ej_whyte
Well-known member
So here is my first proper design, which I would like some feedback on from the great minds here. It is nothing groundbreaking though.
The idea for this was initially conjured up whilst in my 2nd year of my degree. We were asked to submit preliminary ideas for our final year major project, and this is basically a cut-down console master section, including a monitor controller. The key feature I wanted to have was the ability to route different groups to different types of summing make-up gain, and keep separate inserts for each group bus. The angle behind this was for small project/home studios without a console (I basically just thought up exactly what would suit my own situation )
The signal flow is as follows, showing 1 side of the hard-wired stereo only (16 inputs).
Each gain stage can have be set between roughly 3 to 30 dB of gain, and also has an output fader (post insert). This is enough that if all you want all 8 channels sent to one gain stage, there is still more than 10dB in hand.
The solid state gain stage is pretty much a standard 312 style circuit, with the output fader post-transformer.
The tube gain stage is a simple common cathode single stage which feeds into a 5532 voltage follower to keep the output impedance down for the 1646-based send. For tube purist this may be blasphemy, but I didn’t want to use an output transformer, mainly due to cost (already 6 transformers being used). Whilst I could have used a cathode follower, as most of the ‘tube’ sound comes from the common cathode stage, and the cathode follower being a pretty transparent topology, I chose to go for solid state for cost and board space. Besides, the audio has already been through many opamps so what is one more. Internal level is set at -2dBu nominal. The tube stage has a max input of about -4dBu, and when traced back to the main inputs that is about 19dBu. That seems quite low, however that is with tube gain set to full. At system unity it would increase to roughly 33dBu. The unit is designed to sit right on the converter DA outputs, so I was aiming for 18dBu at a minimum. With max input and max gain, the following opamp stage would be clipping before the tube anyway, so I do not see the tube stage as a bottleneck.
THAT 1646 & 1206 sends & returns throughout, except for the solid state gain stage, where the 2503 transformer is used as it is a key part of the API sound.
Bypass switch chooses between the summed outputs of the gain stages or just the first LR pair of inputs and then feeds this to the master insert.
From there it is sent to the main output fader and 1646-based outputs. The monitor controller section can then be fed either from the main outputs, or an aux in (front panel 3.5mm jack or rear panel RCAs). One interesting feature I have included is that when the monitor controller is fed from the aux input, the summing section can still be used independently (providing that it in not bypassed). The monitor controller is not overly complicated, including mute, dim, mono, main/alt outputs, a headphone output and obviously a volume pot.
The VUs are fed from whatever is hitting the monitor controller, and are fed by an adaptation of JLM’s meter driver.
I have used calibration trimmers throughout to maintain stereo balance.
I know that this is not the most pure or elegant design, for example, the whole summing section could be done with just one opamp and would be much lower noise, but that would then be missing the point of the main features I wanted to include.
Likewise, I could have used a circuit such as Ian’s mu follower for the tube stage, but I wasn’t looking for ultra-clean. I don't expect the noise performance to be amazing as there is quite a lot of attenuation at the start.
I am sure my inexperience will shine through here, but I have been through the design checking things over and over again and I am pretty happy with it now. It would have probably been a lot quicker and easier if I had just posted on here with what I wanted to build, but I wanted to learn how to design it myself not just follow instructions.
I’m sure there is loads I have forgotten to say or explain, but I have been working on this for a long time so there must be good reasons for most things I have done.
I am just looking for some feedback please and for all you more experienced people to point out my miserable mistakes lol.
Finally, massive thanks to Tom Waterman for helping me start out with this idea, as well as Abbey, JR, Ruffrecords Ian, PRR, NYDave, Ethan and everyone else who has posted extremely helpful information on this forum. I’ve only been in to this stuff about a year and a half, but after building my first SSL its all happened pretty quickly. I’m just about to finish my years placement at an Avid/Mackie/R.N.D service centre which has been an amazing year, but I would never have been able to get that opportunity without this place being around.
Schematics:
https://www.dropbox.com/sh/3vueak9kkvm911k/WTf4aLYfcN/Complete%20Edited.pdf
Cheers
The idea for this was initially conjured up whilst in my 2nd year of my degree. We were asked to submit preliminary ideas for our final year major project, and this is basically a cut-down console master section, including a monitor controller. The key feature I wanted to have was the ability to route different groups to different types of summing make-up gain, and keep separate inserts for each group bus. The angle behind this was for small project/home studios without a console (I basically just thought up exactly what would suit my own situation )
The signal flow is as follows, showing 1 side of the hard-wired stereo only (16 inputs).
Each gain stage can have be set between roughly 3 to 30 dB of gain, and also has an output fader (post insert). This is enough that if all you want all 8 channels sent to one gain stage, there is still more than 10dB in hand.
The solid state gain stage is pretty much a standard 312 style circuit, with the output fader post-transformer.
The tube gain stage is a simple common cathode single stage which feeds into a 5532 voltage follower to keep the output impedance down for the 1646-based send. For tube purist this may be blasphemy, but I didn’t want to use an output transformer, mainly due to cost (already 6 transformers being used). Whilst I could have used a cathode follower, as most of the ‘tube’ sound comes from the common cathode stage, and the cathode follower being a pretty transparent topology, I chose to go for solid state for cost and board space. Besides, the audio has already been through many opamps so what is one more. Internal level is set at -2dBu nominal. The tube stage has a max input of about -4dBu, and when traced back to the main inputs that is about 19dBu. That seems quite low, however that is with tube gain set to full. At system unity it would increase to roughly 33dBu. The unit is designed to sit right on the converter DA outputs, so I was aiming for 18dBu at a minimum. With max input and max gain, the following opamp stage would be clipping before the tube anyway, so I do not see the tube stage as a bottleneck.
THAT 1646 & 1206 sends & returns throughout, except for the solid state gain stage, where the 2503 transformer is used as it is a key part of the API sound.
Bypass switch chooses between the summed outputs of the gain stages or just the first LR pair of inputs and then feeds this to the master insert.
From there it is sent to the main output fader and 1646-based outputs. The monitor controller section can then be fed either from the main outputs, or an aux in (front panel 3.5mm jack or rear panel RCAs). One interesting feature I have included is that when the monitor controller is fed from the aux input, the summing section can still be used independently (providing that it in not bypassed). The monitor controller is not overly complicated, including mute, dim, mono, main/alt outputs, a headphone output and obviously a volume pot.
The VUs are fed from whatever is hitting the monitor controller, and are fed by an adaptation of JLM’s meter driver.
I have used calibration trimmers throughout to maintain stereo balance.
I know that this is not the most pure or elegant design, for example, the whole summing section could be done with just one opamp and would be much lower noise, but that would then be missing the point of the main features I wanted to include.
Likewise, I could have used a circuit such as Ian’s mu follower for the tube stage, but I wasn’t looking for ultra-clean. I don't expect the noise performance to be amazing as there is quite a lot of attenuation at the start.
I am sure my inexperience will shine through here, but I have been through the design checking things over and over again and I am pretty happy with it now. It would have probably been a lot quicker and easier if I had just posted on here with what I wanted to build, but I wanted to learn how to design it myself not just follow instructions.
I’m sure there is loads I have forgotten to say or explain, but I have been working on this for a long time so there must be good reasons for most things I have done.
I am just looking for some feedback please and for all you more experienced people to point out my miserable mistakes lol.
Finally, massive thanks to Tom Waterman for helping me start out with this idea, as well as Abbey, JR, Ruffrecords Ian, PRR, NYDave, Ethan and everyone else who has posted extremely helpful information on this forum. I’ve only been in to this stuff about a year and a half, but after building my first SSL its all happened pretty quickly. I’m just about to finish my years placement at an Avid/Mackie/R.N.D service centre which has been an amazing year, but I would never have been able to get that opportunity without this place being around.
Schematics:
https://www.dropbox.com/sh/3vueak9kkvm911k/WTf4aLYfcN/Complete%20Edited.pdf
Cheers