Open source project: Customized mixing console

[mmadu]

24.4.15 New progress: The construction of the q8am10 operational amplifier has been completed, and the 9K style preamplifier has been replaced with an API style preamplifier. Completed PCB drawing for 500 series API 312/325 combination modules, PCB Gerber file attached (note: not tested!)



Good evening everyone, I've been on this forum for a while. Now I'm going to try building my first custom mixer. Currently, I've finished painting the Pre and EQ sections of the channel, inspired by the channel strip xarolium I built for his Soundcraft mixer, which features SSL 9K style pre and EQ.



Once assembled and tested I will publish all its build files.



Any suggestions are welcome! Especially for the bus part

 

[mmadu]

2024.2.18
Revised incorrect potentiometer schematic, updated PCB, and completed drawing of Fader section

 

[Harpo]

Good evening everyone, I have been on this forum for some time now. Now, I will try to build my first customized mixing console. At present, I have completed the drawing of the Pre and EQ parts of the channel, inspired by the channel bar built by xarolium for his Soundcraft mixing console, which has SSL 9K style Pre and EQ.

After assembly and testing, I will release all its build files.

Welcome any suggestions! Especially for the bus section.

Missing link between U30-pin1 and J?VOL7.1-pin2 ?
Parts value of C7 probably not 5.6pF.

 

[mmadu]

Missing link between U30-pin1 and J?VOL7.1-pin2 ?
Parts value of C7 probably not 5.6pF.

Oh, that was a mistake! Thank you for your correction.

The modified file has been added

But according to the schematic of Xarolium, C7 is indeed 5.6pF

https://groupdiy.com/threads/built-custom-channel-for-soundcraft-boards-ssl-like.62157/

13th layer

 

[Brian Roth]

I see several errors.

1. Mic/line schematic from post #2. Phantom resistor R2 should be 6.81k, not 10k. I assume R4 and R5 are an attempt at some sort of pad, but doesn't make sense to me. C2 and C3 seem very low value at 2.2 nF but that's just my guesstimate. I am seeing a bunch of 3.3 nF compensation caps between pins 5 and 8 on 5534 opamps in the mic preamp section. As I recall, 22 pF makes a 5534 unity gain stable, so why such a huge value on those multiple opamps? I think you need a coupling cap at the output of the mic pre section to minimize "clicks" from mic/line switch U25.

2. Newest EQ schematic from post #4. Looks like "send" and "receive" labels at U26 are reversed....and what's up with R1 and C1? If U35 is EQ in/out, it won't work as drawn.

3. Faders schemo from post #2, Missing "bias" resistor from U12 pin 3 to ground. I'm trying to make sense out of the pan pot circuit.

And, we need a better plan for keeping up with all the reversions as we go, so we all are looking at the same schemos as the thread progresses and not jumping around from one message to another. "Version control" is a common term.

Bri

 

[mmadu]

I see several errors.

1. Mic/line schematic from post #2. Phantom resistor R2 should be 6.81k, not 10k. I assume R4 and R5 are an attempt at some sort of pad, but doesn't make sense to me. C2 and C3 seem very low value at 2.2 nF but that's just my guesstimate. I am seeing a bunch of 3.3 nF compensation caps between pins 5 and 8 on 5534 opamps in the mic preamp section. As I recall, 22 pF makes a 5534 unity gain stable, so why such a huge value on those multiple opamps? I think you need a coupling cap at the output of the mic pre section to minimize "clicks" from mic/line switch U25.

2. Newest EQ schematic from post #4. Looks like "send" and "receive" labels at U26 are reversed....and what's up with R1 and C1? If U35 is EQ in/out, it won't work as drawn.

3. Faders schemo from post #2, Missing "bias" resistor from U12 pin 3 to ground. I'm trying to make sense out of the pan pot circuit.

And, we need a better plan for keeping up with all the reversions as we go, so we all are looking at the same schemos as the thread progresses and not jumping around from one message to another. "Version control" is a common term.

Bri

Thanks for your help Brie! This was my first time trying to draw such a huge project that I got a little confused (which led to a lot of mistakes, ha!). In this case, I will suspend publishing PCB related files until all errors in the schematic are corrected.

1. The phantom power supply resistor and the switch in the Pad part are a bug and it has been modified in the latest version. The preamplifier is from a SSL9K, in the Xarolium's schematic, C2/C3 is 2.2nF, I managed to find the original drawing of the SSL, it's a bit unclear, but it seems to be 2.2uF, I've modified it. The compensation capacitor for the 5534 seems to be shown as 3.3pF(?) in the original drawing. I'm trying to figure out what difference the values of these capacitors make and if anyone can provide further information I'd be grateful. What will be the value of the coupling cap? Is 47uF enough and what is its polarity?

2. R1/C1 of the EQ schematic has been removed and the labels have been replaced, but I can't figure out why U35 doesn't work properly. Harpo thinks C7 shouldn't be 5.6pF, this circuit seems to be from lafond audio labs but I haven't been able to find the original drawing, which really confuses me

3. The bias resistor from U12 pin 3 to ground has been modified, that is a mistake, the POT is designed as a pan knob and seems to be wired in reverse to adjust the send amount of both channels, wouldn't it work?

 

[Brian Roth]

I thought I had actual SSL schematics for a 9K, but all I can find is a a GDIY "kit" project. I attached that file.

1. As I suspected, the two input caps are 2.2 uF and NOT 2.2 nF. Also, many (but not all) of the compensation caps are 3.3 pF and NOT 3.3 nF. The "too low" values for the input caps will cause a severe low frequency roll off. The "too high" values for the compensation caps will probably cause the opamps to not operate at all, or at the least, with SEVERELY low slew rate. 47 or 100 uF should be fine for the coupling cap.

2. U35 needs to be at the output of the EQ block. I don't have a 9K schematic so I can't comment further.

3. Is that an actual 9K pan circuit? There may be reasons why it seems confusing to me. But yes, a panpot uses a dual gang pot with one section increasing audio level while the other decreases.

Finally....if you're re-doing the schematics, I suggest all of the switches have a "S" or "SW" prefix and use the "U" prefix just for the opamps.

Bri

 

[Brian Roth]

Also, see post #4 here:

https://groupdiy.com/threads/ssl-solid-state-logic.45604/

Bri

 

[Brian Roth]

@mmadu Am I correct that your post #1 contains all the latest/current revisions? If so....

Mic pre. I see the phantom resistor is corrected. There are additional parts for the pad (I didn't verify the resistor values). But, I think you misunderstood what I meant about the compensation capacitors. Check the schematics I posted in #7 and #8 above. Both show multiple 3.3 pF caps. I only mentioned 22 pF as a value required for unity gain stability, according to the datasheets. Since you are cloning a 9K, use the values shown in the schemos above. You still need a coupling cap .... probably instead of R42.

EQ. I see the send and returns are corrected, but U35 switch connections are still wrong.

Faders shcemo. I see the missing bias resistor has been added, I still don't understand the pan circuit. Where did you get that from?

I'll look at the bus amp later .....after dinner! <g>

Bri

 

[mmadu]

@mmadu Am I correct that your post #1 contains all the latest/current revisions? If so....

Mic pre. I see the phantom resistor is corrected. There are additional parts for the pad (I didn't verify the resistor values). But, I think you misunderstood what I meant about the compensation capacitors. Check the schematics I posted in #7 and #8 above. Both show multiple 3.3 pF caps. I only mentioned 22 pF as a value required for unity gain stability, according to the datasheets. Since you are cloning a 9K, use the values shown in the schemos above. You still need a coupling cap .... probably instead of R42.

EQ. I see the send and returns are corrected, but U35 switch connections are still wrong.

Faders shcemo. I see the missing bias resistor has been added, I still don't understand the pan circuit. Where did you get that from?

I'll look at the bus amp later .....after dinner! <g>

Bri

Thank you Brie, without your help this project would never have been completed.

Yes, future schematic updates will be posted at #1 so people don't see the wrong version.

The value of the compensation capacitor has been updated to 3.3pF and R42 has been replaced with a 47uF capacitor.

The EQ section switch has been moved to the output, will it work properly?

The fader schematics are from a custom channel strip that Xarolium made for his Soundcraft, in fact most of the original schematics came from him, (I don't understand why there are so many bugs but his channel strips still work fine) Will the panner work properly?

Thanks again for your help!

 

[Brian Roth]

@mmadu Yes, the EQ switch is now in the correct position. As I said, the panner design is unusual and probably adding some sort of subtle "feature" I am not comprehending. Can you link me to a location where I can see the original schematic? Perhaps there will be some additional comments that will help me understand. It is not necessarily a bug....just an unusual design I am not familiar with.

I attached a schematic screenshot from a Neotek Elan module showing a typical pan circuit as used in many consoles (with some minor variations). I am not saying it is "better"....but you can see how simple it is by comparison. Hence my confusion.

EDIT....now it's sinking in to me. It's a more complex version of what is mentioned here (I thought something looked a bit familiar...yet different):

https://groupdiy.com/threads/built-a-custom-500-series-mixer.84757/page-3#post-1113017

Bri

 

[Brian Roth]

@mmadu I looked at the bus driver. A minor tweak for the summing amp is to increase capacitor "U4" to at least 100 uF (and change to "C4" <g>).

Vee and Vcc for the output transistor section are reversed. "U10" PNP transistor has collector and emitter connections swapped.

For that output stage, have you looked at the 1646 chips from THAT Corp?

https://thatcorp.com/that-1606-1646-balanced-line-driver-ics/

Bri

 

[Brian Roth]

General questions/comments/.

1. None of the various pots have ohms value or taper listed. What make/models will you use?
2. For the PFL switch, you need the extra contacts and a bus to "trigger" a PFL "relay" somewhere in the (not yet shown) monitor section.
3. Any planned provisions for aux sends?
4. Curious what make/model fader you plan to use.

Bri

 

[mmadu]

General questions/comments/.

1. None of the various pots have ohms value or taper listed. What make/models will you use?
2. For the PFL switch, you need the extra contacts and a bus to "trigger" a PFL "relay" somewhere in the (not yet shown) monitor section.
3. Any planned provisions for aux sends?
4. Curious what make/model fader you plan to use.

Bri

OK, the bus driver schematic has been updated, thank you for your help.

Fader section from #9
https://groupdiy.com/threads/built-custom-channel-for-soundcraft-boards-ssl-like.62157/

For the bus out section I plan to add a Trident CB9146 bus compressor behind the driver and add a fader section for control, and after the fader I will add a balanced driver (that or a transformer? Still thinking about it)

I've added the resistance information for all the potentiometers, and the faders are connected via XH connectors, so compatibility with all fader models shouldn't be a problem. As for the knob, it will be a Alps RK097, which is very easy to find at my place, and likewise, it will be very easy to modify (some adapter board or,,,)

In fact, PFL is not commonly used in my work process. I usually use the monitoring controller in the DAW, which leads to me not knowing how PFL works. Is there any relevant documentation?

The same goes for the aux sends, I've added direct outputs to each channel so it seems like it would be easier to just use a patch panel and attach the channels, but I'll also add some aux channels if I can

Thank you!

 

[Brian Roth]

Perhaps I wasn't clear about my fader question <g>. I was interested about which brand and model you intend to use. Alps? P&G? TKD? 100mm "throw" length? etc. Just curious.

In a "classic" recording console the PFL (Pre Fader Listen) switch sends the signal from the selected channel(s) to a bus. Pressing a PFL switch(es) also sends a control signal to the monitoring section of the console. When the monitor section receives the control signal, it mutes whatever is being monitored and substitutes the audio from the PFL bus into the monitor speakers.

NOTE! In some consoles specifically designed for radio or TV broadcast, the PFL audio goes into a totally separate amplifier and speaker This allows the audio mixer operator to hear a selected audio source without interrupting the audio heard by the other operators (video switcher operators, etc) in that same control room. Live TV is an amazing process with more than one person all working together in a common control room area! Imagine what that would be like at the Superbowl broadcast control room!! Anyway, I digress.......

I am trying NOT to cause what is often called "feature creep" by adding every possible function that everyone in the world will want! LOL!! But, Aux sends are a common feature on even the simplest mixers.

The fact that this design already includes mic preamps and EQ moves it away from a simple "summing" mixer into the realm of a recording/broadcast/live PA mixer. The "trick" is to plan out what the desired feature set will be and NOT go overboard. Else it will be like this <lol>

 

[Brian Roth]

@mmadu I was saving the newest schematics from post #1 to my hard drive and saw the text at the top of that message had become Chinese language! <g>

Bri

 

[mmadu]

Perhaps I wasn't clear about my fader question <g>. I was interested about which brand and model you intend to use. Alps? P&G? TKD? 100mm "throw" length? etc. Just curious.

In a "classic" recording console the PFL (Pre Fader Listen) switch sends the signal from the selected channel(s) to a bus. Pressing a PFL switch(es) also sends a control signal to the monitoring section of the console. When the monitor section receives the control signal, it mutes whatever is being monitored and substitutes the audio from the PFL bus into the monitor speakers.

NOTE! In some consoles specifically designed for radio or TV broadcast, the PFL audio goes into a totally separate amplifier and speaker This allows the audio mixer operator to hear a selected audio source without interrupting the audio heard by the other operators (video switcher operators, etc) in that same control room. Live TV is an amazing process with more than one person all working together in a common control room area! Imagine what that would be like at the Superbowl broadcast control room!! Anyway, I digress.......

I am trying NOT to cause what is often called "feature creep" by adding every possible function that everyone in the world will want! LOL!! But, Aux sends are a common feature on even the simplest mixers.

The fact that this design already includes mic preamps and EQ moves it away from a simple "summing" mixer into the realm of a recording/broadcast/live PA mixer. The "trick" is to plan out what the desired feature set will be and NOT go overboard. Else it will be like this <lol>

View attachment 122789

I think the Alps 75MM faders will suit my needs.

Yes, I totally agree with the idea of a universal mixer, so as you can see I kept the preamp, EQ and faders completely separate so everyone can add the parts they need, ha!

The idea was that after the first version was built, I would release all the original files so anyone could modify it and end up with their own modular mixer.

 

[mmadu]

@mmadu I was saving the newest schematics from post #1 to my hard drive and saw the text at the top of that message had become Chinese language! <g>

Bri

Oh yes, my "SMART" Chrome translator keeps trying to translate all the text lol.

 

[Brian Roth]

I think the Alps 75MM faders will suit my needs.

Yes, I totally agree with the idea of a universal mixer, so as you can see I kept the preamp, EQ and faders completely separate so everyone can add the parts they need, ha!

The idea was that after the first version was built, I would release all the original files so anyone could modify it and end up with their own modular mixer.

OK, very interesting. I don't know which model number Alps fader you have selected for that module. I asked because of the selector switches placed to the right side of the module in the panel diagram in post #1 .....which seems to mean the fader has to be "skinny" in width. I am an "Olde Fart"...lol... who prefers faders with a long track. 100mm faders are very usable....maybe I could get used to a 75mm stroke fader.

I suddenly realized that I have no idea of the physical dimensions of the panels you proposed in the first post. 1.5" wide was a common module width for decades and now is "enshrined" as width for 500 series modules. But, in this project you can make the modules any size you choose. From the schematics we're discussing, I see you do NOT plan to follow the 500 series 15-pin module edge connector format.....which is cool....but rather you propose using an assortment of ribbon cables, so the modules don't have to be 1.5" wide.

Bri

EDIT perhaps Eurorack dimensions as used for synthesizer modules????

EDIT 2. I had what I thought was a GOOD idea to adopt the Eurorack format for this project but alas, specs are +/- 12 Volts for the power rails.

https://en.wikipedia.org/wiki/Eurorack

 

[mmadu]

OK, very interesting. I don't know which model number Alps fader you have selected for that module. I asked because of the selector switches placed to the right side of the module in the panel diagram in post #1 .....which seems to mean the fader has to be "skinny" in width. I am an "Olde Fart"...lol... who prefers faders with a long track. 100mm faders are very usable....maybe I could get used to a 75mm stroke fader.

I suddenly realized that I have no idea of the physical dimensions of the panels you proposed in the first post. 1.5" wide was a common module width for decades and now is "enshrined" as width for 500 series modules. But, in this project you can make the modules any size you choose. From the schematics we're discussing, I see you do NOT plan to follow the 500 series 15-pin module edge connector format.....which is cool....but rather you propose using an assortment of ribbon cables, so the modules don't have to be 1.5" wide.

Bri

EDIT perhaps Eurorack dimensions as used for synthesizer modules????

To be honest, I didn't think so much when I started this project. The PCB drawing was just based on the free manufacturing standards of jlcpcb (the PCB manufacturer that developed EasyEDA) (within 10X10cm). But now, as the project gradually becomes larger, It seems necessary to build modules that comply with the standards. Are there still problems with the preamplifier part? If not, I will redraw the schematics and reset all designs to 500 module standards.