Relay-based passive volume control project

[BrianGT]

Originally posted by apassgear
Brian,

In my case at least I will need to make a separate PSU to drive the PIC PCB, so if the relays have the same voltage that what's needed for the PIC board this is excellent for me.

What would be the voltages requiered?

Currently, I am using 5v relays, as that is the voltage that the PIC, display and other control chips. It is obtained from a 9v 1A wallwart, and a LM-340T-5.0v regulator. The VFD draws about 500mA of current, or so it seems, but everything else doesn't draw much. Since none of the power is in the signal path, I didn't figure that it needed a better power supply. Am I wrong?

Here is the schematic for the pic board that I am using (page 6):
http://www.picbook.com/%7Epbpdf001/bookinfo/CA1.pdf

It is from a class here at georgia tech. More details at:
www.picbook.com You can actually purchase pcbs and a parts kit from digikey: 18F452-KIT-ND if you are interested in making your own pic development board. The whole thing could be obtained for about $120 including the book.

--
Brian

[apassgear]

Originally posted by BrianGT


Currently, I am using 5v relays, as that is the voltage that the PIC, display and other control chips. It is obtained from a 9v 1A wallwart, and a LM-340T-5.0v regulator. The VFD draws about 500mA of current, or so it seems, but everything else doesn't draw much. Since none of the power is in the signal path, I didn't figure that it needed a better power supply. Am I wrong?

--
Brian

I guess a simple PSU, as you suggest, would be enough. In my case I will do a "formal" small PSU to go in a separate box with the main power transformer for the active circuit of the preamp, and have the 5V IC regulator at the PIC board as I supose its provided. Haven't look to the layout yet.

[apassgear]

Yes, i see the regulator on the schematic so it will be on the PCB I guess.

Another question Brian. Should we tie both grounds?

I mean the PIC board ground to the star ground of the preamp?

Or this will contaminate the ground of the preamp?

[BrianGT]

Originally posted by apassgear
Yes, i see the regulator on the schematic so it will be on the PCB I guess.

Another question Brian. Should we tie both grounds?

I mean the PIC board ground to the star ground of the preamp?

Or this will contaminate the ground of the preamp?

Not sure about this. I haven't given much thought to it. I am considering making a small power supply with one of those talema pcb mount toroids on it, on a seperate pcb for my power supply, and make it a regulated 5v. The vfd draws a lot of power, and worry about the long term reliability of the voltage regulator, as it is rated for 1A and it gets pretty damn hot, we had to upgrade the heatsink (originally had none). I am thinking about just making a 5v input to the passive volume control board, and then an input for the relay voltage, and if you are using 5v relays, just tie this the same. My roommate is doing almost all of the work for this project now, and I am trying to learn it as quick as I can so that I can help out with it.

What is a good plan for a regulated 5v power supply? It doesn't seem to be too important, as it only powers the control logic.

As for an earlier comment about the vfds making a lot of noise, if you look at the Passlabs amplifiers, all of the expensive ones have the vfd in the same chassis as the analog circuit, so it can't be that bad:


--
Brian

[apassgear]

Good pic Brian, never saw that before. Its the Aleph P 1.7?

I think a good alternative for a reg PSU would be a similar to the one used by Nelson on preamps (and even Zen amp), series FET with a zener reference, but I don't know if the voltage is to low for this arangement.

[BrianGT]

Originally posted by apassgear
Good pic Brian, never saw that before. Its the Aleph P 1.7?

I think a good alternative for a reg PSU would be a similar to the one used by Nelson on preamps (and even Zen amp), series FET with a zener reference, but I don't know if the voltage is to low for this arangement.

It is the Pass Labs X1 preamp:
http://www.passlabs.com/prodlit/x1lit.htm

The power supply doesn't need to be overly complex, since it is jus for control logic.

--
Brian

[fcel]

Brian,
You mentioned that it's a passive volume controller and it appears that it's connected to the line out. Do I have to remove the two 2 gang pots that I have already installed on my BOSOZ? I know it sounds elementary but I'm asking anyway.

[BrianGT]

Originally posted by fcel
Brian,
You mentioned that it's a passive volume controller and it appears that it's connected to the line out. Do I have to remove the two 2 gang pots that I have already installed on my BOSOZ? I know it sounds elementary but I'm asking anyway.

I am planning on connecting it directly to my BOSOZ with no pots whatsoever. I don't think that you will need the pots in the bosoz if you use the volume control that I am making. By passive, I meant that there are no active elements in the signal path.

--
Brian

[moses]

BrianGT, not too related, but why did your class choose to use a MAX232A verses a MAX233(A)?

[fcel]

o.k. then, I'll be looking forward to your completed design.