I've been thinking about making a thread about this for ages. This is because I am so slow at getting this finished.
Anyway, as a brief introduction, this project stems from when I asked about what to do with a Klein and Hummel preamp board which had a Beyer input transformer. As it turned out, it looked best to forget the preamp board and just use the transformer in a better-performing circuit. After a few lab members offered suggestions, Samuel offered to adapt a schematic of his which would be suited for the application.
The design is a "shared-gain" preamp using a single linear pot to control gain for both opamps with transformer-balanced inputs, and unbalanced outputs. The design can obviously be easily adapted for particular needs.
So first things first, I order in most of the components to make a 1u rack of four preamps. It is at this point that you remember just how many bits you need to make a simple preamp!
That's some of the main components - most notably; beadboard, 4X beyer trannies, 4X OPA604s, 4X NE5534s, bipolar electrolytics, SSL Tech PSU board, toroidal tranny..... You get the idea. The silver box is my original prototype which has served me very well.
Other than that, there is my hardware - eg. rack case, knobs, stand-offs, zip ties, blah, blah.
Now, when doing DIY, try not to get ahead of yourself! I had fun messing about with Jaydee's and Frank from NRG Recording's .fpd files and printed out a lovely paper front panel..... But wait - there isn't any circuitry to go behind it :razz:
Now on to the fun part (this is where all you fake-ass pre-fab PCB users should go to the brewery :razz: ) - breadboarding!
Here is the first channel in place with IC sockets ready for plugging in trannies and ICs :
This worked straight away, but it had very little headroom and sounded distorted unless it was at very low levels... I wondered if my NE5534P opamps would be to blame (I thought the suffix P meant higher temperature though...) so I swapped them for OPA604s and right enough, it worked perfectly! I wonder what is up with my (free) NE5534s? I am running on bvatteries at +/- 9V for the meantime.
Here's a close-up:
I will update this thread as I go along. The plan just now is to populate the rest of the board so I have have four working channels...
Anyway, as a brief introduction, this project stems from when I asked about what to do with a Klein and Hummel preamp board which had a Beyer input transformer. As it turned out, it looked best to forget the preamp board and just use the transformer in a better-performing circuit. After a few lab members offered suggestions, Samuel offered to adapt a schematic of his which would be suited for the application.
The design is a "shared-gain" preamp using a single linear pot to control gain for both opamps with transformer-balanced inputs, and unbalanced outputs. The design can obviously be easily adapted for particular needs.
So first things first, I order in most of the components to make a 1u rack of four preamps. It is at this point that you remember just how many bits you need to make a simple preamp!
That's some of the main components - most notably; beadboard, 4X beyer trannies, 4X OPA604s, 4X NE5534s, bipolar electrolytics, SSL Tech PSU board, toroidal tranny..... You get the idea. The silver box is my original prototype which has served me very well.
Other than that, there is my hardware - eg. rack case, knobs, stand-offs, zip ties, blah, blah.
Now, when doing DIY, try not to get ahead of yourself! I had fun messing about with Jaydee's and Frank from NRG Recording's .fpd files and printed out a lovely paper front panel..... But wait - there isn't any circuitry to go behind it :razz:
Now on to the fun part (this is where all you fake-ass pre-fab PCB users should go to the brewery :razz: ) - breadboarding!
Here is the first channel in place with IC sockets ready for plugging in trannies and ICs :
This worked straight away, but it had very little headroom and sounded distorted unless it was at very low levels... I wondered if my NE5534P opamps would be to blame (I thought the suffix P meant higher temperature though...) so I swapped them for OPA604s and right enough, it worked perfectly! I wonder what is up with my (free) NE5534s? I am running on bvatteries at +/- 9V for the meantime.
Here's a close-up:
I will update this thread as I go along. The plan just now is to populate the rest of the board so I have have four working channels...