Aleph P 1.0 volume control board question?

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I have made an Aleph P 1.0 volume control board using ADC0804 chip (see photo below). It is working fine, but I have these symptons and not sure if I can make it better? The only change to the original design is that I separate the psu to provide both +5VDC for control and relay boards.

They symptons are:

1. when I turn the 100K VR (I use the Audio 100K pot), the first 20-30 degrees or so, the relays are silent; then the relays start to work... This is my first relay volume board, therefore, not sure if this is correct? (I tried the linear type pot, the result is similar!)

2. In a rare occation, I can hear relay kicking back and forth. Of course if I move the pot a little forward or backward, it will be fine, but is there a way to prevent it from happening?

3. (this is minor, but) I found out I have to short all the 33.2K resistors to the tip29, or the relays won't respond. what's the purpose of these resistors? are they protecting anything?

I have a habit to keep my diy journal and you can find it here:
http://www.penguinlovers.net/audio/alephp_vr.html

I thank in advance for any suggestion and thanks to Nelson for your sharing to us all. It is fun to do the diy.

Thanks,

Thomas
 

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The one and only
Joined 2001
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#2 is a real artifact, not a function of the pot, but a function
of the A/D converter, which can sit there switching back and
forth between 1 bit values.

You can stick a little hysteresis in such a circuit so that it doesn't
do that, or you can inhibit the A/D until there is a significant
change, or you can just go to a microcontroller.

We went to the microcontroller, as it was cheaper and easier.
 
For some reason I just don’t like programming microcontrollers and I happen to be a professional java programmer working in a government nuclear high energy physics laboratory. I for one don’t have the equipment, and have never done it before.

I think an optical encoder hooked up to a flip-flop and an 8 bit up down counter like the 74f269 would work just as well. I can’t find an example of a full circuit online. However it would be something what you see below (just two chips).

By the way, do you get a good range out of that volume control? That is to say, does it go from dead silent to loud in nice uniform steps? How much noise do you get out of that thing when you change the volume (mechanical / electrical)?

By the way maybe Nelson can tell us how to make a better volume control, using transistors instead of relays. I know he knows how .
:D
 

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By the way, do you get a good range out of that volume control? That is to say, does it go from dead silent to loud in nice uniform steps? How much noise do you get out of that thing when you change the volume (mechanical / electrical)?

Even though the board is working, but I found the 64 steps are not evenly distributed to my audio type VR. I felt less clicking for the first 150 degrees and more congested clicking sound at the last 100 degrees in turning VR. For this reason, I have not test it on my BZLS or Aleph P1.7. I plan either to see if it can be resolved or begin studying a microprocess one and make a new controller board out of it.

Will keep you posted.

Thanks,

Thomas
 
The one and only
Joined 2001
Paid Member
LBHajdu said:
I think an optical encoder hooked up to a flip-flop and an 8 bit up down counter like the 74f269 would work just as well. I can’t find an example of a full circuit online. However it would be something what you see below (just two chips).

By the way maybe Nelson can tell us how to make a better volume control, using transistors instead of relays. I know he knows how .

I think the encoder and flip flop is an excellent way to go.

We do have a great transistor based volume control, but we're
still waltzing with the patent office - probably a waste of time,
considering that they didn't even look at the application for
four years.
 
I have used the encoder and the 8 bit counter and it works like a charm !! Simple and reliable, no software hassle.

I designed the relayboards and a separate board for the control circuitry. It uses 6 relays which activate banks of resistors (1 % MF). The impedance is a constant 10k, regardless of the volumesetting.

Sound; rocksolid imaging regardless of volume setting (try that with a regular pot), channeltracking is as perfect as it gets (my Audio Precision measured a maximum tracking error of 0.01 dB), and this thing has a purity of sound that's addictive.

I built this thing about 6 years ago and I've never looked at conventional pots again. Tried to make it more luxurious with a microcontroller, but that's a projetc that's still waiting to be finished. I did design the boards and wrote the software though.

Xcel
 
Can you share your design (like schematic) and post few photos?

Well, Thomas, let me think about that...You see, at one time I did have some commercial plans with this design. I have several designs for this particular function, so maybe I can give you one of the least commercial versions

I can however show you some pictures, so hang around and give me time to retrieve them.

Xcel
 
I use it with Nelsons balanced Line Stage, were i don´t expect it to be a problem. Also in case someone needs it constant impedance, the same controller should be usable with relays wired differently on the signal side. For everyone who is interested and has acess to a Pic pogrammer or is able to build his own (very simple, about 5€ parts) the code is free for download.

For those who are interested and are not able to programm their own Pic, i send it preprogrammed by letter.
 
Regarding the balanced volume control, regardless of 6-bit or 8-bit, I did saw a few diyers mentioned using the constant impedance design. Are there any published one for diy available now? (Anyone seen in other thread?)

I searched, but did not find one (some mentioned it, but no design shown!)

Thomas
 
Here are some pictures of the 8 bit version. Unfortunately for you, I can't show any schematics since I only have paper versions at the moment. The electronic versions are on my other PC, but maybe I can convert them into a picture, let me see what I can do for you.

:)

Xcel
 

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