tablebeast
Well-known member
Hi, I just got back from Hamfest in Shelby, NC. I did get one big score, this 4U Rack Mount Military-Grade Decibel Meter Model ME-22A/PCM. I was told my one guy at the fest that it could be made into a Mic Pre easily. Is he right?
Here is what I have:
There are 8 tubes, as follows:
3x 6SJ7WGT as Audio Frequency Amplifiers.
1x 6H6 as the Meter Rectifier
1x 5881 as Voltage Control
1x OC3 as Voltage Control Regulator
1x 6SQ7 as Voltage Control Amplifier
1x 5Y3WGTA as the Rectifier
All the tubes are JAN. Every Part is top quality and it was built by Borg-Warner. I think its from 1959 by the date stamped in the input transformer. The Freed input transformer has a 600 ohm primary for balanced input with a switch that flips to bridging (for unbalanced input?). It is a HUGE transfmormer, check out this picture of the input transformer!
The power transformer is equally huge. Check out this picture of the power transformer! A pretty hefty unit overall and one heck of an overbuilt Decibel Meter.
So, here is what I want to do. I would like to make it into not just a mic pre, but if possible a channel strip with compressor and EQ circuits that I can switch in and out of the signal path. I don't want it to be any normal kind of mic pre. I'd like to be able to adjust the gain on each of the AF amplifier sections seperately for more control over distortion. I'd also like to use the Voltage Control circuit possibly as a compressor of some sort. The transformers are Freed so I will probably be looking for a similar era Freed output transformer to go along with this project.
My questions are:
Is this going to work as a mic pre? How about the other stuff like EQ and compression? I have the time and willingness to pull this off if the existing circuit (Here is the full size schematic) can be relaced and remade as a Mic Pre. How feasible is this? What parts need to be replaced? What needs to be removed/added/moved around? How much of the exisiting circuit can I reuse for my purposes? Can I reuse this decibel meter's meter to guage audio levels?
Even if I have to gut it and completely rewire a whole new circuit that's fine with me, I'm just looking at the shortest distance between this thing and a mic pre. I figure it has a meter, power transformer, input transformer, audio tubes, and the case. Even if I have to replace everything else that would be fine. I would prefer to reuse as much of the exisiting parts as possible, though.
Thanks so much for your help in advance. Here is the page with all the pictures and a copy of the schematic. DB Pre Project Page
Here is what I have:
There are 8 tubes, as follows:
3x 6SJ7WGT as Audio Frequency Amplifiers.
1x 6H6 as the Meter Rectifier
1x 5881 as Voltage Control
1x OC3 as Voltage Control Regulator
1x 6SQ7 as Voltage Control Amplifier
1x 5Y3WGTA as the Rectifier
All the tubes are JAN. Every Part is top quality and it was built by Borg-Warner. I think its from 1959 by the date stamped in the input transformer. The Freed input transformer has a 600 ohm primary for balanced input with a switch that flips to bridging (for unbalanced input?). It is a HUGE transfmormer, check out this picture of the input transformer!
The power transformer is equally huge. Check out this picture of the power transformer! A pretty hefty unit overall and one heck of an overbuilt Decibel Meter.
So, here is what I want to do. I would like to make it into not just a mic pre, but if possible a channel strip with compressor and EQ circuits that I can switch in and out of the signal path. I don't want it to be any normal kind of mic pre. I'd like to be able to adjust the gain on each of the AF amplifier sections seperately for more control over distortion. I'd also like to use the Voltage Control circuit possibly as a compressor of some sort. The transformers are Freed so I will probably be looking for a similar era Freed output transformer to go along with this project.
My questions are:
Is this going to work as a mic pre? How about the other stuff like EQ and compression? I have the time and willingness to pull this off if the existing circuit (Here is the full size schematic) can be relaced and remade as a Mic Pre. How feasible is this? What parts need to be replaced? What needs to be removed/added/moved around? How much of the exisiting circuit can I reuse for my purposes? Can I reuse this decibel meter's meter to guage audio levels?
Even if I have to gut it and completely rewire a whole new circuit that's fine with me, I'm just looking at the shortest distance between this thing and a mic pre. I figure it has a meter, power transformer, input transformer, audio tubes, and the case. Even if I have to replace everything else that would be fine. I would prefer to reuse as much of the exisiting parts as possible, though.
Thanks so much for your help in advance. Here is the page with all the pictures and a copy of the schematic. DB Pre Project Page