Preamp using Jensen JE16 Input Transformer? circuit shown on Fred Forssell?s schematics page. The 12 position switch sets the gain in 5dB steps and the pot is a 5dB gain trim. The 3 switches are pad, phase and phantom power.
For the record, I am NOT using the API type output transformer in this configuration ? I just threw it in there for ?looks? while taking pictures. The chassis is from Par-Metal and I punched the holes using a manual press-punch at work.
Except for one or two schematic screw-ups (that ended up being pc board screw-ups, hehe) it works great. Sounds great too. I can crank the gain up to 70dB and it?s extremely quiet. In comparison the pres in my Aardvark Q10 sound muddy, and with the gain set to 70dB using the same monitoring levels, the noise sounds like Niagara Falls!
I wanted to try something different and put the transformer immediately after the XLR, hoping that the extra gain would improve the signals S/N a little before traveling across the board to the switches. Also, since I?m using the LL1538XL and plan to mostly record acoustic music, I reasoned that it couldn?t hurt to try it this way.
In hindsight, I should have kept the pad and phase switching on the primary side of the transformer using relays and silver DPDTs instead of 4P4T gold push buttons. The relay version would have actually been cheaper, plus you can?t find the needed make-before-break pushbuttons anyway. To be honest, I can?t remember why I was so hell-bent not to use relays. Ah well? learning ? that?s what it?s all about, isn?t it?
Needless to say, a new ?improved? version is in the works. Now, if I just had some more money? :wink: