Intrest Check : Pretty Simple Digital Preamp / Volume Control

[rhysh]

I am in the process of designing a pcb for a digital preamp & volume control. The volume level is controlled by a PGA2320, which is connected via serial to a ATtiny44 microcontroller. A rotary encoder or pushbuttons can be used to set the volume level, aswell as a pushbutton to fully mute the system. The PGA2320's gain can be turned on or off with a onboard jumper.

On the input side of the PGA2320, i am using a OPA2134 buffer, with a gain of 0db, or 6db (user set), and on the output side i am using another OPA2134, with a gain of 6db, which is also user ajustable.

This board features single ended input, the outputs are balanced AND single ended , (balanced via drv134 opamps on board). The whole thing only needs to be powered by a split rail 15v supply as there is additional regulation on board. I expect the final board size to be around 3"x2".

The board features seperate analogue and digital grounds, aswell as surface mount IC's to keep board size and costs down. I expect the whole thing to not cost much more then $40 to build.

A quick run thru the I/O,

Power: 15+/-
Audio In: Single ended via molex KK
Audio Out: Single ended via pads, Balanced via pads.
Rotary Encoder: 3 pin rotary encoder via molex KK
Mute: Mute button via molex KK
Mute LED: Wire pads on board.

SMD resistors are used in the digital sections, and standard thru hole resistors are used in all signal paths.

If anyone is intrested, or has any comments feel free to let me know!

 

[rhysh]

Here is the unfinished version 1 of the board.

An externally hosted image should be here but it was not working when we last tested it.

I expect the pcb to cost under $10 hopefully. I may be able to offer pre programmed AVR's for everyone that wants them.

 

[Dr_EM]

Am certainly interested as I will eventually need 6-8 channels of volume control for my system and planned to use PGA2320 for this. My questions is can multiple units be linked together to form an accurate multichannel control via one rotary (for tri-amplification in my case)? Also, how easily could this be linked to a remote control system (ie, not through the use of a motorised encoder)?

Nice to see your in the UK too, makes shipping easier and less costly!

 

[rhysh]

Am certainly interested as I will eventually need 6-8 channels of volume control for my system and planned to use PGA2320 for this. My questions is can multiple units be linked together to form an accurate multichannel control via one rotary (for tri-amplification in my case)? Also, how easily could this be linked to a remote control system (ie, not through the use of a motorised encoder)?

Nice to see your in the UK too, makes shipping easier and less costly!

Thanks for the reply, i am going to be including points on the board, so they can be stacked and controlled by the same microcontroller.

You will be able to use the identical board, but in slave mode, so you just dont populate the AVR, some resistors and a couple of pin headers.

By remote control system, do you meen linked to a existing remote control system, or have one built in? Basicly i have designed this board as totally simple preamp, so i have disgarded the idea of having LCD's and IR etc, but it can be done, on a external board by using another microcontroller to convert IR protocol to a rotary encoder standard, instead of a rotary encoder itself.

 

[theAnonymous1]

.....using another microcontroller to convert IR protocol to a rotary encoder standard, instead of a rotary encoder itself.

I would be VERY interested in something like this. I have an existing remote I would like to have a receiver capable of learning it's vol up/down signals and output a rotary encoder signal.

 

[rhysh]

I would be VERY interested in something like this. I have an existing remote I would like to have a receiver capable of learning it's vol up/down signals and output a rotary encoder signal.

I will look into this, but im not the most advanced programmer.

 

[Dr_EM]

The remote control feature is something I could live without, just I bought this:

http://www.maplin.co.uk/Module.aspx?ModuleNo=220037

with the intention of implementing it thus. I'm sure I can figure out a way regardless, or just manage without it (one of the buttons on that system will effectively jump the volume to full so mabye it's best not to use ). Main thing is they can be daisy chained for multiple channels

I see you're using the SMD PGA chip. In the UK the DIP actually looks to be cheaper (Farnell). Do you know of a cheap supplier for this chip? at farnells prices several will be expensive. Am trying to chase up a set of DIP I ordered from Taiwan ages ago actually. Were very cheap but alas haven't arrived

 

[rhysh]

The remote control feature is something I could live without, just I bought this:

http://www.maplin.co.uk/Module.aspx?ModuleNo=220037

with the intention of implementing it thus. I'm sure I can figure out a way regardless, or just manage without it (one of the buttons on that system will effectively jump the volume to full so mabye it's best not to use ). Main thing is they can be daisy chained for multiple channels

I see you're using the SMD PGA chip. In the UK the DIP actually looks to be cheaper (Farnell). Do you know of a cheap supplier for this chip? at farnells prices several will be expensive. Am trying to chase up a set of DIP I ordered from Taiwan ages ago actually. Were very cheap but alas haven't arrived

Hi again, i am buying my PGA's from digikey in the US, works out a lot cheaper, if you are intrested i can order you the required amount in when i order mine, they come out around 8 pounds each.

If i do decide to do the remote control feature, it will come along later as a daughterboard.

Hope this helps!

 

[rhysh]

I have >100 peices of PGA2320 if anyone needs some.

How much would you be offering them for?

Rhys

 

[theAnonymous1]

I have >100 peices of PGA2320 if anyone needs some.

rhysh, maybe we can work out a trade if you think you can put together an IR controller like mentioned above.

 

[rhysh]

I have >100 peices of PGA2320 if anyone needs some.

rhysh, maybe we can work out a trade if you think you can put together an IR controller like mentioned above.

I will see what i can do.

 

[Dr_EM]

It'd be good if through buying large quantities and possibly supplying the chips with the PCB costs could be kept down.

I mention the DIP PGA chips since there is a supplier where they can be obtained very cheaply:

http://cgi.ebay.co.uk/ws/eBayISAPI....ksid=p3907.m29&_trkparms=algo=LVI&its=I&otn=1

I ordered 2 sets a fair while back but after chasing it up it appears they were lost and are being re-sent. If they do actually arrive I will be sure to let you know as that price (about £3.50 each) is pretty unbeatable I'd think. Plus DIP easier to solder or mess with on breadboards

 

[rhysh]

It'd be good if through buying large quantities and possibly supplying the chips with the PCB costs could be kept down.

I mention the DIP PGA chips since there is a supplier where they can be obtained very cheaply:

http://cgi.ebay.co.uk/ws/eBayISAPI....ksid=p3907.m29&_trkparms=algo=LVI&its=I&otn=1

I ordered 2 sets a fair while back but after chasing it up it appears they were lost and are being re-sent. If they do actually arrive I will be sure to let you know as that price (about £3.50 each) is pretty unbeatable I'd think. Plus DIP easier to solder or mess with on breadboards

The DIP PGA's do look cheaper, but rerember to look out for fake IC's, there are a huge amount floating around at the moment (im not trying to suggest there is anything wrong with your purchase).

I have got my mind set on using SMD for this project, i can think of 5 advantages right now.

1. Digital traces remain on one layer only unless needed (no thru holes)
2. Smaller IC size (between 30-50% of dip size), smaller board.
3. SMD resistors are 20% the size of normal resistors
4. Less noise, no leads that need trimming in the digital section etc.
5. Components can be placed on the layer below, as SMD does not cross layers.
6. No routing round parts is required on the layer below, as there are no pins or pads to avoid.

Put it this way, you can probably fit 11 of these boards on one sheet of A4 paper, if i was using DIP packages the board would be quite a lot bigger then this.

If you are intrested in boards, and you really did want to use the DIP package im sure i would be able to find a way into using it.

 

[theAnonymous1]

Have you seen the similar project by fellow member error404?

http://audio.gotroot.ca/minivol/

I have a bunch of these boards and they work great. This is what I would like the IR controller for.

 

[rhysh]

Have you seen the similar project by fellow member error404?

http://audio.gotroot.ca/minivol/

I have a bunch of these boards and they work great. This is what I would like the IR controller for.

Yes, that is where i got the idea for the project, except that i wanted a input and output buffer on there. The firmware by error401 is compatible with my pcb, except that i do not offer the mute led function.

It looks like if i do get around to developing this IR controller, it will be directly compatible with your PCB, as we are working off the same microcontroller, basic schematic and firmware.

 

[chatziva]

Hi rhysh

I am very interested in this project, bored of messing about with expensive attenuators. So count me in for a couple of those boards if you decide to go for it.

I agree with your choice of smt components & through hole for signal path - i think you could use smt throughout to minimize signal path

I don't quite like the choice of DRV134 for balanced output, I would prefer a THS4131 in smd as well.

 

[rhysh]

Hi rhysh

I am very interested in this project, bored of messing about with expensive attenuators. So count me in for a couple of those boards if you decide to go for it.

I agree with your choice of smt components & through hole for signal path - i think you could use smt throughout to minimize signal path

I don't quite like the choice of DRV134 for balanced output, I would prefer a THS4131 in smd as well.

Hi, thanks for the reply. The real reason i picked the drv134 is becuase i have a few to hand, and i am confident with using it. I will take a look at the THS4131 and see how easy it is to implament.

Rhys

 

[Dr_EM]

Have definately considered they may be fakes, will have to check when/if they arrive. Thats some fair points on SMD though, guess I'll have to get my soldering skills up a bit

I probably wouldn't be using the balanced outs since I never made my power amplifiers balanced (might have been wise to do so though in hindsight). The chip could be bypassed and/or not installed if wanted?

Small board size is nice, especially when 3 or 4 must be installed along with active crossovers, power supplies and other bits!

Through hole resistors might be lower noise due to thier higher thermal mass? I like them anyhow

 

[rhysh]

Have definately considered they may be fakes, will have to check when/if they arrive. Thats some fair points on SMD though, guess I'll have to get my soldering skills up a bit

I probably wouldn't be using the balanced outs since I never made my power amplifiers balanced (might have been wise to do so though in hindsight). The chip could be bypassed and/or not installed if wanted?

Small board size is nice, especially when 3 or 4 must be installed along with active crossovers, power supplies and other bits!

Through hole resistors might be lower noise due to thier higher thermal mass? I like them anyhow

Dr.EM,

Yes, if you are not using balanced outs you may indeed bypass those chips, that is all you need to miss out. This was intended to be an option anyway.

Basicly, i have used SMD resistors in all the digital paths to save space, and through hole resistors in all the signal paths so higher quality resistors can be used, as you can see round the input and output buffers.

The actual board size is 93x44 mm, very small and easy to fit a few in a enclosure.

SMD is not that hard to solder at all! just flood all the legs then remove the excess solder with the braid, this has been the easiest way for me! (before i bought a toaster oven from argos)

Rhys

 

[rhysh]

I will be doing a low profile power supply to go with this board, for anyone who is intrested. (under 4cm height).