Monitoring Controller "Class A" - Help us & Join us to design it !

[drask]

Hello Guys !

We are (with a friends) currently designing a monitoring controller based around the chip MUSES 72320.
We already did the control section of the Muses, choice of the input and output, mute ... and almost all the control of the unit. 

Unfortunately we're more "computer geek" and not "electronic geek".
So Muses, input and output choice are okay and easy for us to control and to design the circuit.


But we're stuck on the electronic part, Input & output. We'd like it to be a Class A unit and Not a passive unit.

So, what we need is more information about the signal flow we could work on and in the best case help to design this part.. 

I'm thinking about an op-amp / input amp to get a single ended signal (Class A) with the possibility the trim the input..
and a output amp Class A (and do we need a buffer to drive the output amp?)


There'll be an headphone amp too (will see about that later)


Here the signal flow we thought about.
Not sure about buffer and if it's what we need.

Impedance wanted

• Balanced Input  : 80K - 100K (100k is maybe a bit  too high)
• Balanced Ouput :  around 300 ohm
• and  Later : Unbalanced input

Any help will be appreciate and if someone want to join us in the adventure we'll welcome him.


We will share the projet and all schematic, maybe a PCB run, but anyway will release  all the files and information here to anyone who want to build this Monitoring Controller.

We have plenty idea of features. But we want to start with only the basics.
We know it's going to be a long project ..

Thank you all !

 

[gyraf]

Some important questions about target specs:

Why this chip?
(datasheet: http://www.njr.com/semicon/PDF/MUSES72320_E.pdf )
Why class-A?
Why that high input impedance?
Why that high output impedance?

And on the project in general:

- What controls/options/inputs/outputs are you planning on the controller? How will you prevent feature creep?

Jakob E.

 

[Rochey]

Looks similar to another volume control IC

Knockoff merchants.

/R

 

[drask]

Some important questions about target specs:

Why this chip?
(datasheet: http://www.njr.com/semicon/PDF/MUSES72320_E.pdf )
Why class-A?
Why that high input impedance?
Why that high output impedance?

And on the project in general:

- What controls/options/inputs/outputs are you planning on the controller? How will you prevent feature creep?

Jakob E.

Hi Jakob,
Thanks for the input.

Why this chip :
We started month ago with a Relay Based attenuator controlled by Arduino, which was working. After we found that Chip, and we wanted to have a try. The controlled level is already working. There are no particular reason. Maybe if it not fit the circuit will go to another chip. But this one is easy to control, and I think could work fine (Let see?  )

Why Class-A :
We want something really linear, clear, no color  and the possibility to have a positive gain at the output. First we      went to do it passively but after some brainstorming we thought about an active controller to have a positive gain.
But maybe Class-A is not the better solution? We dig to see what pro-monitoring controller do and there are a lot in Class A.

Why that high input impedance?
Why that high output impedance? :
Maybe the input and output impedance are a bit too high, there is no particular reason, we haven't spoke a lot about that. So maybe missed that part a bit. Standard input impedance are 10K and ouput around 100 ohm, should be better , I think.

What controls/options/inputs/outputs are you planning on the controller? :
We are planning the following features.

• 3 Balanced Input
• 1 Unbalanced Input (later)
• 3 Balanced Output
• Phase Reverse
• DIM
• Mute
• Mono

Of course, any though are welcome. We're not closed to proposition and to change our signal flow ....

We'd like something "modular", everyone could build it with the features they need. 

Thanks ! 

 

[tmuikku]

hi,

wayne kirkwood has good sounding , well tested and documented board that might be suitable. it is class a output, but no voltage gain.

please read the information from his forum here:
http://proaudiodesignforum.com/forum/php/viewtopic.php?f=7&t=509

 

[drask]

hi,

wayne kirkwood has good sounding , well tested and documented board that might be suitable. it is class a output, but no voltage gain.

please read the information from his forum here:
http://proaudiodesignforum.com/forum/php/viewtopic.php?f=7&t=509

Hi !
Thanks for the information, I'll take a look 

best

 

[JohnRoberts]

Deciding to make the audio path Class A should involve a little more research and understanding.

You can deliver very high performance without using Class A.

JR

 

[drask]

Deciding to make the audio path Class A should involve a little more research and understanding.

You can deliver very high performance without using Class A.

JR

We know, that's why we're asking advice, help, and maybe other directions here.

Like I said we're open to any proposal, we're not fixed on the Class A. The Class A was to have a really good sounding product and clean. But if you have any other idea that keeps the philosophy of no color, clean .. We'll be happy to have your suggestion.

Thanks for the input JR

Best,
J.

 

[Andy Peters]

Deciding to make the audio path Class A should involve a little more research and understanding.

You can deliver very high performance without using Class A.

JR

We know, that's why we're asking advice, help, and maybe other directions here.

Like I said we're open to any proposal, we're not fixed on the Class A. The Class A was to have a really good sounding product and clean. But if you have any other idea that keeps the philosophy of no color, clean .. We'll be happy to have your suggestion.

JR's suggestion is that you don't understand what is meant by Class A, and as such you should do some research.

 

[Andy Peters]

Looks similar to another volume control IC

Knockoff merchants.

That's exactly what I thought when I saw this chip first mentioned some time ago. It's the PGA2320 without the output amplifiers but with a wacky digital control port.

Oh, and CMOS logic thresholds with at 5 V supply, which means you can't drive it from any modern 3.3 V micro.

-a

 

[JohnRoberts]

Deciding to make the audio path Class A should involve a little more research and understanding.

You can deliver very high performance without using Class A.

JR

We know, that's why we're asking advice, help, and maybe other directions here.

Like I said we're open to any proposal, we're not fixed on the Class A. The Class A was to have a really good sounding product and clean. But if you have any other idea that keeps the philosophy of no color, clean .. We'll be happy to have your suggestion.

JR's suggestion is that you don't understand what is meant by Class A, and as such you should do some research.

And more specifically that class A will not magically deliver lower distortion or lower noise. It's kind of a fashion trend that appeals to exotic esoteric designers.

A search will reveal me saying this and worse about class A a bunch of times...

BTW I think Andy did a monitor controller design, I guess a search would reveal that too.

JR

 

[Andy Peters]

What controls/options/inputs/outputs are you planning on the controller? :
We are planning the following features.

• 3 Balanced Input
• 1 Unbalanced Input (later)
• 3 Balanced Output
• Phase Reverse
• DIM
• Mute
• Mono

Of course, any though are welcome. We're not closed to proposition and to change our signal flow ....

We'd like something "modular", everyone could build it with the features they need. 

Thanks ! 

How do you propose to implement the multiplexing of the input sources to the outputs? And to implement the polarity reverse and mono and such?

a

 

[drask]

Deciding to make the audio path Class A should involve a little more research and understanding.

You can deliver very high performance without using Class A.

JR

We know, that's why we're asking advice, help, and maybe other directions here.

Like I said we're open to any proposal, we're not fixed on the Class A. The Class A was to have a really good sounding product and clean. But if you have any other idea that keeps the philosophy of no color, clean .. We'll be happy to have your suggestion.

JR's suggestion is that you don't understand what is meant by Class A, and as such you should do some research.

And more specifically that class A will not magically deliver lower distortion or lower noise. It's kind of a fashion trend that appeals to exotic esoteric designers.

A search will reveal me saying this and worse about class A a bunch of times...

BTW I think Andy did a monitor controller design, I guess a search would reveal that too.

JR

Thanks all for your inputs !
But like I said, we're not "electronic geek" we're a programmers and we're here to have your opinions, advice, maybe others way than the class A .... and your help to design something cool !

This chip is maybe not the better solution we know, we found it, we bought one to try and the acces and the control of the MUSES et quite really easy.

We didn't know about the PGA2320. Maybe it's an others (better ?) solution. Don't know but we can (and we'll certainly) try it too.

The chip, is not the problem, it's more what around it.

Thanks !
Best

 

[Gold]

I can think of a few commercial products that have everything you want. Unless you are in it for the education or want to make a commercial product I'd just get something off the shelf. Easier and cheaper.

 

[Andy Peters]

The chip, is not the problem, it's more what around it.

That is absolutely the truth. This is why I asked how you intended to handle all of the switching and muxing needed to implement the selections and mono and polarity reverse.

Then, too, the layout of all of this is not trivial.

My design is here. I've stuffed one set of boards, and so far after fixing a couple of firmware bugs, it all works as expected. This weekend I hope to do some rigorous noise and crosstalk tests.

 

[drask]

The chip, is not the problem, it's more what around it.

That is absolutely the truth. This is why I asked how you intended to handle all of the switching and muxing needed to implement the selections and mono and polarity reverse.

Then, too, the layout of all of this is not trivial.

My design is here. I've stuffed one set of boards, and so far after fixing a couple of firmware bugs, it all works as expected. This weekend I hope to do some rigorous noise and crosstalk tests.

Just checked your design.
We don't want such a "complexing" routing.
There is "one circuit" where you can choose different input and different output.
Not like yours where any input can be routed to any output.
He we just want to choose the input we want to listen and on which output we want.

Thanks !

 

[drask]

I can think of a few commercial products that have everything you want. Unless you are in it for the education or want to make a commercial product I'd just get something off the shelf. Easier and cheaper.

Hi Gold,
We don't intend to make a commercial product. We're here to design something cool with the community and share all the files with you after

 

[Andy Peters]

Just checked your design.
We don't want such a "complexing" routing.
There is "one circuit" where you can choose different input and different output.
Not like yours where any input can be routed to any output.
He we just want to choose the input we want to listen and on which output we want.

If you think more about it, what I came up with is what you want.

Say you have four inputs and four outputs.  You need a 4:1 mux for each output. That's how you "choose the input you want to listen [to]."

You choose the output you want by muting all others. And that's basically what I do.

 

[drask]

Just checked your design.
We don't want such a "complexing" routing.
There is "one circuit" where you can choose different input and different output.
Not like yours where any input can be routed to any output.
He we just want to choose the input we want to listen and on which output we want.

If you think more about it, what I came up with is what you want.

Say you have four inputs and four outputs.  You need a 4:1 mux for each output. That's how you "choose the input you want to listen [to]."

You choose the output you want by muting all others. And that's basically what I do.

Okay ! You not using any relay to do that ?

 

[Andy Peters]

Just checked your design.
We don't want such a "complexing" routing.
There is "one circuit" where you can choose different input and different output.
Not like yours where any input can be routed to any output.
He we just want to choose the input we want to listen and on which output we want.

If you think more about it, what I came up with is what you want.

Say you have four inputs and four outputs.  You need a 4:1 mux for each output. That's how you "choose the input you want to listen [to]."

You choose the output you want by muting all others. And that's basically what I do.

Okay ! You not using any relay to do that ?

Why? There is a volume control element, the PGA2320, for each output which mutes on its lowest volume setting. I am pretty sure that the "Muses" part works the same way.

The micro keeps track of each output's working level and mute and dim status.

Note: In my design the four PGA2320 SPI ports are daisy chained, so to change one volume level you must load all four. This is not a problem.

When the user presses the "Use Output 1" button, the micro builds a list of values to write to all of the PGA2320s.  It takes Output 1's working level, and uses 0 for all of the other outputs.

If the user then presses "Use Output 2," a new list of values to write is built, and it uses 0 for outputs 1, 3 and 4 and whatever was stored for output 2.

If the user adjusts the volume of output 2, that value is remembered, so if the user switches to output 1 and then back to 2, the latest value of output 2 is used.

If a channel is dimmed, then 12 dB is subtracted from the volume value before it is sent to the PGA2320.

-a