Relay-based passive volume control project

[BrianGT]

I am currently working with my roommate on a remote controlled passive volume control. Here is my current, first working version:


This is basically a proof of concept version, consisting of 2 channels with 4 relays per channel, giving 16 total volume steps. The design is based on 8 relays per channel, but there wasn't room on the protoboard for more then 4 for each channel. Currently, only one side of each relay is being used, but with both sides being used, it will act as a 2 channel balanced volume control with 256 steps including mute. Here is the schematic for the relay volume control:


We are currently working on the details of the project, and starting to make a pcb to accomidate all 16 relays, and the microcontroller, a PIC18F452.

Others on this forum have expressed interest in this project, as a lot of people are looking for a high quality volume control. By simply using relays and resistors, it is quite a clean volume control. Significant lengths will be taken to ensure a clean audio path on the pcb.

How many people on this forum would be interesting in making this a group project?

I could supply the finished pcb, relays, programmed microcontroller and control logic in the form of a kit. I thought about just providing pcbs, but relays and other parts are much cheaper when purchased in large quantity, and I will need to program all of the microcontrollers for this project for people anyway.

As for the remote control aspect, my roommate is working on the code for a universal learning remote control unit for it now, so that it will work with any remote control. I like this, because I like to use the unused buttons on my normal remotes for stuff like this.

As for display, I am using this display for mine:

(image from other project with it)
It costs $100, but for the kit, I am considering making it work without a display, with this display, or with a significantly cheaper lcd display (~$10).

As for using it, I am planning on using mine for two setups, one for my normal leach amp, seperate from it, and the other, integrating it in the same chassis as my bosoz.

Anyone on the forum interested in making this a group project, with my supplying of a kit for this? Any comments on what you would like in a passive volume control?

Most of the credit for this project goes to my roommate, who spent a lot of time making the first prototype for a school project this semester.

--
Brian

[dorkus]

not sure it's a practical approach for SoD (son of dork) since i need lots of 1dB attenuation steps, but the control scheme is cool. where'd you get the nice VFD?

[BrianGT]

Originally posted by dorkus
not sure it's a practical approach for SoD (son of dork) since i need lots of 1dB attenuation steps, but the control scheme is cool. where'd you get the nice VFD?

Not enough steps? There are 256 steps, including mute with the 8 relays... add 2 more relays, and you have 1024 steps total. Modify the 8 resistors to get whatever resistance that you want.

I ordered the vfd direct from Noritake. Here is the page for this one:
http://www.noritake-elec.com/7000.htm

It was just under $100 shipped.

The model number is:
GU140X32F-7002

It is very useful to use, and has many advanced features over normal vfds. You can set different windows on it.

--
Brian

[Dennis Hui]

Hi Brian,

I am definitely interested in this project. One thing I
really like is that this is balance is also handled, but
probably with greater ease of use than standard dual
mono attenuators.

Dennis

[dorkus]

have you figured out the optimal resistor values for precise 1dB attenuation increments? i sure haven't... i wonder if there's a mathmatical solution better than brute force (iterative).

[apassgear]

Yes Brian, good idea to make a kit.

As I told you before I'm also interested in a set as volume control for BOSOZ. The idea of adding a display is very nice too.

I'm in for a two channel balanced vol.

Take your time is OK for Jan/Feb.

Since aparently the signal is going through the relays we maybe don't want to cheep-out on these?

[dorkus]

why switch the signal thru the relays? any opposition to a simple shunt control with fixed series resistor?

[jackinnj]

there has been a seller of Noritake displays off and on -- check Businesss Equipment/Electronic Components on the Bay

[BrianGT]

Originally posted by dorkus
have you figured out the optimal resistor values for precise 1dB attenuation increments? i sure haven't... i wonder if there's a mathmatical solution better than brute force (iterative).

I haven't even tried yet Currently, it is just using 4 resistors for the proof of concept:

2k
1k
500
250

This gives 15 positions plus mute, which works fine to see how it works. I will test the next version with these values:

8k
4k
2k
1k
500
250
125
60

--
Brian

[BrianGT]

Originally posted by apassgear
Yes Brian, good idea to make a kit.

As I told you before I'm also interested in a set as volume control for BOSOZ. The idea of adding a display is very nice too.

I'm in for a two channel balanced vol.

Take your time is OK for Jan/Feb.

Since aparently the signal is going through the relays we maybe don't want to cheep-out on these?

I am using NEC MR82 relays:
http://www.nec-tokin.net/now/english...lay_MR82_e.pdf

I will try other types of relays once to see the difference with it. I have no problems with these relays thus far. Here is the technical info for the relays:
http://www.nec-tokin.net/now/english...tehcdata_e.pdf

I love the Noritake 7000 series display. It is great looking, and very capable for advanced features and programming.

--
Brian