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-   -   Aleph P 1.0 volume control board question? (http://www.diyaudio.com/forums/pass-labs/37178-aleph-p-1-0-volume-control-board-question.html)

tomchaoda 3rd July 2004 08:28 PM

Aleph P 1.0 volume control board question?
 
2 Attachment(s)
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

till 3rd July 2004 09:02 PM

I have build the ADC0804 relay volume control in my BOZ, and it works without shorting the resistors (i used 10k or so), it did not show symptome #1, and i fear there is no real cure for #2.

I changed over to mikrocontroller based relay volume control for my BZLS: http://home.tu-clausthal.de/~tpa/relais/index.html

tomchaoda 3rd July 2004 09:21 PM

Till:

Your link did provides many helps to my project. Just wanted to say thanks and I will try the 10K resistor and see how it goes...

I will keep you posted.

Thomas

zygibajt 3rd July 2004 10:21 PM

I think the cure for #2 might be another/diffrent POTentiometer.
Try other brands.I think the one that is sliding very hard and holds the resistance stiff and steady is needed.
Otherwise just the tiny,tiny move (itself) couses relay clicking.

Nice work!

Bartek

Nelson Pass 4th July 2004 07:40 PM

#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.

LBHajdu 6th July 2004 02:45 AM

2 Attachment(s)
For some reason I just donít like programming microcontrollers and I happen to be a professional java programmer working in a government nuclear high energy physics laboratory. I for one donít 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 canít 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

tomchaoda 6th July 2004 05:01 PM

Quote:

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

Nelson Pass 6th July 2004 07:46 PM

Quote:

Originally posted by LBHajdu
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 canít 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.

xcel 9th July 2004 10:36 AM

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

tomchaoda 9th July 2004 01:38 PM

Quote:

I have used the encoder and the 8 bit counter and it works like a charm !! Simple and reliable, no software hassle.
Xcel:

Can you share your design (like schematic) and post few photos? I would like to make my board work better.

Thomas


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