8ch Active Volume Control

[AJ]

Neil Davis and I have started working on this (mostly Neil :D ) based on talk in an earlier thread. My plan as of now is based around the PGA2310, and the goal of using through hole parts for everything to make construction easier for most DIYers. The other goal is keeping it relatively inexpensive. My current thinking is going the modular route. We would have a microcontroller board which is standard, and two different analog boards for the PGA's. One would be for eight balanced channels, the other would be for eight unbalanced channels. You would buy the standard microcontroller board, and whichever version of the analog board you wanted. For people not into active crossovers, we could do a 2ch balanced/unbalanced board later.

Features list:

• IR Remote Control
• Front Panel Volume Control
• Regulated power supply on the microcontroller board minus the transformer(s)
• Small LCD screen to show volume level

The power supply would be based on LM317/LM337 regulators, with an LM7805 for the +5V rail. Ideally, two small transformers would be used to keep the +5V separate from the +/-15V, and to limit dissipation in the +5V regulator.

This is all dependent on interest so if you're interested but see something you don't like, speak up. However, do not expect tons of additional features. This has to stay relatively simple to be affordable.

[cjd]

Re: 8ch Active Volume Control

This definitely interests me.

[dlr]

Re: 8ch Active Volume Control

Do you have a price target and with/without case?

dlr

[sunandmoon]

Re: 8ch Active Volume Control

Very interested in this...

[keager]

Re: 8ch Active Volume Control

me tooo

[AJ]

Re: 8ch Active Volume Control

Do you have a price target and with/without case?

dlr

I have a goal, but it's just a dream until we're further along in the design. The PGA2310's alone for the 8ch balanced version will be $150 from Mouser since you need one for each channel. If we used the PGA4311 that cost would drop to $70, but they are surface mount only. They're in a 28pin SOIC package so it's not impossible to solder by hand, but I assume most would prefer the 16pin DIP package of the PGA2310.

So, add the costs for the PCBs, the microcontroller, the small parts, the LCD, the connectors, the case... $500 for the balanced version would not be a bad guess. I imagine the 8ch unbalanced version to be $100-$200 cheaper.

It's worth noting that I'm not planning on selling assembled units. I will provide the circuit boards, the parts lists, and any help I can from a distance, but that's about it. This will not be an entry level project. If we end up having to use any surface mount parts, I will help with soldering them if required.

[cjd]

Re: 8ch Active Volume Control

I have a goal, but it's just a dream until we're further along in the design. The PGA2310's alone for the 8ch balanced version will be $150 from Mouser since you need one for each channel. If we used the PGA4311 that cost would drop to $70, but they are surface mount only. They're in a 28pin SOIC package so it's not impossible to solder by hand, but I assume most would prefer the 16pin DIP package of the PGA2310.

So, add the costs for the PCBs, the microcontroller, the small parts, the LCD, the connectors, the case... $500 for the balanced version would not be a bad guess. I imagine the 8ch unbalanced version to be $100-$200 cheaper.

It's worth noting that I'm not planning on selling assembled units. I will provide the circuit boards, the parts lists, and any help I can from a distance, but that's about it. This will not be an entry level project. If we end up having to use any surface mount parts, I will help with soldering them if required.

Those aren't horrible to solder surface-mount at all, though not for the faint of heart. I wonder if it would be possible to put together the PCB such that either could be used.

Also, since these can be control chained, it is probably worth looking at building 4 channel boards (2-ch balanced/4ch SE) with a separate power supply+control board in such a way they can be stacked to achieve the desired number of channels.

C

[AJ]

Re: 8ch Active Volume Control

...I wonder if it would be possible to put together the PCB such that either could be used.

I'd rather stay away from trying to do that. The board surface area would increase, and the trace routing would turn into a nightmare. I have to stick to two layers to keep costs inline.

Also, since these can be control chained, it is probably worth looking at building 4 channel boards (2-ch balanced/4ch SE) with a separate power supply+control board in such a way they can be stacked to achieve the desired number of channels.

C

I like this idea. It would make it slightly more complicated as far as the wiring goes for those that want to build an 8ch balanced unit, but it would lighten the PCB design workload for me. Instead of doing multiple different versions with a different number of channels, I could just design one 2ch balanced/4ch unbalanced board using the PGA2310 (for those who want through hole devices) and one using the PGA4311 (for those looking to save money and don't mind soldering surface mount devices)...

[r-carpenter]

Re: 8ch Active Volume Control

I think that's a great idea. A unit as such would negate the need to use digital volume control in DSP units.

Would it be possible to offset the volume on 2 or 4 channels? In other words, let's say I am using Ch1 and Ch4 for the tweeters and Ch2 and Ch3 for woofer. Tweeters are more efficient and I'd like to have -2db on the Ch1 and Ch4? Is that something that could be done or would it turn the project in completely new overcomplicated design?

[charlielaub]

Re: 8ch Active Volume Control

Neil Davis and I have started working on this (mostly Neil :D ) based on talk in an earlier thread. My plan as of now is based around the PGA2310, and the goal of using through hole parts for everything to make construction easier for most DIYers. The other goal is keeping it relatively inexpensive. My current thinking is going the modular route. We would have a microcontroller board which is standard, and two different analog boards for the PGA's. One would be for eight balanced channels, the other would be for eight unbalanced channels. You would buy the standard microcontroller board, and whichever version of the analog board you wanted. For people not into active crossovers, we could do a 2ch balanced/unbalanced board later.

Features list:

• IR Remote Control
• Front Panel Volume Control
• Regulated power supply on the microcontroller board minus the transformer(s)
• Small LCD screen to show volume level

The power supply would be based on LM317/LM337 regulators, with an LM7805 for the +5V rail. Ideally, two small transformers would be used to keep the +5V separate from the +/-15V, and to limit dissipation in the +5V regulator.

This is all dependent on interest so if you're interested but see something you don't like, speak up. However, do not expect tons of additional features. This has to stay relatively simple to be affordable.

Before you go too far down the road with the PGA2310, you might want to take a look at the multi-channel VCA-based preamp that Rod Elliot recently published on his web site:

http://sound.westhost.com/project141.htm

Not sure how you would control channel-to-channel gain tracking (which is easy to do with a VCA) when using PGA2310s for more than 2 channels.

On the plus side, the THD+N performance of the PGA2310 is likely 10x better than the THAT VCAs that Rod uses. Not sure how the cost works out on balance. I think that Neil actually did a multichannel VCA project using ssm2018T VCAs a few years back (10 years ago?) but I don't have the link available to me at the moment.

-Charlie

[neildavis]

Re: 8ch Active Volume Control

Those aren't horrible to solder surface-mount at all, though not for the faint of heart.
C

Right--the leads are 1.27mm spacing. That's a LOT easier to solder than the .5mm spacing that's very common in today's circuitry.

Another possibility is finding someone who can solder to do the assembly. The original concept for AudioDevelopers.com was to have a collaborative web site where people with different skills could come together to offer products and services. So someone does board design and kit packaging, someone else does coding and programming the micros, someone else does assembly, etc.

I've had the AudioDevelopers domain name for a long time but I've never had the time to implement that original vision. I still like the concept and will be happy to set it up, but I'll need some help--and some ideas to make it work.

[AJ]

Re: 8ch Active Volume Control

I think that's a great idea. A unit as such would negate the need to use digital volume control in DSP units.

Would it be possible to offset the volume on 2 or 4 channels? In other words, let's say I am using Ch1 and Ch4 for the tweeters and Ch2 and Ch3 for woofer. Tweeters are more efficient and I'd like to have -2db on the Ch1 and Ch4? Is that something that could be done or would it turn the project in completely new overcomplicated design?

Couldn't the individual level controls be done in the DSP?

I think this question is better suited to Neil. Could the level for the individual channels be adjusted without having a large LCD? Could you scroll through them on a one or two line LCD using a rotary encoder and a function switch? If so, I guess that would be a good option to have.

[r-carpenter]

Re: 8ch Active Volume Control

Another possibility is finding someone who can solder to do the assembly. The original concept for AudioDevelopers.com was to have a collaborative web site where people with different skills could come together to offer products and services. So someone does board design and kit packaging, someone else does coding and programming the micros, someone else does assembly, etc.

I could certainly machine nice wooden cases. May be some metal-work as well.

Couldn't the individual level controls be done in the DSP?

It could. The idea would be to get away from digital volume control.
I may be out of my element here so feel free to slap.

[charlielaub]

Re: 8ch Active Volume Control

I'm back on my main computer and I tracked down the link for the VCA volume control. This was actually done by Dave Reite (dreite) back around 2003 or earlier I think. The web page is NLA, but I found a copy using the wayback machine. There is some material missing, but I PDF'd it back when it was still available so I have the circuit details. He made a couple of minor changes to the SSM2018T datasheet design, and built a variable voltage source to control all of the channels from a single pot setting a voltage reference. This has been hanging around in my brain since then and it is the basis of the digital loudspeaker control interface that I am building.

Here is a pic of the completed project from the old web page:


Here is the PDF of the old web page:
http://audio.claub.net/temp/Six%20ch...20SSM2018T.pdf

And finally the SSM2018T datasheet:
http://audio.claub.net/temp/SSM2018T.pdf

What is nice about this kind of setup is that you can trim the levels of the other channels by introducing a voltage offset that corresponds to the difference in control voltage needed to change the level by that many dB from channel to channel. I am sure that you do some PIC programming (Neil) to do something similar, but this is so simple and it works well.

I think that something along these lines using the THAT VCA would be great. You can add IR control to the main control voltage if you desire. Also you can still have a display showing the level if you simply use a voltage display and adapt the control voltage. There is a section in the SSM2018T datasheet explaining how to do Digital Control of the Gain using a DAC to set the control voltage. This would still let you do PIC programming, have a better display, etc but use the VCAs.

Anyway, not necessarily advocating a change, but I thought I would bring it up as an alternative and for info purposes. I always thought that this was a pretty interesting project by Dave, and I have a few SSM2018Ts on hand so I might actually build something like this myself someday... yah, someday...

-Charlie

[robertcottiers]

Re: 8ch Active Volume Control

I have provided a link to a very high performance 8 ch volume control.In my opinion this device has equal performance when compared to the PGA series from TI.

The software capability is far superior to the PGA series,You have much better control over each channel,you can use either I2C or SPI Protocol..I won't go any further describing the capabilities have a look and draw your own conclusions.

Link:

http://www.cirrus.com/en/products/cs3308-18.html

Regards
Bob C.